Electron other core levels

BEs of the electrons in all the elements in the period table up to Z= 70 are plotted in Figure 2, as a function of their atomic number Z, up to the usual l486.6-eV accessibility limit. Chance overlaps of BE values from core levels of different elements can usually be resolved by looking for other core levels of the element in doubt. 

As the most important result, APS has proven to be an appropriate technique for the investigation of the electronic structure of lanthanide compounds in a way similar to other core-level spectroscopies such as XPS, XAS and CEELS, with the advantage of a rather simple experimental setup. Furthermore, when applied to 4f systems, APS offers the potential of studying correlation effects directly because of the allowed addition of two electrons to the partially occupied 4f level. 

In contrast to 3d and 4d levels 4p and 4s core levels have received less attention up to now either from EELS or from other core level spectroscopies. The case of 4p excitation is complicated by breakdown of the one-electron approximation for 4p core holes, which in this part of the Periodic Table may decay by 4p <—>4d f giant Coster-Kronig coupling, leading to broad ill-defined peaks in photoemission (Wendin 1981). In the rare earths (except Yb) such processes are allowed for 4pi/2 holes but not for 4p3/2- In electron loss the unstable 4p /2 excitations lead to ill-defined structure in the corresponding energy region, but sharp peaks are observed near the 4p3/2 ionisation threshold (Strasser et al. 1984). 

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. 

L3M45M4 5 would often appear as L3M2,3V and L3W, respectively, and similarly 1 2,3 4,5 4,51 as M2,3W. In Fig. 2.22 the increase in the intensity of the L3W peak relative to the other two, upon going from chromium to iron, is because of the progressive increase in the electron density in the valence band. The characteristic doublet seen in the MNN series arises from the M4 5N4,sN4,5 transitions, in which the doublet separation is that of the core levels M4 and M5. 

Two other types of peaks that can be observed in the XPS spectrum of solid materials are referred to as a shake-up and shake-off satellites. When a core-level electron is ejected from an atom by photoemission, the valence... 

Because of the l/r dependence, the exchange interaction rapidly decreases with an increase in the difference between the principal quantum numbers of the impaired electrons and the core vacancy. Thus multiplet splitting is negligible in the Is spectra of paramagnetic transition metal compounds. On the other hand, shake-up intensity is essentially independent of the core level involved. Hence one can distinguish between shake-up and multiplet satellites by changing the principal quantum number of the core electron ionized76. ... 

Two rather different techniques that exploit the same underlying phenomenon of coherent interference of elastically scattered low energy electrons are photoelectron diffraction [5] and surface extended X-ray absorption fine structure (SEXAFS) [6,7]. Figure 1.1. shows schematically a comparison of the electron interference paths in LEED and in these two techniques. In both photoelectron diffraction and SEXAFS the source of electrons is not an electron beam from outside the surface, as in LEED, but photoelectrons emitted from a core level of an atom within the adsorbate. In photoelectron diffraction one detects the photoelectrons directly, outside the surface, as a function of direction or photoelectron energy (or both). The detected angle-resolved photoemission signal comprises a coherent sum of the directly emitted component of the outgoing photoelectron wavefield and other components of the same wavefield elastically scattered by atoms (especially in the substrate) close... 

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