Photodesorption of disilane physisorbed on hydrogen terminated Si(100) and the dramatic consequences of weak molecular chemisorption

摘要

The adsorption of disilane (Si2H6) oriD terminated Si(IOO) has been investigated using photodesorption to probe the coverage over a range of surface temperatures. Incident Si2H6 molecules can become molecularly (nondissociatively) chemisorbed after being trapped in a physisorbed precursor state. At temperatures higher than approximately 116 K, nearly all the physisorbed molecules des orb rather than chemisorb. Photofragmentation products are readily observed when chemisorbed Si2H6 is irradiated with 6.4eV photons but surprisingly, none are observed in the case of physisorbed Si2H6.Consequently, Si can be deposited by reaction& of the photofragmentation products with th~ surface, put only at temperatures lower than) 16 K. The photodesorption cross section is also extremely dependent on the chemical nature of the Si(IOO) surface. It is high when the surface is terminated with a monodeuteride phase but much small~r when dideuteride species are present, suggesting that the presence of sUiface gap states is of importance. We consider how de sorption might be initiated by electron attachment or by electron-hole reco",binatiqn at the surface.