Photoelectron peaks

Photoelectron peaks are labelled according to the quantum numbers of the level from which the electron originates. An electron coming from an orbital with main quantum number n, orbital momentum / (0, 1, 2, 3,. .. indicated as s, p, d, f,. ..) and spin momentum s (+1/2 or -1/2) is indicated as For every orbital momentum / > 0 there are two values of the total momentum j = l+Ml and j = l-Ml, each state filled with 2j + 1 electrons. Flence, most XPS peaks come in doublets and the intensity ratio of the components is (/ + 1)//. When the doublet splitting is too small to be observed, tire subscript / + s is omitted. 

In addition to primary features from copper in Eig. 2.7 are small photoelectron peaks at 955 and 1204 eV kinetic energies, arising from the oxygen and carbon Is levels, respectively, because of the presence of some contamination on the surface. Secondary features are X-ray satellite and ghost lines, surface and bulk plasmon energy loss features, shake-up lines, multiplet splitting, shake-off lines, and asymmetries because of asymmetric core levels [2.6]. 

Section 2.1.3 shows that in an XPS spectrum. X-ray excited Auger peaks are often as prominent as the photoelectron peaks themselves. For many elements, the chemical shifts in Auger peaks are actually greater than the shifts in photoelectron peaks. The two shifts can be combined in a very useful quantity called the Auger parameter a, first used by Wagner [2.30] and defined in its modified form [2.31] as... 

In some cases, a valence electron can be completely ionized, resulting in vacancies in both the core and valence levels. In those cases, weak peaks referred to as shake-off satellites are also observed at binding energies a few electron volts higher than the photoelectron peak. Such cases are, however, not very common. 

In the majority of spectrometers, A1 and Mg are commonly used as x-ray target materials. With two anodes, A1 and Mg, it is possible to resolve overlapping photoelectron and Auger electron peaks. This is because in an XPS spectrum the position of the Auger peaks changes if Al radiation is replaced by Mg K radiation, but the positions of the photoelectron peaks are unaltered. 

Spin-orbit splittings as well as binding energies of a particular electron level increase with increasing atomic number. The intensity ratio of the peaks from a spin-orbit doublet is determined by the multiplicity of the corresponding levels, equal to 2j + 1. Hence, the intensity ratio of the j = and j = components of the Rh 3d doublet is 6 4 or 3 2. Thus, photoelectron peaks from core levels come in pairs -doublets - except for s levels, which normally give a single peak. 

The identification of the major peaks in the spectrum is accomplished by comparison with reference data (e.g. Wagner et al. 1978). The qualitative analysis of XPS spectra is more complex than for AES due to the presence of Auger peaks in addition to photoelectron peaks. If a photoelectron line of one element is close in energy to an Auger line of another, the problem may be resolved by taking spectra at two different photon energies. 

Transition-metal and rare-earth atoms that contain partially occupied d or f valence subshells also give rise to spectral tine structure, often with very complicated multiplet splitting [2,27,28]. The spin-unpaired valence d or f electrons can undergo spin-orbit coupling with the unpaired core electron (remaining in the orbital from which the photoelectron was removed), producing multiple non-degenerate final states manifested by broad photoelectron peaks [2,27]. 

Photoelectron peaks are labeled according to the quantum numbers of the level from which the electron originates. An electron with orbital momentum / (0,1, 2, 3,.. 

Figure 3. Peak intensity versus electron binding energies for the Cs 3d5/2 photoelectron peaks. Upper solid lines are after washing with D.I. water, lower dashed lines are after washing with 0.1N HCI, lower solid lines are background Cs concentrations.

Figure 2. Curve-fitted S 2s photoelectron peak for SPSF-Na (0.53)...

Figure 6. Photoelectron peaks of Na Is and K 2pi in a SPSF-Na (0.42) membrane before (A, B) and after (C, D) ion exchange. Binding energies (in electron volts) and peak intensities (counts/second) are indicated.

Table 6.4 shows the composition corresponding to different PtSn catalysts submitted to XPS and EXAFS/XANES analyses, while Table 6.5 gives XPS results giving the position of all of the main photoelectron peaks after referencing them to the C Is BE of 284.6eV [30, 62]. Figure 6.8 depicts XPS spectra of the Sn3d5/2 level for the tin-modified catalysts. 

Minerals Treated with Polyacrylamide. Minerals were treated with HPAM as outlined in Section 2. Any unadsorbed or weakly bound HPAM was removed from the mineral by washing and rinsing. Adsorption on the mineral surface was monitored by the N Is photoelectron peak from the HPAM. To compare HPAM adsorption between minerals, peak integration was used to obtain surface atomic % of N Is, Si 2p and Al 2p. The ratio Nis (Si2p -1- A12p) was used to normalise all the samples, which eliminates the contribution of C 7s hydrocarbon contamination from the analysis. 

Figure 2 ( ) Using the N Is photoelectron peak to follow the adsorption of HPAM on kaolinite. Inset shows bulk HPAM concentration in order of peak intensity, (h) HPAM adsorption isotherm onto kaolinite (squares) and feldspar (circles)...

Figure 3 (a) Backscattered electron image of a kaolin-quartz mix (b) Si 2p photoelectron peak image (c) Al 2p photoelectron peak image... 

In order to analyze the intensity of the various photoelectron peaks, it is necessary to know their associated transition probabilities, or photoelectric cross-sections. 

X-ray sources on most instruments use either Ka peaks of magnesium (1254 eV) or aluminum (1487 eV). The Ka peaks of light elements have a smaller full width at half maximum (FWHM), 0.7-0.9 eV, than those from the more energetic heavy elements, such as copper and molybdenum. That is, they are almost monochromatic and yield more narrow photoelectron lines, which are a measure of the spectrometer resolution. These two sources are suitable particularly because the x-rays produced have sufficient energy to excite electrons below 1000 eV, the region where most of the useful photoelectron peaks occur. 

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