Composites valence band emission

The valence-region uv photoelectron spectrum of pyrite shows an intense peak at low binding energy arising from the six spin-paired electrons in the 2g levels (Fig. 6.11). Less pronounced features arise from the other valence-band electrons. The photoelectron spectrum can be aligned with x-ray emission spectra using more deeply buried core orbitals and, as shown from Fig. 6.11, provide further experimental data on the composition of the valence region. Thus, the Fe (5 spectrum shows the contri bution from orbitals that are predominantly Fe 4p in character, the S p... 

Such studies were focused, as a rule, on the energy changes of the atomic core levels and on the changes in structure of the valence state spectra of condensates when their composition alters during the deposition or under some treatment of the film (ionic bombardment, oxidation, etc.). It has been found by Kuznetsov (1990) that the formation of Ti-N and Ti-Al-N films is accompanied by charge transfer from the metal to the nonmetal atoms. The charge transfer is enhanced when the N content of the films increases. Analysis of the XES of the valence bands of Ti-Al-N films (Fig.. 8.11) leads to qualitative conclusions on the nature of chemical bonding in the condensate, where interatomic bonds are due to the overlap of Tid-Tid and Tid-Als,p-N2p states. Here, the intensity of emission from the hybridised p-d states decreases sharply as the film is depleted of N. 

In the intrinsic part of the photoemission spectrum, that is, the elastic lines, there are basically three observables associated with each core-level or valence band peak line positions, line intensities, and line widths or line shapes. From these, different pieces of information can be gained. In core-level emission, the rough line positions reveal the elemental composition of the sample surface, whereas the exact positions are characteristic of the specific chemical environment of the atoms [6j. The intensities are determined not only by the atomic concentrations but also by the photoelectric cross sections and instrumental effects such as the photon flux and the transmission of the spectrometer. Finally, information on the many-body dynamics of the solid after the sudden creation of a photohole (the missing electron that has been ejected) is contained in the shape and width of the peak. In the simplest case, the line shape is Lorentzian and its width is a measure of... 

Using UV radiation for excitation the valence orbitals of molecules can be resolved with great lucidity. As examples, the two mentioned N2 and are shown as UV excited electron spectra in Figs.27 and 28. It is the vibrational sequence of the tt 2p band in N2 (Fig.27) which causes the broad N2 band in the X-ray emission spectrum of Fig.24. Correspondingly, the and bands in the spectrum of CO2 in Fig.28 causes the composite band in Fig.25. These two spectra were excited by the Hel resonance radiation at 21.22 eV. 

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