The electronic structure change in the valence band of molybdenum (110) during argon ion bombardment is studied. The UPS measurements using synchrotron radiation show that argon ion bombardment induces a reduction in intensity of the peak at 4.10 eV below Fermi energy and a decrease in the work function. This peak reduction is explained in terms of substitution of a vacancy for a molybdenum atom. The decrease in the work function also suggests that vacancies are being created in the surface region due to argon ion bombardment.
