Dr. Iris Nandhakumar
University of Southampton
Host: Dr. Teng Jinghua (Strategic Research Office, IMRE)
Current focus on energy sustainability and stricter legislation on the emission of CO2 have sparked a renewed interest in thermoelectric (TE) power harvesting technologies which can directly convert thermal waste heat into useful electricity. Thermoelectric devices offer advantages over other energy harvesting techniques which include solid-state operation with no moving parts, zero-emission, silent operation, vast scalability and high reliability with no maintenance and long operating lifetimes. Despite these merits, the use of TE generators has been vastly limited to niche applications due to their low efficiency and bulky size. Calculations by Dresselhaus et al. on low dimensional structures have predicted that the thermoelectric efficiency in these systems could be dramatically increased which offers an exciting opportunity to engineer novel thermoelectric materials.
The current best performing TE materials in commercial TE devices are based on bulk alloys of bismuth telluride such as n-type Bi2Te3 and p-type Bi0.5Sb1.5Te3 for refrigeration and waste heat recovery up to 200°C. A wide range of different fabrication methods have been employed to prepare nanostructures of n-and p-type bismuth telluride alloys. However, these have clear limitations in the size and density of thermoelectric elements that can be prepared whilst not being compatible with silicon microfabrication processes. Ion-track etch lithography on the other hand is a low-cost process that can produce templates with deep vertical and narrow channels suitable for nanowire growth. It employs heavy accelerated ions as a source to damage the material, making it susceptible to chemical etching in the direction defined by the irradiation. This can produce low-cost templates for nanowire growth with diameters < 50 nm and high aspect ratio (>1000). It was reported that the fabrication of high density arrays of n-type Bi2Te3 and p-type Bi0.5Sb1.5Te3 nanowires by electrodeposition into ion-track etched polyimide Kapton templates. This material offers a number of distinct advantages over porous alumina templates which include high flexibility, a low thermal conductivity (0.12 Wm-1K-1), high chemical and heat resistance (3K to 593K) and compatibility with silicon microfabrication, which make it promising for thermoelectric applications.
ABOUT THE SPEAKER
Dr. Iris Nandhakumar received a first-class Dipl.-Chem. degree (MSc in Chemistry) from the Technical University of Berlin and gained her PhD in Chemistry at the University of Southampton. She also holds an MPhil in Physics from the University of Cambridge, Cavendish Laboratory. Following several post-doctoral appointments at the University of Southampton and visiting research fellow positions at the University of Georgia Athens and the University of California in the USA, Dr. Nandhakumar was appointed to a joint faculty position at the University of Southampton in both Physics and Chemistry. Her research focuses on the nanoscale fabrication and characterisation of materials, in particular on semiconducting materials.
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