Tailoring crystallinity and configuration of silica nanotubes by electron irradiation

Taguchi, Tomitsugu; Yamaguchi, Kenji

Nuclear Instruments and Methods in Physics Research B, 350, p.1 - 5, 2015/05

https://doi.org/10.1016/j.nimb.2015.03.040

SiO nanotubes show potential in applications such as nanoscale electronic and optical devices, bioseparation, biocatalysis, and nanomedicine. As-grown SiO nanotubes in the previous studies always have an amorphous wall, and here we demonstrate the successful synthesis of single-crystal nanotubes for the first time by the heat treatment of SiC nanotubes at 1300 C for 10 h under low-vacuum conditions. According to TEM observations, the single-crystal SiO was -cristobalite. We also demonstrate that single-crystal SiO nanotubes can be transformed into amorphous SiO nanotubes by electron beam irradiation. Moreover, we synthesized a crystalline/amorphous SiO composite nanotube, in which crystalline and amorphous SiO coexisted in different localized regions. In addition, for biomedical applications such as drug delivery systems, controlling the configuration of the open end, the diameter, and capsulation of SiO nanotubes is crucial. We can also obturate, capsulate, and cut a SiO nanotube, as well as modify the inner diameter of the nanotube at a specific, nanometer-sized region using the focused electron beam irradiation technique.

2D neutron diffraction imaging on an ammonite

Shamoto, Shinichi; Kodama, Katsuaki; Imaki, Tadashi*; Nakatani, Takeshi; Oshita, Hidetoshi*; Kaneko, Naokatsu*; Masuko, Kenji*; Sakamoto, Kensaku; Yamaguchi, Kenji; Suzuya, Kentaro; et al.

JPS Conference Proceedings (Internet), 1, p.014011_1 - 014011_5, 2014/03

https://doi.org/10.7566/JPSCP.1.014011

2D neutron diffraction imaging of an ammonite fossil was carried out at high-intensity total diffractometer NOVA in J-PARC. Observed diffraction profiles consist of calcite, siderite and amorphous structures.

Optimization of substrate pretreatment and deposition conditions for epitaxial growth of -FeSi film on Si(100)

Yamaguchi, Kenji; Hamamoto, Satoshi*; Hojo, Kiichi

Physica Status Solidi (C), 10(12), p.1699 - 1703, 2013/12

https://doi.org/10.1002/pssc.201300355

Effect of substrate treatment conditions, deposition temperature and deposition rate on the crystallinity of -FeSi films formed on Si substrate was investigated. The substrates were treated with Ne ion beams at room temperature and then annealed at 1073 K prior to film fabrication by means of ion beam sputter deposition (IBSD) method. Combinations of experimental parameters which promote the epitaxial relationship of -FeSi (100) // Si (100) were defined. Complicated dependence of these experimental parameters on the film structure indicated that careful optimization of substrate treatment conditions and deposition parameters would enable to obtain -FeSi films with excellent crystalline properties.

Direct stress measurement of Si(111) 77 reconstruction

Asaoka, Hidehito; Yamazaki, Tatsuya; Yokoyama, Yuta; Yamaguchi, Kenji

Journal of Crystal Growth, 378, p.37 - 40, 2013/09

https://doi.org/10.1016/j.jcrysgro.2012.12.124

We have focused on stress measurements of the reconstructed Si(111) 77 and the H-terminated Si(111) 11 surfaces. In order to obtain information on both the surface stress and the surface structure simultaneously, we have combined the surface-curvature and the reflection-high-electron-energy-diffraction instrumentations in an identical ultrahigh vacuum system. At the beginning of Ge wetting layer growth on H-terminated Si(111), the stress gradient drastically changes accompanied by change in the surface structure resulting from the H desorption. Comparison of the surface stress behaviors between Ge wetting layer growth on the H-terminated Si(111) 11 and the Si(111) 77 surfaces reveals that the Si(111) 11 surface releases 1.6 N/m (=J/m), or (1.3 eV/(11 unit cell)), of the surface energy from the strong tensile Si(111) 77 reconstruction.

Fabrication of highly-oriented silicide film on Si substrate treated by low-energy ion beam

Hamamoto, Satoshi*; Yamaguchi, Kenji; Hojo, Kiichi

Transactions of the Materials Research Society of Japan, 38(1), p.89 - 92, 2013/03

https://doi.org/10.14723/tmrsj.38.89

Experimental and computational studies on tritium permeation mechanism in erbium oxide

Mao, W.*; Chikada, Takumi*; Suzuki, Akihiro*; Terai, Takayuki*; Yamaguchi, Kenji

Journal of Plasma and Fusion Research SERIES, Vol.10, p.27 - 32, 2013/02

http://www.jspf.or.jp/JPFRS/PDF/Vol10/jpfrs2013_10-027.pdf

A tritium permeation barrier (TPB) is strongly required in fusion blankets for the reduction of loss of fuel and radiological hazard. However, the precise tritium permeation mechanism through the TPB coatings has not been clarified yet, because of their complicated crystal structures. To understand the microscopic mechanism, we have not only prepared and characterized nanostructured ceramic ErO thin films, but also studied the energetics and mobility of hydrogen atom in cubic bulk ErO using ab initio density-functional calculations. The estimated diffusion activation energy () of interstitial H is somewhat higher than the diffusion energy barrier observed experimentally at 873 K. It is then considered that diffusion and permeation of hydrogen and its isotopes through the ErO coatings are likely to be dominated by the grain boundary rather than by the grain.

