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Hydrogen chemisorption on Pt single crystal surfaces in acidic solutions
A15 Surface Science 102 (1981) 4 4 3 - 4 6 2 © North-Holland Publishing Company MOLECULAR ORBITAL STUDY OF NITROGEN CHEMISORPTION ON TANTALUM (100) AND (110) SURFACES Yoji ISSHIKI
Tokyo Metropolytan Industrial Technical Institute, Nishigaoka, Kita-ku, Tokyo 115, Japan and N. H I R A S H I T A , T. O G U C H I , G. Y O K O Y A M A , H. Y A M A Z A K I , T. K A M B A R A a n d K.I. G O N D A 1 R A
The University of Electro-Communications, Chofu, Tokyo 182, Japan Received 16 April 1980; accepted for publication 17 June 1980 The electronic structures and binding energies of a nitrogen atom adsorbed at three symmetry sites on the Ta(100) and (110) surfaces are obtained by means of the extended H/ickel molecular orbital method. The Ta surfaces are represented by finite arrays of Ta atoms and the repulsive energy between nitrogen and Ta is calculated by using Anderson's approximation [A.B. Anderson and R. Hoffmann, J. Chem. Phys. 60 (1974) 4217]. The most stable site for nitrogen adsorption is found to be the five coordination number site for the (100) surface and the two coordination number site for the (110) surface. The calculated binding energies for the most stable sites are close to the value evaluated from the observed chemisorption heat. The difference in the binding energy between the adsorption sites on the (110) surface is fairly small as compared with the difference on the (100) surface. The charge of adsorbed nitrogen and the equilibrium bond distance between adatom and the nearest neighbor Ta atom do not vary sensitively with adsorption site: the charge is about -0.25 lel and the bond distance is about 3.1 A.
Surface Science 102 (1981) 4 6 3 - 4 8 5 © North-Holland Publishing Company H Y D R O G E N C H E M I S O R P T I O N O N Pt S I N G L E C R Y S T A L S U R F A C E S IN A C I D I C S O L U T I O N S Philip N. R O S S , Jr.
Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720, USA Received 29 April 1980; accepted for publication 15 August 1980
Hydrogen chemisorption from dilute acidic solution onto Pt single crystal surfaces was examined using an electrochemical cell directly coupled to LEED/Auger analytical system. No pre-anodization was used prior to observing hydrogen adsorption by cyclic voltammetry so that clean surfaces having the ordered structures indicated by LEED were studied. The problem of contributions from non-ordered parts of the electrode like support wires and edges was solved by using a gold evaporation masking technique. The specific contribution of atomic imperfections to the voltammetry curve was deduced from the ordered and countable imperfections occurring on high Miller index single crystal surfaces that have a stepped structure. The H - P t bond energy was found to be structure sensitive, and sensitive both to local site geometry and long range order in the surface. The bond strength was found to vary systematically: n(111) × (100) > (100) > n ( l l l ) X (111) > (110) > (111). Distinct states for hydrogen at steps versus hydrogen on terraces could be distinguished. The (110) surface is shown to be a (111)vicinal,
A16 probably the [3(111) × 2(111)] microfacetted surface. The zero coverage heat of adsorption on the well-ordered (111) surface (48 kJ/mol) in solutions is the same as the value reported by Ertl and co-workers for adsorption on a (111) surface in vacuum. Adsorption isotherms for hydrogen on the (111) and (100) surfaces are adequately fit by the classical model for immobile adsorption at single sites with nearest neighbor repulsive interaction.
Surface Science 102 (1981) 486-505 © North-Holland Publishing Company ATOMIC, M O L E C U L A R , A N D C O N T I N U U M R A D I A T I O N F R O M
ION-BOMBARDED B AND B20 3 R. K E L L Y * IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598, USA S. D Z I O B A * Bell Northern Research, Ottawa, Ontario, K1 Y 4H7, Canada and N.H. T O L K and J.C. T U L L Y Bell Laboratories, Murray Hill, New Jersey 07974, USA Received 23 April 1980; accepted for publication 11 August 1980
Inert-gas ion impact on elemental boron and B203 in the presence of hydrogen or oxygen containing gases results in a rich variety of atomic, molecular, and "continuum" optical emission. In the presence of gaseous O2, some 20 different features due to OII are observed with elemental B. These are the first oxygen photon signals in the visible reported in a sputtering experiment. Independent of the gas present, B203 yields unresolved radiation ("continuum"), the latter coinciding with the general region of the A2FI --+ X2E ÷ system of BO. Bombardment of elemental B in the presence of gaseous H 2 or CH 4 leads to emission from the AIFI ~ X1E ÷ system of BH. The BH molecule can be characterized in terms of an effective rotational "temperature" (2700-3800 K), a kinetic-energy threshold (12 20 eV), and a saturation-type dependence of the signal on the beam current. Radiation from the BH molecule was observed to be surprisingly intense. We note that the emitting A1H state correlates adiabatically with groundstate B and H atoms. It is hypothesized that this may play a major role in the mechanism of ion-bombardment-induced creation of molecular excited species.
Surface Science 102 (1981) 506-517 © North-Holland Publishing Company
THE ADSORPTION OF WATER ON THE RECONSTRUCTED Ir(110)-(1 × 2) S U R F A C E * T.S. WITTRIG **, D.E. IBBOTSON and W.H. W E I N B E R G * * * Division oi" Chemistry and Chemical Engineering, Pasadena, California 91125, USA Received 12 June 1980; accepted for publication 11 August 1980 The interaction of water with the reconstructed Ir(110)-(1 × 2) surface has been studied with LEED, CPD, XPS and thermal desorption mass spectrometry. It is shown that at most, 6% of the adsorbed water dissociates upon adsorption at a temperature of 130 K. Water does dissociate to OH groups when adsorbed on an lr(110)-(1 × 2) surface with preadsorbed oxygen.
