Adsorbate-covered surfaces, scanning

The late 1980s saw the introduction into electrochemistry of a major new technique, scanning tunnelling microscopy (STM), which allows real-space (atomic) imaging of the structural and electronic properties of both bare and adsorbate-covered surfaces. The technique had originally been exploited at the gas/so id interface, but it was later realised that it could be employed in liquids. As a result, it has rapidly found application in electrochemistry. 

H.-J. Guntherodt and R. Wiesendanger (eds) Scanning Tunneling Microscopy I General Principles and Applications to Clean and Adsorbate-Covered Surfaces, Springer, Berlin, 1992. 

Winterlin J and Behm R J 1994 Adsorbate covered metal surfaces and reactions on metal surfaces Scanning Tunnelling Microscopy I ed R Wiesendanger and H-J Guntherodt (Berlin Springer) ch 4... 

The Scanning Tunneling Microscope has demonstrated unique capabilities for the examination of electrode topography, the vibrational spectroscopic imaging of surface adsorbed species, and the high resolution electrochemical modification of conductive surfaces. Here we discuss recent progress in electrochemical STM. Included are a comparison of STM with other ex situ and in situ surface analytic techniques, a discussion of relevant STM design considerations, and a semi-quantitative examination of faradaic current contributions for STM at solution-covered surfaces. Applications of STM to the ex situ and in situ study of electrode surfaces are presented. 

Fig. 8 CV and MSCV of formic acid oxidation as in Fig. 7, but using preadsorbed H COOH in order to form a labeled adsorbate up to saturation coverage, followed by oxidation of H COOH at the covered surface. The second MSCV below shows, in addition, the first cathodic and the second anodic scan [30, 31].

Figure Bl.25.2 shows the XPS spectra of two organoplatinum complexes which contain different amounts of chlorine. The spectrum shows the peaks of all elements expected from the compounds, the Pt 4f and 4d doublets (the 4f doublet is iimesolved due to the low energy resolution employed for broad energy range scans). Cl 2p and Cl 2s, N Is and C Is. Flowever, the C Is caimot be taken as characteristic for the complex only. All surfaces that have not been cleaned by sputtermg or oxidation in the XPS spectrometer contain carbon. The reason is that adsorbed hydrocarbons from the atmosphere give the optimum lowering of the surface free energy and hence, all surfaces are covered by hydrocarbon fragments [9].

Surface diffraction experiments have to be done in UHV. Otherwise the surfaces are covered with a monolayer of adsorbed molecules. At this point the reader might ask why do we not have to use UHV in scanning tunneling or the atomic force microscope In both techniques the tip penetrates through the surface contamination layer. In the scanning tunneling microscope it is often just invisible because contamination layers are usually not good conductors. In... 

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