Understanding of the thermal transport properties of nanowires is essential for the development of nanometer-scale electronic devices. We compute the thermal transport properties of silicon nanowires (SiNWs) and carbon nanotubes (CNTs) using the non-equilibrium Green's function technique with the interatomic potentials by Tersoff and Brenner to calculate the thermal conductance. This approach is suitable for the calculations of ballistic thermal conductance of nanowires, taking the effects of shapes of nanowires into account. We study the dependence of thermal conductance on the temperature, diameter, and shapes of nanowires and clarify their features. We find that thermal conductance of CNTs agrees very well with experiments. On the other hand, we need to include defects for the thermal conductance of SiNWs.
We demonstrate here a creation of superhydrophobic and superhydrophilic patterned surface by using reactive ion etching (RIE) of silicon with a self-organized porous polymer structures and UV-O3 treatments through the photo-mask. Honeycomb-patterned films of polystyrene and amphiphilic polymer were prepared by casting of their chloroform solution. After UV-O3 treatment, honeycomb-patterned films were fixed on silicon substrates up side down with Poly (vinyl alcohol) solution. After peeling of the bottom layer of the honeycomb-patterned films, porous polymer masks were formed on the silicon substrate. After RIE, the silicon nanospike-array structure was obtained. Water contact angles on the silicon nanospike-array structures were c. a. 165 degree. From the results of X-ray photoelectron spectrum of the silicon nanospike-structures, fluorine was detected. The result suggests that superhydrophobicity was originated by absorbed fluorocarbons on the surface of the silicon nanospike-array structures and their surface structures. After UV-O3 treatment with photo-masks, fluorine was partially removed at irradiation area, and the area shows superhydrophilicity. These results suggest that we can easily design superhydrophobic and superhydrophilic patterned surfaces by UV-O3 treatment through photo-masks.
Conductive atomic force microscope (C-AFM) writing is attracting attention as a technique which enables to clarify a switching mechanism of resistive random access memory (ReRAM) by providing a filament with large radius. We observed a C-AFM writing area of a NiO film using scanning electron microscope (SEM), and a correlation between contrast in a secondary electron image and a resistance written by C-AFM was confirmed. In addition, it was suggested that the resistance change effect occurred near the surface of the film. We also studied effects of a baking at low temperature and an electron irradiation with low electron energy on the resistance of the C-AFM writing area. As a result, it was suggested that the resistance change effect was caused by a defect-induced-distortion which is relaxed with low energy.
We made resistive random access memory (ReRAM) structures of Al/Bi2Sr2CaCu2O8+δ (Bi-2212) single crystal/Pt and Pt/Bi-2212 single crystal/Pt, and evaluated both their memory characteristics and superconducting properties. The memory effect was confirmed only in the former. Taking advantage of the large anisotropy of a Bi-2212 single crystal, it was clarified that the memory effect occurred at the boundary between Al and Bi-2212. The memory effect was enhanced with decreasing critical temperature by annealing the sample. This showed that the introduction of oxygen vacancies to the Bi-2212 single crystal was required for the development of the memory effect and could be achieved by depositing electrodes with low Gibbs free energies. The model which explains the resistance switching of perovskite-oxide-based-ReRAM was proposed based on the results.
An X-ray free electron laser (XFEL) has been constructed at the SPring-8 site and will be open for users at the beginning of 2012. Fundamental experimental facilities for user experiments have been developed; for example, photon beamline, beam diagnostics systems, two dimensional X-ray detectors, and a femtosecond laser system which is synchronized to XFEL pulses. Extensive researches using SPring-8 and a prototype free electron laser (SCSS test accelerator) have been performed for developing experimental techniques for XFEL applications.
