The atomic structure of the (001) plane was examined by using field ion microscopy. The image of the surface structure of this plane exhibited several bright parallel lines. This feature was explained in terms of the concept of dangling orbitals of surface Si atoms. In higher electric fields, the atoms of this plane rearranged into a (2 x 1) superstructure which was different to a bulk lattice plane. The images which were obtained in the absence of heat treatment revealed the presence of a dimer-type or zig-zag chain-type reconstruction. These were inconsistent with a vacancy model. In addition to the reconstruction of the uppermost layer, the atoms of the layer which underpinned the superstructure were found to be moved from bulk sites to other sites.

T.Adachi, T.Ariyasu: Philosophical Magazine A, 1992, 66[3], 405-14