Effects of stoichiometry and crystalline morphology on transport in topological insulator nanowires*

In nanostructured topological insulators with increased surface-to-volume ratio the contribution of charge transport through topological surfaces relative to the bulk will be enhanced. Here we report on electrochemical synthesis and characterization of Bi$_2$Te$_3$ and Sb$_2$Te$_3$ nanowires in which the effect of materials' stoichiometry as well as nanowire size was investigated. Nanowires were grown in porous anodic aluminum oxide membranes with pore diameters varying from 18 to 150 nm. Stoichiometry and the wire morphology were tuned by electrochemical cell voltages in the 30 - 150 mV range. Topological signatures and surface conductance are affected by both crystallinity and chemical composition. We found that in the narrow range of the electrochemical potential (130 mV-150 mV) when stoichiometry changes were very small the nanowire conductance could still be hugely different. The results of high-field magnetotransport and I-V characteristic measurements on nanowires with crystallinity and morphology controlled by a suitable annealing protocol and imaged using transmission (TEM) and scanning (SEM) electron microscopies will be presented.