ACKNOWLEDGEMENTS

19 May 2023

Submitted by (Bold are A*STAR Staff): Dillon W. P. Tay, Naythan Z. X. Yeo, Krishnan Adaikkappan, Yee Hwee Lim & Shi Jun Ang 

Research Institute: ISCE2, IHPC

Title of Paper: 67 million natural product-like compound database generated via molecular language processing

Published in: Data Descriptors

Abstract: Natural products are a rich resource of bioactive compounds for valuable applications across multiple fields such as food, agriculture, and medicine. For natural product discovery, high throughput in silico screening offers a cost-effective alternative to traditional resource-heavy assay-guided exploration of structurally novel chemical space. In this data descriptor, we report a characterized database of 67,064,204 natural product-like molecules generated using a recurrent neural network trained on known natural products, demonstrating a significant 165-fold expansion in library size over the approximately 400,000 known natural products. This study highlights the potential of using deep generative models to explore novel natural product chemical space for high throughput in silico discovery.

URL: https://doi.org/10.1038/s41597-023-02207-x

12 May 2023

Submitted by (Bold are A*STAR Staff): Shengwei Ma, Keni Chih-Hua Wu, Stephen Wan, Cary Turangan, Kai Liang Tan, Wei Shin Cheng, Jun Ming Tan, Bud Fox

Research Institute: IHPC, ARTC

Title of Paper: Numerical simulation and experimental study of normal force and particle speed in the robotic stream finishing process

Published in: Manufacturing Processes

Abstract: Normal force and particle speed are the two most important parameters in determining the mass removal rate on the workpiece in the stream finishing process. However, quantifying them is still a big challenge due to the complexity of the interaction between media flow and the workpiece. In this study, a continuum-based (μ(I) rheology) numerical model was developed to simulate the granular media flow in a robotic stream finishing (RSF) system and validated with in-house experimental data. A novel frictional wall-slip model was developed to describe the media flow speed on the surface of a rectangular workpiece. The impact of three key process variables: (i) immersion depth (D), (ii) angle of attack (θ), and (iii) radial distance (r) on the resulting normal force and media flow speed was analyzed. The resulting normal force on the workpiece strongly depends on the immersion depth. A small increase in the hydrostatic pressure is amplified through elevated effective viscosity near the workpiece, resulting in a significant increase in the normal force. A critical θ for the dependency of normal force was identified. Below the critical θ, the normal force varies slightly with the increase in θ. Above the critical θ, the normal force decreases rapidly with the increase in θ. The normal force also increases linearly with the increase in radial distance. In general, the media flow speed increases rapidly with θ. However, the increase peaks at θ = 75° due to the wake effect behind the leading edge. As D increases, the media flow speed only changes marginally, given the same θ. The media flow speed increases with radial distance, and the relationship is quadratic. We have validated – through experiments – that the numerical model can reliably predict both normal force and media flow speed on the rectangular workpiece. As the local material removal rate has a direct correlation to the normal force and the media flow speed, this numerical model is capable of predicting material removal distribution on an actual polished component and, therefore, will be an indispensable tool for conducting in-process optimization and toolpath planning.

URL: https://doi.org/10.1016/j.jmapro.2023.04.081

02 May 2023

Submitted by (Bold are A*STAR Staff): Wenwen Liu, Jian Liang Cheong, Man-Fai Ng, Jackie Y. Ying

Research Institute: IMRE, IHPC, ID Labs

Title of Paper: Carbon nitride mediated synthesis of titanium-based electrodes for high-performance asymmetric supercapacitors

Published in: Nano Energy

Abstract: Rational design of electrode materials with specific compositions and unique morphological and structural features to achieve supercapacitors (SCs) with high energy densities without compromising their inherent electrochemical merits remains a great challenge. Herein, a carbon nitride (C3N4) mediated “one-for-two” strategy was proposed to synthesize titanium nitride/carbon nanosheets (TiN/C) and titanium carbide/carbon nanosheets (TiC/C) with three-dimensional morphology and hierarchical structure, respectively. The derived TiN/C and TiC/C were used as cathode and anode materials, respectively, with excellent capacitor behavior in aqueous electrolyte. Specifically, asymmetric SCs constructed with the TiN/C cathode and the TiC/C anode delivered a large operation voltage of 0.3–1.8 V, a high specific capacitance of 103 F·g−1, and a remarkable energy density of 45.2 Wh·kg−1, outperforming most of the previously reported TiN- and TiC-based SCs. Ex situ XRD and TEM characterizations as well as DFT simulation indicated that the excellent performance could be attributed to reversible pseudocapacitive redox reaction and electro-adsorbed anions at the TiN/C cathode, and fast adsorption/desorption of cations at the TiC/C anode, as well as unique surface morphology and heterostructure. The strategy presented in this work also provides new design concepts for the synthesis of other transition metal nitrides (or carbides)/carbon composites for other advanced energy applications.

URL: https://doi.org/10.1016/j.nanoen.2023.108489

29 Apr 2023

Submitted by (Bold are A*STAR Staff): Guodong Liu, Chenye Shen and Anqi Qiu

Research Institute:

Title of Paper: Amyloid-β Accumulation in Relation to Functional Connectivity in Aging: a Longitudinal Study

Published in: NeuroImage

Abstract: The brain undergoes many changes at pathological and functional levels in healthy aging. This study employed a longitudinal and multimodal imaging dataset from the OASIS-3 study (n=300) and explored possible relationships between amyloid beta (Aβ) accumulation and functional brain organization over time in healthy aging. We used positron emission tomography (PET) with Pittsburgh compound-B (PIB) to quantify the Aβ accumulation in the brain and resting-state functional MRI (rs-fMRI) to measure functional connectivity (FC) among brain regions. Each participant had at least 2 to 3 follow-up visits. A linear mixed-effect model was used to examine longitudinal changes of Aβ accumulation and FC throughout the whole brain. We found that the limbic and frontoparietal networks had a greater annual Aβ accumulation and a slower decline in FC in aging. Additionally, the amount of the Aβ deposition in the amygdala network at baseline slowed down the decline in its FC in aging. Furthermore, the functional connectivity of the limbic, default mode network (DMN), and frontoparietal networks accelerated the Aβ propagation across their functionally highly connected regions. The functional connectivity of the somatomotor and visual networks accelerated the Aβ propagation across the brain regions in the limbic, frontoparietal, and DMN networks. These findings suggested that the slower decline in the functional connectivity of the functional hubs may compensate for their greater Aβ accumulation in aging. The Aβ propagation from one brain region to the other may depend on their functional connectivity strength.

URL: https://doi.org/10.1016/j.neuroimage.2023.120146

17 Apr 2023

Submitted by (Bold are A*STAR Staff): Qingwei Meng, Jiaxuan Zang, Wenli Zhang, Chengwu Qiu, Peng Zhao, Jia Zhang and Tiejun Wang

Research Institute: IHPC

Title of Paper: Selective furanyl ring hydrogenation of 5-hydroxymethylfurfural at sub-ambient temperature via steric effect on decorated Pd surfaces

Published in: International Journal of Hydrogen Energy

Abstract: It is a great challenge to synthesize the medical intermediate 5-hydroxymethyltetrahydrofurfural (HMTHF) from selective hydrogenation of 5-hydroxymethylfurfural (HMF), as the branched Cdouble bondO group is usually preferentially hydrogenated over active metal, e.g. Pd sites. Herein, we designed a surface-decorated Pd@NSi@Al2O3 catalyst and achieved selective hydrogenation of HMF, yielding 83.5% HMTHF at sub-ambient temperature (5 °C). Combination of experiments and DFT calculations verify the steric effect caused by the decoration of Pd surfaces led to larger bond lengths between O or C in –CHO ligand of HMF and the closest surface Pd sites. The total activation barrier for the hydrogenation reactions on the –CHO group of HMF becomes larger from 0.60 eV on Pd(111) to 0.83 eV on the cramped Pd(111). As a result, Cdouble bondC groups in the furanyl ring was preferentially hydrogenated over the branched Cdouble bondO of HMF. Furthermore, hydrogen bonds between the hydroxymethyl of the adsorbed HMF and the amine groups on Pd surfaces promote the adsorption of HMF and significantly increase the catalytic activity. Notably, this catalyst is robust and readily applicable in the furanyl ring hydrogenation of furfural and 5-methylfurfural. Overall, a controllable surface decoration strategy has been delivered that tailoring an efficient catalyst for selective hydrogenation of aromatic aldehyde.

URL: https://doi.org/10.1016/j.ijhydene.2023.03.227

10 Apr 2023

Submitted by (Bold are A*STAR Staff): Andrew Jun Yao Wong, Wei Ying Lieu, Deviprasath Chinnadurai, Man-Fai Ng, and Zhi Wei She

Research Institute: IMRE, IHPC

Title of Paper: Uncovering the Binder Interactions with S-PAN and MXene for Room Temperature Na–S Batteries

Published in: Nano Letters

Abstract: MXenes and sulfurized polyacrylonitrile (S-PAN) are emerging as possible contenders to resolve the polysulfide dissolution and volumetric expansion issues in sodium–sulfur batteries. Herein, we explore the interactions between Ti3C2Tx MXenes and S-PAN with traditional binders such as polyvinylidene difluoride (PVDF), poly(acrylic acid) (PAA), and carboxymethyl cellulose (CMC) in Na–S batteries for the first time. We hypothesize that the linearity and polarity of the binder significantly influence the dispersion of S-PAN over Ti3C2Tx. The three-dimensional polar CMC binder resulted in better contact surface area with both S-PAN and Ti3C2Tx. Moreover, the improved binding of the discharge products with the CMC binder effectively traps them and prevents unwanted shuttling. Consequently, the Na–S battery using the CMC binder displayed a high initial capacity of 1282 mAh/g(s) at 0.2 C and a low capacity fading of 0.092% per cycle over 300 cycles. This work highlights the importance of understanding MXene-binder interactions in sulfur cathodes.

URL: https://pubs.acs.org/doi/10.1021/acs.nanolett.3c00778

06 Apr 2023

Submitted by (Bold are A*STAR Staff): Krishna M. Gupta, Xavier Chin, Parijat Kanaujia 

Research Institute: ISCE2

Title of Paper: Molecular Interactions between APIs and Enteric Polymeric Excipients in Solid Dispersion: Insights from Molecular Simulations and Experiments

Published in: Pharmaceutics

Abstract: Solid dispersion of poorly soluble APIs is known to be a promising strategy to improve dissolution and oral bioavailability. To facilitate the development and commercialization of a successful solid dispersion formulation, understanding of intermolecular interactions between APIs and polymeric carriers is essential. In this work, first, we assessed the molecular interactions between various delayed-release APIs and polymeric excipients using molecular dynamics (MD) simulations, and then we formulated API solid dispersions using a hot melt extrusion (HME) technique. To assess the potential API–polymer pairs, three quantities were evaluated: (a) interaction energy between API and polymer [electrostatic (Ecoul), Lenard-Jones (ELJ), and total (Etotal)], (b) energy ratio (API–polymer/API–API), and (c) hydrogen bonding between API and polymer. The Etotal quantities corresponding to the best pairs: NPX-Eudragit L100, NaDLO–HPMC(P), DMF–HPMC(AS) and OPZ–HPMC(AS) were −143.38, −348.04, −110.42, and −269.43 kJ/mol, respectively. Using a HME experimental technique, few API–polymer pairs were successfully extruded. These extruded solid forms did not release APIs in a simulated gastric fluid (SGF) pH 1.2 environment but released them in a simulated intestinal fluid (SIF) pH 6.8 environment. The study demonstrates the compatibility between APIs and excipients, and finally suggests a potential polymeric excipient for each delayed-release API, which could facilitate the development of the solid dispersion of poorly soluble APIs for dissolution and bioavailability enhancement.

URL: https://doi.org/10.3390/pharmaceutics15041164

28 Mar 2023

Submitted by (Bold are A*STAR Staff): Naythan Z. X. Yeo, Dillon W. P. Tay, Shi Jun Ang

Research Institute: ISCE2,IHPC

Title of Paper: Benchmarking tandem mass spectra of small natural product molecules via ab initio molecular dynamics

Published in: ChemRxiv

Abstract: Natural products have proven to be valuable, particularly in the fields of drug discovery and chemogenomics. Tandem mass spectrometry, along with reference mass spectral libraries, has been frequently used to assist the characterization of natural products present in unknown complex mixtures. As current spectral libraries only contain a small percentage of known natural products, their continual expansion is crucial for accurate molecular identification. However, doing so through experimental means is often expensive and time-consuming. This study explores the use of ab initio molecular dynamics simulations (AIMD) based on the lightweight GFN2-xTB semiempirical Hamiltonian, to generate mass spectra for small natural products molecules. Through this approach, more than 2,700 unique mass spectra were generated and analysed in relation to the Global Natural Products Social Molecular Networking (GNPS) database. This study found that AIMD performs relative well (mean cosine similarity score of 0.68), with improved performance observed in aromatic molecules but limitations found when applied to molecules with carboxylic acid groups. Other key findings relating to experimental and simulated conditions also led to several recommendations for future work in this area. Overall, AIMD proved to have huge potential to be used to develop a putative natural product mass spectral library.

URL: https://doi.org/10.26434/chemrxiv-2023-7k5x8

27 Mar 2023

Submitted by (Bold are A*STAR Staff): Shuai Chen, Zachary H. Aitken, Subrahmanyam Pattamatta, Zhaoxuan Wu, Zhi Gen Yu,David J. Srolovitz, Peter K. Liaw, Yong-Wei Zhang

Research Institute: IHPC

Title of Paper: Short-range ordering alters the dislocation nucleation and propagation in refractory high-entropy alloys

Published in: Materials Today

Abstract: The role of short-range ordering (SRO) in the dislocation kinetics in refractory high-entropy alloys (RHEAs) remains controversial. On one hand, it was shown by simulations that the mobility of edge dislocations was enhanced while that of screw dislocations was reduced, leading to the conclusion that screw dislocations should be dominant. On the other hand, experiments exclusively showed the dominance of edge dislocations. Here, we investigate the impact of SRO in the grain interior and grain boundary on dislocation nucleation and propagation in a BCC MoTaTiWZr RHEA, using a combination of the density-functional theory calculations, Monte Carlo method, and molecular dynamic simulation. Our results show that this RHEA is energetically favorable to undergo SRO, thus forming a pseudo-composite microstructure. This microstructure consists of three categories of clusters: high energy clusters (HECs), medium energy clusters (MECs), and low energy clusters (LECs), with the HECs in grain boundaries acting as weak fillers to induce dislocation nucleation while the MECs/LECs serving as a strong matrix to stabilize the weak HECs. Importantly, SRO is found to enhance the energy barriers for both edge and screw dislocation motion and make the mobility of edge dislocations comparable to or even lower than screw dislocations, contributing to the dominance of edge dislocations in the BCC RHEA. Our work highlights the importance of SRO in influencing the dislocation activity of RHEAs and presents a fascinating route for designing RHEAs to achieve superior mechanical properties.

URL: https://doi.org/10.1016/j.mattod.2023.03.009

20 Mar 2023

Submitted by (Bold are A*STAR Staff): Changhong LINGHU, Yangchengyi Liu, Yee Yuan Tan, Jun Heng Marcus Sing, Yuxuan Tang, Aiwu Zhou, Xiufeng Wang, Dong Li, Huajian Gao, K. Jimmy Hsia

Research Institute: IHPC

Title of Paper: Overcoming the adhesion paradox and switchability conflict on rough
surfaces with shape-memory polymers

Published in: Applied Physical Sciences

Abstract: Smart adhesives that can be applied and removed on demand play an important role in modern life and manufacturing. However, current smart adhesives made of elastomers suffer from the long-standing challenges of the adhesion paradox (rapid decrease in adhesion strength on rough surfaces despite adhesive molecular interactions) and the switchability conflict (trade-off between adhesion strength and easy detachment). Here, we report the use of shape-memory polymers (SMPs) to overcome the adhesion paradox and switchability conflict on rough surfaces. Utilizing the rubbery–glassy phase transition in SMPs, we demonstrate, through mechanical testing and mechanics modeling, that the conformal contact in the rubbery state followed by the shape-locking effect in the glassy state results in the so-called rubber-to-glass (R2G) adhesion (defined as making contact in the rubbery state to a certain indentation depth followed by detachment in the glassy state), with extraordinary adhesion strength (>1 MPa) proportional to the true surface area of a rough surface, overcoming the classic adhesion paradox. Furthermore, upon transitioning back to the rubbery state, the SMP adhesives can detach easily due to the shape-memory effect, leading to a simultaneous improvement in adhesion switchability (up to 103, defined as the ratio of the SMP R2G adhesion to its rubbery-state adhesion) as the surface roughness increases. The working principle and the mechanics model of R2G adhesion provide guidelines for developing stronger and more switchable adhesives adaptable to rough surfaces, thereby enhancing the capabilities of smart adhesives, and impacting various fields such as adhesive grippers and climbing robots.

URL: https://doi.org/10.1073/pnas.2221049120

17 Mar 2023

Submitted by (Bold are A*STAR Staff): Anqi Qiu, Chaoqiang Liu

Research Institute:

Title of Paper: Pathways link environmental and genetic factors with structural brain networks and psychopathology in youth

Published in: Neuropsychopharmacology

Abstract: Adolescence is a period of significant brain development and maturation, and it is a time when many mental health problems first emerge. This study aimed to explore a comprehensive map that describes possible pathways from genetic and environmental risks to structural brain organization and psychopathology in adolescents. We included 32 environmental items on developmental adversity, maternal substance use, parental psychopathology, socioeconomic status (SES), school and family environment; 10 child psychopathological scales; polygenic risk scores (PRS) for 10 psychiatric disorders, total problems, and cognitive ability; and structural brain networks in the Adolescent Brain Cognitive Development study (ABCD, n = 9168). Structural equation modeling found two pathways linking SES, brain, and psychopathology. Lower SES was found to be associated with lower structural connectivity in the posterior default mode network and greater salience structural connectivity, and with more severe psychosis and internalizing in youth (p < 0.001). Prematurity and birth weight were associated with early-developed sensorimotor and subcortical networks (p < 0.001). Increased parental psychopathology, decreased SES and school engagement was related to elevated family conflict, psychosis, and externalizing behaviors in youth (p < 0.001). Increased maternal substance use predicted increased developmental adversity, internalizing, and psychosis (p < 0.001). But, polygenic risks for psychiatric disorders had moderate effects on brain structural connectivity and psychopathology in youth. These findings suggest that a range of genetic and environmental factors can influence brain structural organization and psychopathology during adolescence, and that addressing these risk factors may be important for promoting positive mental health outcomes in young people.

URL: https://doi.org/10.1038/s41386-023-01559-7

13 Mar 2023

Submitted by (Bold are A*STAR Staff): Cihan Acar, Kuluhan Binici, Alp Tekirdağ, Wu Yan

Research Institute: I2R

Title of Paper: Visual-Policy Learning through Multi-Camera View to Single-Camera View Knowledge Distillation for Robot Manipulation Tasks

Published in: arXIV [cs.CV]

Abstract: The use of multi-camera views simultaneously has been shown to improve the generalization capabilities and performance of visual policies. However, the hardware cost and design constraints in real-world scenarios can potentially make it challenging to use multiple cameras. In this study, we present a novel approach to enhance the generalization performance of vision-based Reinforcement Learning (RL) algorithms for robotic manipulation tasks. Our proposed method involves utilizing a technique known as knowledge distillation, in which a pre-trained ``teacher'' policy trained with multiple camera viewpoints guides a ``student'' policy in learning from a single camera viewpoint. To enhance the student policy's robustness against camera location perturbations, it is trained using data augmentation and extreme viewpoint changes. As a result, the student policy learns robust visual features that allow it to locate the object of interest accurately and consistently, regardless of the camera viewpoint. The efficacy and efficiency of the proposed method were evaluated both in simulation and real-world environments. The results demonstrate that the single-view visual student policy can successfully learn to grasp and lift a challenging object, which was not possible with a single-view policy alone. Furthermore, the student policy demonstrates zero-shot transfer capability, where it can successfully grasp and lift objects in real-world scenarios for unseen visual configurations.

URL: https://doi.org/10.48550/arXiv.2303.07026

9 Mar 2023

Submitted by (Bold are A*STAR Staff): Wen-Qing Li, Juan Manuel Arce-Ramos, Michael B. Sullivan, Chee Kok Poh, Luwei Chen, Armando Borgna, Jia Zhang

Research Institute: IHPC, ISCE2

Title of Paper: Mechanistic insights into selective ethylene formation on the χ-Fe5C2 (510) surface

Published in: Journal of Catalysis

Abstract: While iron carbide catalysts are widely used to produce diverse hydrocarbons during Fisher-Tropsch synthesis, the complexity of the catalyst and reaction makes it very challenging to obtain a deep understanding of the chemical process and to further improve the performance. In this work, we propose a novel mechanism through density functional theory simulations for CO-derived surface C hydrogenation to C2H4 involving previously unexplored surface diffusion of partially hydrogenated intermediates (CH, CHCH), which significantly reduces the effective energy barrier (Ea-eff) of CH2CH2 from 2.89 eV to 2.10 eV. The hydrogenation of CH2CH to C2H4 is the key step of the entire process. Studies on the correlation between the average Bader charge of surface Fe and the Ea-eff of CH4 and CH2CH2 formation indicate that an increase in the positive charge of iron can enhance the activity and selectivity (with reference to CH4) of ethylene formation.

URL: https://doi.org/10.1016/j.jcat.2023.03.014

8 Mar 2023

Submitted by (Bold are A*STAR Staff): Fabio Bussolotti, Hiroyo Kawai, Ivan Verzhbitskiy, Wei Tao, Duc-Quan Ho, Anirban Das, Junxiang Jia, Shantanu Mukherjee, Bent Weber, and Kuan Eng Johnson Goh

Research Institute: IMRE, IHPC

Title of Paper: Interlayer hybridization in a van der Waals quantum spin-Hall insulator/superconductor heterostructure

Published in: AIP Advances

Abstract: In this work, we present an angle-resolved photoemission spectroscopy study of a 1T′-WTe2 monolayer epitaxially grown on NbSe2 substrates, a prototypical quantum spin Hall insulator (QSHI)/superconductor heterojunction. Angle-resolved photoemission spectroscopy data indicate the formation of electronic states in the bulk bandgap of WTe2, which are absent in the nearly free-standing WTe2 grown on the highly oriented pyrolytic graphite substrate, where an energy gap of ∼100 meV is reported. The results are explained in terms of hybridization effects promoted by the QSHI–superconductor interaction at WTe2/NbSe2 interfaces, in line with recent scanning probe microscopy investigation and theoretical band structure calculations. Our findings highlight the important role of interlayer interaction on the electronic properties and ultimately on the engineering of topological properties of the QSHI/superconducting heterostructure.

