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

Abstract

We used photoelectron spectroscopy and the energy-selected-photoelectron photoion coincidence (ESPEPICO) method to study site-specific phenomena in the Si:2p photoionization of X 3Si(CH 2) n Si(CH 3) 3 (X=F or Cl, n=0–2) condensed on a Si(111) surface. The site-specific excitation and the occurrence of different chemical shifts at two Si sites were revealed in the total electron-yield spectra and the photoelectron spectra of F 3Si(CH 2) n Si(CH 3) 3 ( n=1, 2), although they were not clearly revealed in those of Cl 3SiSi(CH 3) 3. We conclude that these site-specific phenomena are easily observed 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. This was supported by our ab initio calculation. Site-specific fragmentation was revealed in the ESPEPICO spectrum of F 3SiCH 2CH 2Si(CH 3) 3, although it was negligible for Cl 3SiSi(CH 3) 3 and was less remarkable in F 3SiCH 2Si(CH 3) 3 than in F 3SiCH 2CH 2Si(CH 3) 3. Site-specific fragmentation also occurred when the two Si sites were located far apart.