Surface Heterogeneity and Defects in Gas-Surface Reactions

化学家使用含有反应物和产物分子符号的公式来描述化学反应。然而，该公式只是了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在固体表面发生的化学反应的分子变化或机制，以揭示这些反应实际上是如何在原子尺度上发生的。他特别感兴趣的是确定组成杂质和原子级结构对反应速度和产物的影响。在某些情况下，这些变化是可取的，例如，在许多具有工业重要性的过程中，特定的缺陷表明了催化活性的增强。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，即使是表面上的少量缺陷也可能导致无法使用的产品。坎德尔博士使用了一种名为扫描隧道显微镜(STM)的成像技术，以“看到”单个原子和分子，以确定在化学反应过程中固体表面在原子水平上如何变化。这些实验产生了延时序列，显示了特定的局部成分和几何结构如何影响和控制化学反应的速度和结果。在这个项目中获得的基本认识有助于未来新催化剂、表面涂层和材料加工方法的设计。坎德尔博士的研究对许多层次的学生都很有吸引力，他每年都会让几名高中生和他们的老师担任研究助理。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。在这个研究计划中，S.Alex Kandel博士得到了大分子、超分子和纳米化学(MSN)计划的支持，研究气相自由基物种与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。氢、氯和甲烷自由基被用来对表征良好的有机单分子膜进行化学修饰，并使用扫描隧道显微镜(STM)监测由它们相互作用引起的原子尺度变化的进展。自由基-表面反应与表面暴露在反应环境中的各种化学过程有关，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，对表面单层结构的各个方面如何影响反应性的系统研究有助于建立表面-自由基相互作用的基础知识和对气体-表面化学的新的机理理解。坎德尔博士让高中生、本科生和研究生参与他的研究，并在当地和国际科学竞赛中担任高中生的导师。他还维护着一个STM图像数据库，公众可以通过他在圣母大学的网页访问该数据库。

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.