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Atomic arrangement of alkali adatoms on the Si(001)−2×1 surface
A50 Surface Science 242 (1991) 335-340 North-Holland
335
Bonding states of chemisorbed sulfur atoms on GaAs Hirohiko Sugahara, Masaharu Oshima, Ruth Klauser NTT Applied Electronics Laboratories. 3-9-11, Midori-cho, Musashino-shi, Tokyo 180. Japan
Haruhiro Oigawa and Yasuo Nannichi Institute of Materials Science, University of Tsukuba, Tsukuba-shi, Ibaraki 305. Japan Received 16 May 1990; accepted for publication 3 August 1990 The chemistry of the S / G a A s system is studied using synchrotron radiation photoemission spectroscopy. Monolayer-order sulfur atoms are successfully chemisorbed on clean n-GaAs (001) surfaces at room temperature by using an A g / A g I / A g 2 S / P t eleetrocbemical cell, which generates an atomic sulfur flux. Photoemission spectra of core levels are measured with a photon energy of about 210 eV before and after annealing at 360°C for 10 rain in vacuum. Ga3d, As3d, and S2p spectra indicate that G a - S and A s - S bonds are formed on the as-chemisorbed GaAs surfaces at room temperature, and that G a - S bonds become dominant after annealing at 360 o C. These results are the same as for the (NH4)2Sx-treated n-GaAs surfaces. It is found that the G a - S bonding formation is the key for passivating GaAs surfaces for both sulfur-chemisorbed and (NH4)2S~-treated GaAs.
Surface Science 242 (1991) 341-348 North-Holland
341
Theory of alkali adsorption on simple metal surfaces H. Ishida Institute for Solid State Physics, University of Tokyo, Roppongi, Minato-kL~ Tokyo 106, Japan Received 16 May 1990; accepted for publication 15 June 1990 The electronic structure of alkali adlayers on metal surfaces is studied by first-principles calculations as a function of coverage (0). Hexagonal Na layers with varying lattice constants are used as adlayers, and the substrate is represented by the semi-infinite jellium. The results obtained show that the classical Gurney model is insufficient to describe the Na-jellium bonding: despite the large potential lowering in the vacuum, the density of states in a Na sphere is rather insensitive to 0. The bonding-antibonding boundary regarding the Na-jellium bonding coincides with the Fermi level at the lowest 0, implying that the covalency in the Na-jellium bond becomes the largest at the lowest 0. The rapid decrease of the Na-induced dipole moment is caused mainly by the direct N a - N a interaction due to the orbital overlap rather than by the indirect dipole interaction.
Surface Science 242 (1991) 349-353 North-Holland
349
Atomic arrangement of alkali adatoms on the Si{001)-2 x 1 surface K. Kobayashi, S. Bltigel, H. Ishida and K. Terakura Institute for Solid State Physics, University of Tokyo, Roppongi, Minato-ku, Tokyo 106, Japan Received 21 July 1990; accepted for publication 1 August 1990 Adsorption sites of Na and Li on the Si(001)-2 x 1 surface at the saturation coverage are determined theoretically by using the simulated annealing method proposed by Williams and Soler. For Na, the most stable configuration is the combination of the hoilow site along the dimer chain and the trough site on top of the third layer Si atom in contradiction to an earlier cak~alation. The substrate relaxation is a crucial factor for stabilizing this configuration. On the other hand Li atoms are adsorbed at low symmetry positions. For both of Na and Li, we observe a significant movement of the substrate atoms towards the ideal surface configuration.
335
Bonding states of chemisorbed sulfur atoms on GaAs Hirohiko Sugahara, Masaharu Oshima, Ruth Klauser NTT Applied Electronics Laboratories. 3-9-11, Midori-cho, Musashino-shi, Tokyo 180. Japan
Haruhiro Oigawa and Yasuo Nannichi Institute of Materials Science, University of Tsukuba, Tsukuba-shi, Ibaraki 305. Japan Received 16 May 1990; accepted for publication 3 August 1990 The chemistry of the S / G a A s system is studied using synchrotron radiation photoemission spectroscopy. Monolayer-order sulfur atoms are successfully chemisorbed on clean n-GaAs (001) surfaces at room temperature by using an A g / A g I / A g 2 S / P t eleetrocbemical cell, which generates an atomic sulfur flux. Photoemission spectra of core levels are measured with a photon energy of about 210 eV before and after annealing at 360°C for 10 rain in vacuum. Ga3d, As3d, and S2p spectra indicate that G a - S and A s - S bonds are formed on the as-chemisorbed GaAs surfaces at room temperature, and that G a - S bonds become dominant after annealing at 360 o C. These results are the same as for the (NH4)2Sx-treated n-GaAs surfaces. It is found that the G a - S bonding formation is the key for passivating GaAs surfaces for both sulfur-chemisorbed and (NH4)2S~-treated GaAs.
Surface Science 242 (1991) 341-348 North-Holland
341
Theory of alkali adsorption on simple metal surfaces H. Ishida Institute for Solid State Physics, University of Tokyo, Roppongi, Minato-kL~ Tokyo 106, Japan Received 16 May 1990; accepted for publication 15 June 1990 The electronic structure of alkali adlayers on metal surfaces is studied by first-principles calculations as a function of coverage (0). Hexagonal Na layers with varying lattice constants are used as adlayers, and the substrate is represented by the semi-infinite jellium. The results obtained show that the classical Gurney model is insufficient to describe the Na-jellium bonding: despite the large potential lowering in the vacuum, the density of states in a Na sphere is rather insensitive to 0. The bonding-antibonding boundary regarding the Na-jellium bonding coincides with the Fermi level at the lowest 0, implying that the covalency in the Na-jellium bond becomes the largest at the lowest 0. The rapid decrease of the Na-induced dipole moment is caused mainly by the direct N a - N a interaction due to the orbital overlap rather than by the indirect dipole interaction.
Surface Science 242 (1991) 349-353 North-Holland
349
Atomic arrangement of alkali adatoms on the Si{001)-2 x 1 surface K. Kobayashi, S. Bltigel, H. Ishida and K. Terakura Institute for Solid State Physics, University of Tokyo, Roppongi, Minato-ku, Tokyo 106, Japan Received 21 July 1990; accepted for publication 1 August 1990 Adsorption sites of Na and Li on the Si(001)-2 x 1 surface at the saturation coverage are determined theoretically by using the simulated annealing method proposed by Williams and Soler. For Na, the most stable configuration is the combination of the hoilow site along the dimer chain and the trough site on top of the third layer Si atom in contradiction to an earlier cak~alation. The substrate relaxation is a crucial factor for stabilizing this configuration. On the other hand Li atoms are adsorbed at low symmetry positions. For both of Na and Li, we observe a significant movement of the substrate atoms towards the ideal surface configuration.