Do Kyung Lim

Low resistivity of Pt silicide nanowires measured using double-scanning- probe tunneling microscope

We measure the resistivity of platinum-silicide nanowires (Pt2Si NWs) epitaxially formed on a Si(100) surface using double-scanning-probe tunneling microscope. Despite the large Schottky barrier height reported on a macroscopic Pt2Si∕n-Si interface, leakage current through the substrate is observed in the resistance measurement, and is quantitatively estimated to be separated from the current through the nanowire. The measured resistivity of Pt2Si NWs is about half the reported resistivity of thick Pt2Si films, which could be due to additional conduction paths through surface or interface states on NWs.

Structure and electronic properties of self-assembled Pt silicide nanowires on Si(100)

We investigated the formation of Pt silicide nanowires on a Si(100) surface using scanning tunnelling microscopy and high-resolution photoemission spectroscopy. Pt silicide nanowires with a tetragonal Pt2Si structure are formed along the step edges of Si(100). Pt-induced c(4 × 2) reconstructions also appear adjacent to the tetragonal Pt2Si nanowires. Formation of the Pt2Si nanowires is attributed to the anisotropic lattice mismatches between the tetragonal Pt2Si structure and Si(100). Scanning tunnelling spectroscopy data show that the nanowires are metallic. The stoichiometry of Pt silicide is confirmed by high-resolution photoemission spectroscopy.

Electronic structures of thiophene on Ge(100) : the roles of coverage and temperature

We investigated the adsorption and decomposition of thiophene (C4H4S) on Ge(100) using high-resolution photoemission spectroscopy. We found that the Ge 3d and C 1s core-level spectra revealed three adsorption geometries, which we assigned to a weakly bound state (i.e., a Ge–S dative bonding state), a [4+2] cycloaddition bonding state, and a decomposed bonding state (a desulfurization reaction product) as functions of the molecular coverage and the annealing temperature. In this study, we systematically elucidated the changes occurring in the bonding states of thiophene species adsorbed on a Ge(100) substrate.

Unidirectional Pt silicide nanowires grown on vicinal Si(100).

We investigated the structure and electronic properties of unidirectional Pt(2)Si nanowires (NWs) grown on a Si(100)-2 degrees off surface. We found that Pt(2)Si NWs were formed along the step edges of the Si(100)-2 degrees off surface with c(4x6) reconstructions that occurred on the terraces of Si(100) using scanning tunneling microscopy and the structure of formed NWs was found to be Pt(2)Si by core-level photoemission spectroscopy. Moreover, we confirmed that the electronic band structures of the NWs along the NW direction are different from those perpendicular to the NWs and the surface state induced by the Pt(2)Si NWs was observed with a small density of state using the angle-resolved photoemission spectra.

1‐D Molecular Chains of Thiophene on Ge(100)

The adsorption geometry of thiophene on Ge(100) have been studied by high‐resolution core‐level photoemission spectroscopy (HRPES) using synchrotron radiation and scanning tunneling microscopy (STM). From the analysis of the Ge 3d, S 2p, and C 1s core‐level photoemission spectra, we found three different adsorption geometries, which were assigned to a dative bonding feature, a [4+2] cycloaddition reaction product, and a desulfurization reaction product. Furthermore, we investigated that the ratio of the components induced by three adsorption geometries changed depending on the molecular coverage and the annealing temperature. At low coverage, the kinetically favorable dative bonding features favorably form 1‐D molecular chains. Increasing the molecular coverage, the energetically more stable [4+2] cycloaddition reaction products are additionally created.