Extending the range of low energy electron diffraction (LEED) surface structure determination: Co-adsorbed molecules, incommensurate overlayers and alloy surface order studied by new video and electron counting LEED techniques
LEED multiple scattering theory is briefly summarized, and aspects of electron scattering with particular significance to experimental measurements such as electron beam coherence, instrument response and phonon scattering are analyzed. Diffuse LEED experiments are discussed. New techniques that enhance the power of LEED are described, including a real-time video image digitizer applied to LEED intensity measurements, along with computer programs to generate I-V curves. The first electron counting LEED detector using a ''wedge and strip'' position sensitive anode and digital electronics is described. This instrument uses picoampere incident beam currents, and its sensitivity is limited only by statistics and counting times. Structural results on new classes of surface systems are presented. The structure of the c(4 x 2) phase of carbon monoxide adsorbed on Pt(111) has been determined, showing that carbon monoxide molecules adsorb in both top and bridge sites, 1.85 +- 0.10 A and 1.55 +- 0.10 A above the metal surface, respectively. The structure of an incommensurate graphite overlayer on Pt(111) is analyzed. The graphite layer is 3.70 +- 0.05 A above the metal surface, with intercalated carbon atoms located 1.25 +- 0.10 A above hollow sites supporting it. The (2..sqrt..3 x 4)-rectangular phase of benzene and carbon monoxide coadsorbed on Pt(111) is analyzed. Benzene molecules adsorb in bridge sites parallel to and 2.10 +- 0.10 A above the surface. The carbon ring is expanded, with an average C-C bond length of 1.72 +- 0.15 A. The carbon monoxide molecules also adsorb in bridge sites. The structure of the (..sqrt..3 x ..sqrt..3) reconstruction on the (111) face of the ..cap alpha..-CuAl alloy has been determined.
- Research Organization:
- Lawrence Berkeley Lab., CA (USA)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6062638
- Report Number(s):
- LBL-22593; ON: DE88001401
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Molecular & Chemical Physics-- Beams & their Reactions
656003 -- Condensed Matter Physics-- Interactions between Beams & Condensed Matter-- (1987-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
A CODES
ADSORPTION
ALLOYS
ALUMINIUM ALLOYS
AROMATICS
ATOMIC BEAM DIFFRACTION
BEAMS
BENZENE
CARBON
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
CHARGED PARTICLE DETECTION
CHEMICAL COMPOSITION
CHEMICAL REACTIONS
CHEMISORPTION
COHERENT SCATTERING
COMPUTER CALCULATIONS
COMPUTER CODES
COPPER ALLOYS
DATA
DATA ACQUISITION SYSTEMS
DETECTION
DIFFRACTION
DOMAIN STRUCTURE
ELECTRON BEAMS
ELECTRON DETECTION
ELECTRON DIFFRACTION
ELECTRON GUNS
ELEMENTAL MINERALS
ELEMENTS
EXPERIMENTAL DATA
FORTRAN
GRAPHITE
HYDROCARBONS
INFORMATION
ION BEAMS
LEPTON BEAMS
MATERIALS
MATHEMATICS
METALS
MINERALS
MULTIPLE SCATTERING
NONMETALS
NUMERICAL DATA
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PARTICLE BEAMS
PLATINUM
PLATINUM METALS
PROGRAMMING LANGUAGES
RADIATION DETECTION
RHODIUM
SCATTERING
SEMICONDUCTOR MATERIALS
SEPARATION PROCESSES
SORPTION
SURFACE PROPERTIES
SURFACES
THEORETICAL DATA
TOPOLOGY
TRANSITION ELEMENTS