Time-resolved study of beryllium surface reactions using electron momentum spectroscopy of the core-level

We have measured the binding energy of the Be 1s core-level in metallic beryllium using an electron-impact ionisation technique - electron momentum spectroscopy (EMS). The value we obtain, 111.7 ± 0.1 eV, is in good agreement with previous results. We have also determined the chemical shift of the core level in an oxygen environment to be 2.68 ± 0.06 eV. Using the same technique, we have followed the evolution of the core-level peak as Be undergoes surface reaction induced by background gases present in the vacuum (mainly water vapour and nitrogen). The core-level peak intensities as a function of time clearly show that reaction of the Be surface progresses in two distinct steps. The initial relatively rapid stage progresses up to a coverage of around 18 L of H₂O and N₂ after which the onset of a slower reaction process is observed. These results demonstrate the ability of EMS to provide time-resolved electronic structure measurements as a solid undergoes chemical modification.