X-ray Source Energies and Widths

XPS source energies and widths in eV.

Common sources for ultraviolet photoelectron spectroscopy (UPS) include He(I) at 21.22 eV and He(II) at 40.80 eV. Watts and Castle [4] present an excellent history on the development of  laboratory X-ray sources for XPS including higher energy sources used for HAXPES (hard X-ray photoelectron spectroscopy).  

References:

[1] G.M. Bancroft, H. W. Nesbitt, R. Ho, D. M. Shaw, J. S. Tse, M. C. Biesinger, Physical Review B 80 (2009) 075405.
[2] H.W. Nesbitt, G.M. Bancroft, R. Davidson, N.S. McIntyre, A.R. Pratt, American Mineralogist 85 (2004) 878-882.

[3] G.M. Bancroft, H.W. Nesbitt, V.P. Zakaznova-Herzog, J.S. Tse, Recent Advances in XPS of Non-Conductors in Turning Point in "Solid-State Materials and Surface Science" K.D.M. Harris and P.P. Edwards eds., Royal Society of Chemistry, pp. 651-664, 2007.

[4] J.F. Watts, J.E. Castle, Surface and Interface Analysis, 56 (2024) 408-424.