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Isotopes and materials


1. Preparation of isotopically-controlled materials and their physical properties

1.1 Preparation of isotopically-controlled materials by ion beam deposition

1.2 Development of an appratus to measure thermal diffusivity of thin films using a subpicosecond pulse laser

1.3 Improvement of a calorimeter for small sample


2. Isotope effects for functional materials and improvement of a calorimeter

2.1 D-H replacement on perovskite-type oxides

2.2 Location of hydrogen atoms in proton conducting oxides


3. Development of functional materials by application of isotope ion irradiation

3.1 Development of a new material providing luminescence in ultraviolet light region by isotope ion irradiation

3.2 Interface reaction and embedded N-isotope-rich film growth under ion implantation


4. Behaviors of hydrogen isotope ions injected into solids and their applications

- Surface blistering mechanism of solids studied by grazing incidence electron microscopy -

 


1. Preparation of isotopically-controlled materials and their physical properties

1.1 Preparation of isotopically-controlled materials by ion beam deposition


We have been prepareing isotopically controlled materials by ion beam deposition (see below).

IBD
Fig.1 The low-energy ion accelerator for ion beam deposition.

We have already succeeded in preparing single crystals of 56Fe, 28Si, 74Ge and so on. Electron diffraction (see below) and Rutherford backscattering spectroscopy have indicated that the 74Ge single crystals include few defects in them.

Electron diffraction patterns of 74Ge film

Fig.2 Electron diffraction patterns of the 74Ge film prepared by ion beam deposition; left: RHEED, right: LEED.

[Published papers]

  1. Takahiro Asai, Masanori Takeuchi, Akihiro Urano, Yasushi Kobayashi, Yuuichi Fukuda, Junji Yuhara, Takanori Nagasaki, Tsuneo Matsui, "Characterization of ion beam deposited 107Ag thin films on Si(111) surface by means of Rutherford backscattering spectroscopy and reflection high energy electron diffraction," J. Nucl. Sci. Technol. 43 (2006) 386-390.

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1.2 Development of an appratus to measure thermal diffusivity of thin films using a subpicosecond pulse laser

We have been developing an appratus to measure thermal diffusivity of isotopically controlled thin films using a subpicosecond pulse laser. It is unique in that it can measure temperature transient with high time resolution (<1 ps) for relatively long time (>10 ns).

Subpicosecond laser flash appratus
Fig.3 Subpicosecond laser flash appratus.

[Published papers]
  1. T. Nagasaki, H. Ohno, Y. Arita, T. Matsui, "Applicability of subpicosecond pulse lasers to determining thermal diffusivity of metals," J. Phys. Chem. Solids 66 (2005) 560-564.

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1.3 Improvement of a calorimeter for small sample

A calorimetr which is used for measurement of specific heat capacity and electrical conductivity has been improved to measure small specimens.

Target of small specimen
Fig.4 Target of small specimen.

[Published papers]

  1. Arita Y, Suzuki K, Matsui T, "Development of High Temperature Heat Capacity Measurement by Direct Heating Pulse Calorimetry", J.Phys.Chem.Solids, 66(2005) 231-234.

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2. Isotope effects for functional materials and improvement of a calorimeter

2.1 D-H replacement on perovskite-type oxides


Deutrium implanted in perovskite-type oxide was exposed to Ar gas including a little water at room temperatures. The exchange of D implanted in near surfaces for H was in-situ measured using the ERD technique. It was found that the exchange of D for H increased with increasing the temperature.

ERD spectra
Fig.5 Typical ERD spectra of H and D recoiled from BaCe0.9Y0.1O3-δ, implanted with D and subsequently exposed to Ar gas including water vapor.

[Published papers]

  1. Morita K, Tsuchiya B, Nagata S, Katahira K, Yoshino M, Arita Y, Ishijima T, Sugai H, "Temperature dependence of the D-H replacement rates in D-implanted oxide ceramics exposed to H2O vapor", Nucl. Inst. Meth. B, 258 (2007) 282-286.

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2.2 Location of hydrogen atoms in proton conducting oxides


Some of the aliovalently doped oxygen-deficient perovskite oxides absorb water in humid atmosphere, thereby becoming proton conductors. They are of fundamental interest as well as of practical one because of their potential applications to protonic devices including fuel cells. In order to understand the transport of hydrogen in these materials, it is necessary to locate the crystallographic sites and trace the diffusion paths of protons in them.

