Site-specific phenomena in Si : 2p core-level photoionization of X3Si(CH2)(n)Si(CH3)(3) (X = F or Cl, n=0-2) condensed on a Si(111) surface

We used photoelectron spectroscopy and the energy-selected-photoelectron ph otoion coincidence (ESPEPICO) method to study site-specific phenomena in th e Si:2p photoionization of X3Si(CH2)(n)Si(CH3)(3) (X = F or Cl, n = 0-2) co ndensed on a Si(111) surface. The site-specific excitation and the occurren ce of different chemical shifts at two Si sites were revealed in the total electron-yield spectra and the photoelectron spectra of F3Si(CH2)(n)Si(CH3) (3) (n = 1, 2), although they were not clearly revealed in those of Cl3SiSi (CH3)(3). We conclude that these site-specific phenomena are easily observe d in molecules in which the two Si sites are located far apart and in which electron migration between the two Si-containing groups does not occur. Th is was supported by our ab initio calculation. Site-specific fragmentation was revealed in the ESPEPICO spectrum of F3SiCH2CH2Si(CH3)(3), although it was negligible for Cl3SiSi(CH3)(3) and was less remarkable in F3SiCH2Si(CH3 )(3) than in F3SiCH2CH2Si(CH3)(3). Site-specific fragmentation also occurre d when the two Si sites were located far apart. (C) 1999 Elsevier Science B .V. All rights reserved.