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Electronic structure of monolayer graphene with metal contacts can be modified by control of interfacial interaction. Here, we show that the strength of local interfacial interaction between graphene and Au(111) surface can be electrochemically controlled by the hydrogen evolution reaction process. Graphene/Au(111) electrodes were prepared by the chemical vapour deposition. Raman spectroscopy indicated existence of monolayer of graphene over Au surface. Local interaction of graphene/Au(111) interaction can be differentiated by intercalation of H2 molecules at interface. This study shed lights on the possibility of proton penetration through the graphene to modify the strength of interaction between graphene and Au(111) surface.

Herein, we report the control of the optical properties of metal nanodimer structures using electrochemical metal dissolution reactions. The reaction rate could be precisely tuned by changing the electrochemical potential and, as a consequence, fine tuning of the size and gap distance of metal nanodimers was achieved as the functions of applied potential and polarization time. The observed linear correlation between the scattering intensity and charge resulting from nanostructure dissolutions suggested that the surface dissolution rate was 0.30 nm min-1, corresponding to the surface dissolution of a single atomic layer per min. The present method can control the change in the volume of the structures, leading to the change in the gap distance of nanodimers at an atomic-scale level.

We have studied the quantized conductance behavior of Ni nanoconstrictions prepared on Au and Pt substrates in solution under electrochemical control. The conductance histogram of Ni nanoconstriction showed a clear feature at 1–1.5G0 under the hydrogen evolution condition. The choice of substrate metals, Au and Pt, did not affect the characteristics of conductance quantization. The results obtained using the system suggest that a particular atomic structure of Ni can be stabilized in solution on the basis of the intrinsic properties of Ni metal evolving hydrogen in solution. We have also evaluated the effect of applying an external magnetic field on the quantized conductance behavior of Ni nanoconstrictions in solution.

In optical trapping using photon force much enhanced by localized surface plasmon (LSP) in solution, we found that a resonant excitation effect can further enhance photon force. In this LSP-based optical trapping under a resonant excitation condition, an incident laser beam excites both LSP and electronic resonant transition of a target object simultaneously. Fluorescence microspectroscopy clearly showed that nanospheres under the resonant condition were much more efficiently trapped as compared to that under a non-resonant condition. The resonant LSP-based trapping mechanism was further reinforced by theoretical calculations taking the resonant excitation effect into account. Such resonant LSP-based trapping methodology will provide a novel approach for efficient trapping of small molecules.

The local density of states (LDOS) of an isolated single-walled carbon nanotube (SWNT) was characterized by electrochemical scanning tunneling microscopy and spectroscopy (EC-STM and EC-STS). Discrimination of individual semiconducting and metallic nanotubes adsorbed on a Au(111) surface was demonstrated by analyzing EC-STS spectra under electrochemical control at a nanometer scale. Two distinct LDOS determined from differential EC-STS spectra are found to be characteristic of the conduction and valence bands, corresponding to van Hove singularities of the SWNT. The absolute potential of the energy level and the band gap between these bands for semiconducting nanotubes could be also evaluated.

Electric conductance of the metal atomic contacts of Au and Pd was investigated using a scanning tunneling microscope (STM) in solution under electrochemical potential control. At the hydrogen evolution potential, a fractional conductance peak appeared around 0.5 G(0) (G(0) = 2e(2)/h) in the conductance histograms of Au contacts. For Pd contacts, peaks appeared around 1.0 G(0) in the conductance histograms at the hydrogen evolution potential. The conductance behavior and atomic configuration of the metal atomic contacts at hydrogen evolution potential were discussed based on previously reported experimental results and theoretical calculation results. We have proposed the formation of hydrogen adsorbed metal Au and Pd contacts in solution at the hydrogen evolution potential.

We have developed the mechanically controllable break junction system (in-situ MCBJ) to investigate the conductance of a single molecular junction in ultra high vacuum (UHV). Gas or liquid sample of bridging molecules was introduced to metal electrodes with a gas doser. For the introduction of solid sample, a Knudsen cell was used. In the present system, molecular junctions can be prepared without breaking vacuum. Thus, the atomic structure and chemical property of single molecular junction could be well defined. The electrical conductance of a single ethanedithiol molecule bridging between two Au electrodes was investigated with this in-situ MCBJ system. The conductance was determined to be 0.2 G0 (G0 = 2e2/h).

Diffusion of individual dye-labeled molecules in self-spreading lipid bilayer on glass substrate in aqueous solution was observed directly using total internal reflection fluorescence microscopy (TIRFM). The molecular diffusion was evaluated quantitatively by the mean square displacement (MSD) analysis for the trajectories of individual molecules. The mode of normal Brownian diffusion in lipid bilayer was changed in the presence of the periodic triangular Ag nanoparticles on the surface of the substrate. Suppressed diffusivity observed at the system with the triangular Ag nanoparticles was attributed to the confinement of the molecular motion in the micro-compartment surrounded by the Ag triangles.

The effect of photoillumination on electrochemical reactions of a gold electrode in KCl electrolyte solution was investigated. The electrode was dissolved by positive polarization in the electrolyte solution. Anodic current increased when the electrode was illuminated by 830-nm light. Scanning tunneling microscope images proved that dissolution of the gold electrode was accelerated by the photoillumination. The surface of the photodissolved electrode consisted of islands with a flat top and relatively narrow size distribution. In some cases, uniform structure consisted of small islands was formed by the illumination. The contribution of a highly localized photoexcitation mode at the surface was discussed to explain the characteristics of the photoformed surface nanostructure.

Anisotropic agglomeration of gold nanoparticles (diameter ca. 6 nm) was induced in aqueous media by modifying the particle surface with various organic thiols. The structural anisotropy of the agglomerates in solution depended on the type of the modifying reagents. Scanning tunneling microscopic images of the agglomerates transferred on gold (111) surfaces show that the agglomerates on the gold surface formed dot-interconnected lines with a single particle width. The length of the dot-interconnected lines was much longer on the surface than that in solution.

Size controlled CdS and ZnS nanocrystallites with well-defined crystallinity were simply prepared by reacting M2+ (M=Cd2+ or Zn2+) and S2- (H2S or Na2S) in N,N-dimethylformamide (DMF) without adding any surface stabilizers. The mean diameter of CdS nanocrystallites can be rigorously controlled over a range from 1.8 to 4.2 nm maintaining the hexagonal crystalline structure by varying the sulfur source and by regulating the preparation temperature. The band-gap dependence estimated from the absorption peak wavelength on the size of the hexagonal CdS nanocrystallites was in good agreement with the pseudopotential calculation using lattice parameters of hexagonal CdS. In the system of ZnS nanocrystallites, crystallinity was controlled by changing the surface modifying reagent. Reactive organic molecules, which can bind onto the surface of ZnS nanocrystallites, induce phase transition of ZnS nanocrystallites from the hexagonal to the cubic phase, maintaining a crystalline size of 3 nm at ambient temperature and pressure.