URL: https://doi.org/10.1063/5.0130393

18 Feb 2023

Submitted by (Bold are A*STAR Staff): Jinghan Huang, Moo K. Chung, Anqi Qiu

Research Institute:

Title of Paper: Heterogeneous Graph Convolutional Neural Network via Hodge-Laplacian for Brain Functional Data

Published in: arXIV [cs.CV]

Abstract: This study proposes a novel heterogeneous graph convolutional neural network (HGCNN) to handle complex brain fMRI data at regional and across-region levels. We introduce a generic formulation of spectral filters on heterogeneous graphs by introducing the k−th Hodge-Laplacian (HL) operator. In particular, we propose Laguerre polynomial approximations of HL spectral filters and prove that their spatial localization on graphs is related to the polynomial order. Furthermore, based on the bijection property of boundary operators on simplex graphs, we introduce a generic topological graph pooling (TGPool) method that can be used at any dimensional simplices. This study designs HL-node, HL-edge, and HL-HGCNN neural networks to learn signal representation at a graph node, edge levels, and both, respectively. Our experiments employ fMRI from the Adolescent Brain Cognitive Development (ABCD; n=7693) to predict general intelligence. Our results demonstrate the advantage of the HL-edge network over the HL-node network when functional brain connectivity is considered as features. The HL-HGCNN outperforms the state-of-the-art graph neural networks (GNNs) approaches, such as GAT, BrainGNN, dGCN, BrainNetCNN, and Hypergraph NN. The functional connectivity features learned from the HL-HGCNN are meaningful in interpreting neural circuits related to general intelligence.

URL: https://doi.org/10.48550/arXiv.2302.09323

14 Feb 2023

Submitted by (Bold are A*STAR Staff): Zi S. D. Toa, Maria V. Chekhova, Leonid A. Krivitsky, Anna V. Paterova

Research Institute: IMRE

Title of Paper: Crystal superlattices for versatile and sensitive quantum spectroscopy

Published in: Optics Express

Abstract: Nonlinear interferometers with quantum correlated photons have been demonstrated to improve optical characterization and metrology. These interferometers can be used in gas spectroscopy, which is of particular interest for monitoring greenhouse gas emissions, breath analysis and industrial applications. Here, we show that gas spectroscopy can be further enhanced via the deployment of crystal superlattices. This is a cascaded arrangement of nonlinear crystals forming interferometers, allowing the sensitivity to scale with the number of nonlinear elements.
In particular, the enhanced sensitivity is observed via the maximum intensity of interference fringes that scales with low concentration of infrared absorbers, while for high concentration the sensitivity is better in interferometric visibility measurements. Thus, a superlattice acts as a versatile gas sensor since it can operate by measuring different observables, which are relevant to practical applications. We believe that our approach offers a compelling path towards further enhancements for quantum metrology and imaging using nonlinear interferometers with correlated photons.

URL: https://doi.org/10.1364/OE.477019

10 Feb 2023

Submitted by (Bold are A*STAR Staff): Choon Wee Kee

Research Institute: ISCE2

Title of Paper: Molecular Understanding and Practical In Silico Catalyst Design in Computational Organocatalysis and Phase Transfer Catalysis—Challenges and Opportunities

Published in: Molecules 2023

Abstract: Through the lens of organocatalysis and phase transfer catalysis, we will examine the key components to calculate or predict catalysis-performance metrics, such as turnover frequency and measurement of stereoselectivity, via computational chemistry. The state-of-the-art tools available to calculate potential energy and, consequently, free energy, together with their caveats, will be discussed via examples from the literature. Through various examples from organocatalysis and phase transfer catalysis, we will highlight the challenges related to the mechanism, transition state theory, and solvation involved in translating calculated barriers to the turnover frequency or a metric of stereoselectivity. Examples in the literature that validated their theoretical models will be showcased. Lastly, the relevance and opportunity afforded by machine learning will be discussed.

URL: https://doi.org/10.3390/molecules28041715

9 Feb 2023

Submitted by (Bold are A*STAR Staff): V. Vijendran, Aritra Das, Dax Enshan Koh, Syed M. Assad, Ping Koy Lam

Research Institute: IMRE, IHPC

Title of Paper: An Expressive Ansatz for Low-Depth Quantum Optimisation

Published in: arXIV [quant-ph]

Abstract: The Quantum Approximate Optimisation Algorithm (QAOA) is a hybrid quantum-classical algorithm used to approximately solve combinatorial optimisation problems. It involves multiple iterations of a parameterised ansatz that consists of a problem and mixer Hamiltonian, with the parameters being classically optimised. While QAOA can be implemented on near-term quantum hardware, physical limitations such as gate noise, restricted qubit connectivity, and state-preparation-and-measurement (SPAM) errors can limit circuit depth and decrease performance. To address these limitations, this work introduces the eXpressive QAOA (XQAOA), a modified version of QAOA that assigns more classical parameters to the ansatz to improve the performance of low-depth quantum circuits. XQAOA includes an additional Pauli-Y component in the mixer Hamiltonian, thereby allowing the mixer to implement arbitrary unitary transformations on each qubit. To benchmark the performance of the XQAOA ansatz at low depth, we derive its closed-form expression for the MaxCut problem and compare it to QAOA, Multi-Angle QAOA (MA-QAOA), a Classical-Relaxed (CR) algorithm, and the state-of-the-art Goemans-Williamson (GW) algorithm on a set of unweighted regular graphs with 128 and 256 nodes and degrees ranging from 3 to 10. Our results show that XQAOA performs better than QAOA, MA-QAOA, and the CR algorithm on all graphs and outperforms the GW algorithm on graphs with degrees greater than 4. Additionally, we find an infinite family of graphs for which XQAOA solves MaxCut exactly and show analytically that for some graphs in this family, special cases of XQAOA can achieve a larger approximation ratio than QAOA. Overall, XQAOA is a more viable choice for implementing quantum combinatorial optimisation on near-term quantum devices, as it can achieve better results with a single iteration, despite requiring additional classical resources.

URL: https://doi.org/10.48550/arXiv.2302.04479

23 Jan 2023

Submitted by (Bold are A*STAR Staff): Nikhil Tulsian, Palur Raghuvamsi, Xinlei Qian, Yue Gu, Bhuvaneshwari D/O Shunmuganathan, Firdaus Samsudin, Yee Hwa Wong, Jianqing Lin, Kiren Purushotorman, Mary Kozma, BEI WANG, Julien Lescar, Cheng-I Wang, Ravindra Gupta, Peter Bond, Paul MacAry

Research Institute: BII, SIgN

Title of Paper: Defining neutralization and allostery by antibodies against COVID-19 variants

Published in: Nature Communications

Abstract: The changing landscape of mutations in the SARS-CoV-2 Spike protein is linked to the emergence of variants, immune-escape and reduced efficacy of the existing repertoire of anti-viral antibodies. A major factor that contributes to the functional activity of the neutralizing antibodies are the intrinsic quaternary changes that occur as a result of antibody-Spike trimer interactions. In this study, we reveal the conformational dynamics and allosteric perturbations linked to binding of human monoclonal antibodies and the viral Spike protein. We identify epitope hotspots of known and novel antibodies, and associated changes in Spike dynamics that define weak, moderate and strong neutralizing antibodies. We show the impact of mutations in Wuhan, Delta, and Omicron variants of concern (VoCs) and differences observed in the antibody-induced conformational changes and illustrate how these render certain antibodies ineffective. Our comparative analyses of the antibody-footprints on Spike variants reveal how antibodies with similar binding affinities may induce destabilizing and stabilizing allosteric effects. These differences have important implications for neutralization efficacy and for developing new antibodies targeting emerging variants. Our results provide mechanistic insights into the functional modes and synergistic behavior of human antibodies against COVID-19, and provide a rationale to design effective antiviral strategies.

URL: https://doi.org/10.21203/rs.3.rs-2465199/v1

20 Jan 2023

Submitted by (Bold are A*STAR Staff): Carina Yi Jing Lim, Meltem Yilmaz, Juan Manuel Arce-Ramos, Albertus D. Handoko, Wei Jie Teh, Yuangang Zheng, Zi Hui Jonathan Khoo, Ming Lin, Mark Isaacs, Teck Lip Dexter Tam, Yang Bai, Chee Koon Ng, Boon Siang Yeo, Gopinathan Sankar, Ivan P. Parkin, Kedar Hippalgaonkar, Michael B. Sullivan, Jia Zhang & Yee-Fun Lim  

Research Institute: IHPC, IMRE

Title of Paper: Surface charge as activity descriptors for electrochemical CO2 reduction to multi-carbon products on organic-functionalised Cu

Published in: Nature Communications

Abstract: Intensive research in electrochemical CO2 reduction reaction has resulted in the discovery of numerous high-performance catalysts selective to multi-carbon products, with most of these catalysts still being purely transition metal based. Herein, we present high and stable multi-carbon products selectivity of up to 76.6% across a wide potential range of 1 V on histidine-functionalised Cu. In-situ Raman and density functional theory calculations revealed alternative reaction pathways that involve direct interactions between adsorbed histidine and CO2 reduction intermediates at more cathodic potentials. Strikingly, we found that the yield of multi-carbon products is closely correlated to the surface charge on the catalyst surface, quantified by a pulsed voltammetry-based technique which proved reliable even at very cathodic potentials. We ascribe the surface charge to the population density of adsorbed species on the catalyst surface, which may be exploited as a powerful tool to explain CO2 reduction activity and as a proxy for future catalyst discovery, including organic-inorganic hybrids.

URL: https://doi.org/10.1038/s41467-023-35912-7

10 Jan 2023

Submitted by (Bold are A*STAR Staff): Sabrina L. Slimani, Roman Kostecki, Ahmed Nuri Kursunlu, Tak W. Kee, Patrick C. Tapping, Adrian M. Mak and James Q. Quach  

Research Institute: IHPC

Title of Paper: Experimental and computational characterisation of an artificial light harvesting complex

Published in: Royal Society of Chemistry

Abstract: Photosynthesis has been shown to be a highly efficient process for energy transfer in plants and bacteria. Like natural photosynthetic systems, the artificial light harvesting complex (LHC) BODIPY pillar[5]arene exhibits Förster resonance energy transfer (FRET). However, extensive characterisation of the BODIPY pillar[5]arene LHC to determine its suitability as an artificial LHC has yet to occur. In this paper we experimentally and computationally investigate the photophysical properties of the LHC by comparing the light absorption of the BODIPY LHC to individual BODIPY chromophores. Our results show evidence for quantum coherence, with oscillation frequencies of 100 cm−1 and 600 cm−1, which are attributable to vibronic, or exciton–phonon type coupling. Computational analysis suggests strong couplings of the molecular orbitals of the LHC resulting from the stacking of neighbouring BODIPY chromophore units. Interestingly, we find a 40% reduction in the absorbance of light for the BODIPY LHC compared to the individual chromophores which we attribute to electronic interactions between the conjugated π-systems of the BODIPY chromophores and the pillar[5]arene backbone.

URL: https://doi.org/10.1039/D2CP03858G

06 Jan 2023

Submitted by (Bold are A*STAR Staff): Yingying Jiang, Martial Duchamp, Shi Jun Ang, Hongwei Yan, Teck Leong Tan & Utkur Mirsaidov

Research Institute: IHPC

Title of Paper: Dynamics of the fcc-to-bcc phase transition in single-crystalline PdCu alloy nanoparticles

Published in: Nature Communications

Abstract: Two most common crystal structures in metals and metal alloys are body-centered cubic (bcc) and face-centered cubic (fcc) structures. The phase transitions between these structures play an important role in the production of durable and functional metal alloys. Despite their technological significance, the details of such phase transitions are largely unknown because of the challenges associated with probing these processes. Here, we describe the nanoscopic details of an fcc-to-bcc phase transition in PdCu alloy nanoparticles (NPs) using in situ heating transmission electron microscopy. Our observations reveal that the bcc phase always nucleates from the edge of the fcc NP, and then propagates across the NP by forming a distinct few-atoms-wide coherent bcc–fcc interface. Notably, this interface acts as an intermediate precursor phase for the nucleation of a bcc phase. These insights into the fcc-to-bcc phase transition are important for understanding solid − solid phase transitions in general and can help to tailor the functional properties of metals and their alloys.

URL: https://doi.org/10.1038/s41467-022-35325-y

27 Dec 2022

Submitted by (Bold are A*STAR Staff): Krishna M. Gupta, Surajit Das, Annie B. H. Wong, and Pui Shan Chow

Research Institute: ISCE2

Title of Paper: Formulation and Skin Permeation of Active-Loaded Lipid Nanoparticles: Evaluation and Screening by Synergizing Molecular Dynamics Simulations and Experiments

Published in: American Chemical Society

Abstract: Encapsulation into nanoparticles (NPs) is a potential method to deliver pharmaceutical/cosmetic actives deep into the skin. However, understanding the NP formulations and underlying mechanism of active delivery to skin has scarcely been studied. We report a simulation platform that screens, evaluates, formulates, and provides atomic-resolution interpretation of NP-based formulations, and reveals the active permeation mechanism from NPs to skin. First, three actives, namely, ferulic acid (FA), clotrimazole (CZE), and tretinoin (TTN), and five lipid excipients’ (Compritol, Precirol, Geleol, Gelot, Gelucire) combinations were screened by MD simulations for the best pairs. For each suggested pair, the actual active and lipid compositions for the synthesis of stable NP formulations were then obtained by experiments. MD simulations demonstrate that in NP formulations, FA and CZE actives are present at the surface of the NPs, whereas TTN actives are present at both the surface and interior of the NP core. The NP shapes obtained by simulation perfectly match with experiments. For each NP, separate MD simulations illustrate that active-loaded NPs approach the skin surface quickly, and then actives translocate from NP surface to skin surface followed by penetration of NPs through skin. The driving force for the translocation which initiates during the penetration process, is the stronger active-skin interaction compared to active-NP interaction. Permeation free energy indicates spontaneous transfer of actives from solution phase to the surface of the skin bilayer. The free energy barriers are increased in the order of FA < TTN < CZE. Significantly lower diffusions of actives are obtained in the main barrier region compared to bulk, and the average diffusion coefficients of actives are in the same order of magnitude (∼10–6 cm2/s). The estimated permeability coefficients (log P) of actives are mainly governed by free energy barriers. The study would facilitate the development of novel lipid-based NP formulations for personal-care/pharmaceutical applications.

URL: https://doi.org/10.1021/acs.langmuir.2c02550

24 Nov 2022

Submitted by (Bold are A*STAR Staff): Chaoqiang Liu, Fei Huang, Anqi QiuResearch Institute: -

Title of Paper: Monte Carlo Ensemble Neural Network for the diagnosis of Alzheimer’s disease

Published in: Sciencedirect

Abstract: Convolutional neural networks (CNNs) have been increasingly used in the computer-aided diagnosis of Alzheimer’s Disease (AD). This study takes the advantage of the 2D-slice CNN fast computation and ensemble approaches to develop a Monte Carlo Ensemble Neural Network (MCENN) by introducing Monte Carlo sampling and an ensemble neural network in the integration with ResNet50. Our goals are to improve the 2D-slice CNN performance and to design the MCENN model insensitive to image resolution. Unlike traditional ensemble approaches with multiple base learners, our MCENN model incorporates one neural network learner and generates a large number of possible classification decisions via Monte Carlo sampling of feature importance within the combined slices. This can overcome the main weakness of the lack of 3D brain anatomical information in 2D-slice CNNs and develop a neural network to learn the 3D relevance of the features across multiple slices. Brain images from Alzheimer’s Disease Neuroimaging Initiative (ADNI, 7199 scans), the Open Access Series of Imaging Studies-3 (OASIS-3, 1992 scans), and a clinical sample (239 scans) are used to evaluate the performance of the MCENN model for the classification of cognitively normal (CN), patients with mild cognitive impairment (MCI) and AD. Our MCENN with a small number of slices and minimal image processing (rigid transformation, intensity normalization, skull stripping) achieves the AD classification accuracy of 90%, better than existing 2D-slice CNNs (accuracy: 63% ~ 84%) and 3D CNNs (accuracy: 74% ~ 88%). Furthermore, the MCENN is robust to be trained in the ADNI dataset and applied to the OASIS-3 dataset and the clinical sample. Our experiments show that the AD classification accuracy of the MCENN model is comparable when using high- and low-resolution brain images, suggesting the insensitivity of the MCENN to image resolution. Hence, the MCENN does not require high-resolution 3D brain structural images and comprehensive image processing, which supports its potential use in a clinical setting.

URL: https://doi.org/10.1016/j.neunet.2022.10.032

20 Nov 2022

Submitted by (Bold are A*STAR Staff): Yuanjian Li, Gaoliang Yang, Chang Zhang, Wei Ying Lieu, Carina Yi Jing Lim, Shengnan Sun, Jianbiao Wang, Shunqiong Jiang, Zhenxiang Xing, Zdenek Sofer, Man-Fai Ng, Wei Liu, Zhi Wei SehResearch Institute: IHPC, IMRE

Title of Paper: Grain-Boundary-Rich Triphasic Artificial Hybrid Interphase Toward Practical Magnesium Metal Anodes

Published in: Wiley Online Library

Abstract: Magnesium metal anodes have attracted widespread attention for their high volumetric capacity and natural abundance, but are precluded from practical applications by poor rate capability and limited lifespan due to sluggish ion-transfer kinetics and uneven deposition behavior. Herein, for the first time a grain-boundary-rich triphasic artificial hybrid interphase, consisting of Sb metal, Mg3Sb2 alloy, and MgCl2, is designed on Mg anode surface by a facile solution treatment method, enabling high-rate and long-cycle Mg plating/stripping behavior. The triphasic artificial hybrid interphase affords high magnesiophilicity and ionic conductivity to reduce the energy barriers for Mg2+ desolvation and deposition. Meanwhile, the abundant grain boundaries redistribute Mg2+ flux at the electrode-electrolyte interface and guide uniform Mg deposition. Accordingly, the as-designed Mg metal anode achieves ultralong cycling life of 350 h at a high current density of 5 mA cm−2 and a large areal capacity of 5 mAh cm−2, outperforming previously reported Mg metal anodes with artificial interphases. Full cells with Mo6 cathode also show extraordinary stability over a long lifespan of 8000 cycles at a high rate of 5 C. The rational artificial interphase design and the understanding of composition-structure-function relationships shed deep insights into the development of fast-charging and long-cycling Mg metal batteries.

URL: https://doi.org/10.1002/adfm.202210639

10 Nov 2022

Submitted by (Bold are A*STAR Staff): Gaoliang Yang, Yuanjian Li, Chang Zhang, Jianbiao Wang, Yang Bai, Carina Yi Jing Lim, Man-Fai Ng, Zhi Chang, Sonal Kumar, Zdenek Sofer, Wei Liu, Zhi Wei SheResearch Institute: IHPC, IMRE

Title of Paper: In Situ Formed Magnesiophilic Sites Guiding Uniform Deposition for Stable Magnesium Metal Anodes

Published in: ACS Publications

Abstract: Owing to its high volumetric capacity and natural abundance, magnesium (Mg) metal has attracted tremendous attention as an ideal anode material for rechargeable Mg batteries. Despite Mg deposition playing an integral role in determining the cycling lifespan, its exact behavior is not clearly understood yet. Herein, for the first time, we introduce a facile approach to build magnesiophilic In/MgIn sites in situ on a Mg metal surface using InCl3 electrolyte additive for rechargeable Mg batteries. These magnesiophilic sites can regulate Mg deposition behaviors by homogenizing the distributions of Mg-ion flux and electric field at the electrode–electrolyte interphase, allowing flat and compact Mg deposition to inhibit short-circuiting. The as-designed Mg metal batteries achieve a stable cycling lifespan of 340 h at 1.0 mA cm–2 and 1.0 mAh cm–2 using Celgard separators, while the full cell coupled with Mo6S8 cathode maintains a high capacity retention of 95.5% over 800 cycles at 1 C.

URL: https://doi.org/10.1021/acs.nanolett.2c03710

08 Nov 2022

Submitted by (Bold are A*STAR Staff): Layal Yaacoub, Indranil Dutta, Baraa Werghi, Benjamin W. J. Chen, Jia Zhang, Edy Abou Hamad, Eleanor Pei Ling Ang, Eva Pump, Anissa Bendjeriou Sedjerari, Kuo-Wei Huang, Jean-Marie BassetResearch Institute: IHPC, IMRE

Title of Paper: Formic Acid Dehydrogenation via an Active Ruthenium Pincer Catalyst Immobilized on Tetra-Coordinated Aluminum Hydride Species Supported on Fibrous Silica Nanospheres

Published in: ACS Publications

Abstract: The demand for harmless and efficient energy sources is remarkably expanding, particularly after the increased awareness of global warming, greenhouse gas emissions, immense fossil fuel consumption, and so forth. Formic acid is considered a potential candidate as an energy carrier for reversible hydrogen storage owing to its decomposition to hydrogen (H2) and carbon dioxide (CO2) in the presence of suitable catalysts. However, selective and efficient decomposition of formic acid using classical heterogeneous catalysis is still challenging because most heterogeneous catalysts which are known are ill defined. Herein, we report a promising heterogeneous approach toward formic acid dehydrogenation using a ruthenium PN3P pincer complex, [Ru–H(CO) (tBuPN3P)] (I), immobilized on a fibrous silica nanosphere, KCC-1, with a strong Lewis acid character [(≡Si–O–Si≡) (≡Si–O−)2Al–H]. The resulting heterogeneous catalyst, [Ru(H) (CO) (tBuPN3P)]@[(≡Si–O–Si≡) (≡Si–O−)2Al–H] (III), has been fully characterized by advanced solid-state characterization techniques. In this compound, Al is tetrahedrally coordinated. It is a single-site catalyst which exhibits good stability toward water, high pressures, and high temperatures as well as good activity in formic acid dehydrogenation. An excellent turnover number of 600,000 and a recyclability of up to 45 cycles are observed.

