Substrate temperature dependence of the initial growth mode ofSiO2on Si(100)-(2×1) exposed toO2: A photoemission study

X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) are used to probe the initial states of oxidation of Si(100)-(2×1) surface, systematically as a function of substrate temperature (from RT to $T_s$600 °C) and low pressure, in the desorption-governed region, the initially oxidized surface is understood as a juxtaposition of ${\mathrm{SiO}}_2$-like regions (Si-${\mathrm{O}}_4$ bondings) and bare silicon terraces still presenting the dimer reconstruction. In contrast to this nonuniform growth, the RT oxidation is explained by a more random distribution of O chemisorption with more intermediate local bondings located near the overlayer and a full surface-state quenching for mean coverages lower than at high $T_s$. The study also focuses on the initial growth-rate differences according to whether exposure changes result from time or pressure variations at high $T_s$. They agree with a seeding process, for the islandlike growth, essentially promoted by pressure increases and concomitant arrival of ${\mathrm{O}}_2$ molecules on a seeding site, in contrast with time increases leading to a more sequential arrival which favors the desorption. This point of view explains the rapid switch, as a function of increasing pressure, from the desorbing to the passivation mode at high $T_s$.