Formation mechanism of a microscale domain and effect on transport properties in strained VO2 thin films on TiO2(001)
Formation mechanism of a microscale domain and effect on transport properties in strained VO2 thin films on TiO2(001)
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DOI：
10.1103/physrevb.90.054203
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发表时间：
2014-08-11
影响因子：
3.7
通讯作者：
Tanaka, Hidekazu
中科院分区：
文献类型：
--
作者：
Kawatani, Kenichi;Kanki, Teruo;Tanaka, Hidekazu
研究了金红石型TiO 2（001）衬底上VO 2薄膜的电畴尺寸和输运性质随膜厚的变化规律，并确定了微畴的形成机制。结果发现，畴尺寸随膜厚的增加而减小，畴界由裂纹和位错组成，高分辨率透射电子显微镜澄清。详细的图像显示，TiO 2（001）接收的拉伸应变VO 2晶格在裂纹和位错周围部分弛豫。在VO 2/TiO 2（001）系统中，弛豫晶格可能恢复到340 K的原始金属-绝缘体转变温度，而张应变晶格的转变温度为300 K。因此，应变和弛豫晶格的混合状态以及较厚膜中位错密度的增加导致了对温度的过宽电阻行为。此外，位错的起源和畴尺寸的厚度依赖性可以解释由钉扎层之间的竞争产生的剪切应力的能量释放在近界面的VO 2层保持的tetraxite结构和近表面层从衬底分离试图晶格转变为单斜结构。这种理解使我们能够更精确地设计这些域的大小和配置及其传输特性。
We investigated film thickness dependence of domain size and transport property in VO2 thin films on rutile TiO2 (001) substrates and identified formation mechanism of the microscaled domain. It was found that domain size decreased with increasing film thickness and the domain boundary consisted of cracks and dislocations, clarified by high-resolution transmission electron microscopy. The detailed images showed, the tensile-strained VO2 lattices received by TiO2 (001) were partially relaxed around the cracks and dislocations. The relaxed lattice is likely to return the original metal-insulator transition temperature of 340 K, whereas the tensile-strained lattice has the transition at 300 K in a VO2/TiO2 (001) system. Thus, the mixed states of strained and relaxed crystal lattice and the increase in dislocation density in thicker films cause the overly broad resistance behavior against temperature. Furthermore, the origin of the dislocations and the thickness dependence of the domain size could be explained by the energy release of shear stress generated by competition between the pinning layers at near-interface VO2 layers holding the tetragonal structure and the near-surface layers separated from the substrate attempting the lattice transformation to a monoclinic structure. This understanding enables us to more precisely design the size and configuration of these domains and their transport properties.