Tailoring the Surface Reactivity of Amorphous Silica Materials through First Principles-based Atomistic Modeling

University Of Texas At Austin, Austin TX

Investigators

Abstract

0933557 Hwang A theoretical research program based on first principles quantum mechanics is planned with the goal of: 1) understanding the surface structure and chemistry of amorphous silica (a-SiO2) materials associated with point-like defects, surface charges, external stresses, and chemical additives, and 2) using this mechanistic understanding toward development of a detailed model for the controlled synthesis of silica-supported semiconductor (silicon [Si]) and metal (gold[Au]) nanostructures which have various novel applications such as nanocrystal memories, optical interconnects, and microporous catalytic membranes for hydrogen purification. Atomic-level manipulation and accurate determination of the surface structure and function of amorphous oxides has long been an issue of importance due to their many applications in electronics, optics, catalysis, and sensors. However, the difficulty of direct characterization has impeded progress towards understanding the complex nature of amorphous oxide surfaces. Recent advances in theoretical techniques and computing power now make it possible to explore chemical and physical phenomena occurring at the oxide surface at the atomic scale. A research program is planned that exploits these recent advances and harnesses the synergism possible by seamlessly coupling various state-of-the-art theoretical methods that range from quantum chemistry, molecular mechanics, to statistical theories. The research will explore Si/Au nanoparticle synthesis on a-SiO2 because of their technological relevance and potential; however, the fundamental insight gained into how oxides function and control the synthesis, structure and function of supported nanomaterials will be generally applicable to additional systems. Three intertwined subtasks will be addressed, including: 1) determining the surface structure and strain of thin a-SiO2 films, particularly in the presence of defects and chemical additives (such as B, P, N and Ti); 2) formation and nature of surface and near-surface defects in a-SiO2, with particular emphasis on the role of external stresses, surface charges, and chemical additives; and 3) effects of surface defects, additives, charges, and strains on the growth, structure and function of Si and Au nanostructures on the defective/modified/strained a-SiO2 surfaces. Successful completion of this project will be facilitated by: leveraging the PI's prior/ongoing research; utilizing the supercomputer facility at UTAustin; and collaborating with UTAustin experimentalists who have worked extensively on the growth and properties of oxide supported semiconductor and metal nanostructures. Intellectual Merit: This project represents the first systematic theoretical effort that attempts to explain and predict the complex surface structure and chemistry of amorphous oxides associated with defects, strains, charges, and chemical additives, as well as the growth, structure and function of Si and Au nanoparticles supported on a-SiO2. While current experimental techniques alone are limited to providing complementary real space information, the PI anticipates that this fundamental mechanistic understanding will greatly contribute to realizing atomic-level control of the surface chemistry of amorphous silica materials with existing experimental techniques, and in turn the nucleation and growth of supported Si and Au nanostructures. The outcome will further provide valuable hints on how to achieve the desired structural, electronic and chemical properties of the silicon-silica and gold-silica nanosystems for future electronic, sensing, heterogeneous catalysis, and hydrogen fuel cell applications. Broader Impact: The research provides a broad interdisciplinary training to students in the nationally important areas of nanoelectronics, hydrogen and fuel cells, encompassing: the growth, structure and function of oxide-supported semiconductor and metal nanostructures; engineering of oxide surface and interface properties; and state-of-the-art computational methods and applications. The fundamental understanding and computational tools obtained from this work can also be applied to explore many important behaviors and properties associated with a variety of nanomaterials. The activity also aims to recruit and train minority and women students and educate K-12 and undergraduate students, as well as the general public about newly emerging nanoelectronic and hydrogen fuel technologies as well as computational nanotechnology.