Highly resolved surface shifts in a mixed-valent system: EuPd2Si2

Synchrotron-radiation-excited photoelectron spectroscopy is employed to study the bulk and surface states of the mixed-valent system EuPd2Si2, which undergoes a valence transition from Eu2.2+ at room temperature to Eu2.9+ at low temperature (2 100 K). The high resolution employed, coupled with a relatively large bulk-to-surface energy shift to the Eu2+ emission, allows a definitive identification of the bulk and surface states of Eu2+. The Eu3+ emission is not observed at room temperature, but is readily apparent in the low-temperature spectra. © 1982 The American Physical Society.