Radiation damage studies by x-ray photoelectron spectroscopy. II. Electron irradiated Li2CrO4 and Li2WO4

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Abstract
Single crystals of Li2CrO4 and Li2WO4 were irradiated in situ with 0.3–1.6 keV electrons in an UHV x-ray photoelectron spectrometer. Chemical shifts of core-level peaks in XPS spectra indicate formation of Cr(III) on the irradiated Li2CrO4 surface and of W (IV) and W (V) on the irradiated Li2WO4 surface. Accompanying formation of the reduced species, new peaks attributable to photoelectrons from non-bonding orbitals appear at binding energies just below the respective Fermi levels. A lower limit of the G value for Cr(III) formation is estimated to be about 1.3×10−2 from the differential energy loss of the incident electrons. Comparison of this G value with previous data determined by ESR suggests that solid surfaces are far more sensitive to radiation damage than the bulk. The irradiation of Li2WO4 causes a shift in the entire XPS spectrum to lower binding energy, initially ∼2 eV, which decreases over a 20 h period until the original peak positions are recovered. This is interpreted in terms of surface charging caused by electron irradiation.