Electron spectroscopy of surfaces

The situation which, ideally, should prevail during spectroscopic investigations of the gas/solid interface is that the radiation(s) incident upon the interface with a view to obtaining information thereon should not significantly perturb the interface. Table 1 gives a partial listing of the wide range of surface spectroscopies for which commercial instrumentation has become available in the past decade. 

Terenin [72] reviewed examples of absorption bands originating mainly from processes of types (13) and (14) involving molecules adsorbed on to non-metallic surfaces from the gas phase. He stressed the difficulties encountered by many workers in observing such absorption bands except by use of high surface area solids. Thus a species with an extinction 

Photoluminescence spectra of high surface area samples of alkaline earth oxides have been reported by Tench et al. [39] and interpreted in terms of the radiative decay of surface excitons. Representative data obtained by Tench et al. [39c] with microcrystalline MgO smoke (obtained by combustion of the metal in oxygen) are reproduced in Fig. 5, together with their schematic model for surfaces of the cubic MgO microcrystallites and their modification by exposure to water vapour. 

Reactions of hydrocarbons or the gases H2 and NH3 when adsorbed and illuminated on these high surface catalysts have been interpreted [74b] in terms of reaction with the O (cus) species produced by the intramolecular charge-transfer process indicated in eqn. (15). 

Chemisorption of nitrous oxide at room temperature on to metal oxides previously outgassed at high temperatures in vacuo has been developed [83—85] into a useful method for production of the monatomic 

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Seah M P and Dench W A 1979 Quantitative electron spectroscopy of surfaces a standard data base for electron inelastic mean free paths in solids Surf, interface Anai. 1 2... 

N.V. Richardson and A.M. Bradshaw. Symmetry and the Electron Spectroscopy of Surfaces. In C.R. Brundle and A.D. Baker, editors. Electron Spectroscopy Theory, Techniques and Applications, Volume 4. Academic Press, New York, 1981. 

Lucas, A.A. and Sunjic, M. (1971) Fast-electron spectroscopy of surface excitations. Phys. Rev. Lett., 26, 229. 

Electronic spectra of surfaces can give information about what species are present and their valence states. X-ray photoelectron spectroscopy (XPS) and its variant, ESC A, are commonly used. Figure VIII-11 shows the application to an A1 surface and Fig. XVIII-6, to the more complicated case of Mo supported on TiOi [37] Fig. XVIII-7 shows the detection of photochemically produced Br atoms on Pt(lll) [38]. Other spectroscopies that bear on the chemical state of adsorbed species include (see Table VIII-1) photoelectron spectroscopy (PES) [39-41], angle resolved PES or ARPES [42], and Auger electron spectroscopy (AES) [43-47]. Spectroscopic detection of adsorbed hydrogen is difficult, and... 

Because of the generality of the symmetry principle that underlies the nonlinear optical spectroscopy of surfaces and interfaces, the approach has found application to a remarkably wide range of material systems. These include not only the conventional case of solid surfaces in ultrahigh vacuum, but also gas/solid, liquid/solid, gas/liquid and liquid/liquid interfaces. The infonnation attainable from the measurements ranges from adsorbate coverage and orientation to interface vibrational and electronic spectroscopy to surface dynamics on the femtosecond time scale. 

For a review of how defects manifest themselves in a LEED experiment, see M. Henzler. In Electron Spectroscopy for Surface Analysis. (H. I. Ibach, ed.) Springer, Berlin, 1977. 

Duncan, J. R., Electron Spectroscopy of Chromated Galvanized Steel Sheet after Heating. Immersion in Water or Outdoor Weathering. Surface Tech., 17, 265-276 (1982)... 

Electron Spectroscopy of Solids and Surfaces, Faraday Discuss. Chem. Soc., 60 (1975). 

Kim KS, Winograd N, Davis RE. 1971. Electron spectroscopy of platinum-oxygen surfaces and application to electrochemical studies. J Am Chem Soc 93 6296-6297. 

