Two-dimensional chirality has attracted interest as an approach to develop novel chiral catalysts and sensors. However, there is no standard tool to distinguish and evaluate the chirality at surfaces and interfaces, since the number of chiral molecules or chiral sites are limited in the two-dimensional system. Linear chiroptical spectroscopy, such as circular dichroism (CD) and Raman optical activity (ROA), cannot be applied to the two dimensional system, because these methods are basing on the optical transition forbidden under the electric dipole approximation and, then, the chiral responses becomes much weak. Recently, one of the nonlinear spectroscopy, infrared-visible sum frequency generation (VSFG) has been established as a novel chiroptical tool to investigate the molecular and surface chirality. In the present study, this optical technique was applied to recognize the chirality at chiral molecules-modified surfaces under the nonelectronic resonant condition. For polycrystalline films of bi-naphthol (BINOL), chiral VSFG signal reached around 50% of achiral SFG signal and the chirality of the thin film could be successfully recognized. On the other hand, for submonolayer of binaphthyl molecules on Au, there was a limitation in the sensitivity and it was desired to introduce the doubly resonant VSFG enhancement for in situ monitoring of chiral recognition processes.
The dynamics of the water molecules on a CO-covered Pt electrode has been studied by laser-induced potential transient measurements. This is a model system to elucidate the behavior of water molecules in the electric double layer during electrochemical reactions. At the potentials where CO is stably adsorbed, the Pt surface is negatively charged and water molecules are oriented pointing the hydrogen atoms toward the surface. The laser irradiation heats the interface and disturbs the orientation of water, which induces a potential jump toward the negative direction. We found that the amplitude of the potential jump on the CO-covered surface is much larger than on the CO-free surface. The finding suggests that the water molecules are more flexible on the CO-covered surface due to the weaker water-CO interaction than water-Pt interaction. Stronger laser pulse irradiation additionally induces the desorption of CO, which result in the adsorption of water with the hydrogen atom pointing toward the surface and induces a positive potential shift. The potential shift takes ∼70 microseconds to reach the maximum, which becomes slower as the electric field becomes intense. The intense field and hydrogen-bonded cations affect water structure in a long range and the collective motion of the water layers.
It is well known that transparent conductive materials are key materials for FPD (Flat Panel Display). A practical transparent conductive material is indium tin oxide (ITO) consisting of indium oxide and tin oxide. However, indium price has increased over the last several years because indium is a rare metal with 0.00001 of Clarke number. Therefore searching alternative transparent conductive materials rather than indium has been very active over the last decades. In this study, rf-magnetron sputtering method is used. Magnesium and graphite target are co-sputtered and Mg-C films were formed. Then, Mg-C film became transparent after being left in moistured air for 10−15 min. Transmittance of 90% in average in the range of wavelength of 380−1000nm. Resistivity of 10−1 Ωcm was observed. In this work it will be demonstrated that black Mg-C non-equilibrium films that became consequently were transparent with electric resistively after exposing in the air.
Thermal decomposition of ultrathin oxide layers on Si(100) surface was investigated with temperature programmed desorption. The SiO desorption spectra for the initial coverages between 1.7 and 2.6 ML exhibit a dominant peak with a subpeak at lower temperature. The desorption rate corresponding to the dominant peak follows Avrami kinetics, suggesting that the decomposition process is spatially inhomogeneous with void formation and growth and is rate-limited by the desorption of SiO molecules at the void perimeter. The desorption energy was determined to be 3.39±0.07 eV from the reactive scattering measurement of the active oxidation process. The fact that Avrami kinetics reproduces the whole decomposition process until the oxide layer has completely decomposed shows that the reaction mechanism is still valid even if the overlap between voids becomes quite large. The Avrami exponent deduced from our measurement indicates that the increase in the initial coverage makes the oxide layer more stable and reduces the void nucleation rate.
For the purpose of close understanding and further improvement of the organic electronics devices, elucidation of the electronic structures of organic-electrode interfaces as well as the organic materials themselves in the ambient pressure condition is highly anticipated. Ultraviolet Photoelectron spectroscopy (UPS) is not a satisfactory technique for this purpose, because UPS needs high vacuum condition in principle and the sample charging problem hinders characterization of the electronic structures of specimens of insufficient conductivity (e.g. organic thick-films and crystals). In the present study, the authors proved that one can observe the occupied electronic structures of insulating materials by photoelectron yield spectroscopy (PYS). A novel mechanism enabling photoelectron measurement on insulators is specified. By adopting this method, the electronic structures of rubrene thin films at a buried interface beneath the rubrene-peroxide layers were directly observed in the ambient air condition. These merits of PYS can be extended to investigate the electronic structure of organic devices.
The nanotribological properties of molecularly thin films of polymer melts were investigated using a surface forces apparatus (SFA). When the droplet of a polymer melt was injected between two smooth mica surfaces and confined by normal compression, the dynamic properties of the polymer melt shifted from bulk rheological to thin film tribological features. The shift of the dynamics was evaluated by measuring the effective viscosity of the confined films and by comparing the viscosity with its bulk value; the results were discussed in terms of confinement-induced glasslike transition. Molecular ordering (layering) in confined polymer melts was also studied. The tribological properties of the thin films of poly(dimethylsiloxane) (PDMS) were evaluated. The results implied well-ordered layer structures in the confined films, which are very different from most of the hydrocarbon-type polymeric lubricants (having disordered molecular conformations in confinement). The experiments described here reveal the unique dynamics of molecularly confined polymer melts, which cannot be obtained by any other experimental techniques than SFA.
This paper reviews our recent approaches for a label-free detection of protein-protein interactions which can perform simultaneous protein conformational analysis by using infrared absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS). Using this method, the target protein was detected in aqueous solution phase based on the peak height of the protein amide I and amide II bands, while discrimination of specific and nonspecific signals is made based on the secondary structure of the target protein. An antigen-antibody interaction on semiconductor surfaces was investigated as a model system, since it is well-known that antibodies largely consist of β-sheet structures. The features of our approach using MIR-IRAS combined with protein secondary structure analysis were discussed in terms of sensitivity, capability of quantitative analysis, and specific/nonspecific discrimination.
Simulation methods for scanning tunneling microscopy (STM) based on first-principles calculations are briefly reviewed. After introducing features and comments on the most familiar Tersoff-Hamann approximation, some extended topics are also mentioned.