Self-organizational tendencies of heteroepitaxial transition-metal silicide nanoislands

The aim of this work was to explore self-organizational tendencies of transition-metal silicide nanoislands formed by heteroepitaxial self-assembled processes, such as CoxSiy/Si, TixSiy/Si, MnxSiy/Si, etc, which may exhibit a variety of intermediate phases, polymorphs, and shape transitions, with unique physical properties and size effects. Recent scanning tunneling microscopy observations of self-assembled growth of CoSi2 nanoislands have shown self-organization of nanoislands at the step-bunches of the vicinal Si(1 1 1) surfaces during solid-phase epitaxial growth, namely room-temperature deposition of sub-monolayer Co followed by elevated-temperature annealing treatments. In the current set of experiments, the specific effects of metal coverage, and of structural mismatch of respective silicide with silicon, were investigated by depositing higher coverage of Co and Ti, respectively, prior to the annealing treatments. Higher Co coverage has drastically modified the process, with flat fractal-type two-dimensional islands covering most of the terraces, though tiny dots were still observed at the step-bunches. The outcome of a higher Ti coverage experiment resembled that of a lower Co coverage with the disc-shaped silicide nanodots preferentially occupying the step-bunch sites; however, with a lesser degree of ordering, quite a few dots were found to populate terrace sites. More importantly, no size-selection took place, i.e., no correlation between the dot size and the parent step-bunch height was observed.