URL: https://doi.org/10.1021/acscatal.2c04137

31 Oct 2022

Submitted by (Bold are A*STAR Staff): Wei Ying Lieu, Daliang Fang, Yuanjian Li, Xue Liang Li, Congjian Lin, Anupma Thakur, Brian C. Wyatt, Shengnan Sun, Tanmay Ghosh, Babak Anasori, Man-Fai Ng, Hui Ying Yang, and Zhi Wei SehResearch Institute: IHPC, IMRE

Title of Paper: Spherical Templating Spherical Templating of CoSe2 Nanoparticle-Decorated MXenes for Lithium–Sulfur Batteries CoSe2 Nanoparticle-Decorated MXenes for Lithium–Sulfur Batteries

Published in: ACS Publications

Abstract: Two-dimensional MXenes produce competitive performances when incorporated into lithium–sulfur batteries (LSBs), solving key problems such as the poor electronic conductivity of sulfur and dissolution of its polysulfide intermediates. However, MXene nanosheets are known to easily aggregate and restack during electrode fabrication, filtration, or water removal, limiting their practical applicability. Furthermore, in complex electrocatalytic reactions like the multistep sulfur reduction process in LSBs, MXene alone is insufficient to ensure an optimal reaction pathway. In this work, we demonstrate for the first time a loose templating of sulfur spheres using Ti3C2Tx MXene nanosheets decorated with polymorphic CoSe2 nanoparticles. This work shows that the templating of sulfur spheres using nanoparticle-decorated MXene nanosheets can prevent nanosheet aggregation and exert a strong electrocatalytic effect, thereby enabling improved reaction kinetics and battery performance. The S@MXene-CoSe2 cathode demonstrated a long cycle life of 1000 cycles and a low capacity decay rate of 0.06% per cycle in LSBs.

URL: https://doi.org/10.1021/acs.nanolett.2c03279

26 Oct 2022

Submitted by (Bold are A*STAR Staff): Xiaopeng Wang, Shibo Xi, Pengru Huang, Yonghua Du, Haoyin Zhong, Qing Wang, Armando Borgna, Yong-Wei Zhang, Zhenbo Wang, Hao Wang, Zhi Gen Yu, Wee Siang Vincent Lee & Junmin XueResearch Institute: IHPC, ICES

Title of Paper: Pivotal role of reversible NiO6 geometric conversion in oxygen evolution

Published in: Nature

Abstract: Realizing an efficient electron transfer process in the oxygen evolution reaction by modifying the electronic states around the Fermi level is crucial in developing high-performing and robust electrocatalysts. Typically, electron transfer proceeds solely through either a metal redox chemistry (an adsorbate evolution mechanism (AEM), with metal bands around the Fermi level) or an oxygen redox chemistry (a lattice oxygen oxidation mechanism (LOM), with oxygen bands around the Fermi level), without the concurrent occurrence of both metal and oxygen redox chemistries in the same electron transfer pathway. Here we report an electron transfer mechanism that involves a switchable metal and oxygen redox chemistry in nickel-oxyhydroxide-based materials with light as the trigger. In contrast to the traditional AEM and LOM, the proposed light-triggered coupled oxygen evolution mechanism requires the unit cell to undergo reversible geometric conversion between octahedron (NiO6) and square planar (NiO4) to achieve electronic states (around the Fermi level) with alternative metal and oxygen characters throughout the oxygen evolution process. Utilizing this electron transfer pathway can bypass the potential limiting steps, that is, oxygen–oxygen bonding in AEM and deprotonation in LOM. As a result, the electrocatalysts that operate through this route show superior activity compared with previously reported electrocatalysts. Thus, it is expected that the proposed light-triggered coupled oxygen evolution mechanism adds a layer of understanding to the oxygen evolution research scene.

URL: https://doi.org/10.1038/s41586-022-05296-7

20 Oct 2022

Submitted by (Bold are A*STAR Staff): Yingzhi Zeng, Mengren Man, Chee Koon Ng, Delvin Wuu, Jing Jun Lee, Fengxia Wei, Pei Wang, Kewu Bai, Dennis Cheng Cheh Tan, Yong-Wei ZhangResearch Institute: IHPC, IMRE 

Title of Paper: Machine learning-based inverse design for single-phase high entropy alloys

Published in: AIP Publishing

Abstract: In this work, we develop an inverse design framework to search for single-phase high entropy alloys (HEAs) subjected to specified phase targets and constraints. This framework is based on the fast grid search in the composition–temperature space, enabled by a highly accurate and efficient machine learning model trained by a huge amount of data. Using the framework, we search through the entire quaternary, quinary, and senary alloy systems, formed by Al, Co, Cr, Cu, Fe, Mn, Ni, and Ti, to identify three types of HEAs: (1) the single-phase FCC HEA with the highest Al content; (2) the single-phase FCC HEA with lower equilibrium temperatures; and (3) single-phase BCC HEAs with Al as the principal element. For the first time, we reveal that the highest Al content in single-phase FCC HEAs is 0.15 in mole fraction, which is higher than the Al contents in all reported single-phase FCC HEAs. The identified HEAs for the quaternary, quinary, and senary groups are Al0.15Co0.34Cr0.16Ni0.35, Al0.15Co0.35Cr0.1Fe0.05Ni0.35, and Al0.15Co0.36Cr0.06Fe0.06Mn0.01Ni0.36, respectively. All the designed HEAs are verified by the equilibrium calculations with Thermo-Calc software and the TCHEA3 database. We further conduct Scheil–Gulliver calculations and experimental fabrications and characterizations for the designed HEAs, to verify the formation of the targeted phases at non-equilibrium conditions. This work demonstrates a viable approach to design HEAs with specified phase targets and constraints.

URL: https://doi.org/10.1063/5.0109491

20 Oct 2022

Submitted by (Bold are A*STAR Staff): Chee Kwan Gan and Eng Kang Koh Research Institute: IHPC

Title of Paper: A size-consistent Grüneisen-quasiharmonic approach for lattice thermal conductivity

Published in: iopscience

Abstract: We propose a size-consistent Grüneisen-quasiharmonic approach (GQA) to calculate the lattice thermal conductivity κ where the Grüneisen parameters that measure the degree of phonon anharmonicity are calculated directly using first-principles calculations. This is achieved by identifying and modifying two existing equations related to the Slack formulae for κ that suffer from the size-inconsistency problem when dealing with non-monoatomic primitive cells (where the number of atoms in the primitive cell n is greater than one). In conjunction with other thermal parameters such as the acoustic Debye temperature θa that can also be obtained within the GQA, we predict κ for a range of materials taken from the diamond, zincblende, rocksalt, and wurtzite compounds. The results are compared with that from the experiment and the quasiharmonic Debye model (QDM). We find that in general the prediction of θais rather consistent among the GQA, experiment, and QDM. However, while the QDM somewhat overestimates the Grüneisen parameters and hence underestimates κ for most materials, the GQA predicts the experimental trends of Grüneisen parameters and κlmore closely. We expect the GQA with the modified Slack formulae could be used as an effective and practical predictor for κ especially for crystals with large n.

URL: https://doi.org/10.1209/0295-5075/ac9c27

19 Oct 2022

Submitted by (Bold are A*STAR Staff): Tanmay Ghosh, Juan Manuel Arce-Ramos, Wen-Qing Li, Hongwei Yan, See Wee Chee, Alexander Genest, Utkur Mirsaidov Research Institute: IHPC

Title of Paper: Periodic structural changes in Pd nanoparticles during oscillatory CO oxidation reaction

Published in: Nature Communications

Abstract: Nanoparticle (NP) catalysts are ubiquitous in energy systems, chemical production, and reducing the environmental impact of many industrial processes. Under reactive environments, the availability of catalytically active sites on the NP surface is determined by its dynamic structure. However, atomic-scale insights into how a NP surface reconstructs under reaction conditions and the impact of the reconstruction on catalytic activity are still lacking. Using operando transmission electron microscopy, we show that Pd NPs exhibit periodic round–to–flat transitions altering their facets during CO oxidation reaction at atmospheric pressure and elevated temperatures. This restructuring causes spontaneous oscillations in the conversion of CO to CO2 under constant reaction conditions. Our study reveals that the oscillatory behavior stems from the CO-adsorption-mediated periodic restructuring of the nanocatalysts between high-index-faceted round and low-index-faceted flat shapes. These atomic-scale insights into the dynamic surface properties of NPs under reactive conditions play an important role in the design of high-performance catalysts.

URL: https://doi.org/10.1038/s41467-022-33304-x

19 Oct 2022

Submitted by (Bold are A*STAR Staff): Jiteng Gu, Jing Lyu, Zhongxin Chen, Haisen Xu, Vicknesh Sahmuganathan, Sze Chieh Tan, John Sudijono, Jiecong Tang, Eswaranand Venkatasubramanian, Abhijit Mallick, Shuo-Wang Yang, Siew Lang Teo, Ming Lin, Kian Ping LohResearch Institute: IHPC, IMRE

Title of Paper: Poly-adamantane as precursor for low temperature chemical vapor deposition of nanocrystalline diamond films

Published in: Sciencedirect

Abstract: Nanocrystalline diamond (NCD) films are technologically important tribological coatings and their large area, uniform growth is needed for a wide range of applications. The conventional growth of NCD requires the seeding of the foreign substrates by detonation nanodiamond particles. In terms of diamond seeds for subsequent NCD film deposition, the use of chemical precursor offers advantages in producing higher purity and higher crystallinity nanodiamond particles than that by detonation method. However, the easy sublimation of chemical precursor in plasma is a serious drawback. Here we report that the poly-adamantane layer formed by the photochemically induced polymerization of adamantane serves as a promising precursor for the growth of wafer scale NCD film using linear antenna plasma-assisted chemical vapor deposition at 500 °C. TEM cross-section analysis of the interface reveals the formation of well-faceted diamond nuclei within the amorphous carbon matrix (sp3% ~ 40 %) decomposed from poly-adamantane. The influence of plasma chemistry on the nucleation process was also discussed. Our work provides guidance for low-temperature deposition of high-quality NCD film by chemical nucleation.

URL: https://doi.org/10.1016/j.diamond.2022.109471

06 Oct 2022

Submitted by (Bold are A*STAR Staff): Changhong LINGHU, Xudong Yang, Yangchengyi Liu, Dong Li, Huajian Gao, K. Jimmy HsiaResearch Institute: IHPC

Title of Paper: Mechanics of Shape-Locking-Governed R2G Adhesion with Shape Memory Polymers

Published in: Sciencedirect

Abstract: Shape memory polymers (SMPs), with unique properties such as tunable elastic modulus, temporary shape locking and shape recovery upon external stimulation, are emerging as a new class of smart materials with switchable adhesion capabilities. A prominent feature of the adhesion between SMP and a spherical indenter is the so-called R2G adhesion, defined as making contact in the rubbery state to a certain indentation depth followed by detachment in the glassy state. While it has been demonstrated that the R2G adhesion with SMPs can achieve orders of magnitude higher adhesive strength compared to conventional elastic adhesive systems with similar geometrical and adhesion parameters, the fundamental mechanics of R2G adhesion and why it leads to such tremendous adhesion enhancement remain largely mysterious at this point. Here, combined experimental testing, theoretical analysis, and finite element analysis (FEA) based on a thermomechanical constitutive model of SMP are performed to investigate the mechanics of R2G adhesion with a rigid spherical indenter. It is shown that the orders of magnitude enhancement of R2G adhesion over conventional elastic adhesion systems is mostly governed by the shape locking effect during the transition from the rubbery to glassy states. The shape locking effect freezes the deformed configuration of the SMP substrate, resulting in nearly conformal contact between the spherical indenter and the glassy-state SMP substrate, thus greatly increases the effective radius of curvature of the contact surface. Our experimental measurements and FEA analysis demonstrate that the net effect of shape locking leads to a pull-off force of a sphere nearly the same as that of a flat punch on an elastic half-space with the same contact radius. An explicit expression of the pull-off force for R2G adhesion is proposed based on flat-punch adhesion. Our results from combined experimentation, modelling and simulations reveal the fundamental mechanics of R2G adhesion. Such understanding provides guidance for the design of SMP smart adhesives.

URL: https://doi.org/10.1016/j.jmps.2022.105091

05 Oct 2022

Submitted by (Bold are A*STAR Staff): Zhidong Leong, Hongmei Jin, Zicong Marvin Wong, Kartik Nemani, Babak Anasori, Teck Leong Tan
Research Institute: IHPC

Title of Paper: Elucidating the Chemical Order and Disorder in High-Entropy MXenes: A High-Throughput Survey of the Atomic Configurations in TiVNbMoC3 and TiVCrMoC3

Published in: ACS Publications

Abstract: Expanding the MXene design space from ordered and random double-transition-metal (DTM) MXenes to include high-entropy (HE) MXenes with four or more principal elements enables a powerful approach for enhancing MXene properties. While many DTM MXenes possess unique structures that strongly influence material properties, HE MXenes are largely unknown because they are only recently synthesized. Since certain combinations of transition metals (TMs), e.g., Mo-Ti and Cr-Ti, lead to ordered DTM MXene phases, where Mo/Cr atoms occupy the outer TM layers and Ti atoms occupy the inner layers, it is critical to investigate any possibilities of TM segregation in the atomic layers of HE MXenes. Therefore, we present a high-throughput first-principles study of the atomic configurations of two recently synthesized HE M4C3 MXenes: TiVNbMoC3 and TiVCrMoC3. Combining density functional theory, cluster expansion, and Monte Carlo simulations, we predict a unique preferential occupancy of the TM atoms in the four layers within the single-phase HE MXenes, even at temperatures as high as 2900 K. Across a wide compositional range, the outer (inner) layers are predominantly occupied by two of the four TM elements, with Cr most preferentially occupying the outer layers, followed by Mo, V, Nb, and Ti. The strong compositional dependence of the interlayer segregation highlights the HE MXenes’ tunability. Within each TM layer, the atoms largely form a solid solution, with a tendency for Nb-V separation at lower temperatures. Our results elucidate the chemical order and disorder in HE MXenes, guiding experiments in designing MXenes with enhanced properties within the huge compositional space.

URL: https://doi.org/10.1021/acs.chemmater.2c01673

04 Oct 2022

Submitted by (Bold are A*STAR Staff): Min Wang, Jing Lyu, Xian Qin, Shuo-Wang Yang, Xiaogang Liu, Guo Qin Xu
Research Institute: IHPC

Title of Paper: Direct Electron Transfer Enables Highly Efficient Dual Emission Modes of Mn2+-Doped Cs2Na1–xAgxBiCl6 Double Perovskites

Published in: ACS Publications

Abstract: Double perovskites with bright emission, low toxicity, and excellent stability have drawn considerable attention. Herein, we report the hydrothermal synthesis of Mn2+-doped Cs2Na1–xAgxBiCl6 double perovskites that exhibit dual emission modes. Introducing Ag+ ions to Cs2NaBiCl6 samples enables a bright self-trapped exciton (STE) emission in orange-red color, whereas Mn2+ dopants induce a yellow-orange emission. Importantly, Mn2+ doping into Cs2Na1–xAgxBiCl6 double perovskites with an indirect bandgap enables a high photoluminescence quantum yield of 49.52 ± 2%. Density functional theory calculations reveal that bringing Ag+ ions into Cs2NaBiCl6 can localize wave function to the [AgCl6]5– octahedron and convert dark transitions to bright STE transitions. Moreover, the 3d orbitals of Mn2+ dopants hybridize with Bi-6p and Cl-3p orbitals at the conduction band minimum, resulting in direct electron transfer from the host to Mn2+ and a significant increase in photoluminescence efficiency. These results shed light on the optical physical process of Mn2+-doped systems, providing useful information for further improvement of the photoluminescence efficiency of double perovskites.

URL: https://doi.org/10.1021/acs.jpclett.2c02694

22 Sep 2022

Submitted by (Bold are A*STAR Staff): Chee Kwan Gan, Abdullah I. Al-Sharif, Ammar Al-Shorman, Abdallah Qteish

Research Institute: IHPC

Title of Paper: A first-principles investigation of the linear thermal expansion coefficients of BeF2: giant thermal expansion

Published in: Royal Society of Chemistry

Abstract: We present the results of a theoretical investigation of the linear thermal expansion coefficients (TECs) of BeF2, within a direct Grüneisen formalism where symmetry-preserving deformations are employed. The required physical quantities such as the optimized crystal structures, elastic constants, mode Grüneisen parameters, and phonon density of states are calculated from first-principles. BeF2 shows an extensive polymorphism at low pressures, and the lowest energy phases [α-cristobalite with space group (SG) P41212 and its similar phase with SG P43212] are considered in addition to the experimentally observed α-quartz phase. For benchmarking purposes, similar calculations are performed for the rutile phase of ZnF2, where the volumetric TEC (αv), derived from the calculated linear TECs along the a (αa) and c (αc) directions, is in very good agreement with experimental data and previous theoretical results. For the considered phases of BeF2, we do not find any negative thermal expansion (NTE). However we observe diverse thermal properties for the distinct phases. The linear TECs are very large, especially αc of the α-cristobalite phase and its similar phase, leading to giant αv (∼175 × 10−6 K−1 at 300 K). The giant αv arises from large Grüneisen parameters of low-frequency phonon modes, and the C13 elastic constant that is negatively signed and large in magnitude for the α-cristobalite phase. The elastic constants, high-frequency dielectric constants, Born effective charge tensors, and thermal properties of the above phases of BeF2 are reported for the first time and hence serve as predictions.

URL: https://doi.org/10.1039/D2RA04860D

13 Sep 2022

Submitted by (Bold are A*STAR Staff): Tristan T. Y. Tan, Xin Li, Ken-ichi Otake, Ying Chuan Tan, Xian Jun Loh, Susumu Kitagawa, Jason Y. C. Lim

Research Institute: IMRE, ISCE2

Title of Paper: UiO-66 Metal Organic Frameworks with High Contents of Flexible Adipic Acid co-Linkers

Published in: Royal Society of Chemistry

Abstract: Adipic acid, an industrially-important chemical which can be sustainably derived from biomass and post-consumer nylon, is traditionally overlooked as a linker for MOFs. Herein, we report the first direct one-pot method for synthesising UiO-66 MOFs with an unprecedented 69 mol% adipate content, as well as the feasibility of these materials for MOF defect engineering by rapid and selective adipate thermolysis.

URL: https://doi.org/10.1039/D2CC03285F

1 Sep 2022

Submitted by (Bold are A*STAR Staff): Jitka Petrlova, Firdaus Samsudin, Peter J. Bond, Artur Schmidtchen

Research Institute: BII

Title of Paper: SARS-CoV-2 spike protein aggregation is triggered by bacterial lipopolysaccharide

Published in: FEBS Letters

Abstract: SARS-CoV-2 spike (S) protein is crucial for virus invasion in COVID-19. Here, we showed that lipopolysaccharide (LPS) can trigger S protein aggregation at high doses of LPS and S protein. We demonstrated the formation of S protein aggregates by microscopy analyses, aggregation and gel shift assays. LPS at high levels boosts the formation of S protein aggregates as detected by amytracker and thioflavin T dyes that specifically bind to aggregating proteins. We validated the role of LPS by blocking the formation of aggregates by the endotoxin-scavenging thrombin-derived peptide TCP-25. Aggregation-prone sequences in S protein are predicted to be nearby LPS binding sites, while molecular simulations showed stable formation of S protein–LPS higher-order oligomers. Collectively, our results provide evidence of LPS-induced S protein aggregation.

URL: https://doi.org/10.1002/1873-3468.14490

1 Sep 2022

Submitted by (Bold are A*STAR Staff): Qiang He, Teck Lip Dexter Tam, Tingting Lin, Sheau Wei Chien, Ming Lin, Hong Meng, Wei Huang, Jianwei Xu

Research Institute: ICES2,IMRE

Title of Paper: π-Extended Poly(benzimidazoanthradiisoquinolinedione) Ladder-type Conjugated Polymer

Published in: ACS Macro Letters

Abstract: Since the 1960s, poly(benzobisimidazobenzophenathrolinedione) (BBL) has been the only n-type ladder-type conjugated polymer (LCP) that is utilized in thin film electronic devices. Its high electrochemical and thermal stabilities make it a promising candidate for organic electrochemical transistors (OECTs) and thermoelectrics (OTEs) applications. Here we report the synthesis and characterization of a new π-extended poly(benzimidazoanthradiisoquinolinedione) (BAL). The tetrachlorinated BAL (Cl4-BAL) is fully soluble in methanesulfonic acid (MSA) and can be spin-coated into good quality thin films, enabling the fabrication and characterization of OTEs. Doping of Cl4-BAL films using our in-house benzyl viologen radical cation (BV●+) n-dopant shows better electrical air-stability as compared to BBL due to its very low LUMO value (−4.83 eV), making it a promising material toward air-stable n-doped conducting polymers.

URL: https://doi.org/10.1021/acsmacrolett.2c00438

19 Aug 2022

Submitted by (Bold are A*STAR Staff): Ming Hui Chua, Kang Le Osmund Chin, Shi Jun Ang, Xiang Yun Debbie Soo, Zhuang Mao Png, Qiang Zhu, Jianwei Xu

Research Institute: ISCE2,IHPC,IMRE

Title of Paper: Aggregation Induced Emission-active Poly(acrylates) for Electrofluorochromic Detection of Nitroaromatic Compounds

Published in: ChemPhotoChem

Abstract: Two aggregation induced emission (AIE) -active poly(acrylates) bearing triphenylvinyl-functionalized phenylcarbazole and triphenylamine pendants, respectively, were synthesized. Their fluorescence response to nitroaromatics and electrofluorochromic (EFC) properties were studied, whereby both the presence of nitroaromatics and applied voltages led to fluorescence quenching. In a very first attempt to perform EFC detection of nitroaromatics, it was surprisingly found that after initial fluorescence quenching, the presence of nitroaromatics unexpectedly turned-on fluorescence at high applied voltages (> +1.0V), demonstrating a promising approach for the EFC detection of nitroaromatic explosives.

