Scanning Tunneling Microscopy for the Study of Heterogeneous Electron Transfer

溶液中和电极表面的电子转移反应的研究目前是一个活跃的研究领域。然而，目前存在着许多实验上的限制，这些限制阻碍了对多方面异质电子转移的研究。Widrig博士项目的一个目标是开发一种检查电极反应的通用技术，该技术将克服目前的许多限制。在她的实验方法中，最近在实现扫描隧道显微镜方面得到改进的技术将应用于单个分子的氧化还原化学研究。这将通过使用扫描隧道显微镜的尖端和平面电极衬底作为双恒电位器的两个工作电极来实现。衬底电极将用含有可逆氧化还原试剂的有组织的单分子层进行衍生化。当针尖位于衬底表面上方的Angstroms内时，将分别向针尖和衬底电极施加适合于固定物种的氧化和还原的电压。当针尖所在的固定分子不断被氧化和还原时，产生的电流的大小将取决于异质电子转移到该物种的速率常数。初步计算表明，对于标准速率常数大于2厘米/S的氧化还原对，将获得可测量的电流。这项技术的成功实施将允许测量以前无法确定的快速电极反应的速率常数，并允许对电极-反应物分离的作用进行前所未有的评估。多相电子转移中的取向和环境。初步工作包括电活性单分子膜的制备和表征，针尖绝缘程序的开发，以及通过单个分子的异质电子转移的模拟。%研究规划补助金使以前没有获得联邦独立研究资助的妇女能够开发具有竞争力的研究项目。该项目涉及使用在扫描隧道显微镜中精确放置电极的技术，以精确电解有组织的单分子层。这将允许测量以前无法测量的电子转移速率。

The study of electron transfer reactions both in solution and at electrode surfaces is currently an area of vigorous research. At the present, however, there exist a number of experimental constraints that hinder the study of many aspects of heterogenous electron transfer. A goal of the project of Dr. Widrig is the development of a general technique for the examination of electrode reactions which will overcome many of these current limitations. In her experimental approach, the technology that recently has been refined in the realization of the scanning tunneling microscope will be applied to the investigation of the redox chemistry of individual molecules. This will be accomplished by using the tip of the scanning tunneling microscope and a planar electrode substrate as the two working electrodes of a bipotentiostat. The substrate electrode will be derivatized with an organized, monomolecular layer containing a reversible redox reagent. As the tip is positioned within Angstroms above the substrate surface, voltages suitable for oxidation and reduction of the immobilized species will be applied to the tip and substrate electrodes, respectively. As the immobilized molecule over which the tip is positioned is continually oxidized and reduced, the magnitude of the resulting current will be dependent on the rate constant for heterogeneous electron transfer to that species. Preliminary calculations indicate that measureable currents will be obtained for redox couples whose standard rate constants are greater than 2 cm/s. Successful implementation of this technique will permit the measurement of formerly indeterminable rate constants for "fast" electrode reactions and allow an unprecedented assessment of the roles of the electrode-reactant separation, orientation, and environment in heterogeneous electron transfer. Preliminary work includes the preparation and characterization of the electroactive monolayer, the development of tip insulation procedures, and modeling of heterogeneous electron transfer through individual molecules. %%% Research Planning Grants enable women who have not had prior independent Federal research support to develop a competitive research project. This project involves the use of technology for the precise placement of electrodes in the scanning tunneling microscope for precision electrolysis of an organized monomolecular layer. This will permit the measurement of the rates of electron transfer previously not measurable.