Soon Jung

Atomic-scale structural evolution of Ge(100) surfaces etched by H and D

The atomic-scale structural evolution of Ge(100) surfaces etched by H(g) and D(g) at Ts=400 K is studied using scanning tunneling microcopy (STM) and field emission-scanning electron microscopy (FE-SEM). The STM investigation reveals that etching of the Ge(100) by H(g) and D(g) proceeds initially via the production of single atom vacancies (SV), dimer vacancies (DV), and subsequently, line defects along the Ge dimer rows. It is also observed that D(g) etches the Ge(100) surface eight times faster than H(g) does. After extensive exposures of the surface to H(g), the FE-SEM images show square etch pits with V-groove shapes, indicating that H(g) etching of the Ge(100) surface proceeds anisotropically.

Cycloaddition on Ge(100) of the Lewis Acid AlCl3

The adsorption and decomposition of AlCl3 on Ge(100) was studied using scanning tunneling microscopy (STM) and high-resolution core-level photoemission spectroscopy (HRCLPES). Through the analysis of the STM image and Ge 3d and Cl 2p core-level spectra of AlCl3 on Ge(100), we found that an AlCl3 molecule reacts with two Ge atoms via a cycloaddition reaction, which forms Cl−Ge and AlCl2−Ge without breaking AlCl3. Additionally, by considering valence shell electron pair repulsion (VSEPR) arguments, the effect of molecular structure on the surface chemistry was explained. To our knowledge, the adsorption of Lewis acid molecules on a semiconductor surface has not been studied in detail. These are the first results for the adsorption structures of Lewis acid molecule on Ge(100).

STM Tip Catalyzed Adsorption of Thiol Molecules at the Nanometer Scale

The tungsten oxide covered tungsten (W) tip of a scanning tunneling microscope was found to act as a catalyst to catalyze the S-H dissociative adsorption of phenylthiol and 1-octanethiol molecules onto a Ge(100) surface. By varying the distance between the tip and the surface, the area of the tip-catalyzed adsorption could be controlled. We have found that the thiol headgroup is the critical functional group for this catalysis and the catalytic material is the tungsten oxide layer of the tip. This local tip-catalyzed adsorption may be used in positive lithographic methods to produce nanoscale patterning on semiconductor substrates.

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.

Molecular seesaw: a three-way motion and motion-induced surface modification.

We introduce a three-way molecular motion which can be a suitable switching system in future molecule-based nanocircuits. A real-space investigation revealed that vinylferrocene adsorbs site-specifically on the Ge(100) surface and then shows a reversible tilting motion, similar to a seesaw. Unlike conventional molecular motions, it not only has three stable switching states at room temperature but also shows a motion-induced surface-structure modification, allowing surface-mediated signal transmission. Demonstrated STM-tip influence on the motion allows the feasibility of tip-induced manipulation.

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.