Electron scattering study of clean (100) tungsten and its interaction with oxygen at low coverages

An electrostatic spectrometer was constructed to measure LEED, energy loss spectroscopy, Auger spectroscopy, electron stimulated desorption of ions, flash desorption, and incremental work functions in uhv vacuum. It is capable of operating over a wide range of incident electron beam energies (4 to 1800 eV) and spectral energies (0 to 1000 eV), and it provides charge/mass identification of desorbed ions through time-of-flight measurements. This spectrometer was applied to a study of the clean (100) surface of single-crystal tungsten and its interaction with oxygen at submonolayer coverages. Emphasis was placed on developing an understanding of the energy loss mechanisms in tungsten in order to obtain information on the electronic structure of the substrate and adsorbate. The loss spectrum of low energy (0 to 200 eV) electron scattering from W(100) was experimentally investigated and mechanisms giving rise to the fine structure analyzed using a dielectric response formalism. During adsorption of oxygen on W(100) at 3000K, sequential filling of two electronically inequivalent bonding states was observed. The oxygen in the second of these states is apparently more tightly bound, and its 2p orbitals may be split in energy into two separate levels. Heating of the oxygen dosed surface results in dramatic changes in the geometric structure. The nature of these changes is determined by both temperature and oxygen coverage. The energy distributions of the ions desorbed from the surface by the electron beam were examined