Ultrathin Al layers on Si(111) and Si(100): Structures and phase transitions

The metal/silicon system Al/Si(111)-7×7 was studied by our group with spot-profile analysis low-energy electron diffraction (SPA-LEED), reflection high-energy electron diffraction (RHEED) and scanning force microscopy (SFM), with emphasis on temperature-dependent order-disorder phase transitions of the surface structures. A review of the Al/Si(111) system describes our results in context with the findings of others. An improved phase formation diagram, including earlier results, is deduced. Between the submonolayer phases and the thick films a cluster phase (the δ-phase) was found that exists in a coverage range of 1-10 monolayers, showing intriguing temperature-dependent effects. At coverages above 20 monolayers the behaviour changes to that of thick films. Although the Al/Si(100) system has completely different reconstructions below one monolayer, the same δ-phase as on Si(111) appears at one monolayer, with similar thermal behaviour.