Physics of periodic and non-periodic nanostructured chromogenic thin films and devices

该研究计划的主要目的是研究过渡金属氧化物（TMO）薄膜的纳米结构和显色性能之间的相关性。这些纳米结构的TMO的显色性能相关的物理和化学的深入了解，预计将导致我们的设计和实现更好地执行各种应用的交互式设备。从科学和技术的角度来看，低维材料或所谓的纳米材料的领域近年来变得极其重要。迄今为止非常公知的材料的光学、电学和其他性质可以通过在一个或两个或所有三个维度上减小它们的尺寸来显著地改变和/或增强。这种尺寸减小到纳米尺度引起它们的变化：1）由于在表面处引起的巨大晶界效应，导致的电学行为，2）由于在膜中引起的光学常数和孔隙率的变化，导致的光学行为，以及3）由于在少量材料周围产生的巨大表面效应（巨大的表面与体积比），导致的化学行为。所有这些变化导致形成一种“新的”或“先进的”介观状态的材料。已经发现一些介观材料表现出在这些材料的本体或天然形式中不存在的性质。因此，在迄今为止众所周知的材料，通过其纳米结构的新性能的可控诱导已成为材料研究中的一个重要领域。我的目标是将纳米结构化方法应用于基于过渡金属氧化物的显色材料和器件。过渡金属氧化物（TMO）以其以各种氧化态存在的能力而闻名。这些TMO中的一些在这些不同状态之间显示出截然不同的光学和电学性质。因此，类似于半导体，TMO可以通过施加以小电场或光或热的形式提供的小活化能在这些亚稳态之间可逆地切换。通过这些外力的作用，它们可以可逆地从透明状态切换到不透明状态，或者从非导电状态切换到导电状态。因此，近年来，基于TMO的显色领域，即TMO通过电场（电致变色）或热（热致变色）或光（光致变色）的作用的可逆转换，吸引了许多研究人员的注意。这一领域日益增长的重要性源于两个方面：建立对这些可逆变化背后的丰富物理和化学的理解，以及这些互动变化的应用。我以前在这方面的工作表明，TMO的显色性能非常敏感地依赖于薄膜的纳米结构。通过仔细控制纳米结构，可以有效地定制这些材料的光学和电学性质的外部诱导可逆变化。此外，通过诱导光学波长尺度上的周期性纳米结构，可以植入各种可逆的光子效应。通过这种光子器件的专利工作，已经证明了一种操纵光传播的新方法。我打算继续我在这方面的研究。更具体地说，我希望将周期性和非周期性纳米结构应用于显色材料，并探索其优点，这项工作不仅将导致对这些材料的物理特性的深入理解，而且还将创造新的材料和器件，用于光子学，光学，通信和能源管理与转换

The principal objective of the proposed research program is to study the correlation between the nanostructure and the chromogenic properties of transition metal oxide (TMO) thin films. The in-depth understanding of the physics and chemistry related to the chromogenic properties of these nanostructured TMOs is expected to lead us to the design and realization of better performing interactive devices for various applications. The area of low dimension materials or the so called nanomaterials has become extremely important in recent years from the scientific and technological point of view. The optical, electrical and other properties of the hitherto very well-known materials can be drastically altered and/or enhanced by reducing their size in one or two or all three dimensions. This reduction in dimensions to nanometric scales induces a change in their 1) electrical behavior due to the immense grain boundary effects induced at the surfaces, 2) optical behavior due to the change in the optical constants and the porosity induced in the films and 3) chemical behavior due to the enormous surface effect created around the small amount of material (enormous surface to volume ratio). All these changes lead to the formation of a “new” or “advanced” mesoscopic state of materials. Some mesoscopic materials have been found to exhibit properties that do not exist in the bulk or natural form of these materials. Hence, a controlled induction of novel properties in hitherto well-known materials through their nanostructuring has become an important field in materials research. My aim here is to apply the nanostructuring approach to transition metal oxide based chromogenic materials and devices. Transition metal oxides (TMO) are known for their ability to exist in their various oxidation states. Some of these TMOs show drastically different optical and electrical properties between these different states. Hence, similar to the semiconductors, the TMOs can be switched reversibly between these metastable states by applying small activation energies provided in the form of either a small electric field or light or heat. They can be reversibly switched from a transparent to an opaque state or from a non-conducting to a conducting state through the action of these external forces. Thus the field of TMO based chromogenics, i.e. the reversible switching of TMOs through the action of an electric field (electrochromics) or heat (thermochromics) or light (photochromics) has attracted the attention of a lot of researchers in recent years. The growing importance of this field stems from two perspectives: building an understanding of the rich physics and chemistry underlying these reversible changes as well as the application of these interactive changes. My previous work in this direction has shown that the chromogenic performance of the TMOs depends very sensitively on the film nanostructure. By carefully controlling the nanostructure, one can effectively tailor the externally inducible reversible change in the optical and electrical properties of these materials. Further, by inducing a periodic nanostructure on optical wavelengths scale, various reversible photonic effects can be implanted. Through a patented work on such photonic devices, a new approach to manipulating light propagation has been demonstrated. I intend to continue my research in this area. More specifically, I would like to apply and explore the virtues of periodic and non-periodic nanostructuring to chromogenic materials.This work will not only lead to the in-depth understanding of the physics of these materials but also to the creation of new materials and devices for application in photonics, optics, communication and energy management & conversion