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

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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