Evidence for tilted chains on the diamond (111)-2x1 surface

We present the first X-ray diffraction structure analysis of the reconstructed diamond (111) surface. The atomic geometry is obtained from the distribution of diffracted intensities along integer-order rods of Bragg scattering perpendicular to the surface. Of all the geometries considered, an atomic arrangement featuring tilted chains of p-bonded surface atoms with distortions in subsurface layers is found to provide the best agreement between the calculated and measured structure factors. The tilted-chain topology explains the origin of the observed surface band gap, but it is at variance with recent theoretical predictions based on the local density approximation.