Nature of vicinal laser-annealed Si(111) surfaces

Low-energy electron diffraction studies of vicinal Si(111) surfaces cut along the [112̄] direction show that a regular array of steps is formed upon laser annealing, with step height (3.06 {}) somewhat less than the double-layer separation (3.14 {}) and edge atoms threefold coordinated. For energy densities between 0.2 and 0.5 J/cm² at 5320 {} a weak buckling reconstruction is present and can be aligned by the step edges. Thermal annealing to 300^∘{} C allows first the atoms in the nighborhood of the step edges to relax, resulting in a small increase of the step height. Further annealing above 400^∘{} C results in the growth of the terrace widths and simultaneous increase of the step height. The 7 ×{} 7 reconstruction is observed as soon as the terrace width is large enough to support several surface unit cells (> 200 {}). Our results indicate that the high-temperature equilibrium configurations for vicinal Si(111) surfaces consist of a regular array of monatomic steps (d~3.1 {}) and can be quenched by laser annealing into a metastable phase. The low-temperature phase displays an effective attractive step-step interaction resulting in the formation of very large terraces and large risers. The nature of this attractive interaction is discussed.