High resolution Ge 3d photoelectron spectra obtained with synchrotron radiation are used to determine the surface oxidation states of Ge(100) and Ge(111) surfaces. For both orientations four discrete chemically shifted core levels are observed that yield a chemical shift of 0.85 eV per Ge-O bond. With this interpretation, Ge forms 1+, 2+, 3+ oxidation states when exposed initially. Upon annealing predominantly the 2+ state is formed. The stability of this 2+ oxidation state is compared within the neighboring elements. © 1986.
Schmeisser, D., Schnell, R. D., Bogen, A., Himpsel, F. J., Rieger, D., Landgren, G., & Morar, J. F. (1986). Surface oxidation states of germanium. Surface Science, 172(2), 455–465. https://doi.org/10.1016/0039-6028(86)90767-3