Neutron diffraction is an ordinary approach to characterize crystal structures including light elements. In the case of neutron diffraction for hydrogen bearing materials, protons are usually replaced by deuterons becasue the former have a very large incoherenet neutron scattering length.

In this study, we prepared D2O-dissolved BaSn0.5In0.5O2.75 samples and collected their neutron powder diffraction data at 10 - 473 K. Analyzing the data by the Rietveld method and the maximum entropy method, we found that hydrogen atoms are located at or very close to the 12h site of the cubic perovskite structure (space group Pm3m) with an O-H distance of 1.0 Å.

3D distributions of nuclear scattering length density

Fig.6 Three-dimensional distributions (isosurfaces at 0.5 fm/Å3) of nuclear scattering length density in BaSn0.5In0.5O2.75 with and without dissolved D2O at 77 K.

[Published papers]
  1. T. Ito, T. Nagasaki, K. Iwasaki, M. Yoshino, T. Matsui, "Water uptake and infrared absorption in SrZr0.95M0.05O3-α (M = Ga, Sc, Y and Nd)," J. Therm. Anal. Calorim. 81 (2005) 545-548.
  2. Tsuyoshi Ito, Takanori Nagasaki, Kouta Iwasaki, Masahito Yohino, Tsuneo Matsui, Naoki Igawa, Yoshinobu Ishii, "The determination of deuteron site in SrZr0.95Sc0.05O3-α by neutron powder diffraction," Solid State Ionics 177 (2006) 2353-2356.
  3. Tsuyoshi Ito, Takanori Nagasaki, Kouta Iwasaki, Masahito Yoshino, Tsuneo Matsui, Naoki Igawa, Yoshinobu Ishii, "Location of deuterium atoms in BaSn0.5In0.5O2.75+α by neutron powder diffraction at 10 K," Solid State Ionics 178 (2007) 13-17.
  4. Tsuyoshi Ito, Takanori Nagasaki, Kouta Iwasaki, Masahito Yoshino, Tsuneo Matsui, Hiroshi Fukazawa, Naoki Igawa, Yoshinobu Ishii, "Location of deuterium atoms in BaSn0.5In0.5O2.75+α at 77-473 K by neutron powder diffraction," Solid State Ionics 178 (2007) 607-613.

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3. Development of functional materials by application of isotope ion irradiation

3.1 Development of a new material providing luminescence in ultraviolet light region by isotope ion irradiation


Ge+ ion implantation to silica glass samples were performed to produce the sites providing luminescence in ultraviolet light region. In order to control the optical property of this sample, the aggregation state of implanted atoms is one of the most important factors. The aggregation state depends on not only the amount of implanted atoms but also the chemical state and amount of produced defects around implanted atoms. In this work, we control the defect density using Ge isotope atoms.

luminescence of silica glass samples
Fig.7 Generation of the sites providing luminescence in ultraviolet light region by Ge+-implantation to silica samples.

Ge-EXAFS
Fig.8 FT of k3-weighted EXAFS spectrum of the Ge+-implanted silica sample with 2×1016/cm2.

Table1 Analytical results of EXAFS

  CN R(Å) Δσ
Ge-O 1.9 1.76 0.09
Ge-Ge 1.5 2.47 0.0
CN: coordination number, R: interatomic distance, Δσ: Debye Waller

We succeeded to produce the site providing luminescence at 3.1.eV in a silica glass. EXAFS analysis revealed that small clusters as Ge dimier and/or trimer are formed in the silica glass.

[Published papers]
  1. Yoshida T., Muto S., Tanabe T., "Measurement of soft X-ray excited optical luminescence of a silica glass," API conference proceedings (XAFS13) 882 (2007) 572-574.
  2. Watanabe M., Yoshida T., Tanabe T., Muto S. Inoue A. and Nagata S., "Observation of defect formation process in silica glasses under ion irradiation," Nucl. Instr. and Meth. B 250 (2006) 174-177.
  3. Yoshida T., Tanabe T. Watanabe M., Takahara S. and Mizukami S., "Study of damaging process in silica by in-situ hyrogen-induced luminescence measurements," J. Nucl. Mater. 329-333 (2004) 982-987.

