Large island formation versus single-site adsorption forCl2chemisorption onto Si(111)-7×7 surfaces

Scanning tunneling microscopy and molecular beam techniques are used to investigate adsorbate structure as a function of reactant translation energy. When a Si(111)-(7×7) surface is dosed with a monoenergetic ${\mathrm{Cl}}_2$ beam of translational energy less than 0.11 eV, the dominant adsorbate structure is SiCl islands. Conversely, for 0.44 eV ${\mathrm{Cl}}_2$ dosing, only single-site center-adatom preferred chemisorption is present. It is proposed that center-adatom preferred reaction results from direct activated chemisorption and island formation results from precursor mediated chemisorption.