Nanoscience Centre, University of Cambridge, Cambridge, United Kingdom.
Nano Lett. 2013 Apr 10;13(4):1822-8. doi: 10.1021/nl400511x. Epub 2013 Mar 6.
We report a morphotropic phase transformation in vanadium dioxide (VO2) nanobeams annealed in a high-pressure hydrogen gas, which leads to the stabilization of metallic phases. Structural analyses show that the annealed VO2 nanobeams are hexagonal-close-packed structures with roughened surfaces at room temperature, unlike as-grown VO2 nanobeams with the monoclinic structure and with clean surfaces. Quantitative chemical examination reveals that the hydrogen significantly reduces oxygen in the nanobeams with characteristic nonlinear reduction kinetics which depend on the annealing time. Surprisingly, the work function and the electrical resistance of the reduced nanobeams follow a similar trend to the compositional variation due mainly to the oxygen-deficiency-related defects formed at the roughened surfaces. The electronic transport characteristics indicate that the reduced nanobeams are metallic over a large range of temperatures (room temperature to 383 K). Our results demonstrate the interplay between oxygen deficiency and structural/electronic phase transitions, with implications for engineering electronic properties in vanadium oxide systems.
我们报告了在高压氢气中退火的二氧化钒（VO2）纳米梁中的形态转变，这导致了金属相的稳定。结构分析表明，在室温下，退火的 VO2 纳米梁具有六方密堆积结构，表面粗糙，而不像生长的 VO2 纳米梁具有单斜结构和清洁的表面。定量化学分析表明，氢气在纳米梁中显著减少了氧，其特征是非线性还原动力学，这取决于退火时间。令人惊讶的是，由于在粗糙表面形成的与氧缺陷相关的缺陷，功函数和电阻纳米梁的电导率遵循与组成变化相似的趋势。电子输运特性表明，还原后的纳米梁在很大的温度范围内（室温至 383 K）为金属。我们的结果表明了氧缺陷与结构/电子相变之间的相互作用，这对工程化氧化钒系统中的电子性质具有重要意义。
