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RHEED-TRAXS study of superstructures induced by Ge and Sn adsorption on a Si(110) surface
A178 Surface Science 281 (1993) 241-252 North-Holland
Chemisorption of CO and H 2 on clean and oxygen-modified Mo(112) Ken-ichi Fukui, Tetsuya Aruga and Yasuhiro Iwasawa Department of Chemistry, Faculty of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan Received 10 April 1992; accepted for publication 2 October 1992 Chemisorption of CO and H 2 on clean and oxygen-modified Mo(112) has been investigated by low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and temperature-programmed desorption (TPD). Oxygen adatoms are expected to be adsorbed in trough sites between close-packed Mo rows and, hence, the first-layer Mo atoms remain accessible to gas-phase molecules. Oxygen adsorption on a clean Mo(l12) surface at 300 K, followed by annealing to 600 K, has produced a series of LEED patterns with increasing oxygen coverage. Models for these structures are presented. These ordered oxygen adlayers are stable up to 1100 K and have been used to examine the effect of oxygen modification on the adsorption and dissociation of CO and H z. Both CO and H 2 molecules are dissociated on clean Mo(112). The amount of dissociated species decreases linearly with oxygen coverage and is suppressed completely on a p(2 x 1)-O surface (0 o = 0.5). The structure of the Mo ensemble required for the dissociation of CO and H 2 is discussed. The desorption peaks of molecular CO show characteristic changes as a function of oxygen coverage. These observations made it possible to discuss the local environment of the first-layer Mo atoms bonded with CO. The spatial extent and the strength of the electronic modification effect of oxygen adatoms is also discussed. We also found that the Mo(l12) surface undergoes an hydrogen-induced surface reconstruction to form a p(1 x 2) structure. The hydrogen coverage corresponding to the completion of p(1 x 2) has been determined to be 1.5.
Surface Science 281 (1993) 253-269 North-Holland
R H E E D - T R A X S study of superstructures induced by Ge and Sn adsorption on a Si(110) surface Youiti Yamamoto JEOL, LTD., 3-1-2 Musashino, Akishima, Tokyo 196, Japan Received 28 April 1992; accepted for publication 8 October 1992 The Ge/Si(ll0) and Sn/Si(ll0) systems have been studied by RHEED-TRAXS (reflection high-energy electron diffraction-total reflection angle X-ray spectroscopy). In the case of the Ge/Si(ll0) system (10,1) x (3,4) and (2,3) x (2,1) structures, and in the case of the Sn/Si(ll0) system (4,3) x (2,2), (3.0) x 0,3) and (3,3) x (if,l) structures are formed depending on the coverage. Each structure transforms reversibly to the 1 × 1 structure at high temperatures. When Ge adsorbs above ~ 3.5 monolayers, the Ge crystal grows according to the Stranski-Krastanov mode. Two-dimensional phase diagrams are made for each system. For these superstructures the arrangements of adsorbed atoms are discussed on the basis of RHEED-TRAXS, and UPS (ultraviolet photoelectron spectroscopy) results.
Surface Science 281 (1993) 270-284 North-Holland
Photoelectron diffraction and photoelectron holography study of a G e ( l l l ) high-temperature surface phase transition T.T. Tran a, S. Thevuthasan b, y.j. Kim c, D.J. Friedman d, A.P. Kaduwela c G.S. Herman e and C.S. Fadley bx a University of Hawaii, Honolulu, HI 96822, USA b University of California-Davis, Davis, CA 95616, USA c Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA d National Renewable Energy Laboratory, Golden, CO 80401, USA e Naual Research Laboratory, Washington, DC 20375, USA
Chemisorption of CO and H 2 on clean and oxygen-modified Mo(112) Ken-ichi Fukui, Tetsuya Aruga and Yasuhiro Iwasawa Department of Chemistry, Faculty of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan Received 10 April 1992; accepted for publication 2 October 1992 Chemisorption of CO and H 2 on clean and oxygen-modified Mo(112) has been investigated by low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and temperature-programmed desorption (TPD). Oxygen adatoms are expected to be adsorbed in trough sites between close-packed Mo rows and, hence, the first-layer Mo atoms remain accessible to gas-phase molecules. Oxygen adsorption on a clean Mo(l12) surface at 300 K, followed by annealing to 600 K, has produced a series of LEED patterns with increasing oxygen coverage. Models for these structures are presented. These ordered oxygen adlayers are stable up to 1100 K and have been used to examine the effect of oxygen modification on the adsorption and dissociation of CO and H z. Both CO and H 2 molecules are dissociated on clean Mo(112). The amount of dissociated species decreases linearly with oxygen coverage and is suppressed completely on a p(2 x 1)-O surface (0 o = 0.5). The structure of the Mo ensemble required for the dissociation of CO and H 2 is discussed. The desorption peaks of molecular CO show characteristic changes as a function of oxygen coverage. These observations made it possible to discuss the local environment of the first-layer Mo atoms bonded with CO. The spatial extent and the strength of the electronic modification effect of oxygen adatoms is also discussed. We also found that the Mo(l12) surface undergoes an hydrogen-induced surface reconstruction to form a p(1 x 2) structure. The hydrogen coverage corresponding to the completion of p(1 x 2) has been determined to be 1.5.
Surface Science 281 (1993) 253-269 North-Holland
R H E E D - T R A X S study of superstructures induced by Ge and Sn adsorption on a Si(110) surface Youiti Yamamoto JEOL, LTD., 3-1-2 Musashino, Akishima, Tokyo 196, Japan Received 28 April 1992; accepted for publication 8 October 1992 The Ge/Si(ll0) and Sn/Si(ll0) systems have been studied by RHEED-TRAXS (reflection high-energy electron diffraction-total reflection angle X-ray spectroscopy). In the case of the Ge/Si(ll0) system (10,1) x (3,4) and (2,3) x (2,1) structures, and in the case of the Sn/Si(ll0) system (4,3) x (2,2), (3.0) x 0,3) and (3,3) x (if,l) structures are formed depending on the coverage. Each structure transforms reversibly to the 1 × 1 structure at high temperatures. When Ge adsorbs above ~ 3.5 monolayers, the Ge crystal grows according to the Stranski-Krastanov mode. Two-dimensional phase diagrams are made for each system. For these superstructures the arrangements of adsorbed atoms are discussed on the basis of RHEED-TRAXS, and UPS (ultraviolet photoelectron spectroscopy) results.
Surface Science 281 (1993) 270-284 North-Holland
Photoelectron diffraction and photoelectron holography study of a G e ( l l l ) high-temperature surface phase transition T.T. Tran a, S. Thevuthasan b, y.j. Kim c, D.J. Friedman d, A.P. Kaduwela c G.S. Herman e and C.S. Fadley bx a University of Hawaii, Honolulu, HI 96822, USA b University of California-Davis, Davis, CA 95616, USA c Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA d National Renewable Energy Laboratory, Golden, CO 80401, USA e Naual Research Laboratory, Washington, DC 20375, USA