Browsing by Author "Pi, TW"

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Adsorption of chlorine on the Si(001)-2 x 1 surface
(2001-08-10)
Pi, TW
;
Tsai, SF
;
Ouyang, CP
;
Wen, JF
;
Wu, RT
It is shown that the room-temperature dissociative adsorption Of Cl-2 on the Si(0 0 1)-2 x 1 surface results in the bonding of Cl atoms to both the up- and down-dimers which then become symmetrical, At saturation coverage the Si 2p core-level spectra exhibit only a single Cl-induced component with emission twice as strong as that from the up-dimer of the clean surface and with a core-level shift of +930 +/- 8 meV. These results were obtained using an analysis in which the intensities of the core-level spectra from the individual Si layers are constrained by an escape depth. It facilitates the identification of components down to the second subsurface layer and yields an inelastic mean free path of 3.4 +/- 0.2 at a photon energy of 140 eV. (C) 2001 Elsevier Science B.V. All rights reserved.
Coverage-dependent thermal reactions of digermane on Si(100)-(2x1)
(1996-12-15)
Lin, DS
;
Huang, KH
;
Pi, TW
;
Wu, RT
;
物理研究所
In this study, we examine the adsorption and thermal reactions of digermane (Ge6H6) on the Si(100)-(2X1) surface with high-resolution core-level photoemission spectroscopy using synchrotron radiation. At 325 K, the digermane dissociatively chemisorbed to produce GeH3, GeH2, GeH, and SiH species. The sticking coefficient at zero coverage deduced from the photoemission intensity is similar to 0.5. Successive annealing of rhc digermane-saturated surface tc, higher temperatures causes further decomposition of GeH3 and GeH2 and the desorption H from GeH and SiH, leaving atomic Ge on the surface. In light of the sufficiently large chemical and surface shifts in their core-level binding energies fur different surface species, those processes were identified by examining the evolution of Ge 3d and Si 2p line shapes. Experimental results indicate that the reaction for H release from GeH not only occurred in a large temperature range but also depended heavily on the Ge2H6 adsorption coverages. To reaction routes for H release from Ge sites were used to describe the large reaction temperature spreads accurately. GeH decomposition by transferring the H atom to a surface Si dangling bond took place for low coverages at less than or equal to 590K, and H-2 thermal desorption occurred for higher coverages in the range of 590-770 K. The former process of atom transfer of H from Ge to Si sites was directiy observed in the Ge 3d and Si 2p photoemission spectra.