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3.2 Interface reaction and embedded N-isotope-rich film growth under ion implantation


Non-thermal process or interface reaction is investigated for N-ion implantation into Si3N4-film to SiO2-substrate interface and AlN-film to R(11-20)-cut-Al2O3-substrate interface. Applications of non-thermal process under N-isotope-ion implantation are explored to embedded N-isotope-rich-film growth and new functional material generation.

Nitride films were prepared by RF-magnetron-sputter-method in N2 gas (natural abundance 99.63 % 14N). X-ray diffraction (XRD) shows that the Si3N4-film is amorphous and the AlN film hexagonal- wurtzite crystal structure with a-axis orientation. The films were implanted with 14N and 15N ions at room temperature. The film thickness is ~ 200 nm and close to the mean projected range (180 nm) of 100 keV N.

Fig.9 shows the RBS spectra of the 100 keV 14N ion implanted (1.5×1017/cm2) and unimplanted AlN films. It appears that the composition in the film is remained stoichiometric and that the film thickness increases by ~ 20 nm. Nuclear reaction analysis of depth profile for 15N ion implantation shows that 15N's are located around the film-to-substrate interface. The optical absorption also shows a similar amount of the film thickness increase. The increase of the film thickness can be understood as interface reaction and growth of nitride film (Si315N4, Al15N) near the interface for 15N ion implantation.

RBS spectra of AlN film
Fig.9 RBS spectra of AlN film on R-Al2O3 before and after 100 keV 14N-ion implantation at 1.5×1017 cm-2. Al(surf.) and N(surf.) indicate the energies of He scattered from Al and N located at the film surface, and N(int.) indicates the energy of He from the AlN-to-Al2O3 substrate interface.

AlN or Si3N4 growth under N-15 implantation

Fig.10 Schematics of Al15N or Si315N4 growth under 15N implantation.

[Published papers]
  1. N. Matsunami, T. Murase, M. Tazawa, et al.: Analysis of N isotope depth profiles in search for reaction of implanted nitrogen with substrate near Si3N4-nitride-film and SiO2-glass- substrate interface, Nucl. Instr. Meth. B 249 (2006) 185-188.
  2. N. Shinde, N. Matsunami, O. Fukuoka et al: Reaction of implanted N isotope with SiO2 near Si3N4-film and SiO2-substrate interface, J. Nucl. Sci. Technol. 43 (2006) 382-385.
  3. N. Matsunami, T. Shimura, M. Tazawa et al.: Modifications of AlN thin films by ions, Nucl. Instr. Meth. B 257 (2007) 433-437.

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4. Behaviors of hydrogen isotope ions injected into solids and their applications

- Surface blistering mechanism of solids studied by grazing incidence electron microscopy-


Surface blisters: hollow surface protrusions are often formed on materials of fission and fusion reactors, suffering from high density of energetic gas ion irradiation, which is a serious problem from the point of view of materials degradation. We developed a novel method that non-destructively observes surface topography as well as internal structures by introducing the incident electron at an grazing angles to the materials surface, called grazing incidence electron microscopy (GIEM). Furthermore, we clarified the blistering mechanisms on light element semiconductors and tungsten surfaces formed by hydrogen isotopes and helium ion irradiations, by means of computer simulations such as molecular dynamics and finite element method.

GIEM images of blisters on tungsten surface
Fig.11 GIEM images of blisters on tungsten surface by H+ (left) and D+ (right) irradiation.
Irrad. Temperature: room temp., Fluence: 1×1024m-2

strain distributions
Fig.12 Elastic (left) and plastic (right) strain distributions of a H+-irradiated blister on tungsten, simulated by FEM.

The present study enabled us to examine the blister skin structures and quantitatively estimate the internal pressures and gas retentions. We also proposed new mechanism that causes large plastic deformations in non-ductile hard materials.

[Published papers]
  1. S. Nakano, S. Muto and T. Tanabe, "Irradiation-induced hardening/softening in SiO2 studied with instrumented indentation", Mater. Sci. Eng. A 400-401 (2005) 382-385.
  2. S. Muto and N. Enomoto, "Substructures of gas-ion-irradiation induced surface blisters in Si studied with cross-sectional transmission electron microscopy", Mater. Trans. 46(10) (2005) 2117-2124.
  3. S. Nakano, S. Muto and T. Tanabe, "Change in Mechanical Properties of Ion-Irradiated Ceramics Studied by Nanoindentaion Method", Mater. Trans. 47 (2006) 112-121.

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