ELECTRON-SPECTROSCOPY AT DIAMOND (100)2X1-H WITH A SCANNING TUNNELING MICROSCOPE

Topographic scanning tunnelling microscopy on an undoped 2 x 1-reconstructed diamond surface of a polycrystalline film was possible in air, but not in ultra-high vacuum. Elastic electron tunnelling spectroscopy with the scanning tunnelling microscope was when applied to study electronic states at the surface. A surface bandgap was not found for the surface in air, whereas a gap approximately 3.5 eV wide was found in ultra-high vacuum. This gives strong evidence for the monohydrogenated form of the 2 x 1 reconstruction, (100)2 x 1:H. The Fermi level appeared within the gap about 0.5 eV below the upper band edge which thus explained the impossibility of topographic scanning tunnelling microscopy in ultra-high vacuum. Comparison with data for ultraviolet photoelectron spectroscopy taken from the literature indicates that the surface states form one single, approximately 2-eV-wide band to filled states located just above the valence band edge. The Fermi level is accordingly located approximately 0.5 eV below the conduction band edge and not pinned by surface states.