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Vibrational properties of arsenic on Si(111)
A343 D.S.-L. Law SERC Daresbury Laboratory, Warrington WA4 4AD, UK Received 30 October 1990; accepted for publication 16 December 1990 The yield of C1÷ ions from Si(111)7 × 7-C1 has been monitored through both the C1 and Si K-edges, The CI K-edge ion yield EXAFS suggests a majority site origin, the data producing the same result as Auger yield SEXAFS: an atop geometry with a CI-Si bond length of 2.00 + 0.02 ,~. The C1 +-yield data recorded at the Si K-edge are identical to bulk Si EXAFS and the desorption mechanism at this edge is concluded to be X-ray induced electron stimulated desorption (XESD).
Surface Science 251/252 (1991) 551-555 North-Holland
551
Xenon adsorption on AI(ll0) U. Schneider, G.R. Castro 1, H. Isern, T. Janssens and K. Wandelt Institut flir Physikalische und Theoretische Chemie, Universitiit Bonn, Wegelerstrasse 12, W-5300 Bonn 1, Germany Received 1 October 1990; accepted for publication 30 November 1990 The Xe adsorption on AI(ll0) at 45 K has been studied by UPS, TDS and LEED. The Xe-TD spectra at low coverage (0(Xe) < 0.1 ML) consist of a single peak at 70.4 K, independent on the coverage, suggesting a first-order desorption kinetics. An activation energy of desorption of 0.19 eV/atom and a frequency factor of 5 x 1013 s -1 has been determined. Beyond a coverage of 0(Xe) = 0.1 ML a change to zeroth-order desorption kinetics is accompanied by the appearance of a Xe-induced LEED pattern suggesting the formation of Xe islands. The LEED pattern exhibits the same periodicity, perpendicular to the surface rows, as the AI(ll0) substrate and suggests Xe adsorption along the surface troughs with a Xe-Xe interatomic distance of 4.41/k. The Xe 5pl/2 and 5P3/2 photoemission peaks show two different characteristics as a function of the coverage. Below 0(Xe) = 0.1 ML the maximum of the 5pl/2 signal occurs at about 0.2 eV lower energy than above 0.1 ML. Only beyond 0(Xe) = 0.1 ML the 5P3/2 peak exhibits mj-splitting. All these observations are interpreted in terms of a 2D phase transition: 2D-gas (0(Xe)< 0.1 M L ) o 2D-solid (0.1 < 0(Xe) < 1 ML).
556
Surface Science 251/252 (1991) 556-560 North-Holland
Vibrational properties of arsenic on Si(lll) H. Wilhelm, W. Richter, U. Rossow, D. Zahn lnstitut ]'fir Festkrrperphysik, TU Berlin, W.I O00 Berlin 12, Germany
D.A. Woolf, D.I. Westwood and R.H. Williams Department of Physics, University of Wales, Cardiff CF1 3HT, UK Received 1 October 1990; accepted for publication 30 November 1990 Clean silicon substrates, Si(lll), were arsenic capped in a molecular beam of As 4 molecules. These samples were investigated by Raman scattering after transferring them through air into another UHV chamber for analysis. The thick as deposited As layers are identified as being amorphous. With increasing exposure time to air they become partly oxidized. Heating of these layers was then performed in steps from room temperature up to 550°C. As revealed by Raman scattering the amorphous arsenic is removed at first. Around 350-400°C two peaks appear in the Raman spectra at 235 and 356 cm -1. Since at this temperature range all but one monolayer of ordered (1 × 1) As has been desorbed, these peaks are interpreted as a doubly degenerated stretching and a bending vibrational mode of the first monolayer of As on Si(lll). The peaks disappear above 550°C, the temperature where the arsenic monolayer desorbs. Air exposure also causes the peaks to vanish.
Surface Science 251/252 (1991) 551-555 North-Holland
551
Xenon adsorption on AI(ll0) U. Schneider, G.R. Castro 1, H. Isern, T. Janssens and K. Wandelt Institut flir Physikalische und Theoretische Chemie, Universitiit Bonn, Wegelerstrasse 12, W-5300 Bonn 1, Germany Received 1 October 1990; accepted for publication 30 November 1990 The Xe adsorption on AI(ll0) at 45 K has been studied by UPS, TDS and LEED. The Xe-TD spectra at low coverage (0(Xe) < 0.1 ML) consist of a single peak at 70.4 K, independent on the coverage, suggesting a first-order desorption kinetics. An activation energy of desorption of 0.19 eV/atom and a frequency factor of 5 x 1013 s -1 has been determined. Beyond a coverage of 0(Xe) = 0.1 ML a change to zeroth-order desorption kinetics is accompanied by the appearance of a Xe-induced LEED pattern suggesting the formation of Xe islands. The LEED pattern exhibits the same periodicity, perpendicular to the surface rows, as the AI(ll0) substrate and suggests Xe adsorption along the surface troughs with a Xe-Xe interatomic distance of 4.41/k. The Xe 5pl/2 and 5P3/2 photoemission peaks show two different characteristics as a function of the coverage. Below 0(Xe) = 0.1 ML the maximum of the 5pl/2 signal occurs at about 0.2 eV lower energy than above 0.1 ML. Only beyond 0(Xe) = 0.1 ML the 5P3/2 peak exhibits mj-splitting. All these observations are interpreted in terms of a 2D phase transition: 2D-gas (0(Xe)< 0.1 M L ) o 2D-solid (0.1 < 0(Xe) < 1 ML).
556
Surface Science 251/252 (1991) 556-560 North-Holland
Vibrational properties of arsenic on Si(lll) H. Wilhelm, W. Richter, U. Rossow, D. Zahn lnstitut ]'fir Festkrrperphysik, TU Berlin, W.I O00 Berlin 12, Germany
D.A. Woolf, D.I. Westwood and R.H. Williams Department of Physics, University of Wales, Cardiff CF1 3HT, UK Received 1 October 1990; accepted for publication 30 November 1990 Clean silicon substrates, Si(lll), were arsenic capped in a molecular beam of As 4 molecules. These samples were investigated by Raman scattering after transferring them through air into another UHV chamber for analysis. The thick as deposited As layers are identified as being amorphous. With increasing exposure time to air they become partly oxidized. Heating of these layers was then performed in steps from room temperature up to 550°C. As revealed by Raman scattering the amorphous arsenic is removed at first. Around 350-400°C two peaks appear in the Raman spectra at 235 and 356 cm -1. Since at this temperature range all but one monolayer of ordered (1 × 1) As has been desorbed, these peaks are interpreted as a doubly degenerated stretching and a bending vibrational mode of the first monolayer of As on Si(lll). The peaks disappear above 550°C, the temperature where the arsenic monolayer desorbs. Air exposure also causes the peaks to vanish.