Surface structure of the (3×1) and (3×2) reconstructions of Ge(113)

We have studied the clean and well-annealed Ge(113) surface with scanning tunneling microscopy (STM) and low-energy electron diffraction. The surface consists of very large 3×1-reconstructed domains with many small 3×2 antiphase domains scattered in them. STM has disclosed that neither the 3×1 nor 3×2 reconstruction of the surface has a mirror plane. This fact rules out all models proposed so far for the Si(113) surface as candidates for the Ge(113) surface. For further investigations, a model without a mirror plane has been proposed for the 3×1 reconstruction. The model contains a rebonded atom and an adatom as well as five dangling bonds in each unit cell. For the 3×2 reconstruction a model has also been proposed, which is different from but similar to the interstitialcy model recently proposed for the Si(113)3×2 surface. A unit cell of the present 3×2 model consists of two unit cells of the present 3×1 model, and a subsurface interstitial in one of the 3×1 unit cells. Both the proposed models are compatible with the experimental STM images.