Tokyo Metropolytan Industrial Technical Institute, Nishigaoka, Kita-ku, Tokyo 115, Japan and N. H I R A S H I T A , T. O G U C H I , G. Y O K O Y A M A , H. Y A M A Z A K I , T. K A M B A R A a n d K.I. G O N D A 1 R A
The University of Electro-Communications, Chofu, Tokyo 182, Japan Received 16 April 1980; accepted for publication 17 June 1980 The electronic structures and binding energies of a nitrogen atom adsorbed at three symmetry sites on the Ta(100) and (110) surfaces are obtained by means of the extended H/ickel molecular orbital method. The Ta surfaces are represented by finite arrays of Ta atoms and the repulsive energy between nitrogen and Ta is calculated by using Anderson's approximation [A.B. Anderson and R. Hoffmann, J. Chem. Phys. 60 (1974) 4217]. The most stable site for nitrogen adsorption is found to be the five coordination number site for the (100) surface and the two coordination number site for the (110) surface. The calculated binding energies for the most stable sites are close to the value evaluated from the observed chemisorption heat. The difference in the binding energy between the adsorption sites on the (110) surface is fairly small as compared with the difference on the (100) surface. The charge of adsorbed nitrogen and the equilibrium bond distance between adatom and the nearest neighbor Ta atom do not vary sensitively with adsorption site: the charge is about -0.25 lel and the bond distance is about 3.1 A.
Surface Science 102 (1981) 4 6 3 - 4 8 5 © North-Holland Publishing Company H Y D R O G E N C H E M I S O R P T I O N O N Pt S I N G L E C R Y S T A L S U R F A C E S IN A C I D I C S O L U T I O N S Philip N. R O S S , Jr.
Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720, USA Received 29 April 1980; accepted for publication 15 August 1980
Hydrogen chemisorption from dilute acidic solution onto Pt single crystal surfaces was examined using an electrochemical cell directly coupled to LEED/Auger analytical system. No pre-anodization was used prior to observing hydrogen adsorption by cyclic voltammetry so that clean surfaces having the ordered structures indicated by LEED were studied. The problem of contributions from non-ordered parts of the electrode like support wires and edges was solved by using a gold evaporation masking technique. The specific contribution of atomic imperfections to the voltammetry curve was deduced from the ordered and countable imperfections occurring on high Miller index single crystal surfaces that have a stepped structure. The H - P t bond energy was found to be structure sensitive, and sensitive both to local site geometry and long range order in the surface. The bond strength was found to vary systematically: n(111) × (100) > (100) > n ( l l l ) X (111) > (110) > (111). Distinct states for hydrogen at steps versus hydrogen on terraces could be distinguished. The (110) surface is shown to be a (111)vicinal,
A16 probably the [3(111) × 2(111)] microfacetted surface. The zero coverage heat of adsorption on the well-ordered (111) surface (48 kJ/mol) in solutions is the same as the value reported by Ertl and co-workers for adsorption on a (111) surface in vacuum. Adsorption isotherms for hydrogen on the (111) and (100) surfaces are adequately fit by the classical model for immobile adsorption at single sites with nearest neighbor repulsive interaction.
Surface Science 102 (1981) 486-505 © North-Holland Publishing Company ATOMIC, M O L E C U L A R , A N D C O N T I N U U M R A D I A T I O N F R O M
ION-BOMBARDED B AND B20 3 R. K E L L Y * IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598, USA S. D Z I O B A * Bell Northern Research, Ottawa, Ontario, K1 Y 4H7, Canada and N.H. T O L K and J.C. T U L L Y Bell Laboratories, Murray Hill, New Jersey 07974, USA Received 23 April 1980; accepted for publication 11 August 1980
Inert-gas ion impact on elemental boron and B203 in the presence of hydrogen or oxygen containing gases results in a rich variety of atomic, molecular, and "continuum" optical emission. In the presence of gaseous O2, some 20 different features due to OII are observed with elemental B. These are the first oxygen photon signals in the visible reported in a sputtering experiment. Independent of the gas present, B203 yields unresolved radiation ("continuum"), the latter coinciding with the general region of the A2FI --+ X2E ÷ system of BO. Bombardment of elemental B in the presence of gaseous H 2 or CH 4 leads to emission from the AIFI ~ X1E ÷ system of BH. The BH molecule can be characterized in terms of an effective rotational "temperature" (2700-3800 K), a kinetic-energy threshold (12 20 eV), and a saturation-type dependence of the signal on the beam current. Radiation from the BH molecule was observed to be surprisingly intense. We note that the emitting A1H state correlates adiabatically with groundstate B and H atoms. It is hypothesized that this may play a major role in the mechanism of ion-bombardment-induced creation of molecular excited species.
Surface Science 102 (1981) 506-517 © North-Holland Publishing Company
THE ADSORPTION OF WATER ON THE RECONSTRUCTED Ir(110)-(1 × 2) S U R F A C E * T.S. WITTRIG **, D.E. IBBOTSON and W.H. W E I N B E R G * * * Division oi" Chemistry and Chemical Engineering, Pasadena, California 91125, USA Received 12 June 1980; accepted for publication 11 August 1980 The interaction of water with the reconstructed Ir(110)-(1 × 2) surface has been studied with LEED, CPD, XPS and thermal desorption mass spectrometry. It is shown that at most, 6% of the adsorbed water dissociates upon adsorption at a temperature of 130 K. Water does dissociate to OH groups when adsorbed on an lr(110)-(1 × 2) surface with preadsorbed oxygen.