DIFFRACTION OF HE ATOMS AT A SI(111) 7X7 SURFACE

We report the diffraction of He atoms at the Si(111) 7×7 reconstructed surface. The atom diffraction patterns consist of numerous sharp peaks filling out the seventh-order net observed by low-energy electron diffraction (LEED). In contrast to low-energy electron diffraction, the diffraction intensities in this seventh-order net are determined by only the outermost exposed layer of silicon atoms. These results should be sufficient to allow a semiclassical scattering calculation to test critically the various structural models which have been proposed for this reconstruction. © 1979 The American Physical Society.