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Low energy back-reflection electron diffraction (LEED) is a powerful method for studying monocrystalline surfaces, either in the clean state or with adsorbed substances. Weak penetration of slow electrons means that mainly surface atoms are important for scattering whether they belong to the substrate or to an adsorbed species. Clean surfaces can be produced and studied prior to adsorption experiments. LEED studies show that gases can be adsorbed in 2-dimensional arrangements peculiar to the specific crystallographic orientation of a particular single crystal substrate. Chemisorption often causes reconstruction of the surface with substrate atoms moving to new positions to incorporate foreign atoms in 2-dimensional matrices. Heating gas-covered surfaces may bring about faceting to expose other crystallographic planes (gross reconstruction). Heating may also cause the adsorbate to decompose, dissolve in the substrate or partially evaporate to leave behind different structures of lower coverage. Experiments illustrating many of these features are described for nickel and tungsten surfaces after adsorption of oxygen.
May, J. W.