Huiting Li

Atomic structure of Si(5512)‐2×1: Confirmation of the structural model having two kinds of chains through homoepitaxy at 550°C

Recent empty-state scanning tunneling microscopy (STM) images of Si(5512)‐2×1 have shown that this surface consists of four types of one-dimensional structures such as honeycomb (H) chain, π-bonded (π) chain, dimer-adatom (D‐A) row, and tetramer (T) row. To confirm this revised structural model of the Si(5512)‐2×1 surface, the authors performed homoepitaxy on the reconstructed Si(5 5 12) surface held at 550°C and studied the results by STM. Under equilibrium at 550°C there exists three kinds of phases composed of (225), D(337), T(337), and (112) subunits. These subunits consist of only two commutable rows, D‐A and T rows, as well as two commutable chains, H and π chains. Mutual transformations among three phases by means of additional Si atoms are well explained by a new structural model having only two kinds of chains.Recent empty-state scanning tunneling microscopy (STM) images of Si(5512)‐2×1 have shown that this surface consists of four types of one-dimensional structures such as honeycomb (H) chain, π-bonded (π) chain, dimer-adatom (D‐A) row, and tetramer (T) row. To confirm this revised structural model of the Si(5512)‐2×1 surface, the authors performed homoepitaxy on the reconstructed Si(5 5 12) surface held at 550°C and studied the results by STM. Under equilibrium at 550°C there exists three kinds of phases composed of (225), D(337), T(337), and (112) subunits. These subunits consist of only two commutable rows, D‐A and T rows, as well as two commutable chains, H and π chains. Mutual transformations among three phases by means of additional Si atoms are well explained by a new structural model having only two kinds of chains.

Surface reconstruction at the initial Ge adsorption stage on Si(114)-2 × 1

By combined investigation of scanning tunneling microscopy and synchrotron core-level photoemission spectroscopy on the structural and chemical evolution at the initial stage of Ge adsorption on Si(114)-2 × 1, it has been observed that one-dimensional (1D) sawtooth-like nanostructures composed of (113) and (117) facets and 1D trenches adjacent to the (113) facets are readily formed without any wetting layer. Due to the absence of chain structures on the reconstructed Si(114)-2 × 1, enhanced Ge interdiffusion detected from Ge/Si(5 5 12)-2 × 1 has not been found. Instead, Si atoms originating from etched surfaces and arriving Ge atoms form the alloy facets with Ge-rich surfaces. These experimental results prove that, if the direction of the Ge overlayer corresponding to that of the substrate is unstable like the present case, the arriving atoms prefer to form facets covered with the species of lower surface free energies rather than a uniform wetting layer.

Synchrotron photoemission studies on reconstructed strained surfaces

Recently, based on scanning tunneling microscopy studies of the reconstructed Si(5 5 12)−2×1 surface, it has been suggested that its unit cell simply consists of four kinds of one-dimensional (1D) structures: π-bonded (π) chain, honeycomb (H) chain, tetramer (T) row, and dimer-adatom (D-A) row. In the present study, by angle-resolved ultraviolet photoelectron spectroscopy, it has been found out that the Si(5 5 12)−2×1 surface has two kinds of surface states, one with a negligible dispersion originating from row structures (T/D-A) and the other with a strong dispersion originating from chain structures (π/H). Also, the Si 2p core-level spectrum shows at least two kinds of surface components, one with 0.23 eV higher binding energy originating from upward-relaxed surface atoms and subsurface atoms, and the other with 0.52 eV lower binding energy originating from downward-relaxed surface atoms. It can be realized that these spectroscopic results quantitively match with the structural model of Si(5 5 12)−2×1 h...