Template-assisted electrosynthesis of thick stoichiometric thermoelectric Bi2Se3 micropillars

Abstract

A method is presented that enables the template assisted electrochemical deposition of tens of micrometer thick, compact and stoichiometric Bi2Se3 micropillars. This is achieved by modifying the acidic electrolyte that contains 1 M HNO3 with potassium chloride salt and introducing resting pulses during the plating process. We demonstrate the successful deposition into photoresist templates with mold diameters down to 30 µm and thicknesses up to 45 µm. Cross-sectional EDX line measurements confirm an optimal stoichiometry of Bi:Se 40:60 along the growth direction, independent of the micropillar diameter. XRD and Raman measurements after electrochemical deposition point to a primarily orthorhombic structure. To illustrate the potential of this electrochemical method for thermoelectric applications, Seebeck coefficient and electrical conductivity of 45 µm thick orthorhombic Bi2Se3 pillars with 30 and 50 µm diameter are measured for five different electrodeposition runs. An average electrical conductivity of 8.6 S/m (SD = 4.5 S/m) and a high average negative Seebeck coefficient of -162 µV/K (SD = 32 µV/K) was determined. The process presented here is highly promising for the reliable synthesis of Bi2Se3 micropillars, which can be integrated in thermoelectric micro generators or sensors.