URL: https://doi.org/10.1002/cptc.202200168

15 Aug 2022

Submitted by (Bold are A*STAR Staff): Zicong Marvin Wong, Xue Yong, Tianqi Deng, Wen Shi, Gang Wu, Ning Li, He-Kuan Luo, and Shuo-Wang Yang

Research Institute: IHPC,IBB,ISCE2

Title of Paper: Neutral Antiaromatic Bis(1,2-dithiolene)-Chelated Nickel Complexes Bearing Multiradical Characters

Published in: The Journal of Physical Chemistry A

Abstract: Metal–organic complexes with radical characteristics are unique species attracting immense attention in recent years due to their peculiar properties and promising applicability in a wide variety of innovative research fields. However, the reported complexes typically do not exceed diradicality. This study systematically investigates a series of square planar neutral Ni-bis(1,2-dithiolene) and Ni-bis(1,2-dioxolene) complexes with linear, branched, and macrocyclic configurations via ab initio calculations. The linear Ni-complexes display strong singlet diradical characters, while their branched counterparts can also exhibit moderate singlet multiradical characters. Importantly, the macrocyclic Ni-complexes can possess extremely strong singlet multiradical characters up to dodeca-radicality along with their global antiaromaticity and hence strong induced ring current in the presence of an external magnetic field, ascribed to the localization of unpaired α and β electrons residing in the highest few molecular orbitals at different molecular sites, minimizing their coupling and annihilation. Our work represents the first indication in the rational design of novel multiradical neutral antiaromatic macrocyclic complexes for potential applications in molecular machines and electronic devices.

URL: https://doi.org/10.1021/acs.jpca.2c04134

10 Aug 2022

Submitted by (Bold are A*STAR Staff): Yuanjian Li, Gaoliang Yang, Shengnan Sun, Chang Zhang, Carina Yi Jing Lim, Andrew Jun Yao Wong, Wei Ying Lieu, Zdenek Sofer, Man-Fai Ng, Wei Liu, and Zhi Wei Seh

Research Institute: IMRE,IHPC

Title of Paper: High Utilization of Composite Magnesium Metal Anodes Enabled by a Magnesiophilic Coating

Published in:  Nano Letters

Abstract: Metallic magnesium is a promising high-capacity anode material for energy storage technologies beyond lithium-ion batteries. However, most reported Mg metal anodes are only cyclable under shallow cycling (≤1 mAh cm–2) and thus poor Mg utilization (<3%) conditions, significantly compromising their energy-dense characteristic. Herein, composite Mg metal anodes with high capacity utilization of 75% are achieved by coating magnesiophilic gold nanoparticles on copper foils for the first time. Benefiting from homogeneous ionic flux and uniform deposition morphology, the Mg-plated Au–Cu electrode exhibits high average Coulombic efficiency of 99.16% over 170 h cycling at 75% Mg utilization. Moreover, the full cell based on Mg-plated Au–Cu anode and Mo6S8 cathode achieves superior capacity retention of 80% after 300 cycles at a low negative/positive ratio of 1.33. This work provides a simple yet effective general strategy to enhance Mg utilization and reversibility, which can be extended to other metal anodes as well.

URL: https://doi.org/10.1021/acs.nanolett.2c02829

9 Aug 2022

Submitted by (Bold are A*STAR Staff): Han Gao, Chao Ding, Jaeseok Son, Yangyu Zhu, Mingzheng Wang, Zhi Gen Yu, Jianing Chen, Le Wang, Scott A. Chambers, Tae Won Noh, Mingwen Zhao & Yangyang Li

Research Institute: IHPC

Title of Paper: Ultra-flat and long-lived plasmons in a strongly correlated oxide

Published in:  Nature Communications

Abstract: Plasmons in strongly correlated systems are attracting considerable attention due to their unconventional behavior caused by electronic correlation effects. Recently, flat plasmons with nearly dispersionless frequency-wave vector relations have drawn significant interest because of their intriguing physical origin and promising applications. However, these flat plasmons exist primarily in low-dimensional materials with limited wave vector magnitudes (q < ~0.7 Å−1). Here, we show that long-lived flat plasmons can propagate up to ~1.2 Å−1 in α-Ti2O3, a strongly correlated three-dimensional Mott-insulator, with an ultra-small energy fluctuation (<40 meV). The strong correlation effect renormalizes the electronic bands near Fermi level with a small bandwidth, which is responsible for the flat plasmons in α-Ti2O3. Moreover, these flat plasmons are not affected by Landau damping over a wide range of wave vectors (q < ~1.2 Å−1) due to symmetry constrains on the electron wavefunctions. Our work provides a strategy for exploring flat plasmons in strongly correlated systems, which in turn may give rise to novel plasmonic devices in which flat and long-lived plasmons are desirable.

URL: https://doi.org/10.1038/s41467-022-32359-0

26 July 2022

Submitted by (Bold are A*STAR Staff): Shuai Chen, Tian Wang, Xiaoyan Li, Yuan Cheng, Gang Zhang, Huajian Gao

Research Institute: IHPC

Title of Paper: Short-Range Ordering and its Impact on Thermodynamic Property of High-Entropy Alloys

Published in: Acta Materialia

Abstract: Short-range ordering and atomic segregation have been observed experimentally in high-entropy alloys (HEAs). Understanding their impact on the melting temperature is crucial to the rational design of HEAs. Here we perform molecular dynamics simulations combined with Monte Carlo calculations to study the effects of elemental concentration, short-range ordering and atomic segregation on the melting temperature of AlCoFeNiCux HEAs (x = 0, 0.5 and 1). The simulation results demonstrate that the melting temperature of HEAs increases with decreasing Cu concentration and Cu atoms tend to break bonds more readily than other four types of atoms (Al, Co, Fe and Ni) during heating, even though Cu is not the one with the lowest melting temperature among the constituent component in pure form (melting temperature: Al < Cu < Ni < Co < Fe). We find that the reduced melting temperature is due to the formation of more short-range ordering and atomic segregation with phase boundary when the Cu concentration increases. The formation of short-range ordering and atomic segregation within Cu atoms are consistent with previous experimental observation of Al0.5CoCrFeNiCu HEAs and simulation results of CoCrFeNiCux HEAs (x = 0.4, 0.7 and 1) using another interatomic potential. Our findings highlight the importance of short-range ordering and atomic segregation in influencing the melting temperature of HEAs and provide guide for designing HEAs with desired thermodynamic properties.

URL: https://doi.org/10.1016/j.actamat.2022.118201

14 July 2022

Submitted by (Bold are A*STAR Staff): Jingwen Zhu & Anqi Qiu

Research Institute:

Title of Paper: Interindividual Variability in Functional Connectivity Discovers Differential Development of Cognition and Transdiagnostic Dimensions of Psychopathology in Youth

Published in: NeuroImage

Abstract: Cognitive and psychological development during adolescence is different from one another, which is rooted in individual differences in maturational changes in the adolescent brain. This study employed multi-modal MRI data and characterized interindividual variability in functional connectivity (IVFC) and its associations with cognition and psychopathology using the Philadelphia Neurodevelopmental Cohort (PNC) of 755 youth. We employed resting state functional MRI (rs-fMRI) and diffusion weighted images (DWIs) to estimate brain structural and functional networks. We computed the IVFC of individuals and examined its relation with structural and functional organizations. We further employed sparse partial least squares (sparse-PLS) and meta-analysis to examine the developmental associations of the IVFC with cognition and transdiagnostic dimensions of psychopathology in early, middle, and late adolescence. Our results revealed that the IVFC spatial topography reflects the brain functional integration and structure-function decoupling. Age effects on the IVFC of association networks were mediated by the FC among the triple networks, including frontoparietal, salience, and default mode networks (DMN), while those of primary and cerebellar networks were mediated by the cerebello-cortical FC. The IVFC of the triple and cerebellar networks explained the variance of executive functions and externalizing behaviors in early adolescence and then the variance of emotion and internalizing and psychosis in middle and late adolescence. We further evaluated this finding via meta-analysis on task-based studies on cognition and psychopathology. These findings implicate the emerging importance of the IVFC of the triple and cerebellar networks in cognitive, emotional, and psychopathological development during adolescence.

URL: https://doi.org/10.1016/j.neuroimage.2022.119482

13 July 2022

Submitted by (Bold are A*STAR Staff): V. Sorkin, Z. G. Yu, S. Chen, Teck L. Tan, Z. H. Aitken & Y. W. Zhang

Research Institute: IHPC

Title of Paper: A first-principles-based high fidelity, high throughput approach for the design of high entropy alloys

Published in: Scientific Reports

Abstract: Here, we present a preselected small set of ordered structures (PSSOS) method, a first principles-based high fidelity (HF), high throughput (HT) approach, for fast screening of the large composition space of high entropy alloys (HEAs) to select the most energetically stable, single-phase HEAs. Taking quinary AlCoCrFeNi HEA as an example system, we performed PSSOS calculations on the formation energies and mass densities of 8801 compositions in both FCC and BCC lattices and selected five most stable FCC and BCC HEAs for detailed analysis. The calculation results from the PSSOS approach were compared with existing experimental and first-principles data, and the good agreement was achieved. We also compared the PSSOS with the special quasi-random structures (SQS) method, and found that with a comparable accuracy, the PSSOS significantly outperforms the SQS in efficiency, making it ideal for HF, HT calculations of HEAs.

URL: https://doi.org/10.1038/s41598-022-16082-w

20 June 2022

Submitted by (Bold are A*STAR Staff): Soumya Kumar Sinha, Subir Panja, Jagrit Grover, Partha Sarathi Hazra, Saikat Pandit, Yogesh Bairagi, Xinglong Zhang, and Debabrata Maiti

Research Institute: IHPC

Title of Paper: Dual Ligand Enabled Nondirected C–H Chalcogenation of Arenes and Heteroarenes

Published in: Journal of the American Chemical Society

Abstract: Chalcogenide motifs are present as principal moieties in a vast array of natural products and complex molecules. Till date, the construction of these chalcogen motifs has been restricted to either the use of directing groups or the employment of a large excess of electronically activated arenes, typically employed as a cosolvent. Despite being highly effective, these methods have their own limitations in the step economy and the deployment of an excess amount of arenes. Herein, we report the evolution of a catalytic system employing arene-limited, nondirected thioarylation of arenes and heteroarenes using a complimentary dual-ligand approach. The reaction is controlled by a combination of steric and electronic factors, and the utilization of a suitable ligand enables the generation of products on a complimentary spectrum to that generated by classical methods. The combination of ligands remains imperative in the reaction protocol with theoretical calculations pointing towards a monoprotected amino acid ligand being crucial in the concerted metalation deprotonation (CMD) mechanism by a characteristic [5,6]-palladacyclic transition state, while the pyridine moiety assists in the active catalyst species formation and product release. Combined experimental and computational mechanistic investigations point toward the C–H activation step being both regio- and rate-determining. Interestingly, oxidative addition of the diphenyl disulfide substrate is found to be unlikely, and an alternative transmetalation-like mechanism involving the Pd–Ag heterometallic complex is proposed to be operative.

URL: https://doi.org/10.1021/jacs.2c02126

20 June 2022

Submitted by (Bold are A*STAR Staff): Jingwen Zhu & Anqi Qiu

Research Institute:

Title of Paper: Chinese adult brain atlas with functional and white matter parcellation

Published in: Scientific Data

Abstract: Brain atlases play important roles in studying anatomy and function of the brain. As increasing interests in multi-modal magnetic resonance imaging (MRI) approaches, such as combining structural MRI, diffusion weighted imaging (DWI), and resting-state functional MRI (rs-fMRI), there is a need to construct integrated brain atlases based on these three imaging modalities. This study constructed a multi-modal brain atlas for a Chinese aging population (n = 180, age: 22–79 years), which consists of a T1 atlas showing the brain morphology, a high angular resolution diffusion imaging (HARDI) atlas delineating the complex fiber architecture, and a rs-fMRI atlas reflecting brain intrinsic functional organization in one stereotaxic coordinate. We employed large deformation diffeomorphic metric mapping (LDDMM) and unbiased diffeomorphic atlas generation to simultaneously generate the T1 and HARDI atlases. Using spectral clustering, we generated 20 brain functional networks from rs-fMRI data. We demonstrated the use of the atlas to explore the coherent markers among the brain morphology, functional networks, and white matter tracts for aging and gender using joint independent component analysis.

URL: https://doi.org/10.1038/s41597-022-01476-2

10 June 2022

Submitted by (Bold are A*STAR Staff): Haitao Liu, Feng Chen, Nannan Zhao, Sai V. C. Vummaleti, Michael B. Sullivan, Jackie Y. Ying, and Lei Wang

Research Institute: IMRE,IHPC

Title of Paper: Rhodium-Catalyzed Ring Expansion Reactions for the Concise Construction of Densely Functionalized Oxathionines and Oxathiocines

Published in: ACS Catalysis

Abstract: Ring expansion reactions have been proven to be efficient tools for building medium-sized rings with broad applications in synthetic and medicinal chemistry. However, the strategy involving pericyclic or pseudopericyclic pathways via sulfur ylide-initiated [1,4]-sigmatropic rearrangement remains an under-exploited area. Herein, we disclose an interesting ring expansion of thiochromenes and aromatic thiophenes via rhodium catalysis, which enables the straightforward assembly of polyaromatic oxathionines and oxathiocines with diverse functionalities. The mechanistic investigation via DFT calculations revealed this ring expansion transformation to be a [1,4]-sigmatropic rearrangement via a metal-free sulfur-based ylide.

URL: https://doi.org/10.1021/acscatal.2c01529

1 June 2022

Submitted by (Bold are A*STAR Staff): Baoshan Tang, Hasita Veluri, Yida Li, Zhi Gen Yu, Moaz Waqar, Jin Feng Leong, Maheswari Sivan, Evgeny Zamburg, Yong-Wei Zhang, John Wang & Aaron V-Y. Thean

Research Institute: IHPC

Title of Paper: Wafer-scale solution-processed 2D material analog resistive memory array for memory-based computing

Published in: Nature Communications

Abstract: Realization of high-density and reliable resistive random access memories based on two-dimensional semiconductors is crucial toward their development in next-generation information storage and neuromorphic computing. Here, wafer-scale integration of solution-processed two-dimensional MoS2 memristor arrays are reported. The MoS2 memristors achieve excellent endurance, long memory retention, low device variations, and high analog on/off ratio with linear conductance update characteristics. The two-dimensional nanosheets appear to enable a unique way to modulate switching characteristics through the inter-flake sulfur vacancies diffusion, which can be controlled by the flake size distribution. Furthermore, the MNIST handwritten digits recognition shows that the MoS2 memristors can operate with a high accuracy of >98.02%, which demonstrates its feasibility for future analog memory applications. Finally, a monolithic three-dimensional memory cube has been demonstrated by stacking the two-dimensional MoS2 layers, paving the way for the implementation of two memristor into high-density neuromorphic computing system.

URL: https://doi.org/10.1038/s41467-022-30519-w

22 May 2022

Submitted by (Bold are A*STAR Staff): Xin Li, Guibin Shen, Xin Ren Ng, Zhiyong Liu, Yun Meng, Yong-Wei Zhang, Cheng Mu, Zhi Gen Yu, Fen Lin

Research Institute: IHPC

Title of Paper: Thermally Evaporated ZnSe for Efficient and Stable Regular/Inverted Perovskite Solar Cells by Enhanced Electron Extraction

Published in: Energy & Environmental Materials

Abstract: Electron transport layers (ETLs) are crucial for achieving efficient and stable planar perovskite solar cells (PSCs). Reports on versatile inorganic ETLs using a simple film fabrication method and applicability for both low-cost planar regular and inverted PSCs with excellent efficiencies (> 22%) and high stability are very limited. Herein, we employ a novel inorganic ZnSe as ETL for both regular and inverted PSCs to improve the efficiency and stability using a simple thermal evaporation method. The TiO2-ZnSe-FAPbI3 heterojunction could be formed, resulting in an improved charge collection and a decreased carrier recombination further proved through theoretical calculations. The optimized regular PSCs based on TiO2/ZnSe have achieved 23.25% efficiency with negligible hysteresis. In addition, the ZnSe ETL can also effectively replace the unstable bathocuproine (BCP) in inverted PSCs. Consequently, the ZnSe-based inverted device realizes a champion efficiency of 22.54%. Moreover, the regular device comprising the TiO2/ZnSe layers retains 92% of its initial PCE after 1000 h under 1 Sun continuous illumination and the inverted device comprising the C60/ZnSe layers maintains over 85% of its initial PCE at 85 °C for 1000 h. This highlights one of the best results among universal ETLs in both regular and inverted perovskite photovoltaics.

URL: https://doi.org/10.1002/eem2.12439

04 May 2022

Submitted by (Bold are A*STAR Staff): Qi Zhang, Sijia Rao, Sai Vikrama Chaitanya Vummaleti, Eng Tuan Poh, Wenrui Dai, Xinhang Cui, Jishan Wu, Jia Zhang, Wei Chen

Research Institute: IHPC

Title of Paper: High-Performance Li-O2 Batteries Enabled by Dibenzo-24-Crown-8 Aldehyde Derivative as Electrolyte Additives

Published in: Advanced Energy Materials

Abstract: Aprotic Li-O2 batteries (LOB) with high theoretical energy density usually experience cathode clogging by insoluble Li2O2, along with high charge overpotential from its insulating nature. A dibenzo-24-crown-8 aldehyde derivative (DB24C8A) is employed as an additive to enhance the binding strength with Li+, hence promoting the solubility of Li2O2. The generated [DB24C8A•Li+] avoids the parasitic reactions caused by reactive O2−. Thus, the LOB achieves a large discharge capacity of 6939 mAh g−1 at 200 mA g−1 and a high Li2O2 yield (≈93%). Moreover, DB24C8A facilitates the efficient decomposition of Li2O2 via Li+ coordination during the charge process, reducing the charge overpotential to 0.77 V and prolonging the lifetime of the LOB over 213 cycles at 1000 mAh g−1 and 500 mA g−1. This work provides a novel approach to boost the performance of LOB by incorporation of crown ether-based compounds to regulate the Li2O2 growth and decomposition pathway.

URL: https://doi.org/10.1002/aenm.202200580

04 May 2022

Submitted by (Bold are A*STAR Staff): Wen-Xin Lv, Hang Chen, Xinglong Zhang, Chang Chin Ho, Yingguo Liu, Shuquan Wu, Haiqi Wang, Zhichao Jin, Yonggui Robin Chi

Research Institute: IHPC

Title of Paper: Programmable selective acylation of saccharides mediated by carbene and boronic acid

Published in: sciencedirect

Abstract: Chemical synthesis or modification of saccharides remains a major challenge largely because site-selective reactions on their many similar hydroxyl groups are difficult. The lack of efficient chemical synthetic tools has therefore become a main obstacle to understanding saccharide-related biological processes and developing saccharide-based pharmaceuticals. Here, we disclose a programmable multilayered selectivity-amplification strategy enabled by boronic acids and N-heterocyclic carbene (NHC) catalysts for site-specific acylation of unprotected monoglycosides. The boronic acids provide transient shielding on certain hydroxyl groups (while simultaneously promoting reactions of other hydroxyl units) via dynamic covalent bonds to offer the first sets of selectivity controls. The NHC catalysts provide further layers of control by mediating selective acylation of the unshielded hydroxyl moieties. Multiple activating and deactivating forces can be easily modulated to yield programmable selectivity patterns. Structurally diverse monosaccharides and their analogs can be precisely reacted with different acylating reagents, leading to quick construction of sophisticated saccharide-derived products.

URL: https://doi.org/10.1016/j.chempr.2022.04.019

04 May 2022

Submitted by (Bold are A*STAR Staff): Guilherme M. D. M. Rúbio, Tristan T. Y. Tan, Alexander Prado-Roller, Jia Min Chin, and Michael R. Reithofer

Research Institute: IMRE

Title of Paper: Reactivity of Diamines in Acyclic Diamino Carbene Gold Complexes

Published in: ACS Publications

Abstract: Acyclic diamino carbenes (ADCs) are interesting alternatives to their more widely studied N-heterocyclic carbene counterparts, particularly due to their greater synthetic accessibility and properties such as increased sigma donation and structural flexibility. ADC gold complexes are typically obtained through the reaction of equimolar amounts of primary/secondary amines on gold-coordinated isocyanide ligands. As such, the reaction of diamine nucleophiles to isocyanide gold complexes was expected to lead to bis-ADC gold compounds with potential applications in catalysis or as novel precursors for gold nanomaterials. However, the reaction of primary diamines with two equivalents of isocyanide gold chlorides resulted in only one of the amine groups reacting with the isocyanide carbon. The resulting ADC gold complexes bearing free amines dimerized via coordination of the amine to the partner gold atom, resulting in cyclic, dimeric gold complexes. In contrast, when secondary diamines were used, both amines reacted with an isocyanide carbon, leading to the expected bis-ADC gold complexes. Density functional theory calculations were performed to elucidate the differences in the reactivities between primary and secondary diamines. It was found that the primary amines were associated with higher reaction barriers than the secondary amines and hence slower reaction rates, with the formation of the second carbenes in the bis-ADC compounds being inhibitingly slow. It was also found that diamines have a unique reactivity due to the second amine serving as an internal proton shuttle.

URL: https://doi.org/10.1021/acs.inorgchem.2c00509

01 Apr 2022

Submitted by (Bold are A*STAR Staff): Chunbao Du, Ting Du, Joey Tianyi Zhou, Yanan Zhu, Xingang Jia, Yuan Cheng 

Research Institute: IHPC

Title of Paper: Enhanced Stability and Mechanical Properties of a Graphene–Protein Nanocomposite Film by a Facile Non-Covalent Self-Assembly Approach

Published in: Nanomaterials

Abstract: Graphene-based nanocomposite films (NCFs) are in high demand due to their superior photoelectric and thermal properties, but their stability and mechanical properties form a bottleneck. Herein, a facile approach was used to prepare nacre-mimetic NCFs through the non-covalent self-assembly of graphene oxide (GO) and biocompatible proteins. Various characterization techniques were employed to characterize the as-prepared NCFs and to track the interactions between GO and proteins. The conformational changes of various proteins induced by GO determined the film-forming ability of NCFs, and the binding of bull serum albumin (BSA)/hemoglobin (HB) on GO’s surface was beneficial for improving the stability of as-prepared NCFs. Compared with the GO film without any additive, the indentation hardness and equivalent elastic modulus could be improved by 50.0% and 68.6% for GO–BSA NCF; and 100% and 87.5% for GO–HB NCF. Our strategy should be facile and effective for fabricating well-designed bio-nanocomposites for universal functional applications.

