Aluminum on the Si(100) surface: Growth of the first monolayer

Scanning tunneling microscopy was used to study the growth of the first monolayer (ML) of Al on the Si(100) surface at room temperature (up to 100 ^∘{}C). The Al forms rows of adsorbed dimers that run perpendicular to the underlying Si dimer rows. As the coverage is increased, the metal configuration evolves from isolated rows, to areas of local 2×{}3 and 2×{}2 structure, to a surface entirely terminated by a 2×{}2 array of Al dimers at 0.5 ML. Deposition of more than 0.5 ML results in the growth of three-dimensional Al clusters on the 2×{}2 surface. Electronic-structure effects are illustrated, and two alternative bonding sites for the Al adatom dimers are suggested.