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

基于第一原理量子力学的理论研究计划的目标是：1)了解与点状缺陷、表面电荷、外部应力和化学添加剂有关的非晶态二氧化硅(a-SiO_2)材料的表面结构和化学成分，以及2)利用这种机理的理解，开发一个详细的模型，用于控制合成二氧化硅支撑的半导体(硅[Si])和金属(金[Au])纳米结构，这些纳米结构具有各种新的应用，如纳米晶体存储器、光学互连和用于氢净化的微孔催化膜。由于非晶态氧化物在电子学、光学、催化和传感器等领域的广泛应用，原子水平操纵和精确确定非晶态氧化物的表面结构和功能一直是一个重要的问题。然而，直接表征的困难阻碍了理解无定形氧化物表面的复杂性质的进展。最近在理论技术和计算能力方面的进步使在原子尺度上探索氧化物表面发生的化学和物理现象成为可能。一个研究计划计划利用这些最新进展，并通过无缝耦合从量子化学、分子力学到统计理论的各种最先进的理论方法来利用可能的协同效应。这项研究将探索在a-SiO_2上合成Si/Au纳米颗粒，因为它们具有技术相关性和潜力；然而，对氧化物如何作用和控制负载型纳米材料的合成、结构和功能的基本见解将普遍适用于其他系统。将涉及三个相互交织的子任务，包括：1)确定a-SiO_2薄膜的表面结构和应变，特别是在存在缺陷和化学添加剂(如B、P、N和Ti)的情况下；2)a-SiO_2中表面和近表面缺陷的形成和性质，特别强调外部应力、表面电荷和化学添加剂的作用；以及3)表面缺陷、添加剂、电荷和应变对缺陷/改性/应变的a-SiO_2表面上Si和Au纳米结构的生长、结构和功能的影响。这个项目的成功完成将得益于：利用PI先前/正在进行的研究；利用UTAustin的超级计算机设施；以及与UTAustin的实验者合作，他们在氧化物支持的半导体和金属纳米结构的生长和性质方面有着广泛的工作。智力优势：该项目是第一个系统的理论工作，试图解释和预测与缺陷、应变、电荷和化学添加剂相关的非晶态氧化物的复杂表面结构和化学，以及a-SiO_2上支撑的Si和Au纳米粒子的生长、结构和功能。虽然目前的实验技术仅限于提供补充的真实空间信息，但PI预计这种基本的机理理解将极大地有助于利用现有的实验技术实现对非晶态二氧化硅材料表面化学的原子水平控制，进而实现支撑的硅和金纳米结构的成核和生长。这一成果将进一步为如何在未来的电子、传感、多相催化和氢燃料电池应用中获得所需的硅-二氧化硅和金-二氧化硅纳米系统的结构、电子和化学性质提供有价值的提示。广泛影响：该研究在纳米电子、氢和燃料电池等国家重要领域为学生提供广泛的跨学科培训，包括：氧化物支撑的半导体和金属纳米结构的生长、结构和功能；氧化物表面和界面属性的工程；以及最先进的计算方法和应用。从这项工作中获得的基本理解和计算工具也可以用于探索与各种纳米材料相关的许多重要行为和性质。该活动还旨在招募和培训少数群体和女性学生，并教育K-12和本科生以及普通公众关于新兴纳米电子和氢燃料技术以及计算纳米技术。

0933557HwangA 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 andAu 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.