Low energy electron diffraction study of carbon monoxide, nitrogen, and their mixtures with argon physisorbed on graphite

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1986

OSTI ID:6925505

You, H

Monolayers of N/sub 2/, CO, and their mixtures with argon were adsorbed on the basal plane of graphite single crystals and studied by low-energy electron diffraction (LEED). Molecular centers of the adsorbed diatomic molecules approximately form two-dimensional lattices. At low temperatures, orientations of their molecular axes undergo ordering transitions and induce superlattice structures. The LEED patterns with missing reflections for the orientationally ordered, low-density (commensurate) two-sublattice in-plane herringbone (2-in HB) structure of nitrogen monolayers previously observed by Diehl and Fain are reproduced. A new triangular incommensurate two-sublattice tilt-out-of-surface herringbone (2-out HB) structure for densities higher than that of the low-density 2-in HB structure is indicated by appearance of certain reflections missing for the 2-in HB. The heterodiatomic molecule of CO, which as a quadrupole moment about 1.4 times larger than N/sub 2/, has a size similar to N/sub 2/. Submonolayers of CO have a commensurate 2-in HB structure similar to that of nitrogen submonolayers. Carbon and oxygen ends of CO molecules in the 2-in HB structure have no apparent end-to-end order. For high densities, a LEED pattern with multiple scattering and no missing reflections indicates an incommensurate four-sublattice pinwheel (PW) structure, where molecular axes of CO are normal to the substrate in one pin-sublattice and parallel in three wheel-sublattices.

• Research Organization: Washington Univ., Seattle (USA)
• OSTI ID: 6925505
• Country of Publication: United States
• Language: English

Related Subjects

640302* -- Atomic
Molecular & Chemical Physics-- Atomic & Molecular Properties & Theory
74 ATOMIC AND MOLECULAR PHYSICS
ADSORPTION
ARGON
CARBON
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
COHERENT SCATTERING
DIFFRACTION
DISPERSIONS
ELECTRON DIFFRACTION
ELEMENTAL MINERALS
ELEMENTS
FLUIDS
GASES
GRAPHITE
MINERALS
MIXTURES
MOLECULAR STRUCTURE
NITROGEN
NONMETALS
ORDER-DISORDER TRANSFORMATIONS
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
RARE GASES
SCATTERING
SORPTION
SUPERLATTICES