Principle and Characteristics of XPS

The experimentally measured energies of the photoelectrons are thus given by 

Since the binding energies of different levels (Eb) of an element depend on the energy level, it follows that (see Fig. 5.2)  

The XPS technique is highly surface specific due to the short range of the photoelectrons that are excited from the solid. For XPS, the AlKa (1486.6eV), MgKa (1253.6eV) or TiKa (2,040eV) are often the photon energies of choice. The photoemission process is often envisaged as a three step-process  

As an example of the XPS spectrum, the photoelectron peaks of Nickel due to MgKa (1253.6 eV) photons are shown in Fig. 5.4. The spectrum indicates Ni 2s, 2pi/2, 2p3/2, 3s and 3p peaks. The Ni 2pi/2 and 2ps/2 are also shown in the inset of the figure for clarity. It is to be noted that Ni Is peak is not present in the spectrum as the Is electrons (having binding energy of 8332 eV) cannot be excited by 1253.6 eV photons. 

AES has the following features 10-50 A analysis depth, 100 A spatial resolution, in-situ fracture analysis, large sample size, color maps and line scans. The AES provides depth profiling and formation about grain boundary particles. Like in XPS, there is a chemical shift, but the spectrum, in this case, is more complex because it involves three levels. 

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