Sometimes when we analyze survey scans, two peaks or features overlap. One common case is to discover an x-ray induced Auger peak overlapping with a photoemission peak. In this case, we look for the presence of other core level peaks to confirm or invalidate the assignments of peaks or features that are otherwise ambiguous.

The core levels from an element escape at different kinetic energies. This means, they sample different relative depths in the material. For this reason, we can in principle use the relative heights of different core levels from the same element to do a pseudo-depth profiling analysis. One example to appreciate the principle is to define the differences between a spectrum from a thin layer of element A on element B versus a spectrum of a homogeneous distribution of element A in element B.

Dear Madam,

in case that you are interested in the chemical state of Zn probing the Zn 2p core level is not an appropriate choice since there is no distinct chemical shift for Zn0 and Zn2+. It is better to refer to the Zn LMM Auger electrons, see, e.g.

Surface and Interface Analysis 18 (1992) 39-46

Regards, FM

Dear Efi Dwi Indari,

Usually the measured core levels in XPS are the outermost orbitals of the shell. If not the intensity is effected by the Coster-Kronig effect.

The other main reason for shooing one of the core levels instead of the other is the relative cross section between them. Usually people measure on the one that has the largest cross section to speed up the measurement.

Best regards,

John