In-situ characterization of electrode-solution interfacial processes by atomic-resolution scanning tunneling microscopy and surface-enhanced Raman spectroscopy
Abstract
The author's research is directed towards the atomic-molecular-level understanding of electrochemical interfacial processes, utilizing in-situ atomic-resolution scanning tunneling microscopy (STM) and surface enhanced Raman spectroscopy (SERS). The majority of this research effort has focussed on a systematic STM study of potential-induced surface reconstruction of gold single crystal electrodes and combined atomic-resolution STM and surface vibrational spectroscopy as in-situ probes of molecular adsorption and electrooxidation on metal electrodes. We have demonstrated for the first time that truly atomic-resolution STM images of gold surface reconstruction and molecular transformation can be observed at electrochemical interfaces under potential control conditions. The findings illustrate in a more general vein the power of STM for elucidating previously unobtainable details of surface atomic structure at electrochemical interfaces. The STM study shows that Au(111), (100), (110), (311), and (533) are observed to undergo reconstruction at the potentials corresponding to small (ca. 10-15 $\mu$c cm$\sp{-2}$) negative electrode charges. Some information regarding the mechanisms of the changes in atomic density required for reconstruction can be obtained from time- and potential-dependent sequences of STM images. In-situ potential-dependent STM studies of electrochemical processes of sulfide and iodide on Au(111), carbon monoxide on Rh(111) and (110) in aqueous solutions have been carried out and compared with SER spectra or infrared spectra. The details of potential-dependent adlayer structures and the formation of electrooxidation products, such as S$\sb8$ rings, polyiodide chains and crystal films, were observed and the results are in good agreement with the surface vibrational spectra. The orientation of adsorbed benzene and monosubstituted benzenes on gold electrodes have also been studied using SER spectroscopy. The results provide strong evidence that SERS selection rules can yield reliable information regarding adsorbate orientation on electrodes.
Degree
Ph.D.
Advisors
Weaver, Purdue University.
Subject Area
Chemistry|Molecules|Condensation
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