Zhang Zongtao, Feng Yifei, Gao Yanfeng, Chen Deliang, Shao Guosheng
School of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450001, China.
School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China.
Nanomaterials (Basel). 2019 Apr 4;9(4):549. doi: 10.3390/nano9040549.
The present investigation reported on a novel oxygen-assisted etching growth method that can directly transform wafer-scale plain VO₂ thin films into pyramidal-like VO₂ nanostructures with highly improved field-emission properties. The oxygen applied during annealing played a key role in the formation of the special pyramidal-like structures by introducing thin oxygen-rich transition layers on the top surfaces of the VO₂ crystals. An etching related growth and transformation mechanism for the synthesis of nanopyramidal films was proposed. Structural characterizations confirmed the formation of a composite VO₂ structure of monoclinic M1 (P21/c) and Mott insulating M2 (C2/m) phases for the films at room temperature. Moreover, by varying the oxygen concentration, the nanocrystal morphology of the VO₂ films could be tuned, ranging over pyramidal, dot, and/or twin structures. These nanopyramidal VO₂ films showed potential benefits for application such as temperature-regulated field emission devices. For one typical sample deposited on a 3-inch silicon substrate, its emission current (measured at 6 V/μm) increased by about 1000 times after the oxygen-etching treatment, and the field enhancement factor β reached as high as 3810 and 1620 for the M and R states, respectively. The simple method reported in the present study may provide a protocol for building a variety of large interesting surfaces for VO₂-based device applications.
本研究报道了一种新型的氧辅助蚀刻生长方法，该方法可以直接将晶圆级的平面VO₂薄膜转变为具有高度改善的场发射特性的金字塔状VO₂纳米结构。退火过程中施加的氧气通过在VO₂晶体顶表面引入薄的富氧过渡层，在特殊金字塔状结构的形成中起关键作用。提出了一种用于合成纳米金字塔薄膜的蚀刻相关生长和转变机制。结构表征证实了薄膜在室温下形成了单斜M1（P21/c）和莫特绝缘M2（C2/m）相的复合VO₂结构。此外，通过改变氧气浓度，可以调节VO₂薄膜的纳米晶体形态，范围包括金字塔状、点状和/或孪晶结构。这些纳米金字塔状VO₂薄膜在诸如温度调节场发射器件等应用中显示出潜在的优势。对于一个沉积在3英寸硅衬底上的典型样品，经过氧蚀刻处理后，其发射电流（在6 V/μm下测量）增加了约1000倍，并且M态和R态的场增强因子β分别高达3810和1620。本研究报道的简单方法可能为构建用于基于VO₂的器件应用的各种大型有趣表面提供一种方案。
