Ab initiocalculations of the atomic and electronic structure of diamond (111) surfaces with steps

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We present ab initio local-density-functional calculations of the atomic and electronic structure of stepped diamond (111) surfaces. The relaxation of an ideal monoatomic step with bulk-terminated terraces results in ${\mathrm{sp}}^{2}$ bonding near the step. The spacing between the surface layers is also increased. A $(2\ifmmode\times\else\texttimes\fi{}1)$ reconstruction of the terraces lowers the surface energy and decreases the distance between the first two bilayers, but the step energy is increased. As on the flat (111) surface, hydrogen stabilizes the unreconstructed $(1\ifmmode\times\else\texttimes\fi{}1)$ surface on the terraces. The carbon atoms at the edge of the step have two dangling bonds. As the energy gained by forming an extra C-H bond is larger than the step-formation energy, exposure of C(111) to atomic hydrogen can lead to a roughening of the surface. The local electronic structure close to the step has been investigated.