Microscopic studies scanning tunneling microscopy

The large size of CPOs allows their direct observation. For this purpose, scanning tunneling microscopy (STM) is the best method [32,34]. Electron microscopic analysis is used for phthalocyanine 3 and its derivatives however, most of the porphyrin derivatives are decomposed by electron beam irradiation. Presently, although only a limited number of researchers are able to perform atomic-scale resolution measurement, this powerful analytical method is expected to be used widely in the future. The author reported a summary of STM studies on porphyrins elsewhere [34]. 

Bonnell, D.A. Scanning Tunneling Microscopy and Spectroscopy Theory, Techniques, and Applications, John Wiley Sons. Inc.. New York, NY, 1993. Ciemmer, C.R. and T,P. Beebe. Jr Graphite A Mimic for DNA and Other Biomolecules in Scanning Tunneling Microscope Studies. Science. 640 (February 8, 1991). 

In this section, we will present and discuss results from Sc2 C84, which is the most widely studied dimetallofullerene to date. Early scanning tunnelling microscopy [26] and transmission electron microscopic [27] investigations provided evidence in favour of the endohedral structure of this system, which was later confirmed by x-ray diffraction experiments utilising maximum entropy methods [28]. Before experimental data from this system were available, the Sc ions were predicted to be divalent from quantum chemical calculations [29]. Subsequent data from vibrational spectroscopy [30,31], core-level photoemission [32] and further theory [33] on this system were indeed interpreted in terms of divalent Sc ions. 

Surface excesses of electroactive species are often examined by methods sensitive to the faradaic reactions of the adsorbed species. Cyclic voltammetry, chronocoulometry, polarography, and thin layer methods are all useful in this regard. Discussions of their application to this type of problem are provided in Section 14.3. In addition to these electrochemical methods for studying the solid electrode/electrolyte interface, there has been intense activity in the utilization of spectroscopic and microscopic methods (e.g., surface enhanced Raman spectroscopy, infrared spectroscopy, scanning tunneling microscopy) as probes of the electrode surface region these are discussed in Chapters 16 and 17. 

Electrochemical measurements of the type described earlier give indirect evidence about dissolution processes. More direct chemical information can be obtained from in-situ spectroscopies, in particular from IR and Raman methods. Chazalviel and coworkers have showed the power of this approach in studies on silicon and GaAs [73,98,99]. Electrochemical and spectroscopic techniques are macroscopic methods giving a view of the whole electrode surface. To study semiconductor dissolution at the microscopic (atomic) level, one needs techniques such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The anodic and chemical dissolution of sihcon has been studied in very elegant work by Allongue and coworkers [100-102]. 

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