Photoelectron satellites

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]. 

The photoelectron line of main interest is Cls. Different bonding in the environments of the carbon atoms leads to very small chemical shifts of this line. High-resolution XPS is, therefore, required and monochromatic radiation should be used to prevent overlap with satellite lines. 

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. 

How then, can one recover some quantity that scales with the local charge on the metal atoms if their valence electrons are inherently delocalized Beyond the asymmetric lineshape of the metal 2p3/2 peak, there is also a distinct satellite structure seen in the spectra for CoP and elemental Co. From reflection electron energy loss spectroscopy (REELS), we have determined that this satellite structure originates from plasmon loss events (instead of a two-core-hole final state effect as previously thought [67,68]) in which exiting photoelectrons lose some of their energy to valence electrons of atoms near the surface of the solid [58]. The intensity of these satellite peaks (relative to the main peak) is weaker in CoP than in elemental Co. This implies that the Co atoms have fewer valence electrons in CoP than in elemental Co, that is, they are definitely cationic, notwithstanding the lack of a BE shift. For the other compounds in the MP (M = Cr, Mn, Fe) series, the satellite structure is probably too weak to be observed, but solid solutions Coi -xMxl> and CoAs i yPv do show this feature (vide infra) [60,61]. 

Fig. 2. The Ols and C 1 s regions of the X-ray photoelectron spectrum of C3O2, showing the shake-up satellites. Reproduced with permission from Ref.77)...

Fig. 15. Angle-integrated photoelectron energy distribution curves of uranium in the region of the giant 5 d -> 5 f resonance (90 eV < hv < 108 eV). The 5 f intensity at Ep is suppressed by more than a factor of 30 at the 5 ds/2 threshold (see the spectra for hv = 92 and 94 eV) and resonantly enhanced above threshold (see, e.g., the spectrum for hv = 99 e V). At an initial energy 2.3eV below Ep a new satellite structure is observed which is resonantly enhanced at the 5 d5/2 and 5 ds onsets. At threshold the satellite coincides with the Auger electron spectrum, which moves to apparently larger initial energies with increasing photon energy (from Ref. 67)...

Complexing silver with TPP or OEP caused small but noticeable chemical shifts in the binding energy of the Ag, C and N peaks.555 Weak N Is satellites have also been observed in the X-ray photoelectron spectra.556... 

Correlations between electrons in initial and final states lead not only to the shift of photoelectron lines, changes of their forms and redistribution of their intensities, but also to the occurrence of so-called satellite lines, corresponding to photoionization with the excitation of the other electron. Correlation effects in photoelectron spectra are caused by mixing of configurations separately in the initial state, in the final ion and in the final state of continuum. 

The Cu(2p3/2) photoelectron and LW Auger spectra obtained from a copper mirror treated with an aqueous solution of y-APS at pH 10.4 are shown in Fig. 13. Two components were observed near 932.4 and 934.9 eV in the Cu(2p3/2) photoelectron spectrum, clearly indicating the presence of Cu(I) and Cu(II), respectively. The presence of Cu(II) was confirmed by a broad, weak shake-up satellite near 944.0 eV. 

Shake-up satellite structure in the X-ray photoelectron spectra of [Mo(CNR)7](PF6) (R = Me, Bu, C6H,) has been observed. The similarity of the nitrogen band carbon s Is/lp ratios to those of Mo(CO)6 oxygen b and carbon b Is/lp ratios argues for a similarity in bonding, as a decrease in the metal-carbon bond length (i.e., stronger M-C bonding) will influence both the satellite position relative to the primary peak and the Is/lp intensity ratio (266). 

Fig. 4. Photoelectron spectrum of O(ls) for water vapor irradiated by the A1X line. To left of the main peak are the satellites. Solid line, experimental data vertical lines, results of calculations.53 The energy is counted from the main peak corresponding to ejection of I s electrons.

Fig. 9. Survey spectrum of 600 eV of K.A1 (S04)2. The different features are clearly visible photoelectron lines resulting from various orbitals, energy loss tails and X-ray satellites (S). The expanded insert of the potassium-carbon region reveals the characteristic spin orbit splitting of the K2p-level. Mg Ka irradation, total observation time 30 min...

Figure 4.37 Spectrum of electrons ejected from helium after photoionization with mono-chromatized Al Ka radiation. The main Is photoline and (magnified by a factor of 20) discrete (n = 2, 3,4) and continuous satellites (above the threshold indicated at 79 eV) are shown as well as structures resulting from the inelastic scattering of Is photoelectrons in the source volume. Reprinted from J. Electron Spectrosc. Relat. Phenom. 47, Svensson et al., 327 (1988) with kind permission from Elsevier Science - NL, Sara Burgerhartstraat 25, 1005 KV Amsterdam, The Netherlands.

Hitherto the discussion of Fig. 5.2 has neglected the possibility of non-radiative decay following 4d shell excitation/ionization. These processes are explained with the help of Fig. 5.2(h) which also reproduces the photoelectron emission discussed above, because both photo- and autoionization/Auger electrons will finally yield the observed pattern of electron emission. (In this context it should be noted that in general such direct photoionization and non-radiative decay processes will interfere (see below).) As can be inferred from Fig. 5.2(h), two distinct features arise from non-radiative decay of 4d excitation/ionization. First, 4d -> n/ resonance excitation, indicated on the photon energy scale on the left-hand side, populates certain outer-shell satellites, the so-called resonance Auger transitions (see below), via autoionization decay. An example of special interest in the present context is given by... 

The existence of satellite lines has already been mentioned several times, for example, in the explanation of the photoelectron spectra of rare gases (see Fig. 2.4), and in the discussion of 2p photoionization in magnesium. In this section the satellite spectrum related to outer-shell photoionization in argon will be treated... 

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