The catalytic water formation reaction on Pt(111) was investigated by time-resolved near-edge X-ray absorption fine structure (time-resolved NEXAFS) experiment and kinetic Monte Carlo (KMC) simulation. An oxygen covered Pt(111) surface with the (2×2) structure was exposed to gaseous hydrogen (5.0×10−9 Torr) at 130 K. O K-edge NEXAFS spectra were measured during the reaction with a time interval of 35 s. Quantitative analyses of the spectra provided the coverage changes of the reaction species (O, OH, and H2O). KMC simulation has well reproduced the reaction kinetics obtained by the NEXAFS experiment. The surface configurations also clearly reproduced the reported STM results, which show that the OH reaction fronts proceed on the O-covered Pt(111) surface by producing H2O islands backwards. The KMC simulation also revealed that proton transfer between H2O and OH plays a significant role for the propagation of the reaction fronts.
We investigated the effect of reductants over Fe-MFI catalysts (Fe-MFI) based on the catalytic performance in N2O reduction in the absence of oxygen. The TOFs of N2O decomposition and N2O reduction by various reductants (H2,CO, CH4)increased with increasing Fe/Al ratio (Fe/Al≥0.15). As the result of extended X-ray absorption fine structure (EXAFS) analysis, only mononuclear Fe species were observed over Fe(0.10)-MFI after N2O or O2 treatment. On the other hand, binuclear Fe species were also observed over Fe(0.40)-MFI after treatment with N2O. More reducible Fe species, which gave lower-temperature O2 desorption, can be due to Fe binuclear species. Since the N2O reduction with reductants proceeds via a redox mechanism, the reducible binuclear Fe species can exhibit higher activity than the mononuclear one. Furthermore, CH4 can be oxidized under the presence of N2O more easily than can H2 and CO, although it is generally known that the reactivity of methane is very low.
We have explored dielectric properties of ultra-thin Si(111) films using two different evaluation methods based on the first-principles calculations, the internal field (IF) method and the dipole moment (DM) method. As the thickness of the film increases, the dielectric constant evaluated at the innermost region of the film approaches a value near to the experimental bulk dielectric constant at a thickness of only 8 bi-layers. The theoretical value of the electronic dielectric constant for the Si(111) film is 12.85, which is only 6.2% higher than the experimental one. Furthermore, we have shown that the IF method is applicable to microscopic analysis of dielectric properties. The spatial variation in dielectric constant near the surface reveals that depolarized charges at the surface penetrate into the film up to the thickness of 3 bi-layers, resulting in an effective reduction of the dielectric constant near the surface. We have also discussed a microscopic picture of polarization on atomic scale.
The low-temperature thermal conductance of single-walled carbon nanotubes has been revealed by theoretical analysis based on the Landauer theory for thermal transports. The phonon-derived thermal conductance is quantized as a universal value of 4π2k2BT/3h in the low-temperature limit, independent of their radii and chiralities. The temperature range where the quantization is observable increases as the tube-radius decreases. For metallic carbon nanotubes, an electronic contribution to thermal conductance is also quantized as the same value as that of phonon in the low-temperature limit and becomes negligibly small compared with a phonon contribution as temperature increases. We also discuss the thermal transport properties of graphitic ribbons as a potential wiring material in nanoscale electronic devices as well as carbon nanotubes.
DNA analysis of specific regions in chromosome is important for acquirement of valuable genes and study of genetic diseases. Recently, atomic force microscopy (AFM) has also been applied to the chromosome dissection and the recovery of the chromosome fragments. However, any recovery method with high reproducibility by AFM has not been established yet. We developed a highly reproducible dissection and recovery method for chromosome fragments by using AFM, named “scratch method”. This method was available for different sized chromosomes both silkworm chromosome in pachytene phase and human metaphase chromosome of somatic cell. The scratch method will contribute to a development of more efficient and rapid DNA analysis in future.
Interaction between molecules and surfaces and nucleation processes during organic thin film growth have been studied by modulated molecular beam experiments. After a brief introduction of the background and the experimental technique, we describe the results of our study on the interaction between pentacene and chemically modified SiO2 surfaces. Molecular migration on regularlly-stepped vicinal surfaces of silicon and crystal nucleation controlled by pulsed supply of the molecules are discussed on the basis of the experimental data on phthalocyanine and quinacridone.
We demonstrate a novel atom manipulation method of ‘Atom-interchange manipulation’ using non-contact atomic force microscopy (NC-AFM). Previously, methods of lateral atom manipulation are performed by manipulating single atoms or molecules adsorbed on metallic surfaces, but in this paper the atom-interchange manipulation is performed by interchanging two different atom species embedded in semiconductor surface layers. We use a Sn/Ge(111)-c(2×8) surface for the Atom-interchange manipulation, where some Ge adatoms are substituted by Sn adatoms. Although the diffusion rate of Sn adatoms is very low at room temperature, the atom interchange between selected Sn adatom and Ge adatom can be controlled by the NC-AFM tip. ‘Atom inlay’, that is, artificial atomic patterns formed from embedded Sn atoms in the plane of the Ge surface, is created at room temperature by rearranging configuration of two kind of atom species on the surface. This paper describes our first experiment of the atom assembly using AFM.
Gold nano wires were mechanically fabricated in solution to study their quantized conductance behavior under the electrochemical potential control. A nano wire 1 nm in length showing a unit value of the quantized conductance (G0 = 2e2/h) was fabricated in solution at room temperature by choosing appropriate electrochemical potential and electrolyte. As well as a unit value, several fractional values also appeared at the quantization. Intensity of the fractional conductance peak at 0.6 G0 in the histogram increased as the electrochemical potential of the wire became negative. Conductance trace proves that the fractional peak in the histogram is due to reversible conductance fluctuation between a unit (1 G0) and the fractional value (0.6 G0). These experimental results strongly suggest the formation of a gold mono-atomic wire showing reversible phase transition between a dimerized state and an equal spacing state. Possibility regarding the mono-atomic wire as a predecessor for Pierls transition in 1 D metal system was discussed.
In the past several years, peptide aptamers that bind to various inorganic materials have been isolated by using evolutional engineering methods including a peptide phage system. We have recently isolated a peptide aptamer, TBP-1, that electrostatically binds to the surface of titanium. So far we have investigated the binding of the peptide by scoring plaque forming units of the eluted phages. In this paper, we estimated the number of phages that bound to the surface of titanium through direct observation by AFM, and concluded that the estimations obtained both from biological method and AFM were consistent. We also performed the analysis of quarts crystal microbalance and viscoelasticity, and concluded that the TBP-1 displaying phage bound on the surface of titanium via its displayed peptide.