Projects : Brief description

• Photon-assisted oxide synthesis

We are interested in exploring how photo-excitation can be utilized as an athermal route for synthesis of functional oxides with controlled point defects. Cabrera pointed out in 1949 that light can perturb electrostatics at the metal-oxide interface leading to altered oxidation kinetics. There are however a number of intriguing aspects that are poorly understood. How does photon-assisted processing lead to changes in microstructure? Can one affect boundary mobility using photo-excitation? Does affecting point defect concentrations in oxides using such an approach manifest in structural evolution during subsequent processing? Particularly, what are the atomic scale mechanisms that lead to such striking effects of photon illumination during growth or annealing of ultra-thin oxides? What are some in-situ diagnostics one can construct to monitor changes in oxygen concentration (or other species through electroneutrality considerations) in oxide thin film structures? Addressing such questions, may lead to valuable insights into advancing this unique processing approach as well as provide a wealth of knowledge on fundamental properties of oxide near-surface regions. The research intersects naturally with contemporary problems in energy including design of energy materials, stability of metal-oxide interfaces for charge storage, photo-electrochemistry. This program also connects to various projects described below and hence may be considered of broad relevance to synthesis of functional energy materials.

• Early Stage Oxidation and Corrosion Science of Metals and Alloys

The initial oxidation of metals is a fascinating research topic that has attracted interest for several decades. Understanding atomic scale mechanisms leading to ultra-thin oxide breakdown may also lead to advances in corrosion protection that can have an impact in energy conservation. There are however several fundamental problems that still need to be understood such as precise experimental determination of oxide growth kinetics at the initial stages and relationship to the Mott potential, structure of oxide layers, chemical nature of oxide films formed on complex alloys. Our work deals with mechanistic studies on gas-phase initial oxidation as well as aqueous corrosion of metals and alloys (particularly Al and Al-alloys) through both simulations and experiments. The structure of oxides formed on metal and alloy surfaces are investigated through kinetic simulations in a range of environmental conditions. Problems of particular interest center around relationship between non-stoichiometry and passive state; spatially-resolved visualization of oxide breakdown, microstructural control utilizing photon interactions, studied through a combination of high-resolution experimental probes, impedance spectroscopy studies and modeling.

• Phase Transitions in Functional Oxides

Functional oxides serve as model systems to investigate correlated electron phenomena as well as hold potential for novel information processing devices. Understanding the mechanisms triggering metal-insulator transitions in thin film vanadium oxide (VO2) and hysteresis phenomena is underway. An outstanding problem in vanadium oxide devices is experimental demonstration of a field effect while de-coupling current driven phenomena. This presents a formidable challenge in synthesis of high-quality oxide films (due to Magneli phases in this system, synthesis of phase pure films is a non-trivial task), lithography and detailed electron transport studies. In related projects, non-invasive techniques to modulate oxygen non-stoichiometry in multi-valent cation(s) containing oxides are being actively investigated. Modulating chemical and structural properties of buried oxide-semiconductor interfaces utilizing photons at low temperatures is being studied. In addition to synthesis and materials characterization, we also fabricate multi-terminal device structures to study electron transport phenomena, electrical switching characteristics as well as mechanisms for improved understanding of the role of materials synthesis; microstructure and defects.

• Solid State Electrochemistry and Renewable Energy Materials and Devices

We are interested in understanding the role of microstructure in determining ion and electron transport in metal-oxides, primarily using thin film and superlattice structures as model systems. An exciting area of research is understanding the role of interfaces in carrier transport in fluorite-structured oxides. A systematic study is in progress to understand the mechanisms governing oxygen incorporation into oxides under photon irradiation. Further, we are interested in developing novel synthesis routes for energy materials as well as experimental realization of renewable energy devices such as solid oxide fuel cells. Novel approaches to investigate high temperature carrier transport in confined systems are being pursued. Ion dynamics and lattice correlations in low-dimensional oxides are worth exploring in this regard. A combination of studies involving high temperature electrical measurements as a function of oxygen partial pressure ranging nearly 25 decades, transmission electron microscopy, micro-fabricated devices to investigate low-dimensional oxide systems is underway to probe carrier transport at various lengthscales.

Please see "Publications" page for further information.