Effects of a depth-dependent specimen potential on x-ray photoelectron spectroscopic data

Effects of a depth-dependent specimen potential on x-ray photoelectron spectroscopic data were analyzed using both numerical simulation and experimental spectral data. The analysis shows that when the potential gradient near the specimen surface is larger than 0.1 V/nm, it will cause significant broadening of the photoelectron spectra. As the sampling depth is decreased by increasing the polar angle of analysis, the broadening effect is minimized together with a shift of each spectral peak because the contribution of photoelectrons emitted from a large depth is discriminated. However, the shifting of the peak maximum is much smaller than the actual overall potential drop. Quantitative measurements of the actual potential gradient using x-ray photoelectron spectroscopy are possible but require a spectral deconvolution procedure, a spectrometer with good energy resolution, and a relatively simple sample structure.