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Changes which occur on, and just below, the surface of a Si(111)-(7x7) crystal when it is dosed with H atoms are complex and still not well described. Measurements of He atom diffraction (HAS) from this surface in the [121] or [211] directions give scans which are asymmetric about the specular angle. The scans become symmetric when the surface is exposed to doses of H atoms sufficient to give coverages...