Core-level photoelectron spectra

Fig. 15 Typical high-resolution (a) Ge 3d and (b) In 3d5/2 core-level photoelectron spectra of mesoporous NU-InGe-2...

Figure 10. High resolution O Is core level photoelectron spectra for a.) base glass and b.) Fe doped glass...

Fig. 13 Core level photoelectron spectra of AB intermetallic compounds and their hydrides. The concentration ratio A B as measured by the integrated peak height is almost the same for the inter-metallics and the hydrides, indicating that there is no significant H-induced surface segregation (Schlapbach et al., 1984).

Fig. 3.10 Examples of core level photoelectron spectra for the s, p, d, and f orbitals...

Nilsson, A. Beyond the chemical shift vibrationally resolved core-level photoelectron spectra of adsorbed CO Phys. Rev. Lett. 81 (1998) 1730. 

Figure 9. Fe 3P core level photoelectron spectrum for Fe doped glasses...

M. Abu-Samha, K.J. Borve, M. Winkler, J. Harnes, L.J. Saethre, A. Lindblad, H. Bergersen, G. Ohrwall, O. Bjomeholm, S. Svensson, The local structure of small water clusters imprints on the core-level photoelectron spectrum. J. Phys B-At. Mol. Opt. Phys. 42(5), 055201 (2009)... 

Figure 4 Schematic electron energy level diagram (a) of a core-level photoelectron ejection process (one electron process) (b) core-level photoelectron ejection process with shake-up (two- electron process) (c) schematic XPS spectrum from (a) plus (b) (d) Cu 2pa/2 XPS spectrum for Cu in CU2O and Cu in CuO. The latter shows strong shake-up features.

Group IV Metal Sulphides. The core-level electron spectrum of CSg, excited by Mg radiation, has been studied to identify shake-up satellite lines associated with ionizations from these levels. A number of such lines were observed and possible assignments suggested using the excited states of the molecule as a guide. The valence spectra were also recorded and they too were found to be rich in shake-up structure. The photoelectron spectra of... 

XPS or ESCA (electron spectroscopy for chemical analysis) is a surface sensitive technique that only probes the outer atomic layers of a sample. It is very useful tool to study polymer surfaces [91]. An XPS spectrum is created by focusing a monochromatic beam of soft (low-energy) X-rays onto a surface. The X-rays cause electrons (photoelectrons) with characteristic energies to be ejected from an electronic core level. XPS, which may have a lateral resolution of ca. 1-10 pm, probes about the top 50 A of a surface. 

A typical x-ray photoelectron spectrum consists of a plot of the intensity of photoelectrons as a function of electron EB or E A sample is shown in Figure 8 for Ag (21). In this spectrum, discrete photoelectron responses from the core and valence electron eneigy levels of the Ag atoms are observed. These electrons are superimposed on a significant background from the Bremsstrahlung radiation inherent in nonmonochromatic x-ray sources (see below) which produces an increasing number of photoelectrons as EK decreases. Also observed in the spectrum are lines due to x-ray excited Auger electrons. 

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. 

The problem of the static and dynamic behavior of a core hole is intimately connected with the question of how the core hole was created. The energy level spectrum of the core hole is uniquely given by the energy level spectrum of the residual ion but the intensity distribution is determined by the excitation process. In order to interpret a photoelectron spectrum we therefore have to understand the photoionization process which gave rise to the photoelectrons. The purpose of this section is to discuss in simple terms the physics of. the photoionization process and to demonstrate how the various contributions to the photoelectron spectrum can arise. A more formal discussion is presented in Section 3. 

In the one-electron picture the photoelectron spectrum thus consists of a number of sharp peaks (Fig. 4 d), one for each core level, with the binding energy given by the negative of the HF eigenvalue (Koopmans theorem261). 

In this section we shall particularly study the dynamic properties of a core hole in terms of its self-energy and spectral function15 19,23,27 32). This is a kind of model problem because one does not discuss by which physical mechanism the core hole is created. The hole is simply created in the system at a specific instant of time and destroyed at a later time. By studying the development of the core hole during this interval one gets a picture of how the core level strength becomes distributed over the various possible levels of the ionic system. Nevertheless, since the creation of the core hole is sudden, the resulting spectral function is very closely connected to the X-ray photoelectron spectrum (XPS) as already briefly discussed in Sect. 2.2, Eq. (6). 

The XPS Measurement. In an XPS spectrometer, the studied material is exposed inside a vacuum chamber to a flux of X-rays (energy 1 keV). The kinetic energy of the photoelectrons ejected from the sample is measured by an appropriate analyzer. This energy is directly related to the binding energy of the electrons inside the sample on a wide scan XPS spectrum, the unscattered electrons result in characteristic peaks their energies serve to identify the elements in the material (atomic composition), to characterize the molecular environment of these atoms (chemical analysis, see inset A of Figure 1), and, by the measurement of the photoelectric lines ratios, to reach some quantitative results. Such type of measurement from the core level peaks can usually be... 

When excited with a UV lan, the photoelectrons have a kinetic energy range (0-40eV) where the escape depth is small (—sS) the contamination problem is then crucial in this case. On the contrary, when excited with a X-ray source, the electrons emitted from the valence levels have a larger escape depth, so that the surfaces features do not contribute as crucially to the valence band spectrum than to the core level peaks. 

Like for the core levels, a valence band photoelectron spectrum is composed of peaks or bands having the following characteristics ... 

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