Papers by Author: Shun Ichiro Tanaka

Abstract: Nanoscale singularity at the reactive wetting front on the 6H-SiC (0006) surface with amorphous oxide layer was studied using video recorded in situ to clarify the dynamic atomistic behaviors of the brazing and the molten tip spreading on a high-temperature stage of a high-resolution transmission electron microscope. A 0.5-nm-thick precursor film spreading ahead of the main molten alloy on SiC (0006) at 1073 K and continuous spreading of the molten alloy were clearly observed on the SiC (0006) surface with a less than 1-nm-thick amorphous layer. Molten Ti and TiC nanolayers preceded the Ti5Si3 nanolayer at the tip and they traveled continuously at a velocity of 14 nm/sec on the plane perpendicular to SiC (0006). Since Ti atoms in the molten alloy diffuse sufficiently rapidly on the SiC surface to the tip, the formation of these layers may be the rate-determining step of spreading. Discontinuous spreading of the precursor tip on SiC (0006) with a thick amorphous film was observed in contrast to the continuous spreading on SiC with a thin film. This suggests that the spreading of the Ti molten alloy on SiC is also controlled by the dissolution of the amorphous layer.

Abstract: Nanoparticles of metastable copper nitride(Cu3N) have been successfully fabricated from Cu mask using Ar ion ‘transcription method’ which is firstly invented by B.-S. Xu, C. Iwamoto and S.-I. Tanaka in 1996 [1]. The structural and morphological changes with irradiation time are studied by transmission electron microscopy (TEM). The thin film-like crystalline Cu3N which is covered with amorphous or polycrystalline cuprite (Cu2O) layer in the as-received Cu mask plays a role of target. Polycrystalline Cu3N nanoparticles nucleate and grow up to the average size of 15nm after 30 sec-irradiation. Coalesence of 50nm-sized grown Cu3N nanoparticles forms polycrystalline thin film after 2min-irradiation and its growth behavior follows Volmer-Weber mode. As irradiation time increases from 30 sec to 15 min, Cu3N nanoparticles are thought to be grown preferentially along the [111] and [100] directions. Cu2O still remain with Cu3N after 15 min.-irradiation.

Abstract: Wetting can be regarded as a kind of effective nanostructure-forming process. To control the structure, a study on the relationship between atomic interactions and the resultant wetting behaviors is required. To model the wetting system, two sets of interatomic potentials for Metal/MgO(100) systems are derived from first principles calculation results for the simple configurations. A molecular dynamics method is applied to simulate the system and shows that Al atoms wet better than Sn atoms on the MgO substrate. The tendency is consistent with the experimental contact angles. The interfacial structures are different between these two systems.

Abstract: Nanoscale singularity at the reactive wetting front on SiC (0006) was studied using video recorded in situ to clarify the dynamic atomistic behaviours of the brazing and the molten tip spreading on a high-temperature stage of a high-resolution transmission electron microscope. An atomistic process controls the wetting at the front of the spreading film where the classical macroscopic phenomenon never holds true and the singularities are observed in a precursor film. A 0.5-nm-thick precursor film spreading ahead of the main molten alloy on SiC (0006) at 1073 K and continuous spreading of the molten alloy were clearly observed on the SiC (0006) surface with a less than 1-nm-thick amorphous layer. Molten Ti and TiC nanolayers preceded the Ti5Si3 nanolayer at the tip and they traveled continuously at a velocity of 14 nm/sec on the plane perpendicular to SiC (0006). Since Ti atoms in the molten alloy diffuse sufficiently rapidly on the SiC surface to the tip, the formation of these layers may be the rate-determining step of spreading. Discontinuous spreading of the precursor tip on SiC (0006) with a thick amorphous film was observed in contrast to the continuous spreading on SiC with a thin film. This suggests that the spreading of the Ti molten alloy on SiC is also controlled by the dissolution of the amorphous layer.

Abstract: Considering the uniqueness of wetting systems consisting of three components, namely, the surface, liquid and liquid/solid interface, it is desirable to construct interatomic potentials following a consistent policy. To investigate the physical meaning of the behavior in terms of the interatomic potentials, the wetting systems are modeled by simple two-body interatomic potentials derived using ab initio molecular orbital calculations for hypothetical clusters representing the above three components. For In and Sn liquid atoms, spreading occurs on a Cu (111) surface, while in contrast, liquid atoms penetrate the substrate and form a surface alloy in the case of a Pd (111) surface.