URL: https://doi.org/10.3390/nano12071181

24 Mar 2022

Submitted by (Bold are A*STAR Staff): Anqi Qiu , Liyuan Xue, Chaoqiang Liu

Research Institute: -

Title of Paper: Predicting diagnosis 4 years prior to Alzheimer’s disease incident

Published in: Sciencedirect

Abstract: This study employed a deep learning longitudinal model, graph convolutional and recurrent neural network (graph-CNN-RNN), on a series of brain structural MRI scans for AD prognosis. It characterized whole-brain morphology via incorporating longitudinal cortical and subcortical morphology and defined a probabilistic risk for the prediction of AD as a function of age prior to clinical diagnosis. The graph-CNN-RNN model was trained on half of the Alzheimer’s Disease Neuroimaging Initiative dataset (ADNI, n = 1559) and validated on the other half of the ADNI dataset and the Open Access Series of Imaging Studies-3 (OASIS-3, n = 930). Our findings demonstrated that the graph-CNN-RNN can reliably and robustly diagnose AD at the accuracy rate of 85% and above across all the time points for both datasets. The graph-CNN-RNN predicted the AD conversion from 0 to 4 years before the AD onset at ∼80% of accuracy. The AD probabilistic risk was associated with clinical traits, cognition, and amyloid burden assessed using [18F]-Florbetapir (AV45) positron emission tomography (PET) across all the time points. The graph-CNN-RNN provided the quantitative trajectory of brain morphology from prognosis to overt stages of AD. Such a deep learning tool and the AD probabilistic risk have great potential in clinical applications for AD prognosis.

URL: https://doi.org/10.1016/j.nicl.2022.102993

22 Mar 2022

Submitted by (Bold are A*STAR Staff): Yingzhi Zeng, Mengren Man, Kewu Bai, Yong-Wei Zhang

Research Institute: IHPC

Title of Paper: Explore the full temperature-composition space of 20 quinary CCAs for FCC and BCC single-phases by an iterative machine learning + CALPHAD method

Published in: Sciencedirect

Abstract: The search for desired complex concentrated alloys (CCAs) remains a daunting task because of the vast temperature/chemical composition space. While CALPHAD is a reliable technique, it requires intensive computations. In contrast, machine-learning (ML) methods can be fast and efficient but rely on a large and high-quality dataset. In this work, we combine these two techniques by implementing a reinforcement learning strategy to accelerate the exploration of CCAs. Starting from an initial small dataset from Thermo-Calc calculations with TCHEA3 database, the reinforcement learning is performed iteratively with the XGBoost ML training/testing and CALPHAD verification to progressively augment the dataset. This strategy allows for the identification of all single-phase FCC and BCC structures in the temperature-composition space of 20 Al-containing quinary alloy families formed by Al, Co, Cr, Cu, Fe, Mn, Ni and Ti, and achieves testing accuracies of above 97% and 92% on Thermo-Calc and on experimental data, respectively. The data analyses show that these 20 families exhibit a large disparity in their single-phase formation ability with AlCoCrFeNi and AlCrFeMnNi having the highest formation ability for FCC and BCC, respectively. Remarkably, this large disparity can be well explained by refined phase selection rules and structural inheritance from binary and ternary systems. Our extensive analysis also reveals the rarity of single-phase CCAs at room temperature. The method proposed and the findings revealed present new dimensions for the design and engineering of CCAs.

URL: https://doi.org/10.1016/j.actamat.2022.117865

11 Mar 2022

Submitted by (Bold are A*STAR Staff): Rui Deng, Shuquan Wu, Chengli Mou, Jianjian Liu, Pengcheng Zheng, Xinglong Zhang, Yonggui Robin Chi 

Research Institute: IHPC

Title of Paper: Carbene-Catalyzed Enantioselective Sulfonylation of Enone Aryl Aldehydes: A New Mode of Breslow Intermediate Oxidation

Published in: ACS Publications

Abstract: A carbene-catalyzed sulfonylation reaction between enone aryl aldehydes and sulfonyl chlorides is disclosed. The reaction effectively installs sulfone moieties in a highly enantioselective manner to afford sulfone-containing bicyclic lactones. The sulfonyl chloride behaves both as an oxidant and a nucleophilic substrate (via its reduced form) in this N-heterocyclic carbene (NHC)-catalyzed process. The NHC catalyst provides both activation and stereoselectivity control on a very remote site of enone aryl aldehyde substrates. Water plays an important role in modulating catalyst deactivation and reactivation routes that involve reactions between NHC and sulfonyl chloride. Experimental studies and DFT calculations suggest that an unprecedented intermediate and a new oxidation mode of the NHC-derived Breslow intermediate are involved in the new asymmetric sulfonylation reaction.

URL: https://doi.org/10.1021/jacs.1c13384

07 Mar 2022

Submitted by (Bold are A*STAR Staff): Jing Cao, Ying Sim, Xian Yi Tan, Jie Zheng, Sheau Wei Chien, Ning Jia, Kewei Chen, Yeow Boon Tay, Jin-Feng Dong, Le Yang, Hong Kuan Ng, Hongfei Liu, Chee Kiang Ivan Tan, Guofeng Xie, Qiang Zhu, Zibiao Li, Gang Zhang, Lei Hu, Yun Zheng, Jianwei Xu, Qingyu Yan, Xian Jun Loh, Nripan Mathews, Jing Wu, Ady Suwardi 

Research Institute: IMRE, IHPC

Title of Paper: Upcycling Silicon Photovoltaic Waste into Thermoelectrics

Published in: Wiley Online Library

Abstract: Two decades after the rapid expansion of photovoltaics, the number of solar panels reaching the end-of-life is increasing. While precious metals such as silver and copper are usually recycled, silicon, which makes up the bulk of a solar cell, goes to landfills. This is due to the defect- and impurity-sensitive nature in most silicon-based technologies, rendering it uneconomical to purify waste silicon. Thermoelectrics is a rare class of material in which defects and impurities can be engineered to enhance its performance. This is thanks to its majority carrier nature, making it defect- and impurity-tolerant. Here, we enables the upcycling of silicon from photovoltaic waste into thermoelectrics. This is done by doping 1% Ge and 4% P, which results in figure of merit (zT) of 0.45 at 873 K, the highest amongst silicon-based thermoelectrics. Our work represents an important piece of puzzle in realizing circular economy for photovoltaics and electronic waste.

URL: https://doi.org/10.1002/adma.202110518

14 Feb 2022

Submitted by (Bold are A*STAR Staff): Milad Ghaemi, Mehdi Jafary-Zadeh, Khoong Hong Khoo, Huajian Gao

Research Institute: IHPC

Title of Paper: Chemical affinity can govern notch-tip brittle-to-ductile transition in metallic glasses

Published in: Sciencedirect

Abstract: Chemical short-range order (CSRO) has emerged as an important index of material properties for multicomponent metallic alloys and glasses, but its role in transition between brittle and ductile fracture mechanisms is not understood. Here, using molecular dynamics simulations of fracture in notched samples of a nominally brittle metallic glass Fe80P20, we show that the fracture mode can be altered from crack propagation to shear banding by tunning CSRO. The underlying mechanism is identified as the agglomeration of metalloid (P) atoms as heterogeneous brittle zones with the formation of CSRO, leading to brittle fracture. By reducing the extent of CSRO, shear banding at the notch tip becomes the dominant failure mechanism.

URL: https://doi.org/10.1016/j.eml.2022.101651

14 Feb 2022

Submitted by (Bold are A*STAR Staff): Xin Zhang, Esther Cai Xia Ang, Ziqi Yang, Choon Wee Kee, Choon-Hong Tan 

Research Institute: ICES

Title of Paper: Synthesis of chiral sulfinate esters by asymmetric condensation

Published in: Nature

Abstract: Achiral sulfur functional groups such as sulfonamide, sulfone, thiols and thioethers are common in drugs and natural products. However, chiral sulfur functional groups are often neglected as pharmacophores1–3; but sulfoximine, with its unique physicochemical and pharmacokinetic properties4,5, has been recently incorporated into several clinical candidates. Thus, other sulfur stereogenic centers, such as sulfinate ester, sulfinamide, sulfonimidate ester and sulfonimidamide have started to attract attention. The diversity and complexity of these sulfur stereogenic centers have the potential to expand chemical space for drug discovery6–10. However, the installation of these structures enantioselectively into drug molecules is highly challenging. Here, we report the straightforward access to enantioenriched sulfinate esters via asymmetric condensation of pro-chiral sulfinates and alcohols using pentanidium as an organocatalyst. We successfully coupled a wide range of sulfinates and bioactive alcohols stereoselectively. The initial sulfinates can be prepared from existing sulfone and sulfonamide drugs, and the resulting sulfinate esters are versatile for transformations to diverse chiral sulfur pharmacophores. Through late-stage diversification11,12 of Celecoxib and other drug derivatives, we demonstrate the viability of this unified approach towards sulfur stereogenic centers.

URL: https://doi.org/10.1038/s41586-022-04524-4

04 Feb 2022

Submitted by (Bold are A*STAR Staff): Benjamin W. J. Chen, Bo Wang, Michael B. Sullivan, Armando Borgna, Jia Zhang

Research Institute: IHPC, ICES

Title of Paper: Unraveling the Synergistic Effect of Re and Cs Promoters on Ethylene Epoxidation over Silver Catalysts with Machine Learning-Accelerated First-Principles Simulations

Published in: ACS Publications

Abstract: Co-promotion of Ag catalysts by Re and Cs leads to ethylene oxide (EO) selectivity higher than that achievable by either promoter alone. However, the atomistic and electronic mechanisms behind this synergistic co-promotion remain unclear. Here, we shed light on how Re and Cs promote ethylene epoxidation by elucidating realistic catalyst models using machine learning-accelerated first-principles simulations, characterizing their electronic properties, and constructing structure–selectivity relationships. Together with a comprehensive set of experimental data, we show that the synergistic effects of co-promotion are twofold. First, Re, in the form of ReO4, increases the dispersion of Cs, thereby maximizing the promotional effects of Cs. Second, combining electron-withdrawing Re and electron-donating Cs balances the amount of charge transferred to the catalyst. Akin to the Sabatier principle, this maximizes EO selectivity by preventing the formation of overly nucleophilic oxygen species that facilitate ethylene combustion and overly electrophilic Ag centers that accelerate EO isomerization. The insights from our work may guide the development of improved promoter combinations, while our methodology may serve as a template for studying other complex, multiply promoted reaction systems.

URL: https://doi.org/10.1021/acscatal.1c05419

30 Jan 2022

Submitted by (Bold are A*STAR Staff): Shih-Gu Huang, Jing Xia, Liyuan Xu, Anqi Qiu

Research Institute: - 

Title of Paper: Spatio-temporal directed acyclic graph learning with attention mechanisms on brain functional time series and connectivity

Published in: Sciencedirect

Abstract: We develop a deep learning framework, spatio-temporal directed acyclic graph with attention mechanisms (ST-DAG-Att), to predict cognition and disease using functional magnetic resonance imaging (fMRI). This ST-DAG-Att framework comprises of two neural networks, (1) spatio-temporal graph convolutional network (ST-graph-conv) to learn the spatial and temporal information of functional time series at multiple temporal and spatial graph scales, where the graph is represented by the brain functional network, the spatial convolution is over the space of this graph, and the temporal convolution is over the time dimension; (2) functional connectivity convolutional network (FC-conv) to learn functional connectivity features, where the functional connectivity is derived from embedded multi-scale fMRI time series and the convolutional operation is applied along both edge and node dimensions of the brain functional network. This framework also consists of an attention component, i.e., functional connectivity-based spatial attention (FC-SAtt), that generates a spatial attention map through learning the local dependency among high-level features of functional connectivity and emphasizing meaningful brain regions. Moreover, both the ST-graph-conv and FC-conv networks are designed as feed-forward models structured as directed acyclic graphs (DAGs). Our experiments employ two large-scale datasets, Adolescent Brain Cognitive Development (ABCD, n= 7693 ) and Open Access Series of Imaging Study-3 (OASIS-3, n = 1786). Our results show that the ST-DAG-Att model is generalizable from cognition prediction to age prediction. It is robust to independent samples obtained from different sites of the ABCD study. It outperforms the existing machine learning techniques, including support vector regression (SVR), elastic net’s mixture with random forest, spatio-temporal graph convolution, and BrainNetCNN.

URL: https://doi.org/10.1016/j.media.2022.102370

29 Jan 2022

Submitted by (Bold are A*STAR Staff): Nan Zhang, Xiang Lv, Xi-xiang Zhang, Jing Lyu, Shuo-Wang Yang, Jiagang Wu

Research Institute: IHPC

Title of Paper: Low-temperature dielectric relaxation associated with NbO6 octahedron distortion in antimony modified potassium sodium niobate ceramics

Published in: Sciencedirect

Abstract: Although the antimony (Sb) has been widely used to modify potassium sodium niobate (KNN) ceramics for tailoring the phase structure and performance, the role of Sb still remains insufficiently understood, consequently hindering the understanding of the physical origin of high-performance KNN-based ceramics. Here, we combine the experiments and first-principles calculations to deeply reveal the effects of Sb on KNN ceramics. Our results reveal a re-entrant-like relaxation behavior near the rhombohedral-orthorhombic (R-O) phase transition at the low content of Sb, which transforms into a canonical one at higher content of Sb. First-principles calculations show a significantly decreased difference in the bond length of six B-O bonds of NbO6 octahedral in Sb-modified KNN ceramics compared to pristine KNN ceramics, responsible for the low-temperature re-entrant-like dielectric relaxation. Furthermore, the addition of Sb would soften the B-O repulsion and gradually break the long-range ferroelectric ordering, resulting in the occurrence of nanoscale domains and enhanced local heterogeneity. Finally, we find that the optimized piezoelectric properties are the trade-off between the long-range ferroelectric ordering and the local heterogeneity. Therefore, this work not only deeply reveals the effects of Sb on KNN ceramics from multi-scale perspectives but also helps the future composition design for achieving high piezoelectricity.

URL: https://doi.org/10.1016/j.jmst.2021.11.033

25 Jan 2022

Submitted by (Bold are A*STAR Staff): Jing Lyu, Zicong Marvin Wong, Haicheng Sun, Shuo-Wang Yang, and Guo Qin Xu

Research Institute: IHPC

Title of Paper: Electric Field-Induced Phase Transition of Nanowires on Germanium(001) Surfaces

Published in: ACS Publications

Abstract: The manipulation of conductive nanowires (NWs) on semiconductor platforms provides important insights into the fabrication of nanoscale electronic devices. In this work, we directly observed the electric field-induced phase transitions in atomic Au-NWs self-assembled on Ge(001) surfaces using scanning tunneling microscopy (STM). The tunneling electrons and electric fields underneath a STM tip apex can effectively trigger a phase transition in Au-NWs on Ge(001) surfaces. Such phase transitions are associated with a remarkable atomic rearrangement in the Au-NWs, thereby modifying their band structures. Moreover, directly monitoring the dynamic reconstruction of Au-NWs on Ge(001) surfaces helps us to understand the NWs’ intricate atomic configurations and their electronic properties. The spatially controlled phase transition at the nanometer scale using STM shows the possibility of modulating NWs’ properties at an atomic scale.

URL: https://doi.org/10.1021/acs.jpclett.1c04020

18 Jan 2022

Submitted by (Bold are A*STAR Staff): Erol Yildirim, Shermin S. Goh, He-Kuan Luo, Hongmei Jin, Gang Wu, Teck Leong Tan, Zicong Marvin Wong, Jianwei Xu, and Shuo-Wang Yang

Research Institute: IHPC, IMRE

Title of Paper: A Dual-Surface Mechanism of Oxidant-Free Pyrrole Polymerization in the Two-Dimensional Titanium Carbide (MXene) Interlayer Nanospace

Published in: ACS Publications

Abstract: The influence of confinement in acidic nanotemplates on the polymerization reaction of pyrrole was previously reported. Similarly, an in situ oxidant-free polymerization of pyrrole on and in between the Ti3C2 MXene layers has been demonstrated experimentally. The newly formed PPy/MXene (PPy/polypyrrole) interface showed high electrical conductivity and supercapacitor features with excellent cycling stability. However, the polymerization mechanism remains unclear. In this study, the pyrrole polymerization mechanisms on Ti3C2 MXene surfaces and in between MXene interlayers with different terminations were investigated based on first-principles calculations. Key factors for such oxidant-free polymerization were identified, including the configuration of surface hydrogen-bonded pyrrole, surface acidity, confinement effect, and charge transfer between MXene surfaces and pyrrole monomers. By controlling these factors, one can design covalently bonded conducting organic molecules/polymers on or in between MXene interlayers for electronic applications. These findings not only uncover the mechanism for a proton-assisted pyrrole polymerization on and in between MXene interlayers but also provide a general mechanistic understanding and guideline for other possible in situ polymerizations on and in between two-dimensional MXene interlayers.

URL: https://doi.org/10.1021/acs.jpcc.1c08231

10 Jan 2022

Submitted by (Bold are A*STAR Staff): Ya Lv, Guoyong Luo, Qian Liu, Zhichao Jin, Xinglong Zhang, Yonggui Robin Chi 

Research Institute: IHPC

Title of Paper: Catalytic atroposelective synthesis of axially chiral benzonitriles via chirality control during bond dissociation and CN group formation

Published in: Nature Communications

Abstract: The applications of axially chiral benzonitriles and their derivatives remain mostly unexplored due to their synthetic difficulties. Here we disclose an unusual strategy for atroposelective access to benzonitriles via formation of the nitrile unit on biaryl scaffolds pre-installed with stereogenic axes in racemic forms. Our method starts with racemic 2-arylbenzaldehydes and sulfonamides as the substrates and N-heterocyclic carbenes as the organocatalysts to afford axially chiral benzonitriles in good to excellent yields and enantioselectivities. DFT calculations suggest that the loss of p-toluenesulfinate group is both the rate-determining and stereo-determining step. The axial chirality is controlled during the bond dissociation and CN group formation. The reaction features a dynamic kinetic resolution process modulated by both covalent and non-covalent catalytic interactions. The axially chiral benzonitriles from our method can be easily converted to a large set of functional molecules that show promising catalytic activities for chemical syntheses and anti-bacterial activities for plant protections.

URL: https://doi.org/10.1038/s41467-021-27813-4

09 Jan 2022

Submitted by (Bold are A*STAR Staff): Kuluhan Binici, Shivam Aggarwal, Nam Trung Pham,
Karianto Leman, Tulika Mitra

Research Institute: I2R

Title of Paper: Robust and Resource-Efficient Data-Free Knowledge Distillation by Generative Pseudo Replay

Published in: arXivLabs

Abstract: Data-Free Knowledge Distillation (KD) allows knowledge transfer from a trained neural network (teacher) to a more compact one (student) in the absence of original training data. Existing works use a validation set to monitor the accuracy of the student over real data and report the highest performance throughout the entire process. However, validation data may not be available at distillation time either, making it infeasible to record the student snapshot that achieved the peak accuracy. Therefore, a practical data-free KD method should be robust and ideally provide monotonically increasing student accuracy during distillation. This is challenging because the student experiences knowledge degradation due to the distribution shift of the synthetic data. A straightforward approach to overcome this issue is to store and rehearse the generated samples periodically, which increases the memory footprint and creates privacy concerns. We propose to model the distribution of the previously observed synthetic samples with a generative network. In particular, we design a Variational Autoencoder (VAE) with a training objective that is customized to learn the synthetic data representations optimally. The student is rehearsed by the generative pseudo replay technique, with samples produced by the VAE. Hence knowledge degradation can be prevented without storing any samples. Experiments on image classification benchmarks show that our method optimizes the expected value of the distilled model accuracy while eliminating the large memory overhead incurred by the sample-storing methods.

URL: https://arxiv.org/abs/2201.03019

07 Jan 2022

Submitted by (Bold are A*STAR Staff): C.D. Reddy, Zhi-Qian Zhang, S. Msolli, Junyan Guo, N. Sridhara

Research Institute: IHPC

Title of Paper: Impact velocity-dependent bonding mechanisms in metal cold spray

Published in: Sciencedirect

Abstract: In this paper, we probe the bonding mechanisms for an impacting particle on a substrate, as in the cold spray process, over a range of impact velocities using molecular dynamics simulations. For the model copper/copper system, we find that grain boundary-like amorphous phase interlocking and metallurgical bonding are dominant at low and medium impact velocities, respectively, while metallurgical bonding and mechanical interlocking are dominant at high impact velocities. In particular, features including substrate crater depth, particle flattening ratio, and jetting area are tracked with varying impact velocities to further enhance our understanding of the underlying bonding mechanisms and the grain refinement in and around the interface. Because our findings are based only on small particle simulations allowable in MD, size effects can preclude extrapolating the results to physical micron-sized particles used in actual cold spray.

URL: https://doi.org/10.1016/j.surfcoat.2022.128085

28 Dec 2021

Submitted by (Bold are A*STAR Staff): Jagadese J. Vittal, Naifang Liu, Zhihui Chen, Wenxuan Fan, Jie Su, Tingting Lin, Si Xiao, Jianqiao Meng, Jun He, Jianzhuang Jiang

Research Institute: IMRE

Title of Paper: Highly Efficient Multiphoton Absorption of Zn-AIEgen Frameworks

Published in: Wiley Online Library

Abstract: A series of luminescent frameworks were synthesized from the selective combination of AIE-linker tetra-(4-carboxylphenyl)ethylene (H 4 TCPE) and Zn 2+ . Complex 1 was formed by the close packing of Zn-TCPE hinge, and isostructural complexes 2 - 5 were constructed by the linkage of Zn-TCPE layer and pillar ligand. These complexes exhibit highly efficient multiphoton excited photoluminescence (MEPL) concomitant third-harmonic generation (THG). Interestingly, multiphoton apparent parameters of 1 are far superior to some excellent multiphoton emission materials, even the perovskite nanocrystal. The incorporation of pillar linkers slows down the charge transfer between layers of Zn-TCPE, and the aromatic core of pillar linkers has a great influence on the MEA performance of corresponding frameworks. The unprecedented structural and optical tuning of high performance MPA crystalline materials provides efficient suggestion for the design of next generation multiphoton absorption materials.