Surface structures on -FeSi formed by heat-treatment in ultra-high vacuum and their influence for homoepitaxial growth

Matsumura, Seidai*; Ochiai, Kunihito*; Udono, Haruhiko*; Esaka, Fumitaka; Yamaguchi, Kenji; Yamamoto, Hiroyuki; Hojo, Kiichi

Physics Procedia, 11, p.174 - 176, 2011/02

https://doi.org/10.1016/j.phpro.2011.01.048

The surface structures on the surface of -FeSi substrate after heat treatment in ultra high vacuum and their influence on homoepitaxial growth were investigated. It was found that the dip structures appeared on the surface of -FeSi (100) substrate after heat treatment above 1023 K, where the evaporation of surface oxide layer (SiO) occurred. The composition of the dip structure was Fe-rich as compared to nominal -FeSi composition (Si/Fe=2). This result indicates that the decomposition from -FeSi to -FeSi would occur on the surface. The surface morphology observed after heat treatment depended on the orientation of the substrate. In addition, homoepitaxial films with smooth surface on -FeSi (111) substrate at the growth temperature of 973 and 1073 K were obtained.

Spectroscopic characterization of -FeSi single crystals and homoepitaxial -FeSi films by XPS and XAS

Esaka, Fumitaka; Yamamoto, Hiroyuki; Udono, Haruhiko*; Matsubayashi, Nobuyuki*; Yamaguchi, Kenji; Shamoto, Shinichi; Magara, Masaaki; Kimura, Takaumi

Applied Surface Science, 257(7), p.2950 - 2954, 2011/01

https://doi.org/10.1016/j.apsusc.2010.10.097

Chemical state analysis by a combination of X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) using synchrotron radiation is performed for -FeSi single crystals and homoepitaxial -FeSi films. The Si 2p XPS and Fe L-edge XAS spectra imply that the annealing at 1173 K to remove native oxide layers on the crystal induces the formation of FeSi in the surface. The formation of FeSi is also confirmed by Si K-edge XAS analysis. For the homoepitaxial -FeSi films grown on the crystals, the Si K-edge XAS spectra indicate that structurally homogeneous -FeSi films can be grown on the -FeSi single crystals when the substrate temperatures of 973 and 1073 K are applied for molecular beam epitaxy (MBE). Consequently, it is indicated that the combination of XPS and XAS using synchrotron radiation is a useful tool to clarify chemical states nondestructively.

Modelling of hydrogen release from functional materials via cellular automaton

Shimura, Kenichiro*; Yamaguchi, Kenji; Terai, Takayuki*; Yamawaki, Michio*

Journal of Alloys and Compounds, 449(1-2), p.357 - 361, 2008/01

https://doi.org/10.1016/j.jallcom.2005.12.130

no abstracts in English

Local neutron transmutation doping using isotopically enriched silicon film

Yamada, Yoichi; Yamamoto, Hiroyuki; Oba, Hironori; Sasase, Masato*; Esaka, Fumitaka; Yamaguchi, Kenji; Udono, Haruhiko*; Shamoto, Shinichi; Yokoyama, Atsushi; Hojo, Kiichi

Journal of Physics and Chemistry of Solids, 68(11), p.2204 - 2208, 2007/11

https://doi.org/10.1016/j.jpcs.2007.08.056

Si in natural Si has been widely used for a doping source, since Si can be transmuted into P by thermal neutron (Neutron Transmutation Doping, NTD). NTD of nanostructure fabricated from Si-enriched materials can serve as a controlled local doping method with tunable dopant concentration, which cannot be realized by conventional doping methods such as ion implantation. In the present study, Si-enriched thin film has been fabricated in order to demonstrate the local NTD. The Si-enriched film with thickness of 100 nm was deposited on the Si(100) substrate by plasma enhanced chemical vapor deposition using Si-enriched SiF as the source gases. The film contains 7.1 % of Si, which is twice higher than that of natural Si. Possible contaminant, fluorine, is lower than 0.6 at.% determined from X-ray photoelectron spectra. Nanostructure of films and changes of electronic properties by the neutron irradiation will also be discussed.