Kenji Yamaguchi

Cross-sectional Transmission Electron Microscopy of Interface Structure of β-FeSi2/Si(100) Prepared by Ion Beam Sputter Deposition

The effect of a silicon substrate surface pretreatment on epitaxial iron silicide film formation on a Si(100) substrate with ion beam sputter deposition (IBSD) was investigated. In this study, two surface pretreatment methods namely, thermal etching (TE) and sputter etching (SE) with subsequent thermal annealing, were employed. The interface structure between a β-FeSi2 film and a Si substrate was analyzed by cross-sectional observation using a transmission electron microscope (XTEM). High-resolution XTEM images showed that the lattice of the Si substrate is an almost perfect crystal immediately after the TE treatment. However, the TE treatment results in an undulated interface, and the deposited silicide contained coalesced β-FeSi2 islands. On the other hand, the dislocations and stacking faults produced by radiation damage were observed near the Si substrate surface for the SE treatment. Even though this treatment produced defects, the interface of the SE-treated epitaxial β-FeSi2(100) film had a smooth interface after the deposition at 973 K. It can be concluded that a moderate disorder of the silicon substrate surface treated by SE may well enhance the mixing of Fe and Si atoms for the epitaxial growth of β-FeSi2.

Deposition of hydroxyapatite on SiC nanotubes in simulated body fluid

SiC nanotubes can become candidate reinforcement materials for dental and orthopedic implants due to their light weight and excellent mechanical properties. However, the development of bioactive SiC materials has not been reported. In this study, hydroxyapatites were found on SiC nanotubes treated with NaOH and subsequently HCl solution after soaking in simulated body fluid. On the other hand, hydroxyapatites did not deposit on as-received SiC nanotubes, the SiC nanotubes with NH4OH solution treatment and SiC bulk materials with NaOH and subsequently HCl solution treatment. Therefore, we succeeded in the development of bioactive SiC nanotubes by downsizing SiC materials to nanometer size and treating with NaOH and subsequently HCl solutions for the first time.

Aligned defects behaviour of β-FeSi2 thin film on Si(100) substrate prepared by ion beam sputter deposition

β-FeSi2 is one of the possible candidates for a compound semiconductor. Epitaxial β-FeSi2 films grown on a Si substrate are technologically important for microelectronic and silicon-based optoelectronic applications. In earlier studies, we clarified that the treatment of the Si substrate surface greatly influences the crystal structure of the film. Among several surface treatment procedures, it has been reported that the sputter etching (SE) of the substrate with subsequent thermal annealing is fairly effective in obtaining a film that has a favorable epitaxial orientation relationship of β-FeSi2(100)//Si(100) with atomically smooth interface by choosing better conditions. Even though the obtained films have good quality, anomalous patterns were sometime observed in the dark field image of the obtained film by cross-sectional TEM observation. They formed a horizontal line along the β-FeSi2/Si interface. Higher magnification image shows that these spots are aggregated defects. The lines tend to appear in the samples, which are irradiated in higher energy. However, they are also occasionally observed in 1 keV Ne+ irradiated sample. It can be related to the diffusion process of the silicon atoms and the defects formed in the silicon through Ne+ irradiation. Formation behavior of these aligned defects will be discussed in the present study.

2D Neutron Diffraction Imaging on an Ammonite

Materials Science Research Division, Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan Information Technology Systems Management and Operating Office, Center for Computational Science & e-Systems, Tokai, Ibaraki, 319-1195, Japan J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki, 305-0801, Japan