Tuning vanadium dioxide films by extreme straining - local investigations on transition phenomena and exotic phases

二氧化钒是一种相关氧化物，在大约340 K时发生金属-绝缘体转变。这种转变伴随着从金红石金属高温结构到单斜绝缘低温结构的结构相变。转变温度可以通过施加机械应变在宽范围内调谐;外部电场也可以驱动转变。此外，已知在进一步的机械应变下，可能出现外来相。因此，二氧化钒显示出巨大的应用潜力，例如，在本项目中，我们利用低能电子显微镜（LEEM）同时原位研究了二氧化钒薄膜在不同取向的二氧化钌表面上的生长及其结构和电子性质。我们利用的事实，氧化钌表面导致不同的结晶取向的二氧化钌岛，将作为模板在随后的氧化钒生长的共存。氧化钒和氧化钒之间的晶格失配表明不同的发生，在某些情况下，极端应变氧化钒取决于其取向。由于这种极端的应变，我们预计会出现新的，异国情调的阶段，更普遍的是，一个相当宽的调谐范围的转变温度的氧化钒。这些阶段将通过LEEM和相关的局部衍射和光谱技术，包括同步加速器辅助方法进行彻底表征。在一个平行的努力，我们的目标是采用扫描探针显微镜，以获得独特的见解小规模的相分离现象，并解决，注意潜在的应用，施加电场的影响。此外，我们将扩展我们的研究，以钌薄膜沉积在蓝宝石基板上的磁控溅射，从而推动更高的技术相关性。

Vanadium dioxide is a correlated oxide with a metal-insulator transition at approximately 340 K. This transition is accompanied by a structural phase transition from the rutile metallic high-temperature structure to the monoclinic insulating low-temperature structure. The transition temperature can be tuned over a broad range by applying mechanical strain; also external electrical fields may drive the transition. Moreover, it is known that under mechanical straining further, exotic phases may occur. Consequently, vanadium dioxide exhibits a large potential for applications, e.g., in oxide electronics provided that these materials properties may be controlled and manipulated as thin films.In this project we investigate simultaneously and in situ the growth and the structural and electronic properties of vanadium dioxide films on ruthenium dioxide surfaces of different orientations by low-energy electron microscopy (LEEM). We exploit the fact that oxidizing the ruthenium surfaces leads to the coexistence of different crystallographically oriented ruthenium dioxide islands that will act as templates in subsequent vanadia growth. The lattice mismatch between vanadia and ruthenia suggests the occurrence of differently and, in some cases, extremely strained vanadia depending on its orientation. Due to this extreme straining, we expect the occurrence of novel, exotic phases and, more generally, a considerably broadened tuning range for the transition temperature of vanadia. These phases will be thoroughly characterized by LEEM and related local diffraction and spectroscopy techniques, including synchrotron-assisted methods. In a parallel effort, we aim to employ scanning probe microscopy to obtain unique insights into small-scale phase separation phenomena and also address, mindful of potential applications, the influence of applied electrical fields. Furthermore, we will extend our studies to ruthenium thin films deposited on sapphire substrates by magnetron sputtering, thereby pushing for higher technological relevance.