Electrodeposition of Bismuth Telluride from a Weakly Coordinating, Non-Aqueous Solution

Abstract

Thermoelectric materials are of interest for converting waste heat to electricity and could be useful in applications such as power generation.1 Currently, bulk bismuth telluride (Bi2Te3) is the most commonly used material for thermoelectric coolers and waste heat recovery. However, theoretical calculation2 predicts that the thermoelectric performance of Bi2Te3 can be dramatically improved by confining its dimensions to the nanometre scale. Electrodeposition provides a bottom-up technique compared to conventional coating methods, such as physical vapor deposition (PVD). It is of advantage in the efficient use of the starting material and can be used to plate curved surfaces and even inside of topologically demanding surfaces.3 The use of electrodeposition to fill nano-structures is also achievable, which is exploited in the Damascene process to grow 20 nm diameter Cu wire.4 In electrochemical experiments water is the most commonly used solvent but its limitation includes narrow potential window, which is crucial in electrodeposition as water reduction will be a competing process for metal reduction/deposition and introduces complexity to experiments. Here we employ an electrolyte system based on tetrabutylammonium chlorometallate metal sources with compatible tetraalkyl halide supporting electrolytes in non-aqueous, weakly coordinating solvents,5,6 which provides the ability to deposit alloys with desired structures and properties. In this work we report the deposition of Bi2Te3 films from dichloromethane. Bi2Te3 is a narrow band gap layered semi-conductor and it is demonstrated that the composition and structure of the BiTe films can be controlled by tuning the electrochemical parameters, such as the electrolyte concentration and deposition potential (Figure 1).7 We then investigate Bi2Te3 nucleation and growth using transmission electron microscopy (TEM) with a boron doped diamond electrode, acting as the electron transparent substrate.8 We observe the initial stage of Bi, Te and BiTe nuclei after electrodeposition (from individual atoms to atom arrays and nanocrystals) This work is conducted as part of the ADEPT project funded by EPSRC (EP/N035437/1). [1] Materials 7.4 (2014): 2577-2592. [2] Physical review B 47.24 (1993): 16631. [3] Proceedings of the National Academy of Sciences 106.35 (2009): 14768-14772. [4] IBM Journal of Research and Development 42.5 (1998): 567-574. [5] Chemistry-A European Journal 22.1 (2016): 302-309. [6] RSC Advances 3.36 (2013): 15645-15654. [7] Journal of Electroanalytical Chemistry 839 (2019): 134-140. [8] ACS nano 12.7 (2018), 7388-7396 Figure 1