Core-Level Shifts

Relaxation of the Chemical Bond, Springer Series in Chemical Physics 108, DOI 10.1007/978-981-4585-21-7 16, Sjainger Science+Business Media Singapore 2014 

B) of the core-band components with respect to the energy level of an isolated atom, E, 0). AE Si) = A v(oo)[l + Aj]. The intensities of the low-energy bulk component often increase with incident beam energy and the decrease in the polar angle between the incident beam and surface normal (Reprinted with permission from [3]) 

The energy of individual component should be intrinsic, but the resultant peak changes with crystal orientation due to the convoluted contribution from the involved peaks. The dependence of the high-energy-component intensity on the beam conditions and on the atomic density impUes that the surface relaxation 

When a solid reduces its size down to the nanometer scale, the entire core-level features (both the main peak and the chemical satellites) move simultaneously toward lower binding energy and the amounts of shift depend not only on the 

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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. 

M. Said, M. C. Desjonqudres and D. Spanjaard, Surface Core Level Shifts in BCC Transition Metals Deduced from Segregation Energy Calculation, Phys. Rev. B 47 4722 (1993)... 

G. Abramovici, M. C. Desjonqu res and D. Spanjaard, W Surface Core Levels Shifts of O/W(110) Deduced from Surface Segregation Energies, /. de Physique 15 907 (1995)... 

Figure 5.36 shows the excellent agreement between Eq. (5.67) and the measured electrochemical core level shifts of the Zr 3d5/2 electrons of the solid electrolyte, with the Pt working electrode grounded, and of the Pt 4 ... 

Shek ML, Stefan PM, Binns C, Lindau I, Spicer WE. 1982. Chemisorption-induced Pt 4/ surface core level shifts. Surf Sci 115 L81-L85. 

WeinertM, Watson RE. 1995. Core-level shifts in bulk alloys and surface adlayers. Phys Rev B 51 17168-17180. 

Core hole, 34 210 core-hole lifetime, 34 215 Core level shift, C(ls), 29 13-14 Core-state excitation, 34 204 Correlation data, structure effects, 29 159-160 Correlations, adsorptivity, 29 189-190 Co9Sg, structure, 40 222 CoSiOj powders, Fischer-Tropsch synthesis, 39 288-289... 

C(li) Core Level Shifts for Surface Bonded Intermediates... 

The model of Citrin and Wertheim [65], developed to explain the surface atom core level shifts in the XPS spectra of metallic systems, has already been used to explain the extremely low value of the I.S. of the central 13 atoms in the AU55 cluster [44]. 

In order to understand this effective loss of 6s electron density by the core site atoms, use has been made [44] of the model introduced by Citrin and Wertheim [65] to explain the negative surface atom core level shifts, relative to the bulk, observed in the XPS spectra of metals surfaces [127]. Their model used... 

As described in Chapter 2, a number of spectroscopic surface methods give information relating to d band shifts [45]. Ross, Markovic and coworkers have developed synchrotron-based high resolution photoemission spectroscopy to directly measure d band centers giving results in good agreement with the DFT calculations [46]. Another possibility is to exploit the fact that in some cases a shift in the d states can be measured as a core-level shift, as the d states and the core levels shift... 

As mentioned earlier, the existence of surface shifted core levels has been questioned.6 Calculated results for TiC(lOO) using the full potential linearized augmented plane wave method (FLAPW) predicted6 no surface core level shift in the C Is level but a surface shift of about +0.05 eV for the Tis levels. The absence of a shift in the C Is level was attributed to a similar electrostatic potential for the surface and bulk atoms in TiC. The same result was predicted for TiN because its ionicity is close to that of TiC. This cast doubts on earlier interpretations of the surface states observed on the (100) surface of TiN and ZrN which were thought to be Tamm states (see references given in Reference 4), i.e. states pulled out of the bulk band by a shift in the surface layer potential. High resolution core level studies could possibly resolve this issue, since the presence of surface shifted C Is and N Is levels could imply an overall electrostatic shift in the surface potential, as suggested for the formation of the surface states. 

Figure 25.6 Differences in cohesive energies for nitrides of the 3d-, 4d- and 5d-series. These curves show the expected sign of the surface core level shift for (a) nitrogen and (b) metal...

The surface core level shift is defined as the shift in the core level binding energy for a surface atom relative to that of a bulk atom. Different theoretical approaches have been used to calculate surface shifts5,9 and for metals it has recently been shown21 that both initial- and final-state effects have to be included in ab initio calculations to obtain consistent agreement between experimental and calculated results. The basic assumption in this theoretical approach is that the final state is completely screened so the... 

This difference is taken for a compound in which the atoms of the element investigated (a Z-element) are changed to atoms of a Z + 1 element. The surface core level shift for the metal (M) and nonmetal (Y) level can then be expressed as,... 

In a recent investigation31 of TaC(lll) the surface shifted Ta 4f levels were investigated before and after depositing a monolayer of graphite on the surface. A dense carbon overlayer on the polar TaC(lll) surface might be expected to quench the surface Ta core level and to leave only a bulklike core level. The spectrum recorded after deposition of a graphite monolayer, however, showed an attenuated and shifted surface Ta core level, shifted about 0.3 eV closer to the bulk peak. It thus appears that not even a dense graphite monolayer is sufficient to produce a bulk-like electronic environment for the surface Ta atoms on TaC(lll). 

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