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 electrons with the energy of 36 eV were used to excite the correlated electron pairs from a p(2x1) adsorbed oxygen layer. The (e,2e) spectra of clean and oxygen 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 structure in the energy distribution of correlated pairs. This structure corresponds 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 peak was obsewed at 6.5 eV below Fermi level. A theoretical analysis of the emission process is developed and used to explain the main structures in the observed electron pair spectra