Yoshihisa Kimoto

Molecular dynamics studies on mechanical properties of carbon nano tubes with pinhole defects

In this paper, the mechanical properties with defected carbon nano tube (CNT) by pinhole defects are studied by molecular dynamics study to investigate influences to the yield strength and vibration properties for multiple defects of CNT.

Molecular dynamics study of double-walled carbon nanotubes for nano-mechanical manipulation

In this paper, we study the on the mechanical property about the manipulation of the inner tube in DWNTs by a molecular dynamics simulation based on Van der Waals force for mutual interaction between inner and outer tubes.

Molecular Dynamics Study of Yield Stress of Si Mold for Nanoimprint Lithography

Molecular dynamics studies are carried out to investigate the fracture mechanism of a crystalline Si mold for nanoimprint lithography (NIL). The stress–strain characteristics are evaluated for mold models with various crystalline orientations, and temperature effects on strength are calculated. It is found that the behavior of the fracture and the yield stress of the mold are strongly associated with the configurations of the {111} planes in the mold. The simulation results indicate that crystals with a {100} top surface are more suitable for a mold with arbitrary patterns than those with a {110} top surface because of the weaker dependence of yield stress on crystalline orientation.

Mold Design and Fabrication for Surface Relief Gratings by Glass Nanoimprint

Mold shape has been optimized to fabricate one-dimensional glass gratings with a high aspect ratio. Comparison of experimental and simulated results demonstrated that a periodic groove with a tilted sidewall, a parabolic top tooth, and a large width was preferable to imprint high-aspect-ratio gratings on a glass surface. In particular, a mold with a parabolic top tooth and a wide groove was effective to increase the aspect ratio. In the case of a mold with a 500 nm period, a grating of 540 nm height could be imprinted under the respectively optimized imprinting parameters of 430 °C, 5 MPa, and 5 min.

Fabrication of Homogeneous Bulk Nanocrystalline Ni-W Alloys by an Electroforming Process

Many studies have been conducted on mechanical properties in nanocrystalline Ni-W alloys. However, since these results are obtained in the specimens whose thickness is less than 100 μm and whose homogeneity is not strictly controlled, an inherent potential of the nanocrystalline Ni-W alloy may be hidden. Therefore, it is necessary to fabricate the bulk Ni-W alloy with sufficient thickness and homogeneity. In the present study, we develop novel electroforming process and fabricate the homogeneous nanocrystalline Ni-W alloys. The homogeneities of W-concentration in micrometer scale are confirmed by the W-concentration profiles obtained by the linear analyses of the energy dispersed spectroscopy (EDS). The single-phase nanocrystalline bulk Ni-W alloy with the thickness above 2 mm and minimized W-concentration gradient and fluctuation is featured for the first time.

Fabrication of the bulk amorphous Ni-W alloy by an electroforming process

A 2mm-thick bulk amorphous Ni-W alloy is formed by applying a new electroforming process and its states are investigated by the XRD analyses and the EDS measurement. The homogeneities of the electroformed alloys are evaluated by the linear analyses on the cross sections of the sample. The fluctuation of the millimeter-scale W-concentration of the bulk amorphous alloy obtained in the present work is reduced to almost the same as that of the bulk nanocrystalline alloy reported in the previous work. Compared to the thin-film specimen produced by the conventional electroplating processes, the gradient of W-concentration of the bulk amorphous specimen can be reduced to two-fifth in the micrometer-scale profiles. Therefore new electroforming process can be successfully applied to the fabrication of the bulk amorphous Ni-W alloy.

Molecular Dynamics Study on Resolution in Nanoimprint Lithography for Glass Material

A theoretical study of resolution in nanoimprint lithography (NIL) has been carried out using molecular dynamics (MD) simulation. We have performed a MD simulation for glass NIL, monitored the friction force during entire NIL process and evaluated the deformed shapes of glass patterns after the mold releasing. The resolution in NIL is governed by the maximum tensile stress acting on the glass, which is induced by the friction force during the mold releasing. Based on the distribution of average number density of atoms in the molded glass, the ultimate resolution in the glass NIL has been proved to be 0.4 nm.

Microstructural Evolution of Body-Centred Cubic Fe-Al Alloy by Friction Stir Processing with SiC Particles Addition

The surface of body-centred cubic Fe-7Al (mass%) alloy plate was successfully modified by friction stir processing with SiC particles addition. The stir zone with SiC addition had an average grain size of 5.9 μm, smaller than that of 10.1 μm in the stir zone without SiC addition. SiC particles introduced by friction stir processing were converted to fine Fe3AlCx particles by reaction with the ferrite matrix. The hardness near the surface of the stir zone was significantly increased to 351 HV by introduction of particles, compared to the hardness of 200 HV in the stir zone without particles addition. The dispersed particles also contributed to suppression of grain growth of the matrix at elevated temperature.

Molecular Dynamics Study of Electron Irradiation Damages in Carbon Nanomaterials

Molecular dynamics (MD) studies are carried out to investigate the electron irradiation damages in carbon nanomaterials. The interaction between an incident electron and a carbon atom is modeled based on the Monte Carlo method using the elastic scattering cross section. The electron irradiation damages in graphen, graphite, single-walled carbon nanotube (SWNT) and carbon nanopeapod are demonstrated. The cross-links among the nanostructures caused by the knock-on effect are observed as typical damages. The dependence of the damages on the electron primary energy is also shown for the SWNT.

Nanostructurization of Magnesium Alloy via Friction Stir Lap Processing

Friction stir processing (FSP) in a lap configuration of a metal sheet and an alloy plate has been examined to produce surface alloy layer with nanostructures. The 1-pass friction stir lap processing (FSLP) over 0.5 mm-thick Cu sheet on an AZ91 substrate produced multilayer structure with nanograins and/or nanoprecipitates in each layer, but the structure distributed only partially in the stir zone (SZ). Through the 3-pass FSLP along the same line, the multilayer structure has disappeared and the fine structure with precipitates in size ranging from several 100 nanometer to 3 micrometer has yielded among the entire SZ. 2-dimensional microhardness mapping have shown that the standard deviation of microhardness values in the SZ has decreased by half from 1-pass to 3 pass FSLP. Homogeneous microstructure involving nanostructures has been successfully produced via multi-pass FSLP.