Spatio-Temporal and Site-Specific Chemical Dynamics at Interfaces

从金属的腐蚀到计算机芯片的制造，表面上的化学反应无处不在。然而，与研究气体和溶液中的反应相比，表面的化学反应提出了独特的挑战。例如，反应性取决于反应物分子与表面碰撞的速度以及接近的方向。让事情变得复杂的是，表面在原子水平上存在结构上的缺陷，而且到处都是缺陷，包括缺失的原子、岛屿和台阶，每一种缺陷的反应都可能不同。此外，一旦反应发生，它可以移动附近的原子，改变表面结构。在化学系化学结构、动力学和机理A项目的支持下，芝加哥大学的Steven J.Sibener教授正在研究高活性试剂(如氧和氢原子)以及其他含能物种与金属和半导体表面的化学反应。西本纳教授与他的学生合作，以已知的速度和方向将原子束和分子束引导到裸表面或带有分子装饰的表面。然后，该团队使用能够分辨单个原子的强大显微镜来监控不同位置的反应性，以及表面结构如何随反应而变化。他们的发现可能会对先进材料制造、纳米科学、电子材料、多相催化、燃烧和保护性涂层的设计产生广泛的影响。研究小组还参加了当地学校和博物馆的社区外联活动，向芝加哥南部的居民介绍科学问题，这些问题对于理解我们的现代技术世界至关重要。该计划结合使用超声波分子束、原位扫描隧道/原子力显微镜和表面光谱仪来检测清洁和分子装饰表面的特定部位的化学反应性。反应散射测量是通过同时进行原位原子级成像来进行的。这个程序开辟了一条直接的途径，用原子分辨率来理解界面反应性中的时空关联。它专注于表面化学动力学的前沿问题，包括绝热和非绝热气体-表面相互作用，非平衡条件下原子分辨的反应性，薄膜生长和钝化，以及入射碰撞条件下精确空间控制的几何约束反应研究。这种对分子反应性的评估是已知分子取向和局部吸附位置的函数，揭示了关于分子反应性和反应势能面的非常详细的信息，适合与理论和模拟进行定量比较。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Chemical reactions at surfaces are everywhere, from the corrosion of metals to the fabrication of computer chips. However, compared with studying reactions in gases and solutions, chemical reactions at surfaces present unique challenges. The reactivity, for example, can depend on how fast reactant molecules collide with the surface, as well as the direction of approach. To complicate matters, surfaces are structurally imperfect at the atomic level and are littered with defects, including missing atoms, islands, and steps, each of which can react differently. Moreover, once the reaction occurs, it can shift nearby atoms around, changing the surface structure. With support from the Chemical Structure, Dynamics and Mechanism A program in the Division of Chemistry, Professor Steven J. Sibener at The University of Chicago is studying chemical reactions between highly reactive reagents such as oxygen and hydrogen atoms, as well as other energetic species, with metal and semiconductor surfaces. Working with his students, Professor Sibener directs atomic and molecular beams with known speed and direction at either bare surfaces, or surfaces decorated with molecules. The team then uses powerful microscopies capable of resolving individual atoms to monitor the reactivity at different sites, as well as how the surface structure changes in response to the reaction. Their discoveries could have broad implications for advanced materials fabrication, nanoscience, electronic materials, heterogeneous catalysis, combustion, and the design of protective coatings. The research team also participates in community outreach at local schools and museums to introduce the residents of Chicago's south-side to scientific issues that are essential for understanding our modern technological world. This program uses a combination of supersonic molecular beams, in situ scanning tunneling/atomic force microscopy, and surface spectroscopies to examine the site-specific chemical reactivity of clean and molecule decorated surfaces. Reactive scattering measurements are carried out with concurrent in situ atomic-level imaging. This program opens a direct path to understanding, with atomic resolution, spatio-temporal correlations in interfacial reactivity. It has focus on forefront issues in surface chemical dynamics that include adiabatic and non-adiabatic gas-surface interactions, atomically-resolved reactivity under non-equilibrium conditions, thin film growth and passivation, and geometry-constrained reaction studies with precise steric control over incident collision conditions. Such assessment of molecular reactivity as a function of known molecular orientation and local adsorption site is revealing remarkably detailed information on molecular reactivity and reaction potential energy surfaces suitable for quantitative comparison with theory and simulations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.