Shigeo Kotake

Evaluation of thermal rectification at the interface of dissimilar solids by phonon heat transfer

Many investigations have suggested that the heat transfer coefficient at the interface between two dissimilar solids depends on the direction of heat flow across the interface. Although many factors that affect heat transfer across the interface are reasonably well understood, the directional dependence of the heat transfer coefficient, called thermal rectification, has not yet been completely explained. In this paper, we evaluate the thermal rectification from the results of linear response theory by considering scattering and transmission of phonons across the interface, which expresses the dependence of the temperature at the interface. This model explains the reported behavior of thermal rectification.

Vibration manipulation function as general lifting function for discrete sampled-data tracking control of 1DOF oscillator

Intermittent lifting function, termed vibration manipulation function (VMF), is proposed as a general formula of inverse problem to manipulate a linear one-degree-of-freedom (1DOF) oscillator. Discrete sampled-data tracking control is realized by using the continuous intermittent feedforward control and discrete sampled-data feedback decided from previously determined discrete aimed states in every operating instant. Since VMF can be modified repeatedly from the discrete error deviation, we can minimize error deviation between discrete sampled output and discrete aimed value in order to make the system robust.

Cubic BN formation by ion implantation

Abstract Boron nitride was synthesized by nitrogen ion implantation. Boron films were prepared as implantation targets on single-crystal Si(100) substrates by 13.56-MHz radio frequency sputtering. The diatomic single 30-keV nitrogen ions were chosen for implantation. The implantation dose ranged from 1×10 17 ions/cm 2 to 2×10 18 ions/cm 2 . The films were characterized using a transmission electron microscope. Several phases of boron nitride were found at the medium implantation dose. At the high dose of 2×10 18 ions/cm 2 , the pure c-BN phase was observed. It is believed that the transition from the low ordered phases to c-BN phase occurred during implantation. The films showed good adhesion to the Si substrate.

Influence of Containerless Solidification on Hardness in Multifunctional Titanium Based Alloys

A novel synthesis procedure of multifunctional Ti based alloy was suggested under containerless processing using an electromagnetic levitation furnace. In this method, necessary condition to synthesize the alloys with ability of a dislocation-free plastic deformation was determined. That was supported by microstructural observation, hardness measurement and X-ray analysis of the alloys solidified from several undercoolings. The maximum undercooling of the alloy melt was up to 120K. Synthesized alloys that met the condition showed refined microstructures, increase of d-value of (110) plane and a tiny deviation of hardness by cold-working Others partially occurred stress-induced transformation.

MICROSTRUCTURAL OBSERVATION OF BORON NITRIDE FILMS SYNTHESIZED BY ION IMPLANTATION

We report on the synthesis of boron nitride (BN) films by ion implantation and demonstrate the results of microstructural observation of the films. Boron films were initially prepared on single-crystal Si(100) substrates by rf sputtering. Then, 30 keV N2+ was implanted at doses ranging from 1×1017 ions/cm2 to 6× 1017 ions/cm2 to synthesize BN. No substrate heating was used in the sputtering and implantation processes. Chemical composition analysis of the films was carried out by Auger electron spectroscopy. Transmission electron microscopy was employed for microstructural observation. Mixed-phase BN, including t-BN, c-BN, w-BN and B25N, was identified in the implanted films. The BN formation mechanism was discussed and compared with theoretical models. The results of this work are consistent with the stress-induced BN formation model in several aspects.

Origin of Extra Diffraction Spots in C60/C70 Epitaxial Films Sublimed on Mica Substrates

Anomalous diffraction spots in (111) C60/C70 epitaxial films were investigated by high-resolution electron microscopy. It was revealed that the hcp phase existed in a very thin film while the fcc phase became dominant with increasing film thickness. The origin of extra spots and their thickness dependence were explainable by assuming that the hcp phase was stabilized by the interaction produced by the substrate.

Investigation of GaN Solution Growth Processes on Ga- and N-Faces by Molecular Dynamics Simulation

We carried out the molecular dynamics simulation of the solution growth of GaN and investigated the growth processes on Ga- and N-faces. An empirical potential function of the Brenner potential was used for the simulations. The simulation cell consisted of GaN substrates with Ga- and N-faces and Ga solution including N atoms. The results showed that the growth surface on the Ga-face laterally developed from a two-dimensional nucleus and became flat. On the other hand, the growth surface on the N-face developed by adhesive growth and became rough.

Evaluation of Fracture Surface of 11/4Cr-1/2Mo Steel by Residual Magnetization Induced from Inverse-Magnetostrictive Effect

In this study, we propose a new technique to evaluate some properties during fracture propagation, such as stress at the crack surface and the propagating-route by measuring distributions of leaked magnetic flux vector from the residual magnetization in the vicinity of the fracture surface. The technique involves the application of an inverse-magnetostrictive effect in ferromagnetic materials, such as tempered 11/4Cr-1/2Mo steels below the ductile-brittle transition temperature. The maximum magnetic flux density was increased with impact absorption energy measured by Charpy impact test. The highest magnetic flux density located at the crack starting point, where a fish-eye type surface morphology was observed in fractographic analysis. It indicates the highest stress for fracture initiation at this point. According to the analysis, the change in the magnetic flux vectors corresponds with the direction of crack propagation, which was well explained from the magnetostrictive properties of iron. The measurement of magnetic flux density distribution will be useful for the fractographic analysis to discuss the in-situ phenomena that are difficult to obtain in previous methods.

Simulation on the instability of a solid–liquid interface from a molar flux with a diffuse interface layer

Abstract A simulation method based on a diffuse-interface-flux model is proposed for the pattern formation during crystal growth. A numerical scheme was extended for the general treatment of solidification from simple analytical conditions. A diffuse interface with width δ is assumed between the solid and liquid phases. The molar flux between solid and liquid is balanced at the diffuse interface layer as a field of diffusion. The shape of the interface proceeds under the phase transition of the interface layer to solid or liquid. To ascertain the validity of the method, uniaxial solidifications of dilute binary alloy were simulated to observe some morphological transitions from planner to cellular interface. The wavelengths of cellular interface agree well with those from the Mullins–Sekerka model.

Synthesis and characterization of iron carbide nanorod under pulsed plasma

Study on the growth of nanarod by means of pulsed plasma chemical vapor deposition was reported. Pure iron plate was used as a substrate acted as both the supporter and catalyst for growing nanorod. The effects of hydrogen plasma treatment and methane plasma treatment in the synthesis processes were studied. Nanoparticles were formed on substrate treated by negative hydrogen plasma while nanorods were grown on these nanoparticles after further treatment by methane plasma. The suitable times for hydrogen plasma and methane plasma treatment were both 10 min. Nanorod was about 60 nanometers in diameter and about 600 nanometers in length. The diffraction of nanorods was agreed with crystal structure of iron carbide.