Binding energy chemical shift

Photoelectron spectroscopy of Ag(enbisbig)(C104)3 gave binding energy chemical shifts for... 

In order to monitor the progress of interfacial reactions occurring during the metallization of cured polyimide, x-ray photoemission spectroscopy (XPS or ESCA) was used to reveal electronic core-levels indicative of the environment at the interface and adjacent regions. Evidence of chemical reaction would include the appearance of new peaks with characteristic binding energies (chemical shifts) representative of new or altered chemical states of the element. We can thus ascertain the formation of metal-oxygen chelate complexes (1). 

The photoelectron peaks in the XPS spectrum are not only characteristic of the elements from which they originate, but they also provide chemical/oxidation state information. The latter is revealed by small changes in binding energy (chemical shifts) due to the influence of different chemical environments on the electron energy levels of an atom. XPS is sensitive to all elements, except H and He, with a detection limit of ca. 0.1 At.% (1000 ppm). 

Gross atomic charge can be correlated with the electron binding energy chemical shift (normally Is binding energy) offers a fast method time scale 10. Difficulty arises in obtaining reproduceable spectra of ions in solid state (as salts). 

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. 

The left-hand side of Equation (8.15) involves the difference between two electron binding energies, E — E. Each of these energies changes with the chemical (or physical) environment of the atom concerned but the changes in Ek and E are very similar so that the environmental effect on Ek — E is small. It follows that the environmental effect on E -h Ej, the right-hand side of Equation (8.15), is also small. Therefore the effect on is appreciable as it must be similar to that on There is, then, a chemical shift effect in AES rather like that in XPS. 

Figure 5.36. Effect of electrochemical O2 pumping on the Zr 3dj XPS spectra of Pt/YSZ at 400°C (a) Zr 3d5/2 spectrum shift from AUWr=0 (solid curve) to AUwr=1. 2 V (dashed curve) (b) effect of overpotential AUv/r on the binding energy, Eb) and kinetic energy, (AEk--AEb) shifts of Zr 3dS/2 (filled circles, working electrode grounded) and Pt 4f7/2 (open circle, reference electrode grounded).6 Reprinted with permission from the 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. 

Electrochemical reactions are driven by the potential difference at the solid liquid interface, which is established by the electrochemical double layer composed, in a simple case, of water and two types of counter ions. Thus, provided the electrochemical interface is preserved upon emersion and transfer, one always has to deal with a complex coadsorption experiment. In contrast to the solid/vacuum interface, where for instance metal adsorption can be studied by evaporating a metal onto the surface, electrochemical metal deposition is always a coadsorption of metal ions, counter ions, and probably water dipols, which together cause the potential difference at the surface. This complex situation has to be taken into account when interpreting XPS data of emersed electrode surfaces in terms of chemical shifts or binding energies. 

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