SITE-SELECTIVE SIH4 ADSORPTION ON SI(111)(7X7) SURFACES

Scanning tunneling microscopy (STM) was used to investigate room tempe rature adsorption and dissociation of SiH4 on Si(111)(7 X 7) surfaces. The data show a pronounced site selectivity for this process. Initial ly the reaction involves exclusively the corner holes and the adjacent Si adatoms of the (7 X 7) reconstruction, with preferential adsorptio n of SiH3 groups in the corner holes and of H atoms on one of the adja cent corner adatoms. For higher SiH4 exposures the reactivity of the c orner adatoms is significantly reduced, hydrogen adsorption occurs pre ferentially on the center adatoms. Deposited SiHx groups (x = 2, 3) nu cleate now in small clusters on the terraces. A higher density of thes e SiHx clusters on domain boundaries or at steps indicates a higher re activity of these defect sites.