Abstract :
We report results of a combined study of low-energy-electron diffraction (LEED) and Monte Carlo simulations for the Ge-adsorbed single-domain stepped Si(100) surface. The (4×1) structure, least favored energetically among the (2×1) family of the dimer-induced structures, is found to appear on the Ge-adsorbed Si(001) surface in a limited range of temperatures slightly below room temperature. With mild annealing at ∼370 K, the surface undergoes irreversible transitions initially to a (3×1) and then ultimately to a (2×1) structure after prolonged annealing. We propose that the (4×1) structure consists of an antiferromagnetic arrangement of A-type Ge ad-dimers, which decompose and recombine into C-type ad-dimers for the high-temperature structures upon annealing. In addition, results of Monte Carlo simulations suggest that the (4×1) surface is the most stable structure when the signs of the Ge inter-dimer interaction parameters are exactly opposite to those of the c(4×2)+p(2×1) surface.
