Surface Heterogeneity and Defects in Gas-Surface Reactions

S.亚历克斯·坎德尔，气体表面反应中的表面异质性和缺陷化学家使用包含反应物和产物分子符号的公式来描述化学反应。 然而，该公式只是理解反应如何发生以及如何控制它们的一个非常基本的起点。 坎德尔博士正在研究固体表面化学反应的分子变化或机制，以揭示这些反应在原子尺度上是如何发生的。 他特别感兴趣的是确定组成杂质和原子级结构对反应速率和产物的影响。 在某些情况下，这些变化是所需的，例如在许多工业重要性过程中的特定缺陷所证明的增强的催化活性。 在其他方面，例如用于制造计算机芯片和其他半导体器件的制备技术，即使表面上有少量缺陷也会导致产品无法使用。 Kandel博士采用一种称为扫描隧道显微镜（STM）的成像技术来“看到”单个原子和分子，以确定固体表面在化学反应过程中如何在原子水平上发生变化。 这些实验产生的时间流逝序列显示了特定的局部组成和几何形状如何影响和控制化学反应的速率和结果。 在这个项目中获得的基本理解有助于未来设计新的催化剂，表面涂层和材料加工方法。 坎德尔博士的研究对许多层次的学生都有吸引力，他每年都会邀请几名高中生和他们的老师作为研究助理。 他还维护了一个STM图像数据库，公众可以通过他在圣母大学的网页访问。Alex Kandel由大分子，超分子和纳米化学（MSN）计划支持，研究气相自由基物种和固体表面之间的反应，特别强调表面的局部分子结构如何影响化学反应性。 氢，氯，和甲烷自由基被用来化学改性以及表征的有机单分子膜，和由它们的相互作用引起的原子尺度的变化的进展进行监测，使用扫描隧道显微镜（STM）。 自由基表面反应与各种化学过程有关，其中表面暴露于反应性环境，包括燃烧（氢原子），高层大气化学（氯原子），化学气相沉积（氢，甲基）和等离子体处理（氢，氯）。 此外，系统研究表面单层结构的各个方面如何影响反应性，有助于建立表面-自由基相互作用的基础知识和对气体-表面化学的新机制理解。 Kandel博士的研究涉及高中，本科和研究生，并在当地和国际科学竞赛中担任高中生的导师。 他还维护了一个STM图像数据库，公众可以通过他在圣母大学的网页访问。

S. Alex Kandel, Surface Heterogeneity and Defects in Gas-Surface ReactionsChemists use formulas containing reactant and product molecule symbols to describe a chemical reaction. However the formula is only a very basic starting point for understanding how the reactions occur and, therefore, how to control them. Dr. Kandel is investigating the molecular changes, or mechanisms, of chemical reactions taking place at solid surfaces to shead light on how these reactions actually take place at the atomic scale. He is particularly interested in determining the effect of compositional impurities and atomic-level structure on the rate and the products of a reaction. In some cases, these changes are desired, such as the enhanced catalytic activity demonstrated by specific defects in many processes of industrial importance. In others, such as the preparation techniques used to create computer chips and other semiconductor devices, even a small number of imperfections in a surface can result in an unusable product. Dr. Kandel employs an imaging technique known as scanning tunneling microscopy (STM) to "see" individual atoms and molecules in order to determine how the solid surfaces change at the atomic level during the course of a chemical reaction. These experiments produce time-lapsed sequences that show how the particular local composition and geometry influence and control both the rate and the outcome of a chemical reaction. The fundamental understanding gained in this project helps the future design of new catalysts, surface coatings, and materials processing methods. Dr. Kandel's research is attractive to students at many levels, and he involves several high school students and their teachers as research assistants every year. He also maintains a data base of STM images that is accessible to the general public through his web page at the Univeristy of Notre Dame.In this research program, Dr. S. Alex Kandel is supported by the Macromolecular, Supramolecular and Nanochemistry (MSN) Program to study the reactions between gas-phase radical species and solid surfaces, with a particular emphasis on how the local molecular structure of a surface influences chemical reactivity. Hydrogen, chlorine, and methane radicals are used to chemically modify well-characterized organic monolayers, and the progression of atomic-scale changes caused by their interaction is monitored using scanning tunneling microscopy (STM). Radical-surface reactions are relevant to a variety of chemical processes in which a surface is exposed to a reactive environment, including combustion (hydrogen atoms), upper atmosphere chemistry (chlorine atoms), chemical vapor deposition (hydrogen, methyl), and plasma processing (hydrogen, chlorine). In addition, the systematic investigation of how various aspects of the surface monolayer structure influences reactivity helps build fundamental knowledge of surface-radical interactions and new mechanistic understandings of gas-surface chemistry. Dr. Kandel involves high school, undergraduate and graduate students in his research, and serves as a mentor for high school students in local and international science competitions. He also maintains a data base of STM images that is accessible to the general public through his web page at the Univeristy of Notre Dame.