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Scattering of helium atoms by surfaces at low energies and temperatures
A305 LEED. Surface electronic state spectra appeared to have filled (donor) and empty (acceptor) surface bands separated by the gap. The biggest changes of characteristics mentioned were observed at transitions to the (2 × 1) structure. Energy diagrams are drawn for electron spectra at (4 x 5), (2 × 1) and (5 × 1) surface lattices. Some suggestions are made on the physical reasons of structural phase transitions and on geometrical models of the Si(110) surface structures.
Surface Science 171 (1986) 501-514 North-Holland, Amsterdam
501
INITIAL STAGES OF I R I D I U M - S E M I C O N D U C T O R C O M P O U N D F O R M A T I O N A N D THE INTERFACE ATOMIC STRUCTURES: A FIELD ION M I C R O S C O P E S T U D Y H.F. LIU, H.M. LIU * and T.T. T S O N G Plzvsics Department, The Pennsvlt,ania State Unit,ersity, Unicersi O, Park, Pennsvh,ania 16802, USA Received 16 October 1985; accepted for publication 7 January 1986 The early stages of formation of thin layers of IrSi and IrGe on clean Ir surfaces and the interface atomic structures have been studied in the field ion microscope. Distinctive stages of growth of Ir-silicide have been observed. In the earliest stage, two atomic layers of silicide are formed on the lr(001) plane. Atomically resolved images show a structure resembling the C(2 × 2) overlayer structure of the substrate, which we believe to have the (011) Ir-layer structure of the (011) plane of IrSi crystal. In the second stage, the (2 x 1) image structure observed on the It(011) is identified to be the It-layer of the lrSi(001) fundamental planes. Formation of IrGe on the lr(001) is similar to the earliest stage of silicide formation. We believe that the ordered interface atomic structures we have observed with the FIM should also be observable at flat interfaces with conventional techniques.
Surface Science 171 (1986) 515 526 North-Holland, Amsterdam
SCATI'ERING OF HELIUM A T O M S BY S U R F A C E S AT LOW ENERGIES A N D T E M P E R A T U R E S Frank O. G O O D M A N Department of Applied Mathematics" and Department of Pl~vsics, Unicersity of Waterloo, Waterloo, Ontario, Canada N2L 3GI
Nicolas G A R C I A Departamento de Fisica Fundamental, Unit,ersidad Autonoma de Madrid, Canto Blanco, 28049-Madrid, Spain
and
515
A306 Jesus REYES and Jesus GARCIA-FERNANDEZ
Departamento de Fisica, Universidad Autonoma de Puebla, Apartado Postal J-48, Puebla, Puebla, Mexico Received 30 July 1985; accepted for publication 14 January 1986 It is well known that the existing calculations for helium scattering by solid surfaces, made on the first-order distorted-wave Born approximation, within the one-phonon approximation, disagree qualitatively with experiment at low energies and temperatures. Generally, the calculations give sticking probabilities which are too low and which have the wrong trend with incident energy; further, the calculations are incorrect in the limit of zero incident energy. We investigate whether those calculations may be modified in order to correct them and to help them agree better with experiment. The modifications we make are, essentially, the introduction of reflection coefficients and the consideration of surface excitations (modes) different from those considered before.
Surface Science 171 (1986) 527-542 North-Holland, Amsterdam THE EFFECT ON PI(IlI) *
OF OXYGEN
Sohail AKHTER
527 ISLANDING
ON CO AND H 2 OXIDATION
and J.M. WHITE
Department of Chemistry, University of Texas, Austin, Texas 78712, USA Received 23 August 1985; accepted for publication 27 November 1985 A Pt(lll) surface partially covered with 160 islands was postdosed with 1802 to increase the island size under conditions where oxygen atom mobility is limited. Subsequently, these islands were titrated with CO and H 2. Preferential production of species containing 180 was not observed during any stage of the reaction. Assuming there is no extensive mixing of 160 and 180 isotopes within the islands, the results indicate no preferential reaction at island perimeters. The data are consistent with a model in which reaction proceeds uniformly over the whole island but the concentration of the mobile species (CO, H) inside the island is controlled by the island structure. This model qualitatively accounts for several apparent rate anomalies reported for CO and H 2 oxidation.
