CONVERSION OF SICL PAIR AND ISLAND SITES TO SICL SINGLE-SITE UPON ANNEALING OF CL SI(111)-7X7 SURFACES/

Using scanning tunneling microscopy (STM) and molecular beam technique s, we have studied the SiCl spatial distribution after annealing Cl-co vered Si(111)-7x7 surfaces with different initial spatial correlations between adsorbed SiCl. At room temperature, the spatial correlation b etween adsorbed SiCl is a function of Cl-2 incident energy. At an inci dent energy of 0.11 eV, SiCl island formation as well as isolated-site adsorption are observed. However, at an incident energy of 0.44 eV, n o island formation occurs and only isolated-site adsorption is observe d. The isolated-site adsorption results in SiCl singles with no neighb oring SiCl as well as paired SiCl. Annealing all of these Cl-covered s urfaces to similar to 600 degrees C for 60 s results in similar surfac e morphology even though the spatial correlations between adsorbed SiC l on these surfaces before annealing are different. The annealing proc ess results in the complete destruction of SiCl islands and pairs and an increase in the density of adatom vacancies as well as SiCl singles on the surface. One new adatom vacancy is created for each two SiCl s pecies desorbed. The change in surface site can be explained by the re combinative desorption process, SiCl(s) + SiCl(s) --> Si(s) + SiCl2(g) , in which diffusion of SiCl plays an important role. The second-order desorption of SiCl2 can be envisioned as a slow 2D lattice-gas reacti on of SiCl species on the Si(111)-7x7 surface at high temperature.