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Adsorption and reaction of bromine with Ag(110)
A79 Surface Science 151 (1985) 251-259 North-Holland, Amsterdam
251
F O R M A T I O N O F N3+ I N P U L S E D - L A S E R S T I M U L A T E D F I E L D DESORPTION OF NITROGEN FROM METAL SURFACES W . L I U * a n d T.T. T S O N G
Physics Department, The Pennsylvania State University, University Park, Pennsylvania 16802, USA Received 30 May 1984; accepted for publication 31 August 1984 in pulsed-laser stimulated field desorption of nitrogen from metal surfaces, a plenty of N f can be detected. Here we present the result of a study of the field dependence and emitter material specificity 01 N3+ formation in pulsed-laser stimulated field desorption, These ions are formed by field ionization of N 3 molecules which are thermally desorbed from their field adsorption states by laser pulse heating of the surface.
260
Surface Science 151 (1985) 260-270 North-Holland, Amsterdam
VIBRATIONAL CHARACTERIZATION OF CARBON MONOXIDE OXIDATION ON THE Pt(lll) SURFACE J o h n L. G L A N D
* a n d E d w a r d B. K O L L I N
*
Physical Chemistry Department, General Motors Research Laboratories, Warren, Michigan 48090, USA Received 27 March 1984; accepted for publication 11 July 1984 The surface reaction between coadsorbed carbon monoxide and atomic oxygen has been characterized using high resolution electron energy loss spectroscopy, coupled with temperature programmed reaction spectroscopy on a Pt(lll) surface characterized using Auger electron spectroscopy and low energy electron diffraction. Preferential oxidation of bridge bonded CO is not observed despite the fact that bridge bonded CO is adsorbed less vigorously than linearly bound CO. Saturation of the Pt(lll) surface with one quarter of a monolayer of atomic oxygen completely suppresses the adsorption of bridge bonded CO. However, substantial coverages of bridge bonded CO can be coadsorbed if the Pt(111) surface is only partially saturated with atomic oxygen. The vibrational data for reaction of coadsorbed CO and atomic oxygen is consistent with a reaction mechanism involving reaction of mobile CO along oxygen island perimeters.
Surface Science 151 (1985) 271-288 North-Holland, Amsterdam ADSORPTION
AND REACTION
Carsten BENNDORF
271 OF BROMINE
WITH Ag(ll0)
and Bernd KRISGER
Department of Physical Chemistry, University of Hamburg, D-2000 Hamburg 13, Fed. Rep. of German)' Received 19 July 1984, accepted for publication 26 October 1984 The adsorption and reaction of Br 2 with Ag(110) was studied with Auger electron spectroscopy,
LEED, work function measurements and thermal desorption spectroscopy in the temperature range of 130-1000 K. Depending on Br coverage and crystal temperature, four different adsorp-
A80 tion and reaction states could be detected. For fractional monolayer coverages, chemisorbed Br(ad) is found to be the most stable species. This adsorption state saturates for 8(Br)~ 0.75. In the chemisorption stage, two LEED patterns, a p(2 x 1) with 0(Br)-= 0.5 and a c(4 x 2) with 0(Br)-= 0.75, were observed. For higher Br 2 exposures and T = 130 K a layer-by-layer growth of AgBr is detected. At higher temperature, T > 1 9 0 K, there is evidence for a transformation from a 2D growth mechanism of AgBr into a 3D agglomeration of larger AgBr cluster. Molecularly adsorbed Br 2 is only detected at low temperature (130 K) on the AgBr corrosion layer.
