Nature of vicinal laser-annealed Si(111) surfaces

Low-energy electron diffraction studies of vicinal Si(111) surfaces cut along the $\left[11\mathrm{}\overline{2}\right]$ direction show that a regular array of steps is formed upon laser annealing, with step height (3.06 Å) somewhat less than the double-layer separation (3.14 Å) and edge atoms threefold coordinated. For energy densities between 0.2 and 0.5 J/${\mathrm{cm}}^2$ at 5320 Å 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 Å). Our results indicate that the high-temperature equilibrium configurations for vicinal Si(111) surfaces consist of a regular array of monatomic steps ($d\sim 3.1$ Å) 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.