Growth study of Fe on Be(0001) by scanning tunneling microscopy and spectroscopy

Abstract

In this thesis, scanning tunneling microscopy and spectroscopy were used to probe the Be(0001) surface and the growth behavior of iron on top of it. The experiments were performed under ultra-high vacuum conditions with homebuild scanning tunneling microscopes at cryogenic temperatures between 4.2 K and 60 K. A cleaning procedure for the (0001) surface of Be single crystals based on Ar+ ion sputtering at elevated temperatures was developed that yields extended parallel terraces with a low defect density. The electronic band structure of the clean Be(0001) surface was investigated by scanning tunneling spectroscopy. The parabolic dispersion of a surface state band is identified in interference patterns of the surface charge density. Inelastic electron tunneling spectroscopy further reveals the contributions of phonon-assisted tunneling of electrons into Be(0001). The growth of iron on this surface by evaporative deposition was studied in dependence of the iron coverage and of the substrate temperature during and after deposition. At room temperature, island growth in the Volmer-Weber mode occurs. At 300 °C, intermixing of deposited iron with the substrate is observed and substantiated by Auger electron spectroscopy. Alloyed films with a locally (2 × 2)-ordered surface structure form in the process. This growth mode persists for iron coverages between 0.5 atomic layers and 3.8 atomic layers. The surface structure of these ordered alloyed films is found to resemble stretched (0001) planes of bulk-truncated FeBe2 in a Laves structure.