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HREELS, ARUPS and XPS of pyridine on Ni(110)
A133 Surface Science 245 (1991) 1-11 North-Holland
HREELS, ARUPS and XPS of pyridine on Ni(110) M.R. Cohen Nuclear Materials Technology Division, Los Alamos National Laboratory, Los Alamos, N M 87544, USA
and R.P. Merrill School of Chemical Engineering, Cornell University, Ithaca, N Y 14853, USA Received 14 May 1990; accepted for publication 1 August 1990 High-resolution electron energy loss spectroscopy, X-ray photoelectron spectroscopy and angular-resolved UV photoemission are applied to investigate the adsorption of pyridine on Ni(ll0). At low temperature, changes in the intensity of in-plane versus out-of-plane vibrational modes show a change in the surface orientation of the molecule as a function of coverage. T h e molecular plane is parallel to the surface at low coverages, indicating bonding through the ~r molecular orbitals. At high coverages the molecular plane tilts toward normal with respect to the surface. This interpretation is consistent with A R U P ~ observations at normal emission. Heating results in desorption of weakly adsorbed pyridine at 180 K, with chemisorbed pyridine remaining in its low temperature orientation through room temperature. Decomposition occurs by 520 K, where the C - C and C - H stretching modes and the C - H deformation modes which are observed are uncharacteristic of molecular pyridine.
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Surface Science 245 (1991) 12-16 North-Holland
Metal-metal epitaxy on germanium near room temperatures: Ni(100)/Cu(100)/Ge(100) Chin-An Chang I B M T.J. Watson Research Center, Yorktown Heights, N Y 10598, USA Received 1 August 1990; accepted for publication 26 October 1990 • (100) Cfi films have been deposited on (100) Ge using electron-beam evaporation without intentional heating of the substrates, similar to the work using (100) Si substrates. Further deposition of Ni on the (100) Cu retains the (100) growth of Ni also, thus allowing metal-metal epitaxy on germanium. The thermal stability of the (100) N i / C u / G e ( 1 0 0 ) is studied, and compared with that of the (100) Ni/Cu/Si(lO0). The C u - G e reaction starts around 150 o C, lower than the C u - S i one. The N i - G e reaction is observed between 200 and 250 ° C , also at temperatures lower than that of Ni-Si. The Cu (100) lattice is found to rotate by 45 o around its (001) axis relative to the Ge (100) plane. This is shown to be needed for such an epitaxial growth to occur, similar to that observed for the (100) C u / S i structure. The possible fabrication of both the metallic and device structures on a G a A s substrate is discussed, using the Ge layer epitaxially grown on G a A s for the metal growth.
Surface Science 245 (1991) 17-28 North-Holland
Theory of thermal desorption of light noble gases from metals: application to Ne-Cu(111) G.P. Brivio Dipartimento di Fisica, Universit~ di Milano, via Celoria 16, 20133 Milano, Italy
T.B. Grimley The Donnan Laboratories, University of Liverpool, Liverpool L69 3BX, UK
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HREELS, ARUPS and XPS of pyridine on Ni(110) M.R. Cohen Nuclear Materials Technology Division, Los Alamos National Laboratory, Los Alamos, N M 87544, USA
and R.P. Merrill School of Chemical Engineering, Cornell University, Ithaca, N Y 14853, USA Received 14 May 1990; accepted for publication 1 August 1990 High-resolution electron energy loss spectroscopy, X-ray photoelectron spectroscopy and angular-resolved UV photoemission are applied to investigate the adsorption of pyridine on Ni(ll0). At low temperature, changes in the intensity of in-plane versus out-of-plane vibrational modes show a change in the surface orientation of the molecule as a function of coverage. T h e molecular plane is parallel to the surface at low coverages, indicating bonding through the ~r molecular orbitals. At high coverages the molecular plane tilts toward normal with respect to the surface. This interpretation is consistent with A R U P ~ observations at normal emission. Heating results in desorption of weakly adsorbed pyridine at 180 K, with chemisorbed pyridine remaining in its low temperature orientation through room temperature. Decomposition occurs by 520 K, where the C - C and C - H stretching modes and the C - H deformation modes which are observed are uncharacteristic of molecular pyridine.
12
Surface Science 245 (1991) 12-16 North-Holland
Metal-metal epitaxy on germanium near room temperatures: Ni(100)/Cu(100)/Ge(100) Chin-An Chang I B M T.J. Watson Research Center, Yorktown Heights, N Y 10598, USA Received 1 August 1990; accepted for publication 26 October 1990 • (100) Cfi films have been deposited on (100) Ge using electron-beam evaporation without intentional heating of the substrates, similar to the work using (100) Si substrates. Further deposition of Ni on the (100) Cu retains the (100) growth of Ni also, thus allowing metal-metal epitaxy on germanium. The thermal stability of the (100) N i / C u / G e ( 1 0 0 ) is studied, and compared with that of the (100) Ni/Cu/Si(lO0). The C u - G e reaction starts around 150 o C, lower than the C u - S i one. The N i - G e reaction is observed between 200 and 250 ° C , also at temperatures lower than that of Ni-Si. The Cu (100) lattice is found to rotate by 45 o around its (001) axis relative to the Ge (100) plane. This is shown to be needed for such an epitaxial growth to occur, similar to that observed for the (100) C u / S i structure. The possible fabrication of both the metallic and device structures on a G a A s substrate is discussed, using the Ge layer epitaxially grown on G a A s for the metal growth.
Surface Science 245 (1991) 17-28 North-Holland
Theory of thermal desorption of light noble gases from metals: application to Ne-Cu(111) G.P. Brivio Dipartimento di Fisica, Universit~ di Milano, via Celoria 16, 20133 Milano, Italy
T.B. Grimley The Donnan Laboratories, University of Liverpool, Liverpool L69 3BX, UK
17