Relative intensities photoelectrons

The lines of primary interest in an xps spectrum are those reflecting photoelectrons from core electron energy levels of the surface atoms. These are labeled in Figure 8 for the Ag 3s, 3p, and 3d electrons. The sensitivity of xps toward certain elements, and hence the surface sensitivity attainable for these elements, is dependent upon intrinsic properties of the photoelectron lines observed. The parameter governing the relative intensities of these core level peaks is the photoionization cross-section, q. This parameter describes the relative efficiency of the photoionization process for each core electron as a function of element atomic number. Obviously, the photoionization efficiency is not the same for electrons from the same core level of all elements. This difference results in variable surface sensitivity for elements even though the same core level electrons may be monitored. 

Figure 6. Plots of the relative intensities of Pt 4i(5/2 + 7/2) photoelectrons from naked Pt and from Pt coated with 6 polymer films. Intensities are given as integrated peak areas. (Reproduced from Ref. 82. Copyright 1981, American Chemical Society.)...

Fig. 32a, b. Experimental 5s, 5 p X-ray photoelectron spectra for (a) atomic Xe7,8) and (b) metallic La and Ce10). Positions marked 6y arrows and thresholds refer to relativistic JSCF plus Fermi sea correlation (Af chosen to give perfect agreement with the experimental 5p levels). In (a), the vertical dashed lines denote theoretical94,951 relative intensities of the 5s, 5p25d and 5p26d levels... 

Fig. 20. The high resolution X-ray photoelectron spectrum of the 4/ shell of Sm metal. With the atom initially in the Hund s Rule 4/5 ground state, the vertical marks indicate the relative intensities and positions of accessible final 4/4 levels, as predicted by Cox. Ref. (36)...

On thermodynamic grounds, the composition at the surface of an alloy is sometimes expected to be observably different from that in the interior. Measurements of such differences may be effected from the relative intensities of core level lines of the component elements. In such a study of the Pb—In system, Berg-lund and Somorjai (55), who used intensities of Auger lines rather than the photoelectron lines themselves, found that Pb tends to concentrate in the alloy surface. 

Table 2. Relative intensities in gas phase photoelectron spectra of CO [after Huang et al. (65)]...

Additional evidence for the effect of polymerization appears in the x-ray photoelectron spectral intensities of sihcates. DVM-Aa calculations on the energies and intensities of spectra by Sasaki and Adachi (1980a,b) satisfactorily reproduce relative intensities in the upper-valence-band region for SO/ [Fig. 5.8(a)] but seriously underestimate the intensity of the 5 i orbital feature of Si02 using a SiO/ cluster model [Fig. 5.8(b)]. This error may be a result of the influence of polymerization in SiOj, although the calculated spectrum is also somewhat different from that observed for olivine in Fig. 5.7. 

Gofman, M. M., V. A. Andreev, and V. I. Nefedov (1986). Relative intensities in x-ray photoelectron spectra. Part XI. Calculation of photoionization cross sections for valence levels of Sip4. J. Electron Spectrosc. Relat. Phenom. 37, 375-87. 

In contrast to the photoelectron spectra of COFj, but in keeping with that of COCl, the lowest energy band in the spectrum of COBr (band A, Fig. 17.15) is attributed to ionization from a halogen-based orbital, as are bands B, D and E. Band C, which gains in relative intensity in the He II spectrum, is assigned to the oxygen-based lone-pair. Bands F and G are assigned to ionizations from t(CO) and a(CO), respectively, in accord with both... 

The shot noise is associated with random arrival of photons on a detector and corresponding random production of photoelectrons. Conventional hght sources produce photon flux that obeys Poisson statistics, which produces a shot noise as directly proportional to the square root of the detected hght intensity as = where al is relative (intensity-independent) stan-... 

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