Surface Science 151 (1985) 289-300 North-Holland, Amsterdam ORIENTATIONAL
ORDER
289 IN CO AND N 2 MONOLAYERS
ON
GRAPHITE S T U D I E D BY X - R A Y D I F F R A C T I O N K. MORISHIGE
*, C . M O W F O R T H
and R.K. THOMAS
**
Physical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ, UK Received 16 July 1984; accepted for publication 30 October 1984 X-ray diffraction has been used to study the structure and orientational phase transitions of CO and N 2 adsorbed on graphite (Papyex). Both form orientationally ordered 2~f3 × 2vf3R30 ° commensurate phases on graphite at low temperatures (10 K). The in-plane herringbone structure of N 2 has been confirmed but CO has more orientational disorder than N 2, which may be associated either with tilting, random static or systematic, of the molecules away from the surface a n d / o r with orientational order of shorter range than the centre of mass order. In the first case the average tilt would have to be about 26 ° and in the second case the orientational correlation length would have to be 200 ,A compared with 450 A for the translational order. The orientational phase transition is sharp for N 2, occurring over the range 27-30 K, in agreement with previous work. For CO the transition is broad and starts at lower temperatures. This and the structural data indicate that a point quadrupolar interaction is not a suitable model for comparing the properties of N~ and CO layers. The orientational phase transition in the incommensurate phase of N 2 is found to be broad and occurs below 20 K. For CO it is sharper than for the commensurate phase and occurs at a higher temperature. The lattice parameter changes by 0.75% across the orientational phase transition. For both N 2 and CO there is evidence of translational disorder in the commensurate phases but it cannot be interpreted quantitatively.
Surface Science 151 (1985) 301-310 North-Holland, Amsterdam THE
PHENOMENON
J. H A B E R ,
T. MACHEJ
OF WE'ITING
301 AT SOLID/SOLID
INTERFACE
and T. CZEPPE
Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Krakbw, Poland Received 20 June 1984; accepted for publication 16 October 1984 When a V205 crystallite is placed on an anatase pellet and heated at 823-923 K, vanadium ions migrate over the surface of anatase grains enveloping them in a thin overlayer. XPS, X-ray and EPR studies show that at 823 K a very thin layer is formed, its properties being strongly modified by interaction with the anatase support. At 923 K, on top of this inner layer an outer layer migrates, whose properties are similar to V205. As in the same conditions no migration is observed on rutile, it is concluded that this phenomenon is a manifestation of wetting of one oxide by another oxide, the difference in the surface free energy being the driving force of the migration.
251
F O R M A T I O N O F N3+ I N P U L S E D - L A S E R S T I M U L A T E D F I E L D DESORPTION OF NITROGEN FROM METAL SURFACES W . L I U * a n d T.T. T S O N G
Physics Department, The Pennsylvania State University, University Park, Pennsylvania 16802, USA Received 30 May 1984; accepted for publication 31 August 1984 in pulsed-laser stimulated field desorption of nitrogen from metal surfaces, a plenty of N f can be detected. Here we present the result of a study of the field dependence and emitter material specificity 01 N3+ formation in pulsed-laser stimulated field desorption, These ions are formed by field ionization of N 3 molecules which are thermally desorbed from their field adsorption states by laser pulse heating of the surface.
260
Surface Science 151 (1985) 260-270 North-Holland, Amsterdam
VIBRATIONAL CHARACTERIZATION OF CARBON MONOXIDE OXIDATION ON THE Pt(lll) SURFACE J o h n L. G L A N D
* a n d E d w a r d B. K O L L I N
*
Physical Chemistry Department, General Motors Research Laboratories, Warren, Michigan 48090, USA Received 27 March 1984; accepted for publication 11 July 1984 The surface reaction between coadsorbed carbon monoxide and atomic oxygen has been characterized using high resolution electron energy loss spectroscopy, coupled with temperature programmed reaction spectroscopy on a Pt(lll) surface characterized using Auger electron spectroscopy and low energy electron diffraction. Preferential oxidation of bridge bonded CO is not observed despite the fact that bridge bonded CO is adsorbed less vigorously than linearly bound CO. Saturation of the Pt(lll) surface with one quarter of a monolayer of atomic oxygen completely suppresses the adsorption of bridge bonded CO. However, substantial coverages of bridge bonded CO can be coadsorbed if the Pt(111) surface is only partially saturated with atomic oxygen. The vibrational data for reaction of coadsorbed CO and atomic oxygen is consistent with a reaction mechanism involving reaction of mobile CO along oxygen island perimeters.
