Energy dependence of abstractive versus dissociative chemisorption of fluorine molecules on the silicon (111)-(7x7) surface.
Scanning tunneling microscopy and monoenergetic molecular beams have been used to obtain real-space atomic images of the competition between abstractive and dissociative chemisorption. The size distribution of Si-F adsorbates on the Si(111)-(7x7) surface was examined as a function of the incident translational energy of the F(2) molecules. For F(2) molecules with 0.03 electron volt of incident energy, the dominant adsorbate sites were isolated Si-F species. As an F(2) molecule with low translational energy collides with the surface, abstraction occurs and only one of the F atoms chemisorbs; the other is ejected into the gas phase. For F(2) molecules with 0.27 electron volt of incident energy, many adjacent Si-F adsorbates (dimer sites) were observed because F(2) molecules with high translational energy collide with the surface and chemisorb dissociatively so that both F atoms react to form adjacent Si-F adsorbates. For halogens with very high incident energy (0.5-electron volt Br(2)), dissociative chemisorption is the dominant adsorption mechanism and dimer sites account for nearly all adsorbates.
Jensen
J A
JA
Yan
C
C
Kummel
A C
AC