URL: https://doi.org/10.1002/anie.202115205

17 Dec 2021

Submitted by (Bold are A*STAR Staff): Hongmei Jin, Daniel John Blackwood, Ying Wang, Man-Fai Ng, Teck Leong Tan

Research Institute: IHPC

Title of Paper: First-Principles Study of Surface Orientation Dependent Corrosion of BCC Iron

Published in: Sciencedirect

Abstract: Using inputs from first-principles calculations, an ab initio model was employed to investigate crystal orientation dependent corrosion behavior of BCC iron. Results showed that the sequence of corrosion susceptibility of BCC Fe surfaces is in the order of (100)>(111)>(211)>(310)>(110). The higher corrosion current on (100) surface suggests that cathodic hydrogen evolution may largely determine the corrosion reactions under acidic environment. The predicted corrosion potential and current for lower index planes are in general agreement with available experiment. The model was further applied to study alloying effects with results validated via weight loss analysis of alloyant fabricated by arc melting.

URL: https://doi.org/10.1016/j.corsci.2021.110029

10 Dec 2021

Submitted by (Bold are A*STAR Staff): Mehrdad T. Kiani, Zachary H. Aitken, Abhinav Parakh, Yong-Wei Zhang, X. Wendy Gu

Research Institute: IHPC

Title of Paper: Extraordinary strain hardening from dislocation loops in defect-free Al nanocubes

Published in: arXivLabs

Abstract: The interaction of crystalline defects leads to strain hardening in bulk metals. Metals with high stacking fault energy (SFE), such as aluminum, tend to have low strain hardening rates due to an inability to form stacking faults and deformation twins. Here, we use in situ SEM mechanical compressions to find that colloidally synthesized defect-free 114 nm Al nanocubes combine a high linear strain hardening rate of 4.1 GPa with a high strength of 1.1 GPa. These nanocubes have a 3 nm self-passivating oxide layer that has a large influence on mechanical behavior and the accumulation of dislocation structures. Post-compression TEM imaging reveals stable prismatic dislocation loops and the absence of stacking faults. MD simulations relate the formation of dislocation loops and strain hardening to the surface oxide. These results indicate that slight modifications to surface and interfacial properties can induce enormous changes to mechanical properties in high SFE metals.

URL: https://arxiv.org/abs/2112.05723

09 Dec 2021

Submitted by (Bold are A*STAR Staff): Jing Lyu, Zicong Marvin Wong, Haicheng Sun, Shuo-Wang Yang, and Guo Qin Xu
Research Institute: IHPC

Title of Paper: Uncovering the Self-Organized Nanowires on Au-Modified Ge(001) Surfaces

Published in: ACS Publications

Abstract: A fundamental understanding of the atomic and electronic structures of metallic nanowires (NWs) on semiconductors is critical for micro- or molecular electronics. The deposition of Au atoms on Ge(001) surfaces can trigger the self-assembly of atomic NWs extending for hundreds of nanometers, and these NWs raised much controversy on their atomic/electronic configurations. In this work, different types of NWs were characterized on Au/Ge(001) surfaces via scanning tunneling microscopy (STM). Combined with density functional theory (DFT) calculations, the atomic structures of Au-induced NWs on Ge(001) surfaces were decoded, including the NWs-H/L and complex chevron and zigzag (V–W) reconstructions, where simulated V–W patterns at filled states transform to triplets at empty states. Moreover, a quasi-one-dimensional (1D) electronic behavior and anisotropic two-dimensional (2D) electronic states are uncovered in the Au–Ge-modified-dimer-row (AGMDR) and Au-NWs-in-trench (ANT) models, respectively, reconciling the previous controversy about electronic behaviors of NWs on Au/Ge(001) surfaces. Because of the quantum instability, 1D electron systems undergo a transition from metallic to nonconducting, while the atomic NWs (i.e., NWs-H and NWs-L) in the ANT model are metallic, rendering them good conductive channels for micro- or molecular electronics. Our findings provide insights into ascertaining the atomic structures of self-assembled NWs and understanding the discrepancies of the Au/Ge(001) material system.

URL: https://doi.org/10.1021/acs.jpcc.1c09171

01 Dec 2021

Submitted by (Bold are A*STAR Staff): Shuai Chen,Zachary H. Aitken,Viacheslav Sorkin,Zhi Gen Yu,Zhaoxuan Wu,Yong-Wei Zhang

Research Institute: IHPC

Title of Paper: Modified Embedded-Atom Method Potentials for the Plasticity and Fracture Behaviors of Unary HCP Metals

Published in: Wiley Online Library

Abstract: Modified embedded-atom method (MEAM) potentials have been widely used in molecular dynamics (MD) simulations to describe the interatomic interactions in metallic systems. However, conventional MEAM potentials are almost exclusively fit to a limited number of key single-value properties, limiting the predictability of MD simulations, especially for complex hexagonal-close-packed (HCP) metals with multiple slip systems. Here, three MEAM potentials for unary HCP metals (Mg, Co, and Ti) are fit to conventional target properties, as well as continuous-energy curves and their gradients obtained from density-functional theory calculations. These targets include the lattice parameters, cohesive energy, elastic constants, and surface energies as well as the cohesive energy curve, basal plane decohesion energy curve, and generalized stacking fault energy curves for basal, prismatic, pyramidal I, and pyramidal II planes. These interatomic potentials demonstrate excellent reproduction of relevant properties and enable accurate MD simulations of volumetric and plastic deformations, as well as fracture in Mg, Co, and Ti HCP metals. Importantly, the interatomic potentials demonstrate better performance than all existing EAM/MEAM potentials readily available from the literature.

URL: https://doi.org/10.1002/adts.202100377

29 Nov 2021

Submitted by (Bold are A*STAR Staff): V. Sorkin, Q. X. Pei, P. Liu, W. Thitsartarn, C. B. He & Y. W. Zhang 

Research Institute: IHPC,IMRE

Title of Paper: Atomistic-scale analysis of the deformation and failure of polypropylene composites reinforced by functionalized silica nanoparticles

Published in: Nature Scientific Reports

Abstract: Interfacial adhesion between polymer matrix and reinforcing silica nanoparticles plays an important role in strengthening polypropylene (PP) composite. To improve the adhesion strength, the surface of silica nanoparticles can be modified by grafted functional molecules. Using atomistic simulations, we examined the effect of functionalization of silica nanoparticles by hexamethyldisilazane (HMDS) and octyltriethoxysilane (OTES) molecules on the deformation and failure of silica-reinforced PP composite. We found that the ultimate tensile strength (UTS) of PP composite functionalized by OTES (28 MPa) is higher than that of HMDS (25 MPa), which is in turn higher than that passivated only by hydrogen (22 MPa). To understand the underlying mechanistic origin, we calculated the adhesive energy and interfacial strength of the interphase region, and found that both the adhesive energy and interfacial strength are the highest for the silica nanoparticles functionalized by OTES molecules, while both are the lowest by hydrogen. The ultimate failure of the polymer composite is initiated by the cavitation in the interphase region with the lowest mass density, and this cavitation failure mode is common for all the examined PP composites, but the cavitation position is dependent on the tail length of the functional molecules. The present work provides interesting insights into the deformation and cavitation failure mechanisms of the silica-reinforced PP composites, and the findings can be used as useful guidelines in selecting chemical agents for surface treatment of silica nanoparticles.

URL: https://doi.org/10.1038/s41598-021-02460-3

20 Nov 2021

Submitted by (Bold are A*STAR Staff): Ting Yat Wong,  Han Zhang, Tonya White, Liyuan Xu, Anqi Qiu

Research Institute: -

Title of Paper: Common functional brain networks between attention deficit and disruptive behaviors in youth

Published in: Sciencedirect

Abstract: Attention deficits (AD) and disruptive behavior (DB) are highly comorbid youth externalizing behaviors. This study aimed to study reliable functional brain networks shared by AD and DB in youth aged from 8 to 21 years from the Philadelphia Neurodevelopmental Cohort (PNC). The PNC study assessed AD and DB behaviors via Kiddie-Schedule for Affective Disorders and Schizophrenia (K-SADS). This study employed sparse canonical correlation analysis (SCCA) to examine the correlation of AD and DB behaviors with resting-state functional connectivity maps of the brain regions identified via activation likelihood estimation (ALE) meta-analyses on attention deficit/hyperactivity disorder (ADHD) and DB disorder (DBD). Our meta-analyses identified that the middle cingulate cortex, pre-supplementary motor area (pre-SMA), and striatum had a great consensus in existing ADHD studies and the amygdala and inferior parietal lobule were consistently found in existing DBD studies. Our SCCA analysis revealed that the AD and DB behavioral items relevant to inattention and delinquency were correlated with the functional connectivity of the pre-SMA with the ventral attentional and frontoparietal networks (FPN), and the striatum with the default mode (DMN) and dorsal attentional networks. The AD and DB behavioral items relevant to inattention and irritability were associated with the functional connectivity between the amygdala and the DMN and FPN. Our findings suggest that the functional organization of the ADHD- and DBD-related brain regions provides insights on the shared neural basis in AD and DB.

URL: https://doi.org/10.1016/j.neuroimage.2021.118732

09 Nov 2021

Submitted by (Bold are A*STAR Staff): Jingwen Zhu, Han Zhang, Yap-Seng Chong, Lynette P.Shek, Peter D.Gluckman, Michael J.Meaney, Marielle V.Fortier, Anqi Qiu

Research Institute: -

Title of Paper: Integrated structural and functional atlases of Asian children from infancy to childhood

Published in: Sciencedirect

Abstract: The developing brain grows exponentially in the first few years of life. There is a need to have age-appropriate brain atlases that coherently characterize the geometry of the cerebral cortex, white matter tracts, and functional organization. This study employed multi-modal brain images of an Asian cohort and constructed brain structural and functional atlases for 6-month-old infants, 4.5-, 6-, and 7.5-year-old children. We exploited large deformation diffeomorphic metric mapping and probabilistic atlas generation approaches to integrate structural MRI and diffusion weighted images (DWIs) and to create the atlas where white matter tracts well fit into the cortical folding pattern. Based on this structural atlas, we then employed spectral clustering to parcellate the brain into functional networks from resting-state fMRI (rs-fMRI). Our results provided the atlas that characterizes the cortical folding geometry, subcortical regions, deep white matter tracts, as well as functional networks in a stereotaxic coordinate space for the four different age groups. The functional networks consisting of the primary cortex were well established in infancy and remained stable to childhood, while specific higher-order functional networks showed specific patterns of hemispherical, subcortical-cerebellar, and cortical-cortical integration and segregation from infancy to childhood. Our multi-modal fusion analysis demonstrated the use of the integrated structural and functional atlas for understanding coherent patterns of brain anatomical and functional development during childhood. Hence, our atlases can be potentially used to study coherent patterns of brain anatomical and functional development.

URL: https://doi.org/10.1016/j.neuroimage.2021.118716

08 Nov 2021

Submitted by (Bold are A*STAR Staff): Dan-Thien Nguyen, Alex Yong Sheng Eng, Raymond Horia,  Zdenek Sofer, Albertus D.Handoko, Man-Fai Ng, Zhi Wei Seh 

Research Institute: IMRE,IHPC

Title of Paper: Rechargeable Magnesium Batteries Enabled by Conventional Electrolytes with Multifunctional Organic Chloride Additives

Published in: Sciencedirect

Abstract: The development of a conventional electrolyte, based on commercially available magnesium (Mg) salts in organic solvents, remains one of the most challenging quests for rechargeable Mg batteries. Conventional electrolytes typically form a passivation layer on Mg metal anode, necessitating the extensive use of inorganic chloride additives such as MgCl2. Herein, for the first time, we introduce an organic chloride, tetrabutylammonium chloride (TBAC), as a multifunctional electrolyte additive for conventional magnesium triflate (Mg(OTf)2)-based electrolytes. TBAC was found to perform three major roles: (1) enhance Mg(OTf)2 dissociation in aprotic solvent, (2) inhibit the reduction of triflate anions through surface-adsorbed TBA+, and (3) act as a chloride source to form Mg complexes and stabilize the Mg anode-electrolyte interface. The novel electrolyte combination of TBAC and Mg(OTf)2 in 1,2-dimethoxyethane exhibits excellent Mg plating/stripping with Coulombic efficiency of 97.7% over 200 cycles at 0.5 mA cm−2 and 0.5 mAh cm-2. Post-mortem analysis unveils uniform Mg deposition and stable solid electrolyte interphase formation on Mg anode, which enables reversible cycling with Mo6S8 cathode. Together with our findings on another organic chloride additive, 1-ethyl-3-methylimidazolium chloride, and in combination with different electrolyte salts and solvents, we showcase the general promise of high-performance conventional electrolytes for rechargeable Mg batteries.

URL: https://doi.org/10.1016/j.ensm.2021.11.011

26 Oct 2021

Submitted by (Bold are A*STAR Staff): Prithvi Gundlapalli and Junyi Lee

Research Institute: IMRE

Title of Paper: Deterministic, scalable, and entanglement efficient initialization of arbitrary quantum states

Published in: arXivLabs

Abstract: Quantum computing promises to provide exponential speed-ups to certain classes of problems. In many such quantum algorithms, a classical vector b is encoded in the amplitudes of a quantum state |bi. However, efficient amplitude encoding of an arbitrary vector b in |bi is known to be a difficult problem that can reverse the gains of such algorithms. More importantly, an arbitrary quantum state of Q qubits generally requires ∼ 2 Q number of entangling gates, which is problematic for today’s Noisy-Intermediate Scale Quantum (NISQ) computers where large numbers of such errorprone gates will result in significant decoherence before initialization is completed. In this work, we demonstrate a deterministic and scalable initialization algorithm that allows for states with low entanglement to be initialized on actual quantum computers with more than an order of magnitude fewer entangling gates and significantly shallower circuits as compared to isometric decomposition. For states with higher entanglement, optimally approximate states with lower entanglement may be found and initialized with similar performance. We show this to be true for various cases of interest such as the normal and log-normal distributions. Unlike variational approaches, our method requires no classical optimizations in high dimensional spaces and is not plagued with exponentially vanishing gradients or a multitude of local minimas.

URL: https://arxiv.org/abs/2110.13454

25 Oct 2021

Submitted by (Bold are A*STAR Staff): Man-Fai Ng, Daniel John Blackwood, Hongmei Jin, Teck Leong Tan

Research Institute: IHPC

Title of Paper: Revisiting Cl-Induced Degradation of MnS Inclusions Using DFT

Published in: ACS Publications

Abstract: Cl-induced passivity breakdown is one of the major causes of corrosion for ferrous alloys. On a passive layer, manganese sulfide (MnS) inclusions are known to be the preferred sites for pit initiation. While the breakdown process has been examined, relatively less effort has been devoted to discovering ways to mitigate the harmful process. Using DFT + U and ab initio molecular dynamics (AIMD) calculations, we investigated the initial stages of the Cl-induced degradation of MnS inclusions. We found that Cl adsorption on the MnS inclusion would lead to the formation of an amorphous MnxClySz complex on the surface. With increased Cl concentration, a thinned MnS inclusion could be formed. More importantly, we examined the effects of alloying Cr, Fe, and Mo on the inclusion against Cl-induced degradation. Our calculations showed that the addition of Mo can effectively mitigate the degradation process, suggesting a potential way to improve the corrosion resistance of ferrous alloys.

URL: https://pubs.acs.org/doi/10.1021/acs.jpcc.1c07419

20 Oct 2021

Submitted by (Bold are A*STAR Staff): Alexander Genest, Joaquín Silvestre-Albero, Wen-Qing Li, Notker Rösch & Günther Rupprechter

Research Institute: IHPC

Title of Paper: The origin of the particle-size-dependent selectivity in 1-butene isomerization and hydrogenation on Pd/Al2O3 catalysts

Published in: Nature Communications

Abstract: The selectivity of 1-butene hydrogenation/isomerization on Pd catalysts is known to be particle size dependent. Here we show that combining well-defined model catalysts, atmospheric pressure reaction kinetics, DFT calculations and microkinetic modeling enables to rationalize the particle size effect based on the abundance and the specific properties of the contributing surface facets.

URL: https://doi.org/10.1038/s41467-021-26411-8

12 Oct 2021

Submitted by (Bold are A*STAR Staff): Yi Jiang, Quanquan Wang, Xinglong Zhang, Ming Joo Koh

Research Institute: IHPC

Title of Paper: Synthesis of C-glycosides by Ti-catalyzed stereoselective glycosyl radical functionalization

Published in: Sciencedirect

Abstract: C-Alkyl glycosides occur widely in nature and are indispensable in drug development programs, owing to their diverse range of medicinal properties. Previous synthetic efforts often utilize stoichiometric reagents, and catalytic methods that afford such glycosides exhibit limited scope. Here, we describe a stereoselective Ti-catalyzed regime that efficiently merges a vast array of readily available glycosyl chlorides with activated olefins, through stereocontrolled glycosyl radical addition to deliver an assortment of C-alkyl glycosides. By employing alkynes as radical acceptors, the present strategy is amenable to the synthesis of C-alkenyl glycosides bearing a Z olefin appendage. The unexpected greater reactivity of glycosyl chlorides (compared with simple tertiary chloroalkanes) in the presence of an organotitanium complex is elucidated through mechanistic and computational studies. Utility of the protocol is underscored by the concise preparation of therapeutically important carbohydrates and glycopeptide conjugates, which are difficult to access using alternative approaches.

URL: https://doi.org/10.1016/j.chempr.2021.09.008

08 Oct 2021

Submitted by (Bold are A*STAR Staff): Ping Liu, Yucheng Zhong, Qing-Xiang Pei, Viacheslav Sorkin, Yong-WeiZhang

Research Institute: IHPC

Title of Paper: Simultaneously enhancing the strength and toughness of short fiber reinforced thermoplastic composites by fiber cross-linking

Published in: Sciencedirect

Abstract: In recent years, short fiber reinforced thermoplastic composites (SFRTPCs) have attracted significant interest due to their low density, high strength and toughness, environmental resistance and low cost. Currently, an important task is to optimize their internal structures so as to maximize their mechanical properties. Interestingly, a previous experimental study showed that by adding a small amount of a stronger material in the matrix to link up short fibers, the strength of SFRTPCs was enhanced. We note, however, that a micromechanical study on the effect of fiber linkage on the mechanical properties is still lacking. In this work, we have developed a finite element model to conduct such micromechanical analysis. In this model, the polymer matrix is taken as elastic-plastic material, the fiber as a brittle material following a brittle damage model, while the interphase and linkage as the same polymer following a progressive damage model. Our simulations show that for a SFRTPC with a given short fiber weight fraction, by increasing the weight fraction of the linkage material, the Young's modulus, yielding strength, ultimate tensile strength, and tensile toughness of the SFRTPCs are all increased. By increasing the strength of the linkage material, the ultimate tensile strength and tensile toughness of the SFRTPCs are increased. Modified rules of mixing have been proposed to consider the fiber crosslinking effect. The present study provides a useful reference for the optimal design of SFRTPCs to maximize their mechanical performance.

URL: https://doi.org/10.1016/j.compscitech.2021.109076

07 Oct 2021

Submitted by (Bold are A*STAR Staff): Jin W.Kwek, S.Chakraborty, Kai C.Kuan, Wen C.Yeo, H.Yin, Connie K.Liu, L.Guo, J.Zidar, C.Li, Freda C.H.Lim

Research Institute: IHPC,IRES

Title of Paper: Interactions between Poloxamer, PEOx-PPOy-PEOx, and Non-ionic Surfactant, Sucrose Monolaurate: A Study on Potential Allergenic Effect using Model Phospholipid Membrane

Published in: Sciencedirect

Abstract: Sugar-based surfactants are involved in skin related allergy cases in the past decade. Skin irritation starts with the interaction of the surfactant with the skin lipids leading to lipid emulsification and eventual barrier damage. Polymers or co-surfactants can be used to mitigate the allergenic effect but the mechanism of formulation mildness on skin remains unclear. We have used the quartz crystal microbalance (QCM) together with dissipative particle dynamics (DPD) simulation, small angle x-ray scattering (SAXS) as well as cell viability tests to decipher the interactions between poloxamers and sucrose monolaurate (SML), and how these interactions could prevent the disruption of a model supported phospholipid bilayer (SLB). Poloxamer addition to the SML solution can delay or totally prevent the disruption of the SLB depending on poloxamer type and concentration. Poloxamer P407 (Pluronic® F127) delays the onset of disruption while poloxamer P188 (Pluronic® F68) does not preserve the bilayer integrity even at high concentration of up to 15% w/w. Preservation of the SLB is likely due to the differences in the aggregates formation between SML-F127 and SML-F68 mixtures with corresponding retarded motion of SML micelles through the SML-F127 polymer matrix that improved cell viability.

URL: https://doi.org/10.1016/j.colsurfb.2021.112153

23 Sep 2021

Submitted by (Bold are A*STAR Staff): Duy Quang Dao, Thi Chinh Ngo, Thi Thuy Huong Le, Quang Thang Trinh, Thi Le Anh Nguyen, Bui The Huy, Nguyen Ngoc Tri, Nguyen Tien Trung, Minh Tho Nguyen

Research Institute: IHPC

Title of Paper: SERS Chemical Enhancement of 2,4,5-Trichlorophenoxyacetic Acid Adsorbed on Silver Substrate

Published in: ACS Publications

Abstract: Surface-enhanced Raman spectroscopy (SERS) was employed to gain an understanding of the chemical enhancement mechanism of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), an Agent Orange, adsorbed on a silver substrate surface. Experimental measurements were performed using a micro-Raman spectrophotometer with an excitation wavelength of 532 nm and successfully detected 2,4,5-T at a relatively low concentration of 0.4 nM. Density functional theory (DFT) calculations on the interactions of the 2,4,5-T molecule with some small silver clusters, Agn with n = 4, 8, and 20, as well as with extended Ag surfaces, demonstrate that the most stable adsorption configuration is formed via coordination of Cl9 sites and carbonyl C═O group on the 2,4,5-T ligand to the Ag atoms on surfaces. Analyses of charge transfer mechanism and frontier orbitals distributions show an electron transfer from 2,4,5-T to the cluster in the ground state, and an inversed trend occurs for the excited singlet state process, consequently leading to a chemical enhancement of SERS signals. The obtained results are of importance for subsequent work in guiding the design of mobile sensors specifically used for services of rapid screening and detection of these toxic compounds present in the environment, as well as agricultural and food products. Extensive computations pointed out that small silver clusters, in particular of Ag20 size, can be used as appropriate models for a metal nanoparticle surface.

