Alloy, photoelectron spectrum

In Figure 8.19 is shown the X-ray photoelectron spectrum of Cu, Pd and a 60 per cent Cu and 40 per cent Pd alloy (having a face-centred cubic lattice). In the Cu spectrum one of the peaks due to the removal of a 2p core electron, the one resulting from the creation of a /2 core state, is shown (the one resulting from the 1/2 state is outside the range of the figure). 

Figure 8.19 X-ray photoelectron spectrum, showing core and valence electron ionization energies, of Cu, Pd, and a 60% Cu and 40% Pd alloy (face-centred cubic lattice). The binding energy is the ionization energy relative to the Fermi energy, isp, of Cu. (Reproduced, with permission, from Siegbahn, K., J. Electron Spectrosc., 5, 3, 1974)...

X-ray photoelectron spectrum of EuCu2Si2 along with the calculated spectrum for the compound are shown in Fig. 9.26. The spectrum clearly shows the presence of both divalent and trivalent europium in the alloy. The spectrum of YCu2Si2 is also included in Fig. 9.26... 

X-ray and electron spectroscopies are very useful techniques to study the electronic state and chemical bonding of various kinds of functional materials, such as ceramics and alloys. Since the leading achievement by Siegbahn et al. x-ray photoelectron spectroscopy (XPS) is known to be very efficient for chemical state analysis of matters. They provide information not only on chemical components but also that on the valence electronic state and the chemical bonding of atoms constructing the materials. The direct information on the density of state (DOS) for solid state material can be obtained from XPS of the valence state region. Figure 1 schematically illustrates the relationship between the electronic state of matter and photoelectron spectrum as well as x-ray emission and absorption spectroscopies, and also the characteristics of these spectroscopies. 

Fig. 4.4. N Is X-ray photoelectron spectra of nitrogen adsorbed on sputter cleaned Fe9,Zr9 alloy surface at 79 K [4.62]. Top trace was measured under static nitrogen pressure of 5 10 7 Torr. Bottom trace was measured after admission of 8 L hydrogen to the static nitrogen atmosphere. The instrumental resolution had to be limited to 1.5 eV in order to collect each spectrum within 6 h...

Although valence band information could be acquired by conventional X-ray sources, analysis of the valence band region is not as simple as the core region, since all the components in the sample contribute in this narrow region (with E of 30 eV or less). Due to the broad line width of conventional X-ray sources and the low ionization cross section. X-ray-excited valence band spectroscopy is less commonly used for surface analysis. Instead, ultraviolet sources (e.g.. He I and He II) are adopted to acquire the valence band spectra, a surface technique called ultraviolet photoelectron spectroscopy (UPS). He I and He n resonance lines have inherently narrow widths of only a few meVs and high ionization cross sections in the valence band. This technique is widely used in the study of adsorption phenomena and valence band structure of metals, alloys, and semiconductors. Work functions can be derived from the Fermi level and the secondary electron (SE) cutoff of the UPS spectrum. 

An attempt to describe the concentration dependence of the DOS at the Fermi level in NbC Ni (x = 1.0, 0.75, 0.25, 0.12, and 0) was undertaken by Nikiforov and Kolpachev (1988) and Kolpachev and Nikiforov (1988). They used a multiple scattering method in the local coherent potential approximation. Variations in the solid solution composition caused the greatest changes in the nonmetal p-symmetry states and in the part of the d-band located close to the Fermi level. At the same time, comparison of the DOS of the calculated clusters and photoelectron spectra of Nb ternary alloys obtained by Ichara and Watanabe (1981) shows that the calculations only roughly reproduce the peculiarities of the NbC jNi c valence spectrum the energy separation of the p-d- and d-bands is considerably overestimated and there are some additional peaks in the DOS which are not seen in the experimental spectrum. 

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