Core level chemical shift

We use an ab-initio local spin density method to investigate the aluminum/polyimide interface at low coverage. We found in agreement with XPS and EELS experiments, that the aluminum atom bonds to the carbonyl group. Our calculations suggest a formation of a linear C-O-AI complex. We calculated core levels chemical shifts and vibrational frequencies in the vicinity of the carbonyl group. 

The essential features of the dilemma rest on several points. First, as is well known, the measured core level chemical shifts for many oxides (M Oy) symbolized as (M ) relative to their respective metal elemental (M°) states are often quite small, that is. 

Functional Group Labeling (Derivatization). Core level chemical shifts are often ambiguous because of the small dynamic range (see Refs. 4 and 5). Particularly in the case of multifunctional surfaces, often the result of treatments carried... 

X-ray photoelectron spectroscopy (XPS), which is synonymous with ESCA (Electron Spectroscopy for Chemical Analysis), is one of the most powerful surface science techniques as it allows not only for qualitative and quantitative analysis of surfaces (more precisely of the top 3-5 monolayers at a surface) but also provides additional information on the chemical environment of species via the observed core level electron shifts. The basic principle is shown schematically in Fig. 5.34. 

Note that in core-level photoelectron spectroscopy, it is often found that the surface atoms have a different binding energy than the bulk atoms. These are called surface core-level shifts (SCLS), and should not be confiised with intrinsic surface states. Au SCLS is observed because the atom is in a chemically different enviromuent than the bulk atoms, but the core-level state that is being monitored is one that is present in all of the atoms in the material. A surface state, on the other hand, exists only at the particular surface. 

Typical chemical shift values for XPS core levels. 

The spectra of Figure 3 illustrate two further points. All the C Is peaks in Figure 3a are of equal intensity because there are an equal number of each type of C atom present. So, when comparing relative intensities of the same atomic core level to get composition data, we do not need to consider the photoionization cross section. Therefore, Figure 3c immediately reveals that there is four times as much elemental Si present as Si02 in the Si 2p spectrum. The second point is that the chemical shift range is poor compared to the widths of the peaks, especially for the solids in Figures 3b and 3c. Thus, not all chemically inequivalent atoms can be distin-... 

Thus, the combined experimental and theoretical results indicate that the chemical shift observed for the S(2p) core level, of about 1.6 eV, should be due to a secondary effect from the attachment of Al atoms to the adjacent carbon atoms. Indeed, this is fully consistent with tib initio Hartree-Fock ASCF calculations of the chemical shifts in aluminum-oligolhiophene complexes 187], From calculations on a AI2/a-3T complex, where the two AI atoms are attached to the a-car-bons on the central thiophene unit, the chemical shift of the S(2p) level for the central sulfur atom is found to be 1.65 eV, which is in close agreement with the experimental value of about 1.6 eV [84]. It should be pointed out that although several different Al-lhiophene complexes were tested in the ASCF calculations, no stable structure, where an Al atom binds directly to a S atom, was found [87]. 

Figure 6.30. Position of the center of the d band for the three series of transition metals. Note that the d band center shifts down towards the right of the periodic table. When the d band is completely filled, it shifts further down and becomes, effectively, a core level with little influence on the chemical behavior of...

In principle, it should be possible to obtain experimental valence band spectra of highly dispersed metals by photoemission. In practice, such spectra is difficult to obtain because very highly dispersed metals are usually obtained only on nonconductive supports and the resulting charging of the sample causes large chemical shifts and severe broadening of the photoelectron spectra. The purpose of this section is to discuss valence band and core level spectra of highly dispersed metal particles. 

Figure 2. Correlation between the shift in surface core level BE and the shift in CO TPD. The properties of the Pd, Ni, and Cu monolyers are compared with the corresponding values for the (100) face of pure metals. (Reprinted from Ref. [67], 1991, with permission from American Chemical Society.)...

It is also possible that Pd is reduced to a second PdHx phase. When the metalhc Pd chemical shift was compared to PdHx as reported in the hterature (13), the core level Pd 3d5/2 binding energy shift was only 0.2 eV. The article also found that the asyimnetiy of the 3d peak was slightly reduced, and a shakeup satellite peak (indicated by the arrow in Figure 15.6) disappeared. However, in the presence of metalhc Pd, we cannot determine whether a second PdHx phase is present. 

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