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A SIMS study of nickel deposition on TiO2(100)
194
Surface Science 249 ~1991 ) 194- 198 Nor t.,-nolland h ,,
A SIMS study of nickel deposition on TiO2(100) Influence of the stoichiometry of the support S. Bourgeois, F. Jomard and M. Perdereau Facult~ des Sciences Mirande, Laboratoire de Recherches sur la Rdactivit~ des Solides, B.P. 138, 21004 Dijon Cedex, France Received 1 October 1990; accepted for publication 18 December 1990 Nickel deposition on a clean TiO2(100 ) surface was studied mainly by secondary ion mass spectrometry (SIMS). Different kinds of supports exhibiting a more or~less high deviation from stoichiometry were used. For a quasi-stoichiometric support a layer-by-layer growth of 2 or 3 nickel laye~:s is obtained followed by a nucleation stage. For a non-stoichiometric support nickel is found to diffuse into the bulk TiO 2 even at room temperature. The influence of temperature on this diffusion was also studied.
Surface Science 249 (1991) 199-212 North-Holland
199
An ab initio study of H chemisorption on Li clusters in fcc (110) and fcc (111) symmetries A.S. Hira and A.K. Ray Department of Physics, The University of Texas at Arlington, P.O. Box 19059, Arlington, TX 76019, USA Received 13 July 1990; accepted for publication 20 December 1990 M a n y body perturbation theory has been applied to investigate the properties of lithium clusters which model the fcc (110) and (111) surfaces of the crystal lattice. Hydrogen interaction with these clusters has been investigated in detail by considering different approach positions of the hydrogen atoms. Comparison with previous results on Li,, clusters in bcc (100), (110) and ( 1 t l ) , and fcc (100) symmetries and H - L i , systems reveal important differences as well as some points of agreement. Relative stabilities from the points of view of cohesive energies for bare clusters and chemisorption energies for h y d r o g e n - l i t h i u m systems have been discussed in terms of factors such as cluster compactness and the presence of nearest neighbor Li atoms. Charge transfer and p-occupancy effects for the various H - L i . systems have been studied in detail.
Surface Science 249 (1991) 213 222 North-Holland
213
Interactions in the Fe/TiO2(ll0) system * Junzhuo Deng, Dezheng Wang, Xuming Wei, Runsheng Zhai and Hongli Wang Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, People's Republic of China Received 3 July 1990; accepted for publication 8 January 1991 Fe deposited on TiO2(ll0 ) has been studied using AES, LEED, ISS, UPS and HREELS. The deposited Fe overlayer is found to grow in a layer-by-layer mode. Oxygen migrates from the subsurface layers of TiO2(ll0) to the deposited Fe during the deposition process. The chemical species of the deposited Fe depends on the state of oxidation of TiO2(l10) and the a m o u n t of Fe deposition. The state of the adsorbed CO in this system is found to depend remarkably on the amount of Fe deposited on the TiO2(l10) substrate. CO is found to adsorb weakly on a low Fe coverage system of 0.2 ML F e / T i O 2 ( l l 0 ), while it is strongly chemisorbed on a high Fe coverage system of 1.7 ML F e / T i O 2 ( l l 0 ) . Difference in the CO chemisorption behavior is attributed to the different structural characteristics of these two states of the Fe/TiO2(110) system.
Surface Science 249 ~1991 ) 194- 198 Nor t.,-nolland h ,,
A SIMS study of nickel deposition on TiO2(100) Influence of the stoichiometry of the support S. Bourgeois, F. Jomard and M. Perdereau Facult~ des Sciences Mirande, Laboratoire de Recherches sur la Rdactivit~ des Solides, B.P. 138, 21004 Dijon Cedex, France Received 1 October 1990; accepted for publication 18 December 1990 Nickel deposition on a clean TiO2(100 ) surface was studied mainly by secondary ion mass spectrometry (SIMS). Different kinds of supports exhibiting a more or~less high deviation from stoichiometry were used. For a quasi-stoichiometric support a layer-by-layer growth of 2 or 3 nickel laye~:s is obtained followed by a nucleation stage. For a non-stoichiometric support nickel is found to diffuse into the bulk TiO 2 even at room temperature. The influence of temperature on this diffusion was also studied.
Surface Science 249 (1991) 199-212 North-Holland
199
An ab initio study of H chemisorption on Li clusters in fcc (110) and fcc (111) symmetries A.S. Hira and A.K. Ray Department of Physics, The University of Texas at Arlington, P.O. Box 19059, Arlington, TX 76019, USA Received 13 July 1990; accepted for publication 20 December 1990 M a n y body perturbation theory has been applied to investigate the properties of lithium clusters which model the fcc (110) and (111) surfaces of the crystal lattice. Hydrogen interaction with these clusters has been investigated in detail by considering different approach positions of the hydrogen atoms. Comparison with previous results on Li,, clusters in bcc (100), (110) and ( 1 t l ) , and fcc (100) symmetries and H - L i , systems reveal important differences as well as some points of agreement. Relative stabilities from the points of view of cohesive energies for bare clusters and chemisorption energies for h y d r o g e n - l i t h i u m systems have been discussed in terms of factors such as cluster compactness and the presence of nearest neighbor Li atoms. Charge transfer and p-occupancy effects for the various H - L i . systems have been studied in detail.
Surface Science 249 (1991) 213 222 North-Holland
213
Interactions in the Fe/TiO2(ll0) system * Junzhuo Deng, Dezheng Wang, Xuming Wei, Runsheng Zhai and Hongli Wang Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, People's Republic of China Received 3 July 1990; accepted for publication 8 January 1991 Fe deposited on TiO2(ll0 ) has been studied using AES, LEED, ISS, UPS and HREELS. The deposited Fe overlayer is found to grow in a layer-by-layer mode. Oxygen migrates from the subsurface layers of TiO2(ll0) to the deposited Fe during the deposition process. The chemical species of the deposited Fe depends on the state of oxidation of TiO2(l10) and the a m o u n t of Fe deposition. The state of the adsorbed CO in this system is found to depend remarkably on the amount of Fe deposited on the TiO2(l10) substrate. CO is found to adsorb weakly on a low Fe coverage system of 0.2 ML F e / T i O 2 ( l l 0 ), while it is strongly chemisorbed on a high Fe coverage system of 1.7 ML F e / T i O 2 ( l l 0 ) . Difference in the CO chemisorption behavior is attributed to the different structural characteristics of these two states of the Fe/TiO2(110) system.