Geometry of the (2x1) reconstruction of diamond(111)

A quantitative analysis of the (2 x 1) reconstruction of the diamond (I 11) surface by low-energy electron diffraction (LEED) is presented. Spot intensity versus energy data, I (E), were collected fur normal incidence up to electron energies of 500 eV and analysed using the tensor LEED perturbation method. A close fit between experimental and calculated data (according to a Pendry R-factor R = 0.19) confirms the model of 7-bonded chains at the very surface, wherein neighbouring chains are at different heights equivalent to a considerable surface corrugation (0.68 Angstrom). We find that the chains are practically untilted, i.e. the buckling within the chains is negligible (less than or equal to 0.01 Angstrom). The possible dimerization of the chains is also very small (relative bond-length difference d = 0.7%), though the respective limits of error would allow values up to about 7%. For the subsurface structure we find that the surface reconstruction extends rather deep into the surface according to the considerable buckling amplitudes within sublayers down to the fourth bilayer. All structural parameters retrieved, including the negligible tilt and dimerization of chains as well as the extension of the surface reconstruction to deeper layers, are in excellent quantitative agreement with the results of ab initio calculations, so controversies existing up to now in the literature appear to be resolved.