Electron spectroscopy, heterogeneous

Barr, T.L. (1990) In Applications of electron spectroscopy to Heterogeneous Catalysis in Briggs, D. and Seah, M.P. (eds.) Practical Surface Analysis, 2nd edn., John Wiley Sons, Chichester, England. 

Surface Chemical Analysis. Electron spectroscopy of chemical analysis (ESCA) has been the most useful technique for the identification of chemical compounds present on the surface of a composite sample of atmospheric particles. The most prominent examples Include the determination of the surface chemical states of S and N in aerosols, and the investigation of the catalytic role of soot in heterogeneous reactions involving gaseous SO2, NO, or NH3 (15, 39-41). It is apparent from these and other studies that most aerosol sulfur is in the form of sulfate, while most nitrogen is present as the ammonium ion. A substantial quantity of amine nitrogen also has been observed using ESCA (15, 39, 41). 

In the first place there is a host of surface spectroscopies. Some important ones have been discussed in sec. 1.7.II. Adamson gives a list of several tens of approaches and variants ). Most widely used are X-ray photoelectron spectroscopy (XPS), also called electron spectroscopy for chemical analysis (ESCA), Auger electron spectroscopy (AES), and secondary ion mass spectroscopy (SIMS) and. to a lesser extent, ion scattering spectroscopy (ISS). The main characteristics of these techniques have been collected in table 1.7.4. Other techniques may be more widely used in certain areas. For example, XPS is very popular in heterogeneous catalysis. 

Books. M. W. Roberts, Chemistry of the Metal-Gas Interface , Oxford University Press, Oxford, 1978 F. C. Tompkins, Chemisorption of Gases on Metals , Academic Press, London, 1978 Experimental Methods in Catalysis Research , ed. R. B. Anderson and P. T. Dawson, Academic Press, London, 1976 Chemistry and Physics of Solid Surfaces , ed. R. Vanselow and S. Y. Yong, CRC Press, Cleveland, Ohio, 1977 Advances in Characterisation of Metal and Polymer Surfaces , ed. L. H. Lee, Academic Press, New York, 1976 K. Tamaru, Dynamic Heterogeneous Catalysis , Academic Press, London, 1978 The Solid-Vacuum Interface , ed. A. van Oostrom and M. J. Sparnay, Surface Sci., 1977, 64 Electron Spectroscopy , ed. C. R. Brundle and A. D. Baker, Academic Press, New York, 1977, Vol. 1 Auger Electron Spectroscopy (Bibliography 1925—1975) , compiled by D. T. Hawkins, Plenum, New York, 1977. 

The author discusses selected examples of Auger electron spectroscopy applications to the study of the role played by sulfur adsorption in the field of heterogeneous catalysis and its implication for the metallurgical problems of segregation, surface self-diffusion and temper embrittlement. 

For such studies, both electrochemical and nonelectrochemical experimental techniques have been developed. Several of them are outlined here electrosorption methods, surface electron spectroscopies, and isotopic-mass spectrometric techniques, linking electrocatalysis to conventional heterogeneous catalysis. The spectroscopic and isotopic methods have been recently applied to a limited number of simple electrocatalytic systems. The exciting results that these methods have provided demonstrate their power for future electrode reaction studies. 

Barr TL (1990) Applications of electron spectroscopy to heterogeneous catalysis. In Briggs D, Seah MP (eds) Practical siuTace andysis, vol 1. Wiley, Chichester New York, p 357... 

When it comes to the important but difficult issues of scope and limitations, there is one clear-cut borderline. The Handbook covers wet but not dry surface chemistry. This means that important applications of dry surface chemistry, such as heterogeneous catalysis involving gases, and important vacuum analysis techniques, such as Electron Spectroscopy for Chemical Analysis (ESCA) and Selected-Ion Mass Spectrometry (SIMS), are not included. Within the domain of wet surface chemistry, on the other hand, the aim has been to have the most important applications, phenomena and analytical techniques included. 

Electron spectroscopy has been successfully applied to gases and solids and more recently to solutions and liquids. Because of the poor penetrating power of electrons. however, these methods provide information about solids that is restricted largely to a surface layer a few atomic layers thick (2 to S nm). Usually, the composition of such surface layers is significantly different from the average composition of the entire sample. Indeed, the most important and valuable current applications of electron spectroscopy are to the quafitative analysis of the surfaces of solids, such as metals, alloys, semiconductors, and heterogeneous catalysts. Quantitative analysis by electron spectroscopy finds somewhat limited applications. 

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