Atomic and Molecular Diffraction and Scattering from a Tungsten Carbide Surface Characterized by LEED

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Abstract
The scattering of collimated beams of helium, deuterium, neon, and argon are reported from two tungsten carbide surfaces which form on the (110) face of tungsten. On a (3× 5) surface both helium and deuterium give sharp, well-defined diffraction peaks corresponding to the (2̄, 0), (1, 0), (0, 0), (1, 0), (2, 0) directions along the 5 spacing. No diffraction is observed on the (1× 1) carbide surface or the clean metal surface which is also (1× 1). Fractions scattered in the specular ray, (0, 0), as high as 55% have been observed from the carbide surfaces. The scattering of neon is in the inelastic regime and argon is trapping dominated. Analysis of the scattering in combination with the LEED suggests a dense carbide, perhaps WC, with a Debye temperature of 1200°K or higher. This diffractive scattering is the first reported on a surface other than alkali halides and some comments on the sort of periodic potential which is likely to give rise to diffractive scattering of atoms are given.