Oxygen adsorption on W(001) studied by low energy (e,2e) spectroscopy

We applied the low energy (e,2e) spectroscopy in reflection-mode scattering geometry for studying ordered oxygen adsorption on W(001). Primary electro ns with the energy of 36 eV were used to excite the correlated electron pai rs from a p(2x1) adsorbed oxygen layer. The (e,2e) spectra of clean and oxy gen covered W(001) surface were analyzed. It was found that the adsorption of 1 ML of oxygen on W(001) leads to the appearance of an additional struct ure in the energy distribution of correlated pairs. This structure correspo nds to the excitation of electrons from the energy level located at 6.7 +/- 0.5 eV below the Fermi level. This result is consistent with the UPS study of the oxygen adsorption on W(001) [1] where the adsorbate photoemission p eak was observed at 6.5 eV below Fermi level. A theoretical analysis of the emission process is developed and used to explain the main structures in t he observed electron pair spectra.