Vigorous development in the recent years of highly-sensitive methods of surface and gaseous-phase analysis (the electron spectroscopy of sur-... 

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). 

From the perspective of this symposium, analysis of the atomic dynamics and electronic structure of surfaces constitutes an even more exotic topic than surface atomic geometry. In both cases attention has been focused on a small number of model systems, e.g., single crystal transition metal and semiconductor surfaces, using rather specialized experimental facilities. General reviews have appeared for both atomic surface dynamics (21) and spectroscopic measurements of the electronic structure of single-crystal surfaces (, 22). An important emerging trend in the latter area is the use of synchrotron radiation for studying surface electronic structure via photoemission spectroscopy ( 23) Moreover, the use of the very intense synchrotron radiation sources also will enable major improvements in the application of core-level photoemission for surface chemical analysis (13). 

The first surface state was detected as an unexpected bump at — 0.35eV in the energy distribution of the electrons field-emitted by a W(100) tip by Swanson and Crouser in 1966 [35]. Its surface character was claimed on the basis of the sensitivity of the bump to contaminants. It is somewhat ironic that surface resonances in sharp W tips have been recently found to jeopardize local electron spectroscopy of the surface states performed with the STM [36]. 

Chesters MA, Sheppard N (1988) Electron Energy-Loss Spectroscopy. In Clark RJH, Hester RE (eds) Spectroscopy of Surfaces. Wiley, Chichester, p 377 Chi FK. Andrews L (1973) J Phys Chem 77 3062... 

At the time of a recent review [9], there remained very few examples of vibrational studies of adsorbate, or localised substrate modes, at metal oxide surfaces. By far the majority of studies concerned the characterisation by HREELS of phonon modes (such as Fuchs-Kliewer modes) pertaining to the properties of the bulk structure, rather than the surface, or to electronic transitions. Such studies have been excluded from this review in order to concentrate on the vibrational spectroscopy of surface vibrations on well-characterised metal oxide surfaces such as single crystals or epitaxially grown oxide films, for which there is now a substantial literature. Nevertheless, it is important to briefly describe the electronic and phonon properties of oxides in order to understand the constraints and difficulties in carrying out RAIRS and HREELS with sufficient sensitivity to observe adsorbate vibrations, and more localised substrate vibrational modes. 

Because of the high photooxidative reactivity of Ti02, deriving from the high positive potential of a valence-band hole, even water can be oxidized on irradiated Ti02. In aqueous solutions, therefore, direct oxidation of an adsorbed substrate must compete with solvent oxidation [31], The formation of hydroxyl radicals by single-electron oxidation of surface-bound water is usually the dominant process in water, with the radical having been detected by EPR spectroscopy [32-34] and implicated by isotope effects [35]. 

Introduction.—Without doubt the most important recent advance in field emission techniques has been the development of field emission spectroscopy. It has led to a critical re-examination of the theory of field emission and contributed to the recent considerable advance in understanding of the electronic structure of surfaces and of chemisorbed species. A comprehensive review of the theory and practice has been... 

Inelastic effects are exploited in the rapidly developing technique of high resolution electron energy loss spectroscopy (ELS or EELS) which permits identification of adsorbed molecules or molecular fragments by their vibrational spectra. Thus the method has much in common with the infrared spectroscopy of surfaces and, not surprisingly, the classic case of CO adsorption has received attention on Ni(lOO) and on stepped Ni and Pt surfaces. Other recent investigations of interest include H2 on organic species on Ni and Pt, and the observation of... 

M. G. Yang and K. M. Koliwad, Auger electron spectroscopy of cleanup-related contamination on silicon surfaces, J. Electrochem. Soc. 122, 675, 1975. 

Department of Applied Physics, Laboratory of Electron Spectroscopy and Surface Physics, University of Turku, Finland... 

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