URL: https://pubs.acs.org/doi/10.1021/acs.jpca.1c04957

02 Sep 2021

Submitted by (Bold are A*STAR Staff): Zi S.D. Toa, Anna V. Paterova, Leonid A. Krivitsky

Research Institute: IMRE

Title of Paper: Broadband diffraction of correlated photons from crystal superlattices

Published in: arXivLabs

Abstract: Sources of broadband quantum correlated photons present a valuable resource for quantum metrology, sensing, and communication. Here, we report the generation of spectrally broadband correlated photons from frequency nondegenerate spontaneous parametric down-conversion in a custom-designed lithium niobate superlattice. The superlattice induces a nonlinear interference, resulting in an experimentally observed comb-like emission spanning 0.060 um and 1.4 um of spectral bandwidth at 0.647 um and 3.0 um wavelengths, respectively. In addition to useful technological applications, our concept offers an interesting analogy between optical diffraction in quantum and classical optics.

URL: https://arxiv.org/abs/2109.00690

31 Aug 2021

Submitted by (Bold are A*STAR Staff): Guanyu Liu, Parvathala Reddy Narangari, Quang Thang Trinh, Wenguang Tu, Markus Kraft, Hark Hoe Tan, Chennupati Jagadish, Tej S. Choksi, Joel W. Ager, Siva Karuturi, and Rong Xu

Research Institute: -

Title of Paper: Manipulating Intermediates at the Au–TiO2 Interface over InP Nanopillar Array for Photoelectrochemical CO2 Reduction

Published in: American Chemical Society

Abstract: Photoelectrochemical (PEC) reduction of CO2 with H2O is a promising approach to convert solar energy and greenhouse gas into value-added chemicals or fuels. However, the exact role of structures and interfaces of photoelectrodes in governing the photoelectrocatalytic processes in terms of both activity and selectivity remains elusive. Herein, by systematically investigating the InP photocathodes with Au–TiO2 interfaces, we discover that nanostructuring of InP can not only enhance the photoresponse owing to increased light absorption and prolonged minority carrier lifetime, but also improve selectivity toward CO production by providing more abundant interfacial contact points between Au and TiO2 than planar photocathodes. In addition, theoretical studies on the Au–TiO2 interface demonstrate that the charge transfer between Au and TiO2, which is locally confined to the interface, strengthens the binding of the CO* intermediate on positively charged Au interfacial sites, thus improving CO2 photoelectroreduction to form CO. An optimal Au–TiO2/InP nanopillar-array photocathode exhibits an onset potential of +0.3 V vs reversible hydrogen electrode (RHE) and a Faradaic efficiency of 84.2% for CO production at −0.11 V vs RHE under simulated AM 1.5G illumination at 1 sun. The present findings of the synergistic effects of the structure and interface on the photoresponse and selectivity of a photoelectrode provide insights into the development of III–V semiconductor-based PEC systems for solar fuel generation.

URL: https://pubs.acs.org/doi/10.1021/acscatal.1c02043

16 Aug 2021

Submitted by (Bold are A*Star Staff): Shuai Chen, Zachary H. Aitken, Subrahmanyam Pattamatta, Zhaoxuan Wu, Zhi Gen Yu, David J. Srolovitz, Peter K. Liaw & Yong-Wei Zhang

Research Institute: IHPC

Title of Paper: Simultaneously enhancing the ultimate strength and ductility of high-entropy alloys via short-range ordering

Published in: Nature Communications

Abstract: Simultaneously enhancing strength and ductility of metals and alloys has been a tremendous challenge. Here, we investigate a CoCuFeNiPd high-entropy alloy (HEA), using a combination of Monte Carlo method, molecular dynamic simulation, and density-functional theory calculation. Our results show that this HEA is energetically favorable to undergo short-range ordering (SRO), and the SRO leads to a pseudo-composite microstructure, which surprisingly enhances both the ultimate strength and ductility. The SRO-induced composite microstructure consists of three categories of clusters: face-center-cubic-preferred (FCCP) clusters, indifferent clusters, and body-center-cubic-preferred (BCCP) clusters, with the indifferent clusters playing the role of the matrix, the FCCP clusters serving as hard fillers to enhance the strength, while the BCCP clusters acting as soft fillers to increase the ductility. Our work highlights the importance of SRO in influencing the mechanical properties of HEAs and presents a fascinating route for designing HEAs to achieve superior mechanical properties.

URL: https://doi.org/10.1038/s41467-021-25264-5

26 Jul 2021

Submitted by (Bold are A*Star Staff): Jipeng Fei, Bin Ding, See Wee Koh, Junyu Ge, Xingli Wang, Liquan Lee, Zixu Sun, Mengqi Yao, Yonghao Chen, Huajian Gao, Hong Li

Research Institute: IHPC

Title of Paper: Mechanistic Investigation of Electrostatic Field-Enhanced Water Evaporation

Published in: Wiley Online Library

Abstract: Investigations on external electrostatic field (EEF)-enhanced liquid water evaporation have been reported decades ago, which suggest that molecular alignment and polarization tuned by EEF accelerating the phase change process could be responsible for EEF-enhanced water evaporation. However, a detailed study revealing the role of EEF in altering the intermolecular and intramolecular water structure is lacking. Herein, an EEF is proved to tune water state by accelerating the thermal movement of water molecules, lowering the molecular escaping energy, and loosening the hydrogen bond structure. The detailed mechanisms and field interactions (heat and electrostatic) are investigated by in situ Raman characterizations and molecular dynamic simulations, which reveal that an EEF can effectively reduce the free energy barrier of water evaporation and then increase the evaporated water molecule flux. As a proof of concept, an EEF is integrated into an interfacial two dimentional solar steam generator, enhancing the efficiency by up to 15.6%. Similar to a catalyst lowing activation energy and enhancing kinetics of a chemical reaction, the EEF enhances water state tuning, lowers evaporation enthalpy, and then boosts steam generation rate with negligible additional energy consumption, which can serve as a generic method for water evaporation enhancement in water harvesting, purification, and beyond.

URL: https://doi.org/10.1002/advs.202100875

20 Jul 2021

Submitted by (Bold are A*Star Staff): Tianqi Deng, Wen Shi, Zicong Marvin Wong, Gang Wu, Xiaoping Yang, Jin-Cheng Zheng, Hui Pan, Shuo-Wang Yang

Research Institute: IHPC

Title of Paper: Designing Intrinsic Topological Insulators in Two-Dimensional Metal−Organic Frameworks

Published in: American Chemical Society

Abstract: The connection between electronic structures of metal−organic frameworks (MOFs) and their building subunits is a key cornerstone for rational MOF material design. Some two-dimensional conjugated MOFs were reported to be topological insulators. However, many of them are not intrinsic as the Fermi levels are far from the topological gaps. The subunit-to-MOF electronic orbital correspondence should be established to bridge their chemical structure and physical properties, thus understanding the design rules toward intrinsic topological insulators. Herein we reveal the fundamental role of the subunit-to-MOF symmetry relation in determining their orbital interaction and hybridization and, consequently, topological characteristics. In particular, such honeycomb-kagome MOFs possess delocalized symmetry-enforced nonbonding electronic states with the topological spin−orbit gap. The nonbonding nature of these states allows tailored band structure modulation through molecular structure and strain engineering, with the potential realization of an intrinsic metal−organic topological insulator.

URL: https://doi.org/10.1021/acs.jpclett.1c01731

18 Jul 2021

Submitted by (Bold are A*Star Staff): Yajing Cui, Fan Zhang, Geng Chen, Lin Yao, Nan Zhang, Zhiyuan Liu, Qingsong Li, Feilong Zhang, Zequn Cui, Keqin Zhang, Peng Li, Yuan Cheng, Shaomin Zhang, Xiaodong Chen

Title of Paper: A Stretchable and Transparent Electrode Based on PEGylated Silk Fibroin for In Vivo Dual-Modal Neural-Vascular Activity Probing

Published in: Wiley Online Library

Abstract: Transparent electrodes that form seamless contact and enable optical interrogation at the electrode–brain interface are potentially of high significance for neuroscience studies. Silk hydrogels can offer an ideal platform for transparent neural interfaces owing to their superior biocompatibility. However, conventional silk hydrogels are too weak and have difficulties integrating with highly conductive and stretchable electronics. Here, a transparent and stretchable hydrogel electrode based on poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and PEGylated silk protein is reported. PEGylated silk protein with poly(ethylene glycol) diglycidyl ether (PEGDE) improves the Young's modulus to 1.51–10.73 MPa and the stretchability to ≈400% from conventional silk hydrogels (<10 kPa). The PEGylated silk also helps form a robust interface with PEDOT:PSS thin film, making the hydrogel electrode synergistically incorporate superior stretchability (≈260%), stable electrical performance (≈4 months), and a low sheet resistance (≈160 ± 56 Ω sq−1). Finally, the electrode facilitates efficient electrical recording, and stimulation with unobstructed optical interrogation and rat-brain imaging are demonstrated. The highly transparent and stretchable hydrogel electrode offers a practical tool for neuroscience and paves the way for a harmonized tissue–electrode interface.

URL: https://doi.org/10.1002/adma.202100221

15 Jul 2021

Submitted by (Bold are A*Star Staff): Teck Lip Dexter Tam, Albertus Denny Handoko, Ting Ting Lin,  Jianwei Xu

Research Institute: IMRE

Title of Paper: Electron n-doping of a highly electron-deficient chlorinated benzodifurandione-based oligophenylene vinylene polymer using benzyl viologen radical cations

Published in: Materials Chemistry Frontiers

Abstract: Benzodifurandione-based oligophenylene vinylene (BDOPV) is a very strong electron-accepting moiety that has a very low lowest unoccupied molecular orbital (LUMO) value of −4.24 eV. Consequently, benzodifurandione-based polyphenylene vinylene (BDPPV) polymers also possess low LUMO values of less than −4.0 eV and have been reported to show good thermoelectric performances. However, all n-doping of BDPPV polymers have been insofar restricted to hydride-donors. Using tetrakis(dimethylamino)ethylene (TDAE) as a control, we found out that the lack of suitable electron-donors for BDPPV polymers is due to the strong tendency of over-doping, as a result of their very low LUMO values that promotes very rapid electron transfer and near room-temperature alkyl side chain melting that facilitates dopant infiltration. Here, we demonstrate well-controlled n-doping of a highly electron-deficient chlorinated BDPPV polymer (Cl-BDPPV, LUMO = −4.3 eV) using an electron-donor benzyl viologen radical cation (BV˙+). Unlike other electron-donors like N,N′-dimethylbenzimidazoline dimers, BV˙+ can be easily prepared using easily accessible reagents and shows excellent stability under a N2 atmosphere. The BV˙+-doped films were fully characterized and their thermoelectric performances were evaluated. A maximum σ and PF of 0.16 ± 0.01 S cm−1 and 0.43 ± 0.01 μW m−1 K−2 were obtained, respectively. Our results indicate that BV˙+ is a suitable electron-donor n-dopant candidate for highly electron-deficient n-type conjugated polymers.

Impact Factor: 6.482

URL: https://doi.org/10.1039/D1QM00695A

14 Jul 2021

Submitted by (Bold are A*Star Staff): Wen Shi, Tianqi Deng, Zicong Marvin Wong, Gang Wu, Shuo-Wang Yang 

Research Institute: IHPC

Title of Paper: A molecular roadmap towards organic donor-acceptor complexes with high-performance thermoelectric response

Published in: npj Computational Materials

Abstract: As a unique class of molecular electronic materials, organic donor–acceptor complexes now exhibit tantalizing prospect for heat–electricity interconversion. Over the past decades, in design of these materials for thermoelectric applications, consistent efforts have been made to synthesize a wide variety of structures and to characterize their properties. However, hitherto, one of the paramount conundrums, namely lack of systematic molecular design principles, has not been addressed yet. Here, based on ab initio calculations, and by comprehensively examining the underlying correlation among thermoelectric power factors, non-intuitive transport processes, and fundamental chemical structures for 13 prototypical organic donor–acceptor complexes, we establish a unified roadmap for rational development of these materials with increased thermoelectric response. We corroborate that the energy levels of frontier molecular orbitals in the isolated donor and acceptor molecules control the charge transfer, electronic property, charge transport, and thermoelectric performance in the solid-state complexes. Our results demonstrate that tailoring a suitable energy-level difference between donor’s highest occupied molecular orbital and acceptor’s lowest unoccupied molecular orbital holds the key to achieving an outstanding power factor. Moreover, we reveal that the charge-transfer-caused Coulomb scattering governs the charge and thermoelectric transport in organic donor–acceptor complexes.

URL: https://doi.org/10.1038/s41524-021-00580-y

05 Jul 2021

Submitted by (Bold are A*Star Staff): Krishna M. Gupta,  Surajit Das , Pui Shan Chow

Research Institute: ICES

Title of Paper: Molecular dynamics simulations to elucidate translocation and permeation of active from lipid nanoparticle to skin: complemented by experiments

Published in: Nanoscale

Abstract: One of the most realistic approaches for delivering actives (pharmaceuticals/cosmetics) deep into skin layers is encapsulation into nanoparticles (NPs). Nonetheless, molecular-level mechanisms related to active delivery from NPs to the skin have scarcely been studied despite the large number of synthesis and characterization studies. We herein report the underlying mechanism of active translocation and permeation through the outermost layer of skin, the stratum corneum (SC), via molecular dynamics (MD) simulations complemented by experimental studies. A SC molecular model is constructed using current state-of-the-art methodology via incorporating the three most abundant skin lipids: ceramides, free fatty acids, and cholesterol. As a potent antioxidant, ferulic acid (FA) is used as the model active, and it is loaded into Gelucire 50/13 NP. MD simulations elucidate that, first, FA-loaded NP approaches the skin surface quickly, followed by slight penetration and adsorption onto the upper skin surface; FA then translocates from the NP surface to the skin surface due to stronger NP–skin interactions compared to the FA–NP interactions; then, once FA is released onto the skin surface, it slowly permeates deep into the skin bilayer. Both the free energy and resistance to permeation not only indicate the spontaneous transfer of FA from the bulk to the skin surface, but they also reveal that the main barrier against permeation exists in the middle of the lipid hydrophobic tails. Significantly lower diffusion of FA is obtained in the main barrier region compared to the bulk. The estimated permeability coefficient (log P) values are found to be higher than the experimental values. Importantly, the permeation process evaluated via MD simulations perfectly matches with experiments. The study suggests a molecular simulation platform that provides various crucial insights relating to active delivery from loaded NP to skin, and it could facilitate the design and development of novel NP-based formulations for transdermal delivery and the topical application of drugs/cosmetics.

Impact Factor: 7.79

URL: https://doi.org/10.1039/D1NR02652F

26 Jun 2021

Submitted by (Bold are A*Star Staff): Xu Ban, Yifan Fan, Tuan-Khoa Kha, Richmond Lee, Choon Wee Kee, Zhiyong Jiang and Choon-Hong Tan

Research Institute: ICES

Title of Paper: Pentanidium-Catalyzed Direct Assembly of Vicinal All-Carbon Quaternary Stereocenters through C(sp3)-C(sp3) Bond Formation

Published in: CCS Chemistry

Abstract: The stereoselective construction of vicinal all-carbon quaternary stereocenters has long been a formidable synthetic challenge. Direct asymmetric coupling of a tertiary carbon nucleophile with a tertiary carbon electrophile is the most straightforward approach but it is sterically and energetically disfavored. Herein, we described a catalytic asymmetric substitution, where racemic tertiary bromides directly couple with racemic secondary or tertiary carbanion, creating a series of congested carbon (sp3)-carbon(sp3) bonds, including isolated all-carbon quaternary stereocenters, vicinal tertiary/all-carbon quaternary stereocenters and vicinal all-carbon quaternary stereocenters. This double stereoconvergent process, using pentanidium as catalyst, affords substituted products in good enantioselectivities and diastereoselectivities.

URL: https://doi.org/10.31635/ccschem.021.202101013

14 Jun 2021

Submitted by (Bold are A*Star Staff): Alex Yong Sheng Eng, Yong Wang, Dan-Thien Nguyen, Si Yin Tee, Carina Yi Jing Lim, Xian Yi Tan, Man-Fai Ng, Jianwei Xu, Zhi Wei She

Research Institute: IMRE, IHPC

Title of Paper: Tunable Nitrogen-Doping of Sulfur Host Nanostructures for Stable and Shuttle-Free Room-Temperature Sodium–Sulfur Batteries

Published in: American Chemical Society

Abstract: Room-temperature sodium–sulfur batteries have potential in stationary applications, but challenges such as loss of active sulfur and low electrical conductivity must be solved. Nitrogen-doped nanocarbon host cathodes have been employed in metal–sulfur batteries: polar interactions mitigate the loss of sulfur, while the conductive nanostructure addresses the low conductivity. Nevertheless, these two properties run contrary to each other as greater nitrogen-doping of nanocarbon hosts is associated with lower conductivity. Herein, we investigate the polarity–conductivity dilemma to determine which of these properties have the stronger influence on cycling performance. Lower carbonization temperatures produce more pyridinic nitrogen and pyrrolic nitrogen, which from density functional theory calculations preferentially bind discharge products (Na2S and short-chain polysulfides). Despite its lower conductivity, the highly doped composite showed better Coulombic efficiency and stability, retaining a high capacity of 980 mAh g(S)–1 after 800 cycles. Our findings represent a paradigm shift where nitrogen-doping should be prioritized in designing shuttle-free, long-life sodium–sulfur batteries.

URL: https://doi.org/10.1021/acs.nanolett.1c01763

11 Jun 2021

Submitted by (Bold are A*Star Staff): V. Sorkin, S. Chen, Teck L. Tan, Z.G. Yu, M.Man, Y.W. Zhang

Research Institute: IHPC

Title of Paper: First-principles-based high-throughput computation for high entropy alloys with short range order

Published in: Journal of Alloys and Compounds

Abstract: We extend the small set of ordered structures (SSOS) method to calculate several typical materials properties of high entropy alloys (HEAs) with short range order (SRO). Using both equimolar and non-equimolar quinary CoCuFeNiPd HEAs with SRO as an example, we calculate ground state energy, lattice constant, mass density and elastic moduli, and compare them with those obtained from the special quasi-random structure (SQS) method. The calculated properties are in good agreement with those obtained by SQS. Importantly, the computational cost of the SSOS method for achieving the same accuracy is only a small fraction of the computational cost of the SQS method. We further show that the application of machine learning methods can further reduce the computational cost of the SSOS method and maintain the same level of accuracy, making it especially suitable for high-throughput calculations of HEAs with SRO.

URL: https://doi.org/10.1016/j.jallcom.2021.160776

10 Jun 2021

Submitted by (Bold are A*Star Staff): Qingsong Li, Geng Chen, Yajing Cui, Shaobo Ji, Zhiyuan Liu, Changjin Wan, Yuping Liu, Yehu Lu, Changxian Wang, Nan Zhang, Yuan Cheng, Ke-Qin Zhang, and Xiaodong Chen

Research Institute: -

Title of Paper: Highly Thermal-Wet Comfortable and Conformal Silk-Based Electrodes for On-Skin Sensors with Sweat Tolerance

Published in: American Chemical Society

Abstract: Noninvasive and seamless interfacing between the sensors and human skin is highly desired for wearable healthcare. Thin-film-based soft and stretchable sensors can to some extent form conformal contact with skin even under dynamic movements for high-fidelity signals acquisition. However, sweat accumulation underneath these sensors for long-term monitoring would compromise the thermal-wet comfort, electrode adherence to the skin, and signal fidelity. Here, we report the fabrication of a highly thermal-wet comfortable and conformal silk-based electrode, which can be used for on-skin electrophysiological measurement under sweaty conditions. It is realized through incorporating conducting polymers poly(3,4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS) into glycerol-plasticized silk fiber mats. Glycerol plays the role of tuning the mechanical properties of silk fiber mats and enhancing the conductivity of PEDOT:PSS. Our silk-based electrodes show high stretchability (>250%), low thermal insulation (∼0.13 °C·m2·W–1), low evaporative resistance (∼23 Pa·m2·W–1, 10 times lower than ∼1.3 mm thick commercial gel electrodes), and high water-vapor transmission rate (∼117 g·m–2·h–1 under sweaty conditions, 2 times higher than skin water loss). These features enable a better electrocardiography signal quality than that of commercial gel electrodes without disturbing the heat dissipation during sweat evaporation and provide possibilities for textile integration to monitor the muscle activities under large deformation. Our glycerol-plasticized silk-based electrodes possessing superior physiological comfortability may further engage progress in on-skin electronics with sweat tolerance.

URL: https://doi.org/10.1021/acsnano.1c01431

25 May 2021

Submitted by (Bold are A*Star Staff): Junyu Ge, Bin Ding, Shuai Hou, Manlin Luo, Donguk Nam, Hongwei Duan, Huajian Gao, Yee Cheong Lam & Hong Li

Research Institute: IHPC

Title of Paper: Rapid fabrication of complex nanostructures using room-temperature ultrasonic nanoimprinting

Published in: Nature Communications

Abstract: Despite its advantages of scalable process and cost-effectiveness, nanoimprinting faces challenges with imprinting hard materials (e.g., crystalline metals) at low/room temperatures, and with fabricating complex nanostructures rapidly (e.g., heterojunctions of metal and oxide). Herein, we report a room temperature ultrasonic nanoimprinting technique (named nanojackhammer) to address these challenges. Nanojackhammer capitalizes on the concentration of ultrasonic energy flow at nanoscale to shape bulk materials into nanostructures. Working at room temperature, nanojackhammer allows rapid fabrication of complex multi-compositional nanostructures made of virtually all solid materials regardless of their ductility, hardness, reactivity and melting points. Atomistic simulations reveal a unique alternating dislocation generation and recovery mechanism that significantly reduces the imprinting force under ultrasonic cyclic loading. As a proof-of-concept, a metal-oxide-metal plasmonic nanostructure with built-in nanogap is rapidly fabricated and employed for biosensing. As a fast, scalable, and cost-effective nanotechnology, nanojackhammer will enable various unique applications of complex nanostructures in optoelectronics, biosensing, catalysis and beyond.