Surface Science 151 (1985) 271-288 North-Holland, Amsterdam ADSORPTION
AND REACTION
Carsten BENNDORF
271 OF BROMINE
WITH Ag(ll0)
and Bernd KRISGER
Department of Physical Chemistry, University of Hamburg, D-2000 Hamburg 13, Fed. Rep. of German)' Received 19 July 1984, accepted for publication 26 October 1984 The adsorption and reaction of Br 2 with Ag(110) was studied with Auger electron spectroscopy,
LEED, work function measurements and thermal desorption spectroscopy in the temperature range of 130-1000 K. Depending on Br coverage and crystal temperature, four different adsorp-
A80 tion and reaction states could be detected. For fractional monolayer coverages, chemisorbed Br(ad) is found to be the most stable species. This adsorption state saturates for 8(Br)~ 0.75. In the chemisorption stage, two LEED patterns, a p(2 x 1) with 0(Br)-= 0.5 and a c(4 x 2) with 0(Br)-= 0.75, were observed. For higher Br 2 exposures and T = 130 K a layer-by-layer growth of AgBr is detected. At higher temperature, T > 1 9 0 K, there is evidence for a transformation from a 2D growth mechanism of AgBr into a 3D agglomeration of larger AgBr cluster. Molecularly adsorbed Br 2 is only detected at low temperature (130 K) on the AgBr corrosion layer.
Surface Science 151 (1985) 289-300 North-Holland, Amsterdam ORIENTATIONAL
ORDER
289 IN CO AND N 2 MONOLAYERS
ON
GRAPHITE S T U D I E D BY X - R A Y D I F F R A C T I O N K. MORISHIGE
*, C . M O W F O R T H
and R.K. THOMAS
**
Physical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ, UK Received 16 July 1984; accepted for publication 30 October 1984 X-ray diffraction has been used to study the structure and orientational phase transitions of CO and N 2 adsorbed on graphite (Papyex). Both form orientationally ordered 2~f3 × 2vf3R30 ° commensurate phases on graphite at low temperatures (10 K). The in-plane herringbone structure of N 2 has been confirmed but CO has more orientational disorder than N 2, which may be associated either with tilting, random static or systematic, of the molecules away from the surface a n d / o r with orientational order of shorter range than the centre of mass order. In the first case the average tilt would have to be about 26 ° and in the second case the orientational correlation length would have to be 200 ,A compared with 450 A for the translational order. The orientational phase transition is sharp for N 2, occurring over the range 27-30 K, in agreement with previous work. For CO the transition is broad and starts at lower temperatures. This and the structural data indicate that a point quadrupolar interaction is not a suitable model for comparing the properties of N~ and CO layers. The orientational phase transition in the incommensurate phase of N 2 is found to be broad and occurs below 20 K. For CO it is sharper than for the commensurate phase and occurs at a higher temperature. The lattice parameter changes by 0.75% across the orientational phase transition. For both N 2 and CO there is evidence of translational disorder in the commensurate phases but it cannot be interpreted quantitatively.
Surface Science 151 (1985) 301-310 North-Holland, Amsterdam THE
PHENOMENON
J. H A B E R ,
T. MACHEJ
OF WE'ITING
301 AT SOLID/SOLID
INTERFACE
and T. CZEPPE
Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Krakbw, Poland Received 20 June 1984; accepted for publication 16 October 1984 When a V205 crystallite is placed on an anatase pellet and heated at 823-923 K, vanadium ions migrate over the surface of anatase grains enveloping them in a thin overlayer. XPS, X-ray and EPR studies show that at 823 K a very thin layer is formed, its properties being strongly modified by interaction with the anatase support. At 923 K, on top of this inner layer an outer layer migrates, whose properties are similar to V205. As in the same conditions no migration is observed on rutile, it is concluded that this phenomenon is a manifestation of wetting of one oxide by another oxide, the difference in the surface free energy being the driving force of the migration.