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The decomposition of ammonia on the flat (111) and stepped (557) platinum crystal surfaces
A311 Surface Science 109 (1981) 3 8 1 - 3 8 9 North-Holland Publishing Company
381
THERMAL EFFECTS ON THE WORK FUNCTION OF CESIUM ADLAYERS AND ORDER-DISORDER J.-L. D E S P L A T
TRANSITIONS *
Rasor Associates, Inc., 253 Humboldt Court, Sunnyvale, California 94086, USA Received 19 January 1981;accepted for publication 22 April 1981
The increase in the work function minimum of a C s - O - W ( 1 1 0 ) surface, which occurs when the temperature is raised at constant cesium coverage, is analyzed through a simple new model which introduces the effect of thermal motion of the adatoms on their mutual field depolarization. The effect on the average individual dipole moment is treated through the Topping formulation. A good fit with the data is obtained when parameters determined from work function measurements at 300 K are used. However the derived distance from the cesium core to the image plane may be too small to be compatible with the oxygen-cesium duolayer concept. The model allows definition of a disorder temperature which strongly increases with increased adatom coverage and dipole moment. Good agreement is found when this disorder temperature is compared with existing data on alkaline earth layers on refractory metals.
390
Surface Science 109 (1981) 3 9 0 - 4 1 8 North-Holland Publishing Company
THE DECOMPOSITION OF AMMONIA ON THE FLAT (111) AND STEPPED (557) PLATINUM CRYSTAL SURFACES W.L. G U T H R I E , J.D. S O K O L * a n d G.A. S O M O R J A I
Materials and Molecular Research Division, Lawrence Berkeley Laboratory, and Department of Chemistry, University o f California, Berkeley, California 94720, USA Received 11 December 1980; accepted for publication 13 February 1981 Ammonia adsorption, desorption and decomposition to H 2 and N2 has been studied on the fiat (111) and stepped (557) single crystal faces of platinum using molecular beam surface scattering techniques. Both surfaces show significant adsorption with sticking coefficients on the order of unity. The stepped (357) surface is 16 times more reactive for decomposition of ammonia to N2 and H2 than the fiat (111) surface. Kinetic parameters have been determined for the ammonia desorption process from the Pt(111) surface. The mechanism of ammonia decomposition on the (557) face of platinum has been investigated.
381
THERMAL EFFECTS ON THE WORK FUNCTION OF CESIUM ADLAYERS AND ORDER-DISORDER J.-L. D E S P L A T
TRANSITIONS *
Rasor Associates, Inc., 253 Humboldt Court, Sunnyvale, California 94086, USA Received 19 January 1981;accepted for publication 22 April 1981
The increase in the work function minimum of a C s - O - W ( 1 1 0 ) surface, which occurs when the temperature is raised at constant cesium coverage, is analyzed through a simple new model which introduces the effect of thermal motion of the adatoms on their mutual field depolarization. The effect on the average individual dipole moment is treated through the Topping formulation. A good fit with the data is obtained when parameters determined from work function measurements at 300 K are used. However the derived distance from the cesium core to the image plane may be too small to be compatible with the oxygen-cesium duolayer concept. The model allows definition of a disorder temperature which strongly increases with increased adatom coverage and dipole moment. Good agreement is found when this disorder temperature is compared with existing data on alkaline earth layers on refractory metals.
390
Surface Science 109 (1981) 3 9 0 - 4 1 8 North-Holland Publishing Company
THE DECOMPOSITION OF AMMONIA ON THE FLAT (111) AND STEPPED (557) PLATINUM CRYSTAL SURFACES W.L. G U T H R I E , J.D. S O K O L * a n d G.A. S O M O R J A I
Materials and Molecular Research Division, Lawrence Berkeley Laboratory, and Department of Chemistry, University o f California, Berkeley, California 94720, USA Received 11 December 1980; accepted for publication 13 February 1981 Ammonia adsorption, desorption and decomposition to H 2 and N2 has been studied on the fiat (111) and stepped (557) single crystal faces of platinum using molecular beam surface scattering techniques. Both surfaces show significant adsorption with sticking coefficients on the order of unity. The stepped (357) surface is 16 times more reactive for decomposition of ammonia to N2 and H2 than the fiat (111) surface. Kinetic parameters have been determined for the ammonia desorption process from the Pt(111) surface. The mechanism of ammonia decomposition on the (557) face of platinum has been investigated.