FIELD-ION MICROSCOPY OF THE SI(001) SURFACE

The image formation and atomic structure of the Si(001) plane are examined using a field-ion microscope (FIM). The surface structure of this plane observed through the FIM showed several parallel bright lines in spite of forming the bulk lattice structure. This feature of the ion images is explained by the concept of dangling orbitals of surface Si atoms. Furthermore, at a higher electric field, the atoms of this plane had a rearranged (2 x 1) superstructure which is different from the bulk lattice plane. The FIM images obtained without thermal treatment revealed a dimer type or a zig-zag-chain type reconstruction and were inconsistent with a vacancy model. The atoms of the second layer underlying the superstructure were moved from the bulk sites to other sites along with the reconstruction of the topmost layer.