Scanning tunneling microscopy description

We have considered briefly the important macroscopic description of a solid adsorbent, namely, its speciflc surface area, its possible fractal nature, and if porous, its pore size distribution. In addition, it is important to know as much as possible about the microscopic structure of the surface, and contemporary surface spectroscopic and diffraction techniques, discussed in Chapter VIII, provide a good deal of such information (see also Refs. 55 and 56 for short general reviews, and the monograph by Somoijai [57]). Scanning tunneling microscopy (STM) and atomic force microscopy (AFT) are now widely used to obtain the structure of surfaces and of adsorbed layers on a molecular scale (see Chapter VIII, Section XVIII-2B, and Ref. 58). On a less informative and more statistical basis are site energy distributions (Section XVII-14) there is also the somewhat laige-scale type of structure due to surface imperfections and dislocations (Section VII-4D and Fig. XVIII-14). 

On the other hand, optical microscopy, confocal microscopy, ellipsometry, scanning electron microscopy (SEM), scanning tunneling microscopy (STM), atomic force microscopy (AFM) and total internal reflection fluorescence (TIRF) are the main microscopic methods for imaging the surface structure. There are many good books and reviews on spectroscopic and chemical surface analysis methods and microscopy of surfaces description of the principles and application details of these advanced instrumental methods is beyond the scope of this book. 

Diffusion experiments at surfaces are designed to measure self-diffusion or the diffusion of adsorbates. The techniques used [49-55) may provide atomic-scale diffusion data or macroscopic diffusion parameters. The techniques that provide atomic-level information include (a) field ion microscopy, which can be used to observe the surface migration of isolated adatoms or clusters of atoms, (b) field electron microscopy, and (c) scanning tunneling microscopy (for descriptions of the techniques, see references [56-68]. Macroscopic mass transport along the surface can be monitored by the use of radiotracers or by techniques that monitor the restructuring of surfaces as a function of time. 

First it will be reported on the investigation of oxygen adsorbed on rare earth metal surfaces using tunable VUV photoelectron spectroscopy [40] followed by the description of scanning tunneling microscopy experiments [3] which were used to determine the very first steps of the adsorption process. 

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