Two-components catalysts Rh-ReOx/SiO2, Rh-MoOx/SiO2 and Ir-ReOx/SiO2 were active in the C-O hydrogenolysis of glycerol, 1,2-propanediol and tetrahydrofurfuryl alcohol. The activities were much higher than those of monometallic catalysts. The selectivities to terminal alcohols decreased in the following order: Ir-ReOx/SiO2 > Rh-ReOx/SiO2 > Rh-MoOx/SiO2 » Rh/SiO2. Characterization with XRD, TEM, CO adsorption, temperature-programmed reduction (TPR), XANES and EXAFS revealed that noble-metal particles were partially covered with ReOx or MoOx species. The MoOx species in Rh-MoOx/SiO2 formed a monomeric structure. The ReOx species in Rh-ReOx/SiO2 and Ir-ReOx/SiO2 formed monolayer clusters and multilayer clusters, respectively. A reaction mechanism was proposed where the alkoxide species formed on ReOx (or MoOx) was attacked by the active hydrogen species on Rh (or Ir) atoms bonded with the Re (or Mo) atom. The difference of the size of the modifier may affect the selectivity.
Lipid bilayers formed on micropores possess excellent properties for electrical measurements given the low membrane capacitance and high voltage stability. However, conventional methods employed in the fabrication of micropores on semiconducting materials require large-scale equipment with many fabrication steps. To address this problem, we have developed a novel method that generates Teflon micropores in a few seconds by imposing a heated tip onto commercial Polyethylene, Polyethylene terephthalate, Polypropylene and Teflon films. These advantages promise to improve the performance of artificial lipid bilayers when employed in the development of flexible biosensors and a combination system with atomic force microscope (AFM). Thus we succeeded in activating a single channel protein by mechanically stimulating it with an AFM probe, indicating our novel technologies have the potential to be a very powerful tool for the analyses of the activation-deactivation dynamics in channel proteins.
We report the simple preparation of highly aligned metal nanoparticle arrays comprised of Au nanoparticles 30 nm in diameter and their microscopic analysis. The prepared arrays were a hundred nanometers wide and millimeters long. This technique, which is based on the process of evaporation-induced self-assembly with DNA and drying front movement, eliminates the need for lithography and an external field, and is fast, cheap and easy. A combination of dark-field microscopy and microspectroscopy were used to study the optical characteristics of the arrays. Higher optical responses were observed in the arrays when the light was polarized parallel to the arrays, indicating a uniaxial alignment of Au nanoparticles along the arrays. Optical properties of arrays observed in this study were satisfactorily explained by theoretical calculations reported in the other study, and the morphology of the arrays was characterized by scanning electron microscopy (SEM). Our results demonstrate the use of evaporation-induced self-assembly with DNA as a straightforward method to align metal particle arrays, producing highly anisotropic coupling of localized plasmon.
We have investigated the formation of carbon nanotubes (CNTs) by the SiC surface decomposition method using transmission electron microscopy. When the SiC (000-1) surface was irradiated by Ar+ ions at 1 keV with a dose of 5×1015 cm−2 followed by annealing at 1700oC for 2 h, long CNTs were formed on the surface. In the case of SiC (0001) surface, on which graphene layers are obtained without Ar ion bombardment, CNTs were formed on the surface with Ar ion bombardment. These results indicate that a damage of the surface effects the CNT formation in the SiC surface decomposition method.
We have investigated the formation of graphene on the SiO2/Si (111) surfaces using scanning tunneling microscopy. When the SiC (111) film [1500 nm] formed on the SiO2 surfaces was annealed at 980oC, graphene layer was obtained on the SiC surface. When the thickness of the SiC film was 5 nm, the graphene was not observed. However, graphene layer was obtained on the SiO2 surfaces after annealing the C-covered SiC (111) [5 nm] film on the SiO2/Si (111) surfaces at 980oC.
In this study, carbonaceous material was prepared from coffee grounds as follows: coffee grounds were treated with 1 mol/L calcium chloride solution, and calcined at 600, 800, and 1000oC (CG600, CG800, and CG1000). Subsequently, CGs were treated with 6 mol/L hydrochloric acid solution. Amount of nitrate ion or nitrite ion adsorbed was in the order CG1000 < CG800 < CG600, which indicated that amount adsorbed depended on properties of CG surface (specific surface area and pore volume). The adsorption mechanism of nitrate ion or nitrite ion was ion exchange (1:1) present on the surface of CG600. The adsorption isotherm date were fitted to the Freundlich and Langmuir equations. In binary solution, nitrate ion and nitrite ion were competitive adsorption. CG600 was applied for tap water with a column. Condition 3 (S.V.: 4.3 l/hr, L.V.: 0.4 m/hr) was the most suitable for adsorption of nitrate ion.