Electrodeposition of bismuth telluride nanowires with controlled composition in polycarbonate membranes

Abstract

Bismuth telluride nanowires were potentiostatically deposited from a water/DMSO 50%, v/v electrolyte within polycarbonate etched ion-track membranes covered by a platinum substrate. The presence of DMSO shifts the potentials to more negative values and slows down the cation diffusion. Cyclic voltammetries on recessed Pt nanoelectrodes using polycarbonate membranes highlight a complex electrochemical behavior through several cathodic and anodic peaks which are not observed onto platinum discs macroelectrodes. Analytical investigations enabled the determination of appropriate deposition conditions to finely tune the average composition of the nanowires. Calibrated TEM-EDX analyses evidence high aspect ratio nanowires, whose composition is strongly dependent on the deposition potential. In the same manner as for bismuth telluride film electroplating, bismuth enrichment occurs at more cathodic deposition potential whereas tellurium enrichment is observed at low cathodic potentials. Stoichiometric nanowires of 60nm diameter were obtained at −100mV vs Ag/AgCl from an electrolyte which contains [Bi3+]=1.5[HTeO2+]=15mM. The composition is homogeneous along the nanowire except at both edges: the cap is rich in bismuth whereas the base is rich in tellurium. The composition at the nanowire base is adjusted by setting a short initial voltage step (Ui=−300mV vs Ag/AgCl, ti=2s). In the case of stoichiometric compounds, the resulting nanostructures were found to be polycrystalline with a preferential orientation along the direction perpendicular to the planes (015).