URL: https://doi.org/10.1038/s41467-021-23427-y

20 May 2021

Submitted by (Bold are A*Star Staff): Robert Vaser,  Mile Šikić

Research Institute: GIS

Title of Paper: Time- and memory-efficient genome assembly with Raven

Published in: Nature Journals (via Springer Nature Publishing)

Abstract: Whole genome sequencing technologies are unable to invariably read DNA molecules intact, a shortcoming that assemblers try to resolve by stitching the obtained fragments back together. Here, we present methods for the improvement of de novo genome assembly from erroneous long reads incorporated into a tool called Raven. Raven maintains similar performance for various genomes and has accuracy on par with other assemblers that support third-generation sequencing data. It is one of the fastest options while having the lowest memory consumption on the majority of benchmarked datasets.

URL: https://doi.org/10.1038/s43588-021-00073-4

07 May 2021

Submitted by (Bold are A*Star Staff): Teck Lip Dexter Tam,Ming Lin, Albertus Denny Handoko,Ting Ting Lin, Jianwei Xu

Research Institute: IMRE

Title of Paper: High-performance & thermally stable n-type polymer thermoelectrics based on a benzyl viologen radical cation-doped ladder-type conjugated polymer

Published in: Journal of Materials Chemistry A

Abstract: Over the past five years, the understanding of n-doped conjugated polymers has greatly accelerated the science of n-type polymer thermoelectrics. Part of this rapid progress is based on the emergence of new high-performance n-type conjugated polymers. n-Dopants, on the other hand, have not shown a significant breakthrough. Here we show that one of the oldest ladder-type conjugated polymers, poly(benzimidazobenzophenanthrolinedione) (BBL), can have outstanding n-type thermoelectric performance and superior thermal stability (100 °C over 4 days) when n-doped with one of the oldest organic radicals, the benzyl viologen radical cation (BV˙+). The BV˙+-doped BBL films achieved a maximum conductivity of 1.63 (1.60 ± 0.05) S cm−1 and a power factor of 5.37 (4.85 ± 0.46) μW m−1 K−2 in large channel devices (channel length = 2.5 mm; channel width = 20 mm), which are among the highest reported in the literature for n-type polymers, making them the best BBL based n-type thermoelectrics. The enhanced thermoelectric properties of the BV˙+-doped BBL are a consequence of the electrochemically active BV˙+/2+ molecules facilitating electron transport between the BBL fibers. Our results suggest that an electrochemically active counter cation is necessary for better electron transport and thus higher conductivity in fiber-forming/(semi)crystalline n-type organic semiconductors. The same is also likely to be true when the counter anion is electrochemically active for fiber-forming/(semi)crystalline p-type organic semiconductors. These findings will have tremendous impact on the chemical design of p- and n-dopants for organic semiconductors in the future.

Impact Factor: 11.301

URL: https://doi.org/10.1039/D1TA01645H

26 Apr 2021

Submitted by (Bold are A*Star Staff): Siyu Yan, Kaixin Tang, Yuejian Lin, Yuanhang Ren, Wanli Tian, Hua Chen, Tingting Lin, Longzhen Qiu, Xiaoyong Pan, Weizhi Wang

Research Institute: IMRE

Title of Paper: Light-Emitting Diodes with Manganese Halide Tetrahedron Embedded in Anti-Perovskites

Published in: ACS Energy Letters

Abstract: The formability of antiperovskite [MX4]XA3-type (A(I) = alkali metals; M(II) = transition metals; X = Cl, Br, I) can be predicted by building the analysis theory. To validate the prediction model, a series of cesium–manganese antiperovskite single crystals with different halogen mixing ratios were synthesized, which not only have [MX4]XA3-type structures but also are ideal luminescent materials. As the most pure green emission fluorescent antiperovskite, [MnCl2Br2]BrCs3 shows 520 nm emission with the high photoluminescence quantum yield (93.5%) at room temperature and ultrastable luminescent color from 77 to 523 K due to the strict confinement of high-density luminescent centers. By fabricating the perovskite film with the double-source thermal evaporation method, the first all-inorganic cesium–manganese halide antiperovskite light-emitting diode is reported, with maximum external quantum efficiency up to 12.5%, maximum luminance up to 3990 cd m–2, and half-life of 756 min operated at 5.0 V.

Impact Factor: 19.003

URL: https://dx.doi.org/10.1021/acsenergylett.1c00250

18 Apr 2021

Submitted by (Bold are A*Star Staff): Siyu Yan, Wanli Tian, Hua Chen, Kaixin Tang, Tingting Lin, Gaoyu Zhong, Longzhen Qiu, Xiaoyong Pan, Weizhi Wang

Research Institute: IMRE

Title of Paper: Synthesis of 0D Manganese‐Based Organic–Inorganic Hybrid Perovskite and Its Application in Lead‐Free Red Light‐Emitting Diode

Published in: Advanced Functional Materials

Abstract: Lead‐based perovskite light‐emitting diodes (PeLEDs) have exhibited excellent purity, high efficiency, and good brightness. In order to develop nontoxic, highly luminescent metal halide perovskite materials, tin, copper, germanium, zinc, bismuth, and other lead‐free perovskites have been developed. Here, a novel 0D manganese‐based (Mn‐based) organic–inorganic hybrid perovskite with the red emission located at 629 nm, high photoluminescence quantum yield of 80%, and millisecond level triplet lifetime is reported. When applied as the emissive layer in the PeLEDs, the maximum recording brightness of devices after optimization is 4700 cd m−2, and the peak external quantum efficiency is 9.8%. The half‐life of the device reaches 5.5 h at 5 V. The performance and stability of Mn‐based PeLEDs are one order of magnitude higher than those of other lead‐free PeLEDs. This work clearly shows that the Mn‐based perovskite will provide another route to fabricate stable and high‐performance lead‐free PeLEDs.

Impact Factor: 16.836

URL: https://doi.org/10.1002/adfm.202100855

15 Mar 2021

Submitted by (Bold are A*Star Staff): Runjiang Song, Yingguo Liu, Pankaj Kumar Majhi, Pei Rou Ng, Lin Haoa, Jun Xu, Weiyi Tian, Long Zhang, Hongmei Liu, Xinglong Zhang, Yonggui Robin Chi

Research Institute: IHPC

Title of Paper: Enantioselective modification of sulfonamides and sulfonamide-containing drugs via carbene organic catalysis

Published in: Organic Chemistry Frontiers

Abstract: A carbene-catalyzed method for highly enantioselective modification of sulfonamides is disclosed. The reaction proceeds under mild conditions with broad substrate scope, wide functional group tolerance, and good to excellent yields. When multiple sulfonamides or amines are present in the same molecule, the reaction occurs in a highly chemo-selective manner. Application of our method allows for selective modification of sulfonamide-containing drug molecules to form the corresponding phthalidyl derivatives as potential prodrugs. Experimental observations and DFT calculations suggest that the reaction proceeds via a stepwise addition pathway, assisted by Li+ ions or protons. Non-covalent interactions, such as cation–π interactions, play important roles in enhancing the reactivity and controlling the enantioselectivity of the reaction.

Impact Factor: 5.155

URL: https://doi.org/10.1039/D1QO00212K 

22 Feb 2021

Submitted by (Bold are A*Star Staff): Milad Ghaemi, Mehdi Jafary-Zadeh

Research Institute: IHPC

Title of Paper: Effect of Annealing-Induced Tensions on the Mechanical Failure of Copper/Copper Interface in Wafer-to-Wafer Hybrid Bonding

Published in: ECS Journal of Solid State Science and Technology

Abstract: The copper/copper (Cu/Cu) interface has an important role in wafer-to-wafer hybrid bonding for 3D integration applications. Reports indicate the possibility of the formation of post-bonding interfacial voids and cracks which must be avoided. Here, we use molecular dynamics simulations to investigate the effect of annealing-induced tensions on the strength and deformation mechanisms of Cu/Cu interfaces. We perform tensile tests on the pristine and defective Cu/Cu interfaces including a prototypical interfacial grain boundary in two defective limits: the presence of a single (isolated) void, and an array of multiple voids. The latter resembles interfacial nanoscale roughness as a result of weak sample preparation and bonding conditions. We show that in the limit of isolated voids, the strength of the system is lower than that of the pristine interface. The corresponding deformation mechanism is ductile and through dislocation activities which could be accompanied by void growth. In contrast, multiple interfacial voids lead to a ductile-to-brittle transition in the failure mechanism accompanied by a drastic reduction of the system strength. Our findings shed light on the importance of process control to assure the integrity and reliability of the bonded components.

Impact Factor: 2.142

URL: https://doi.org/10.1149/2162-8777/abe590

17 Feb 2021

Submitted by (Bold are A*Star Staff): Jia Liu, Hugues Lambert, Yong-Wei Zhang, Tung-Chun Lee

Research Institute: IHPC

Title of Paper: Rapid Estimation of Binding Constants for Cucurbit[8]uril Ternary Complexes Using Electrochemistry

Published in: Analytical Chemistry

Abstract: Supramolecular complexes are of fundamental interests in biomedicines and adaptive materials, and thus facile methods to determine their binding affinity show usefulness in the design of novel drugs and materials. Herein, we report a novel approach to estimate the binding constants KG2 of cucurbit[8]uril-methyl viologen-based ternary complexes (CB8-MV2+-G2) using electrochemistry, achieving high precision (±0.03) and practical accuracy (±0.32) in logKG2 and short measurement time (<10 min). In particular, we have uncovered a linear correlation (R2 > 0.8) between the reduction potential of CB8-MV2+-G2 ternary complexes and their reported binding constants from isothermal titration calorimetry, which allow a calibration curve to be plotted based on 25 sample complexes. Mechanistic investigation using experimental and computational approaches reveals that this correlation stems from the dynamic host-guest exchange events occurring after the electron transfer step. Binding constants of unknown ternary complexes, where G2 = hydrocarbons, were estimated, illustrating potential applications for sparsely soluble second guests.

Impact Factor: 6.785

URL: https://doi.org/10.1021/acs.analchem.0c04887

10 Feb 2021

Submitted by (Bold are A*Star Staff): Vinh-Tan Nguyen, Pierre Ricco, Gianluca Pironti 


Research Institute: IHPC

Title of Paper: Separation drag reduction through a spanwise oscillating pressure gradient

Published in: Journal of Fluid Mechanics 

Abstract: An oscillating spanwise pressure gradient is imposed numerically to control the flow separation and reduce the drag of a turbulent flow in a channel with square bars. The transverse flow produces a maximum drag reduction of 25 %, due to lower pressure and skin-friction drag forces. The pressure drag reduction reaches a maximum of 22 % and is due to a decrease of the positive high pressure in front of the bars and an increase of the low negative pressure behind the bars. The skin-friction drag reduction is caused by a lower wall-shear stress along the cavity between the bars where the flow is fully attached, while the wall-shear stress on the crest of the bars and in the separated region behind the bars is unaffected. The spanwise laminar flow obtained by neglecting the nonlinear terms involving the turbulent velocity fluctuations is used to compute the power spent for oscillating the fluid along the spanwise direction and an excellent agreement is found with the power spent obtained by the averaged turbulent flow. A marginal or negative net power saved is found by subtracting the power employed for controlling the flow from the power saved thanks to the transverse flow. The control reduces the total drag as the integral of the Reynolds stresses along the horizontal line connecting the corners of two consecutive bars is decreased, which in turn impacts the pressure and wall-shear stress reductions.

Impact Factor: 3.354

URL: https://doi.org/10.1017/jfm.2020.1124

29 Jan 2021

Submitted by (Bold are A*Star Staff): Yingzhi Zeng, Mengren Man, Kewu Bai, Yong-Wei Zhang

Research Institute: IHPC

Title of Paper: Revealing high-fidelity phase selection rules for high entropy alloys: A combined CALPHAD and machine learning study

Published in: Materials & Design

Abstract: We reveal high-fidelity new phase selection rules for high entropy alloys (HEAs) by combining CALPHAD calculations and the machine learning (ML) method. Employing Thermo-Calc and TCHEA3 database, we first generate more than 300,000 equilibrium phase data from 20 quinary families formed by the 8 elements of Al Co, Cr, Cu, Fe, Mn, Ni, and Ti, and choose initially 15 materials/physical descriptors. The eXtreme Gradient Boosting (XGBoost) method is then used to identify 5 most important descriptors that best delineate the single and mixed phases in the complex temperature-composition space of HEAs. The ML model trained by the 5 features is validated by 155 annealing experimental data points from 15 publications and then used to predict 213 new single-phase alloys with BCC and FCC structures of the alloy families of AlCrNiFeMn and AlCrCoNiFeTi. We also highlight the importance of equilibrium temperature and offer in-depth insights into the paradigm of composition-feature-phase of HEAs. On the basis of the 5 important features, we establish new phase selection rules for single FCC and BCC phases with a success rate above 90%, significantly outperforming all existing phase selection rules and providing a powerful tool for mapping single-phase in the complex temperature-composition space of HEAs.

Impact Factor: 6.289

URL: https://doi.org/10.1016/j.matdes.2021.109532

19 Jan 2021

Submitted by (Bold are A*Star Staff): Xing Yang, Yongtao Xie, Jun Xu, Shichao Ren, Bivas Mondal, Liejin Zhou, Weiyi Tian, Xinglong Zhang, Lin Hao, Zhichao Jin, Yonggui Robin Chi

Research Institute: IHPC

Title of Paper: Carbene-Catalyzed Activation of Remote Nitrogen Atoms of (Benz)imidazole-Derived Aldimines for Enantioselective Synthesis of Heterocycles

Published in: Angewandte Chemic International Edition

Abstract: A new mode of carbene-catalyzed heteroatom activation and asymmetric reactions is disclosed. The reaction starts with addition of a carbene catalyst to a (benz)imidazolederived aldimine substrate. Subsequent oxidation and proton transfer lead to the formation of a catalyst-bound triaza-diene as the key intermediate, in which the nitrogen atom at a site remote to the catalyst-substrate bond is activated. This unusual triaza-diene intermediate then undergoes highly enantioselective reactions with activated ketones through a concerted asynchronous pathway, as supported by mechanistic studies and preliminary density function theory calculation.

Impact Factor: 12.959

URL: https://doi.org/10.1002/anie.202016506

19 Jan 2021

Submitted by (Bold are A*Star Staff): Chee Kwan Gan, Zhun-Yong Ong

Research Institute: IHPC

Title of Paper: Complementary local-global approach for phonon mode connectivities

Published in: Journal of Physics Communications

Abstract: Sorting and assigning phonon branches (e.g., longitudinal acoustic) of phonon modes is important for characterizing the phonon bands of a crystal and the determination of phonon properties such as the Grüneisan parameter and group velocity. To do this, the phonon band indices (including the longitudinal and transverse acoustic) have to be assigned correctly to all phonon modes across a path or paths in the Brillouin zone. As our solution to this challenging problem, we propose a computationally efficient and robust two-stage hybrid method that combines two approaches with their own merits. The first is the perturbative approach in which we connect the modes using degenerate perturbation theory. In the second approach, we use numerical fitting based on least-squares fits to circumvent local connectivity errors at or near exact degenerate modes. The method can be easily generalized to other condensed matter problems involving Hermitian matrix operators such as electronic bands in tight-binding Hamiltonians or in a standard density-functional calculation, and photonic bands in photonic crystals.

URL: https://doi.org/10.1088/2399-6528/abd8ed

17 Jan 2021

Submitted by (Bold are A*Star Staff): Shuai Chen, Zachary H. Aitken, Subrahmanyam Pattamatta, Zhaoxuan Wu, Zhi Gen Yu, Rajarshi Banerjee, David J. Srolovitz, Peter K. Liaw, Yong-Wei Zhang

Research Institute: IHPC

Title of Paper: Chemical-Affinity Disparity and Exclusivity Drive Atomic Segregation, Short-Range Ordering, and Cluster Formation in High-Entropy Alloys

Published in: Acta Materialia

Abstract: Recently, atomic segregation, short-range ordering, and cluster formation have been observed experimentally in high-entropy alloys (HEAs). Differences in the atomic size and electronegativity of constituent elements were proposed to be the underlying cause of such ordering. Here, we investigated two HEAs, CoCuFeNiPd and CoCuFeNiTi, using a combination of Monte Carlo and molecular dynamic simulations. Our results show that the CoCuFeNiPd HEA exhibits much stronger atomic segregation and short-range ordering than the CoCuFeNiTi HEA, despite the larger differences in the relative atomic size and electronegativity of Ti with other constituent elements, as compared to those of Pd, suggesting that the differences in the atomic size and electronegativity alone are insufficient to explain the simulation results. We find that it is the chemical-affinity disparity and exclusivity between Ti (Pd) with the remaining species that lead to the different clustering behavior in these two HEAs. Specifically, three conditions for strong atomic segregation and short-range ordering are identified: 1. a large chemical-affinity disparity amongst the chemical elements; 2. a high chemical-element exclusivity in low-, medium-, and high-energy clusters; and 3. a net energy reduction associated with low- and medium-energy-cluster formation that compensates for the energy increase associated with high-energy-cluster formation. Our findings are in agreement with experimental results reported in literature, and highlight the importance of chemical-affinity disparity and exclusivity in influencing the microstructure of HEAs, explain the origin of high-energy-cluster formation in HEAs, and provide guidelines for designing HEAs with excellent properties.

Impact Factor: 7.656

URL: https://doi.org/10.1016/j.actamat.2021.116638

11 Jan 2021

Submitted by (Bold are A*Star Staff): Ke Wang, Xiansong Xu, Yuan Cheng, Min Zhang, Jian-Sheng Wang, Hai Wang, Gang Zhang

Research Institute: IHPC

Title of Paper: Magnon relaxation time in ferromagnetic Cr2Ge2Te6 monolayer governed by magnon-phonon interaction

Published in: Applied Physics Letters

Abstract: Recently, bulk and multi-layer Cr2Ge2Te6 (CGT) has garnered much attention because of its interesting physical properties and promising technological aspects, including information storage and spintronic application. Here, using density functional theory calculations, we investigate the spin-wave spectrum and magnon-phonon interaction (MPI) in the CGT monolayer. The strength of MPI and the magnon relaxation time are estimated by the broadening in the spin-wave spectrum. We find that the MPI in the CGT monolayer exhibits weak in-plane isotropy and a strong wave vector dependence. The broadening of optical magnons is constant near the center of the Brillouin zone, while that for acoustic magnons shows a quadratic wave-vector dependence. Moreover, this wave-vector dependence is independent of temperature. As the temperature increases from 5 K to 55 K, the magnon relaxation time decreases 4 times, revealing the importance of MPI in spin dynamics of the ferromagnetic CGT monolayer. Our work provides an in-depth understanding of the magnon-phonon interaction in the ferromagnetic Cr2Ge2Te6 monolayer.

Impact Factor: 3.597

URL: https://dx.doi.org/10.1063/5.0037081

06 Jan 2021

Submitted by (Bold are A*Star Staff): Qing-Xiang Pei, Viacheslav Sorkin, Ping Liu, Yucheng Zhong, Warintorn Thitsartarn, Chaobin He, Yong-Wei Zhang 

Research Institute: IHPC,IMRE

Title of Paper: Effect of surface coupling agents on the mechanical behaviour of polypropylene/silica composites: a molecular dynamics study

Published in: Journal of Polymer Research

Abstract: We investigate the mechanical behavior of polypropylene/silica composites under mode I and II loading by using molecular dynamics simulations, focusing on the effects of two typical surface coupling agents of HMDZ and APTES on the interface deformation and failure. It is found that under mode I loading, the silica surface functionalized with APTES can enhance the tensile strength of polypropylene/silica composites effectively. In contrast, the silica surface functionalized with HMDZ has little effect on the tensile strength. The simulation results are supported by experiments. Under mode II loading, it is found that both HMDZ and APTES can enhance the shear strength of polypropylene/silica composites with APTES being more effective. The underlying mechanisms for the enhancement of interface strength are analyzed. Our work provides a deep understanding of the interface structure, deformation and failure and will be useful for selecting suitable surface coupling agents in enhancing the interface strength of polymer composites.

Impact Factor: 2.426

URL: https://doi.org/10.1007/s10965-020-02371-3

04 Jan 2021

Submitted by (Bold are A*Star Staff): Wen Shi, Bosi Yin, Yi Yang, Michael B. Sullivan, John Wang, Yong-Wei Zhang, Zhi Gen Yu, Wee Siang Vincent Lee, Junmin Xue

Research Institute: IHPC

Title of Paper: Unravelling V6O13 Diffusion Pathways via CO2 Modification for High-Performance Zinc Ion Battery Cathode

Published in: ACS Nano

Abstract: Vanadium-based oxide is widely investigated as a zinc ion battery (ZIB) cathode due to its ability to react reversibly with Zn2+. Despite its successful demonstration, modification with simple molecules has shown some promise in enhancing the performance of ZIBs. Thus, this presents an immense opportunity to explore simple molecules that can dramatically improve the electrochemical performance of electrodes. Thus, the effect of CO2 modification is studied in this work by decomposing oxalic acid within a hydrated V6O13 framework. Based on the collective results, the presence of CO2 drastically lowers the relative energy of Zn2+ diffusion through the pathways by forming weak electrostatic interactions between OCO2 and Zn2+. This leads to an enlarged diffusion contribution, which consequently results in enhanced stability and better rate performance. The as-synthesized CO2–V6O13 electrode delivers one of the highest specific capacities reported for vanadium-based oxides of ca. 471 mAh g–1. Furthermore, an excellent cyclic stability of 80% capacity retention after 4000 cycles at 2 A g–1 is recorded for CO2–V6O13, which suggests the importance of simple molecules in the material framework toward the enhancement of ZIB cathode performance.

Impact Factor: 14.588

URL: https://doi.org/10.1021/acsnano.0c08432