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Structure and electronic properties of pure and nitrogen doped nanocrystalline tungsten oxide thin films.

机译:纯氮掺杂的纳米氧化钨薄膜的结构和电子性能。

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摘要

Tungsten oxide (WO3) is a multifunctional material which has applications in electronics, sensors, optoelectronics, and energy-related technologies. Recently, electronic structure modification of WO3 to design novel photocatalysts has garnered significant attention. However, a fundamental understanding of nitrogen-induced changes in the structure, morphology, surface/ interface chemistry, and electronic properties of WO 3 is a prerequisite to producing materials with the desired functionality and performance. Also, understanding the effect of thermodynamic and processing variables is highly desirable in order to derive the structure-property relationships in the W-O/W-O-N material system. The present work was, therefore, focused on studying the effects of processing parameters on the microstructure, optical properties, electrical conductivity, and electronic structures of pure and nitrogen-doped (N-doped) WO3 films grown by sputter deposition. Efforts were made to understand the properties and phenomena of pure and N-doped WO3 at reduced dimensionality (i.e., nanoscale dimensions).;The results and analyses indicate that the growth temperature (Ts) has a significant effect on the microstructure of WO3 films. The grain size increases from 9 to 50 nm coupled with a phase transformation in the following sequence: amorphous (a) to monoclinic (m) to tetragonal (t) with increasing Ts (25–500°C). The nanocrystalline t-WO 3 films exhibit a strong (001) texturing. The band gap narrowing from 3.25 to 2.92 eV with grain size occurs due to quantum confinement effects. Correlated with the structure and optical properties, electrical conductivity also increases.;Physical properties such as thickness, grain size, and density are also sensitive to oxygen/ nitrogen partial pressure during W-O/W-O-N sample fabrications. A direct relationship between film density and band gap is evident in nanocrystalline t-WO3 films grown at various oxygen pressures. It is observed that nitrogen doping significantly influences the structure-property relationships. Crystallographic analysis revealed that excess nitrogen trapped in the WO 3 crystal lattice induces a t–m phase transformation. The unique approach adopted in this work indicates a structure-dependent optical band gap variation leading to the lowest optical band gap (∼2.14 eV) at 0.7 at.% of N incorporation into t-WO3 films. The results clearly provide evidence to tune the electronic structure and properties with controlled N doping coupled with specific phase stabilization of WO3. The results provide a road map to phase-controlled synthesis of pure and Ndoped nanocrystalline WO3 films with desired properties.
机译:氧化钨(WO3)是一种多功能材料,在电子,传感器,光电和能源相关技术中都有应用。近来,WO 3的电子结构修饰以设计新颖的光催化剂已经引起了广泛的关注。然而,对WO 3的结构,形态,表面/界面化学和电子性质的氮诱导的变化的基本理解是生产具有所需功能和性能的材料的前提。同样,非常需要了解热力学和工艺变量的影响,以便得出W-O / W-O-N材料系统中的结构-特性关系。因此,目前的工作集中在研究工艺参数对通过溅射沉积生长的纯氮掺杂(N掺杂)WO3薄膜的微观结构,光学性能,电导率和电子结构的影响。努力了解在减小的尺寸(即,纳米级尺寸)下纯的和掺杂N的WO 3的特性和现象。结果和分析表明,生长温度(Ts)对WO 3膜的微观结构具有显着影响。晶粒尺寸从9 nm增加到50 nm,并按以下顺序相变:随着Ts(25-500°C)的增加,非晶态(a)到单斜晶(m)到四方晶(t)。纳米t-WO 3薄膜表现出很强的(001)纹理。由于量子限制效应,带隙随晶粒尺寸从3.25eV缩小到2.92eV。与结构和光学性质相关,电导率也增加。;物理性质,例如厚度,晶粒大小和密度,在W-O / W-O-N样品制造过程中也对氧/氮分压敏感。薄膜密度和带隙之间的直接关系在各种氧气压力下生长的纳米晶t-WO3薄膜中显而易见。观察到氮掺杂显着影响结构-性质关系。晶体学分析表明,WO 3晶格中捕获的过量氮会引起t-m相转变。在这项工作中采用的独特方法表明,与结构有关的光带隙变化会导致在掺入t-WO3薄膜的氮含量为0.7 at。%时最低的光带隙(〜2.14 eV)。结果清楚地提供了证据,证明可控N掺杂与WO3的特定相稳定相结合来调节电子结构和性能。结果提供了路线图,以相位控制合成具有所需特性的纯N掺杂的纳米晶WO3薄膜。

著录项

  • 作者单位

    The University of Texas at El Paso.;

  • 授予单位 The University of Texas at El Paso.;
  • 学科 Chemistry Inorganic.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 149 p.
  • 总页数 149
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 语言学;
  • 关键词

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