Appearance-Potential Study of 4f States of Ytterbium

The soft x-ray appearance potential spectra (SXAPS) of M levels of rare-earth ytterbium has been obtained in 1500-1960 eV range with a nondispersive spectrometer which measures the derivative of the total x-ray fluorescence of an electron-bombarded sample as a function of bombarding-electron energy. The data supplement the information derived from absorption spectroscopy but are applicable to the surface region. The M5 spectrum selectively arising from M5-N7 transition consists of an intense positive peak and an undershoot accompanied by two distinct secondary peaks at 2.0 and 11.0 eV above the threshold. The spectra are representative of the trivalent oxide instead of pure divalent metal which is expected to be void of spectral characteristics due to a full 4f shell. The spectra imply a relatively weak exchange interaction between the 4fN+1 subshell configuration and the M4,5 vacancies.