Surface Science 171 (1986) 543-554 North-Holland, Amsterdam COMPOSITION SURFACE
AND DYNAMICAL
OF SINGLE
CRYSTALS
543 CHARACTERISTICS
OF THE
F e N i 3 (100), (110), (111)
M . A . V A S I L I E V a n d S.D. G O R O D E T S K Y
Institute of Metal Physics, Academy of Sciences, UkrSSR, Kiev-142, USSR Received 14 August 1985; accepted for publication 12 November 1985 Surface segregation as a function of sample temperature has been investigated using AES for the (111), (100) and (110) faces of FeNi 3 single crystal. The surface layer composition is shown to
Surface Science 171 (1986) 501-514 North-Holland, Amsterdam
501
INITIAL STAGES OF I R I D I U M - S E M I C O N D U C T O R C O M P O U N D F O R M A T I O N A N D THE INTERFACE ATOMIC STRUCTURES: A FIELD ION M I C R O S C O P E S T U D Y H.F. LIU, H.M. LIU * and T.T. T S O N G Plzvsics Department, The Pennsvlt,ania State Unit,ersity, Unicersi O, Park, Pennsvh,ania 16802, USA Received 16 October 1985; accepted for publication 7 January 1986 The early stages of formation of thin layers of IrSi and IrGe on clean Ir surfaces and the interface atomic structures have been studied in the field ion microscope. Distinctive stages of growth of Ir-silicide have been observed. In the earliest stage, two atomic layers of silicide are formed on the lr(001) plane. Atomically resolved images show a structure resembling the C(2 × 2) overlayer structure of the substrate, which we believe to have the (011) Ir-layer structure of the (011) plane of IrSi crystal. In the second stage, the (2 x 1) image structure observed on the It(011) is identified to be the It-layer of the lrSi(001) fundamental planes. Formation of IrGe on the lr(001) is similar to the earliest stage of silicide formation. We believe that the ordered interface atomic structures we have observed with the FIM should also be observable at flat interfaces with conventional techniques.
Surface Science 171 (1986) 515 526 North-Holland, Amsterdam
SCATI'ERING OF HELIUM A T O M S BY S U R F A C E S AT LOW ENERGIES A N D T E M P E R A T U R E S Frank O. G O O D M A N Department of Applied Mathematics" and Department of Pl~vsics, Unicersity of Waterloo, Waterloo, Ontario, Canada N2L 3GI
Nicolas G A R C I A Departamento de Fisica Fundamental, Unit,ersidad Autonoma de Madrid, Canto Blanco, 28049-Madrid, Spain
and
515
A306 Jesus REYES and Jesus GARCIA-FERNANDEZ
Departamento de Fisica, Universidad Autonoma de Puebla, Apartado Postal J-48, Puebla, Puebla, Mexico Received 30 July 1985; accepted for publication 14 January 1986 It is well known that the existing calculations for helium scattering by solid surfaces, made on the first-order distorted-wave Born approximation, within the one-phonon approximation, disagree qualitatively with experiment at low energies and temperatures. Generally, the calculations give sticking probabilities which are too low and which have the wrong trend with incident energy; further, the calculations are incorrect in the limit of zero incident energy. We investigate whether those calculations may be modified in order to correct them and to help them agree better with experiment. The modifications we make are, essentially, the introduction of reflection coefficients and the consideration of surface excitations (modes) different from those considered before.
Surface Science 171 (1986) 527-542 North-Holland, Amsterdam THE EFFECT ON PI(IlI) *
OF OXYGEN
Sohail AKHTER
527 ISLANDING
ON CO AND H 2 OXIDATION
and J.M. WHITE
Department of Chemistry, University of Texas, Austin, Texas 78712, USA Received 23 August 1985; accepted for publication 27 November 1985 A Pt(lll) surface partially covered with 160 islands was postdosed with 1802 to increase the island size under conditions where oxygen atom mobility is limited. Subsequently, these islands were titrated with CO and H 2. Preferential production of species containing 180 was not observed during any stage of the reaction. Assuming there is no extensive mixing of 160 and 180 isotopes within the islands, the results indicate no preferential reaction at island perimeters. The data are consistent with a model in which reaction proceeds uniformly over the whole island but the concentration of the mobile species (CO, H) inside the island is controlled by the island structure. This model qualitatively accounts for several apparent rate anomalies reported for CO and H 2 oxidation.
Surface Science 171 (1986) 543-554 North-Holland, Amsterdam COMPOSITION SURFACE
AND DYNAMICAL
OF SINGLE
CRYSTALS
543 CHARACTERISTICS
OF THE
F e N i 3 (100), (110), (111)
M . A . V A S I L I E V a n d S.D. G O R O D E T S K Y
Institute of Metal Physics, Academy of Sciences, UkrSSR, Kiev-142, USSR Received 14 August 1985; accepted for publication 12 November 1985 Surface segregation as a function of sample temperature has been investigated using AES for the (111), (100) and (110) faces of FeNi 3 single crystal. The surface layer composition is shown to