Surface structural analysis of small molecules on transition metal single crystal surfaces with low energy electron diffraction
An attempt was made to go beyond the normal restrictions of surface crystallography. Low-temperature adsorption and coadsorbate induced ordering can be used to stabilize high coverage structures which would otherwise not form. Conventional LEED requires long-range order, digital LEED is sensitive enough to detect weak scattering from disordered adsorbates with no long-range order. Complete surface structures are presented for the first surface structure of NO, CO + benzene, NO + ethylidyne, and CO + ethylidyne all on the Rh(111) surface, and the first disordered molecular adsorbate: CO on Pt(111). Coadsorbate-induced ordering occurs when two adsorbates form a different ordered structure than either would form by itself. The lateral interactions between adsorbates force the molecules to populate new sites. Pure CO or NO overlayers have only top and bridge sites occupied, but if either molecule is paired with a coadsorbate (e.g., CO/benzene, CO/ethylidyne, or NO/ethylidyne) they move to hollow sites. Recent theoretical developments by Pendry et al. and new experimental techniques (digital LEED, this work) have made it possible to study disordered overlayers. The new digital LEED apparatus is sensitive enough to measure the weak diffuse scattering from disordered CO on Pt(111) to determine its structure. The first surface structure of a disordered molecular adsorbate is presented in this work.
- Research Organization:
- Lawrence Berkeley Lab., CA (USA)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6295255
- Report Number(s):
- LBL-26805; ON: DE89010681
- Country of Publication:
- United States
- Language:
- English
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360102* -- Metals & Alloys-- Structure & Phase Studies
440300 -- Miscellaneous Instruments-- (-1989)
47 OTHER INSTRUMENTATION
ABSORPTION
AROMATICS
AUGER ELECTRON SPECTROSCOPY
BENZENE
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
COHERENT SCATTERING
CRYSTAL STRUCTURE
DIFFRACTION
ELECTRON DIFFRACTION
ELECTRON SPECTROSCOPY
ELEMENTS
HYDROCARBONS
LOW TEMPERATURE
METALS
NITROGEN COMPOUNDS
NITROGEN OXIDES
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PLATINUM
PLATINUM METALS
RHENIUM
SCATTERING
SPECTROSCOPY
SURFACE PROPERTIES
TRANSITION ELEMENTS