Also XPS

Experimental observation of the Eu Mossbauer spectra in EuFe4Alg and the unit cell size indicate that the Eu ion is in the mixed-valence (MV) state. However, at low temperature it behaves like an Eu " ion due to the hypeifine field of the Fe sublattice acting below ordering temperature (Felner and Nowik 1978). Also, XPS-3d core level spectroscopy (Malik et al. 1981) and X-ray absorption near edge structure (XANES) results (Darshan and Padalia 1984) showed the Eu ion to be in the MV state with V=2.80 at 300 K. In turn, both unit cell size volume (Felner and Nowik 1978) and X-ray spectroscopy show that the Ce ion is in the MV state as well, and the valence v amounts to 3.28 (Shcherba et al. 1992). 

ESCA electron spectroscopy for chemical analysis (see also XPS) ESI electrospray ionisation... 

X-ray photoelectron spectroscopy (XPS), also called electron spectroscopy for chemical analysis (ESCA), is described in section Bl.25,2.1. The most connnonly employed x-rays are the Mg Ka (1253.6 eV) and the A1 Ka (1486.6 eV) lines, which are produced from a standard x-ray tube. Peaks are seen in XPS spectra that correspond to the bound core-level electrons in the material. The intensity of each peak is proportional to the abundance of the emitting atoms in the near-surface region, while the precise binding energy of each peak depends on the chemical oxidation state and local enviromnent of the emitting atoms. The Perkin-Elmer XPS handbook contains sample spectra of each element and bindmg energies for certain compounds [58]. 

XPS is also often perfonned employing syncln-otron radiation as the excitation source [59]. This technique is sometimes called soft x-ray photoelectron spectroscopy (SXPS) to distinguish it from laboratory XPS. The use of syncluotron radiation has two major advantages (1) a much higher spectral resolution can be achieved and (2) the photon energy of the excitation can be adjusted which, in turn, allows for a particular electron kinetic energy to be selected. 

Figure Bl.25.2. XPS scans between 0 and 450 eV of two organoplatiniiin complexes showing peaks due to Pt, Cl, N and C. The C Is signal represents not only carbon in the compound but also contaminant hydrocarbon fragments, as in any sample. The abbreviation Me in the structures stands for CH (courtesy of J C Muijsers, Eindlroven).

Aiiger peaks also appear in XPS spectra. In this case, the x-ray ionized atom relaxes by emitting an electron with a specific kinetic energy E. One should bear in mind that in XPS the intensity is plotted against the bindmg energy, so one uses ( Bl.25.1) to convert to kinetic energy. 

A monochromator is useful not only for removing unwanted lines from the X-ray source but also for narrowing the otherwise broad lines. For example, each of the MgXa and AlXa doublets is unresolved and about 1 cY wide at half-intensity. A monochromator can reduce this to about 0.2 cY This reduction of the line width is very important because in an XPS specttum, unlike an ultraviolet photoelectron specttum, the resolution is limited by the line width of the ionizing radiation. Unfortunately, even after line narrowing to 0.2 cY... 

The left-hand side of Equation (8.15) involves the difference between two electron binding energies, E — E. Each of these energies changes with the chemical (or physical) environment of the atom concerned but the changes in Ek and E are very similar so that the environmental effect on Ek — E is small. It follows that the environmental effect on E -h Ej, the right-hand side of Equation (8.15), is also small. Therefore the effect on is appreciable as it must be similar to that on There is, then, a chemical shift effect in AES rather like that in XPS. 

Other techniques in which incident photons excite the surface to produce detected electrons are also Hsted in Table 1. X-ray photoelectron Spectroscopy (xps), which is also known as electron spectroscopy for chemical analysis (esca), is based on the use of x-rays which stimulate atomic core level electron ejection for elemental composition information. Ultraviolet photoelectron spectroscopy (ups) is similar but uses ultraviolet photons instead of x-rays to probe atomic valence level electrons. Photons are used to stimulate desorption of ions in photon stimulated ion angular distribution (psd). Inverse photoemission (ip) occurs when electrons incident on a surface result in photon emission which is then detected. 

Xps spectra also bear a relationship between photoelectron intensity and number of surface atoms sampled (19,27). Quantitation of these data can be achieved with a precision to within ca 20%. For a homogeneous sample analy2ed in a fixed geometry, the relationship between xps intensity and number of atoms is given by... 

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