On-Film Formation of Bi Nanowires with Extraordinary Electron Mobility

A novel stress-induced method to grow semimetallic Bi nanowires along with an analysis of their transport properties is presented. Single crystalline Bi nanowires were found to grow on as-sputtered films after thermal annealing at 260−270 °C. This was facilitated by relaxation of stress between the film and the thermally oxidized Si substrate that originated from a mismatch of the thermal expansion. The diameter-tunable Bi nanowires can be produced by controlling the mean grain size of the film, which is dependent upon the thickness of the film. Four-terminal devices based on individual Bi nanowires were found to exhibit very large transverse and longitudinal ordinary magnetoresistance, indicating high-quality, single crystalline Bi nanowires. Unusual transport properties, including a mobility value of 76900 cm2/(V s) and a mean free path of 1.35 μm in a 120 nm Bi nanowire, were observed at room temperature

Direct Growth of Compound Semiconductor Nanowires by On-Film Formation of Nanowires: Bismuth Telluride

Bismuth telluride (Bi2Te3) nanowires are of great interest as nanoscale building blocks for high-efficiency thermoelectric devices. Their low-dimensional character leads to an enhanced figure-of-merit (ZT), an indicator of thermoelectric efficiency. Herein, we report the invention of a direct growth method termed On-Film Formation of Nanowires (OFF-ON) for making high-quality single-crystal compound semiconductor nanowires, that is, Bi2Te3, without the use of conventional templates, catalysts, or starting materials. We have used the OFF-ON technique to grow single crystal compound semiconductor Bi2Te3 nanowires from sputtered BiTe films after thermal annealing at 350 °C. The mechanism for wire growth is stress-induced mass flow along grain boundaries in the polycrystalline film. OFF-ON is a simple but powerful method for growing perfect single-crystal compound semiconductor nanowires of high aspect ratio with high crystallinity that distinguishes it from other competitive growth approaches that have been developed to date