Electrodeposition of Bismuth Telluride Nanowires for Thermoelectric Applications
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1018-EE10-22
Electrodeposition of Bismuth Telluride Nanowires for Thermoelectric Applications Raymond H. Scheffler1,2, Qi Laura Ye1, and Melanie McNeil2 1 Center for Advanced Aerospace Materials and Devices, NASA Ames Research Center, Mail Stop 229-1, Moffett Field, Mountain View, CA, 94035-1000 2 Department of Chemical and Materials Engineering, San Jose State University, San Jose, CA, 95192-0082 ABSTRACT Bismuth telluride (Bi2Te3) and its alloys have long been held as the best bulk commercial thermoelectric (TE) materials. In recent years, significant enhancement of the TE figure of merit (ZT) of these traditional TE materials has been predicted through reduction of dimensions (i.e., nanostructures and nanoengineering). We are particularly interested investigating electrolyte composition variations to control the composition of nanowires to enable large ZT enhancement. We report here the constant current electrochemical deposition of BixTey nanowires of diameters of 35, 55, 73 and 200 nm and lengths up to 50 microns. We are able to obtain controlled, uniform growth of high quality n-type bismuth telluride nanowires. A design of experimental matrix investigating the effects of current density and solution pH values on the overall growth rate and nanowire crystalline quality has been performed. The effects of growth conditions on materials and structural characteristics of BixTey nanowires have been studied by SEM, High Resolution TEM, EDX, concentric beam electron diffraction patterns, and ICP. The TE properties of individual BixTey nanowires are currently being evaluated using micro/nano fabricated devices and UHV Scanning Thermoelectric Microscopy. INTRODUCTION The emergence of nanotechnology, environmental concerns regarding refrigerant chemicals, and the possibility of super cooling electronics has brought renewed interest in thermoelectrics. Decreasing the dimensions of a thermoelectric material such as bismuth telluride to nanoscale is predicted to increase its figure of merit, ZT, as much as an order of magnitude [1-3]. Growing and integrating nanowires with high ZT values into a thermoelectric device can exploit the quantum size effects of increased density of states (DOS) and increased phonon boundary scattering [1-3]. Several papers have been published in literature on the synthesis of bismuth telluride nanowires [4-14]. The majority of the publications describe the electrochemical deposition of bismuth telluride nanowires from aqueous nitric acid solutions into anodic alumina membranes that serve as templates [4-13]. It should be noted that alumina is not an ideal supporting material for thermoelectric devices due to its moderate thermal conductivity [3, 16]. Jin and coworkers and Li and coworkers report on the electrochemical deposition of single crystal bismuth telluride nanowires [12, 13]. Unlike other studies, these researchers adjusted the pH of their deposition solutions; both report using solutions of pH 1 [12, 13]. While Li and coworkers used a pulsed voltage approach, Jin and coworkers report c
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