Elemental structure in Si(110)-"16x2" revealed by scanning tunneling microscopy

Atomic structures of the clean Si(110)-"16x2" surface are studied by scanni ng tunneling microscopy (STM). High-resolution STM images reveal that the e lemental structure in the "16x2" is a pair of pentagons. In the empty-state s images the elemental structure is clearly resolved in ten protrusions, wh ile in eight in the filled-states images. In order to clarify the atomic ar rangement of the pentagons, we pay attention to the disordered area where t he elemental structures are isolated on the bulk-terminated surface. The bu lk-terminated surface structure, on which the pentagons are located, is wel l understood by the rotational-relaxation structural model. In consideratio n of the registry of the pentagon for the rotational-relaxation structure, a "tetramer-interstitial'' model is proposed for the elemental structure, t ogether with three other possible structural models.