Kinetics of the Si(111)2 × 1→ 5 × 5 and 7 × 7 transformation studied by scanning tunneling microscopy

The scanning tunneling microscope is used to study the transformation of the Si(111)2 × 1 surface to the 7 × 7 structure, as a function of time and annealing temperature. Two intermediate states are found in the transition: a disordered adatom covered 1× 1 surface, and a well ordered 5 × 5 structure. The surface transformation is observed to occur in two stages. First, nucleation at steps or 2 × 1 domain boundaries produces disordered arrangements of adatoms on a 1 × 1 surface, which then order, producing small domains of 5 × 5 and 7 × 7 structure. Second, growth from these small domains occurs, with the remaining 2 × 1 surface converting entirely into 5 × 5 structure. It is argued that the 5 × 5 structure is favored over 7 × 7 because it contains the same number of atoms as the 2 × 1 structure. Kinetic measurements of the transformation rate as a function of time and temperature have been performed, for temperatures in the range 280-425 °C. An overall activation energy of 2.1 ± 0.5 eV is obtained. © 1991.