Correlation of Microstructural Properties With Thermoelectric Performance of Bi 0.5 Sb 1.5 Te 3 Films Fabricated by Elec
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1267-DD10-18
Correlation of Microstructural Properties with Thermoelectric Performance of Bi0.5Sb1.5Te3 Films Fabricated by Electroplating
Koukharenko E1., Li X2., Kuleshova J3., Fowler M4., Frety N5., Tudor M.J1., Beeby S.P1., Nandhakumar I3., and White N.M1 1 School of Electronics and Computer Science, University of Southampton, SO17 1BJ, UK 2 School of Engineering Sciences, University of Southampton, SO17 1BJ, UK 3 School of Chemistry, University of Southampton, SO17 1BJ, UK 4 School of Physics and Astronomy, University of Southampton, SO17 1BJ, UK 5 Institut Charles Gerhardt-Equipe PMOF Université Montpellier II, France
ABSTRACT
This study shows for the first time, the correlation between the microstructural properties (chemical composition and its homogeneity) and the thermoelectric properties for p-type Bi0.5Sb1.5Te3 electroplated films (10-15 µm thickness). High microstructural quality of Bi0.5Sb1.5Te3 electroplated films (a close to stoichiometry chemical composition with its high homogeneity elements distribution) was achieved by using an additive in the plating solution (sodium ligninsulfonate) as a surfactant agent. A fine-grained microstructure of 280 nm to 1µm has been observed for these materials, which half that of the plated films without a surfactant. The thermoelectric properties of electrodeposited Bi0.5Sb1.5Te3 films obtained without microstructural optimisation, show modest Seebeck coefficient values of 20-120 µV/K, electrodeposited film with an optimised microstructure exhibits very high values of Seebeck coefficient of 220-300 µV/K. INTRODUCTION
Bismuth telluride-based materials are well known for their thermoelectric applications at near room temperature (thermopiles, thermal sensors, laser diodes, power generation and refrigeration devices) [1]. They are commonly fabricated by using various inorganic materials synthesis methods such as Czochralski, Bridgman, metal organic vapour deposition (MOVPD), molecular beam epitaxy (MBE), liquid phase epitaxy and bulk powder techniques. These methods have difficulty in achieving stoichiometric materials with high chemical homogeneity. This is an important factor as the thermoelectric properties are greatly dependant on material’s chemical homogeneity characteristics. In this respect, the electroplating process provides an attractive low cost, compatible with silicon microfabrication processes and a room temperature route to the fabrication of high homogeneity Bi2-xSbxTe3 films. To date, a considerable amount of research has been undertaken to study the electroplating process optimisation for bismuth telluride-based alloys [2]. Thus, different electrodeposition techniques have been studied (e.g. cyclic, pulsed electroplating); various plating process parameters such as different seed layer, deposition potential, electrolyte composition, temperature, pH, wetting agents, surfactants have been applied in order to find an optimal set of parameters which
allows to reach an optimum stoichiometric chemical composition with good crystallinity for the res
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