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Journal Articles

Optimization of substrate pretreatment and deposition conditions for epitaxial growth of $$beta$$-FeSi$$_2$$ film on Si(100)

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

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

 Times Cited Count:0 Percentile:100

Effect of substrate treatment conditions, deposition temperature and deposition rate on the crystallinity of $$beta$$-FeSi$$_2$$ 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 $$beta$$-FeSi$$_2$$ (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 $$beta$$-FeSi$$_2$$ films with excellent crystalline properties.

Journal Articles

Surface effect on ion track formation in amorphous Si$$_{3}$$N$$_{4}$$ films

Morita, Yosuke*; Nakajima, Kaoru*; Suzuki, Motofumi*; Narumi, Kazumasa; Saito, Yuichi; Ishikawa, Norito; Hojo, Kiichi; Tsujimoto, Masahiko*; Isoda, Shoji*; Kimura, Kenji*

Nuclear Instruments and Methods in Physics Research B, 315, p.142 - 145, 2013/11

 Times Cited Count:6 Percentile:46.23(Instruments & Instrumentation)

Journal Articles

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

Journal Articles

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

Semiconducting silicides, such as $$beta$$-FeSi$$_{2}$$, BaSi$$_{2}$$ and Mg$$_{2}$$Si are quite attractive for their potential as optoelectronic, photovoltaic and thermoelectric materials. Authors have shown that thin, uniform and highly-oriented $$beta$$-FeSi$$_{2}$$ films can be fabricated on Si (100) substrates with an atomically flat interface, when the substrates are pre-treated with low-energy ions. Since the use of ion beam introduces irradiation defects to the substrate and the film, semiconducting properties may be affected by such defects. Dependence of the crystalline properties of $$beta$$-FeSi$$_{2}$$films on the irradiated fluence of sputter etching (SE) of the substrate was investigated to discuss whether it is possible to obtain high crystalline $$beta$$-FeSi$$_{2}$$ thin film with very low defect concentration.

Journal Articles

Direct observation of fine structure in ion tracks in amorphous Si$$_{3}$$N$$_{4}$$ by TEM

Nakajima, Kaoru*; Morita, Yosuke*; Suzuki, Motofumi*; Narumi, Kazumasa; Saito, Yuichi; Ishikawa, Norito; Hojo, Kiichi; Tsujimoto, Masahiko*; Isoda, Shoji*; Kimura, Kenji*

Nuclear Instruments and Methods in Physics Research B, 291, p.12 - 16, 2012/11

 Times Cited Count:11 Percentile:30.67(Instruments & Instrumentation)

Thin films of amorphous Si$$_{3}$$N$$_{4}$$ (thickness 20 nm) were irradiated with 120-720 keV C$$_{60}$$$$^{+,2+}$$ ions and observed using transmission electron microscopy (TEM). The ion track produced in an amorphous material was directly observed by TEM. For quantitative analysis, the ion tracks were also observed using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The observed ion track consists of a low density core (radius $$sim$$2.5 nm) and a high density shell (width $$sim$$2.5 nm), which is very similar to the ion tracks in amorphous SiO$$_{2}$$ irradiated with high energy heavy ions observed by small angle X-ray scattering (SAXS). Although the observed ion tracks may be affected by surface effects, the present result indicates that TEM and HAADF-STEM have potential to observe directly the fine structures of ion tracks in amorphous materials.

Journal Articles

Application of sputter etching treatment to the formation of semiconducting silicide film on Si substrate

Yamaguchi, Kenji; Esaka, Fumitaka; Sasase, Masato*; Yamamoto, Hiroyuki; Hojo, Kiichi

Transactions of the Materials Research Society of Japan, 37(2), p.245 - 250, 2012/06

"Semiconducting silicides", such as $$beta$$-FeSi$$_2$$, BaSi$$_2$$, Mg$$_2$$Si, etc. are composed of elements which are non or less toxic and are naturally abundant, so that they are considered to be ecologically friendly. These materials are being investigated for applications in optoelectronics, photovoltaics, photonics, thermoelectrics, and so on. In order to fabricate silicide films on crystalline Si substrate, sputter-etching (SE) of the substrate with low energy ion beams has been successfully applied. When the conditions are met, a highly-oriented $$beta$$-FeSi$$_2$$ (100) film can be grown on Si (100) substrate by means of ion beam sputter deposition method. According to cross-sectional transmission electron microscopy (TEM) observation, the interface of the SE-treated substrate and the film deposited at 973 K is smooth, although some defects are produced as a result of this treatment. On the other hand, a combination of X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) revealed that relatively homogeneous $$beta$$-FeSi$$_2$$ surface is formed at this temperature. In order to further improve the film properties with smaller amount of defects, SE-treatment is performed with the ions whose incident energy is below 1 keV. X-ray diffraction (XRD) analysis confirmed that highly-oriented $$beta$$-FeSi$$_2$$ (100) film can be also obtained with SE-treatment by 0.8 keV Ne$$^+$$ ions, as in the case of 3.0 keV Ne$$^+$$.

Journal Articles

Surface structures on $$beta$$-FeSi$$_2$$ 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

 Times Cited Count:3 Percentile:20.71

The surface structures on the surface of $$beta$$-FeSi$$_2$$ 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 $$beta$$-FeSi$$_2$$ (100) substrate after heat treatment above 1023 K, where the evaporation of surface oxide layer (SiO$$_x$$) occurred. The composition of the dip structure was Fe-rich as compared to nominal $$beta$$-FeSi$$_2$$ composition (Si/Fe=2). This result indicates that the decomposition from $$beta$$-FeSi$$_2$$ to $$epsilon$$-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 $$beta$$-FeSi$$_2$$ (111) substrate at the growth temperature of 973 and 1073 K were obtained.

Journal Articles

Aalpha-ray detection with a MgB$$_{2}$$ transition edge sensor

Okayasu, Satoru; Katagiri, Masaki; Hojo, Kiichi; Morii, Yukio; Miki, Shigenobu*; Shimakage, Hisashi*; Wang, Z.*; Ishida, Takekazu*

Physica C, 468(15-20), p.1998 - 2000, 2008/09

 Times Cited Count:0 Percentile:100(Physics, Applied)

We have been investigating for neutron detection with the MgB $$_{2}$$ transition edge sensor (TES). For the purpose, we have been developing a low noise measurement system for neutron detection. To confirm the usefulness of our detecting system, alpha-ray detection from an $$^{241}$$Am source was achieved. To improve the sensitivity, short meander samples with 35 $$mu$$m length and 1 $$mu$$m width is used. Samples are fabricated by the Kansai group. Superconducting transition temperature Tc is 23.3 K. The transition width is sharp enough less than 1 K. The detection was achieved under a constant current condition, and the resistivity changes at the sample due to the alpha-ray irradiation were detected. The bias current is 6 $$mu$$A.

Journal Articles

Aligned defects behaviour of $$beta$$-FeSi$$_{2}$$ thin film on Si(100) substrate prepared by ion beam sputter deposition

Sasase, Masato*; Yamaguchi, Kenji; Yamamoto, Hiroyuki; Shamoto, Shinichi; Hojo, Kiichi

Journal of Physics; Conference Series, 100, p.042016_1 - 042016_4, 2008/00

 Times Cited Count:3 Percentile:20.69

Defect formation behavior in the $$beta$$-FeSi$$_{2}$$ on Si(100) has been discussed by using cross sectional transmission electron microscope.

Journal Articles

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

 Times Cited Count:6 Percentile:66.02(Chemistry, Multidisciplinary)

$$^{30}$$Si in natural Si has been widely used for a doping source, since $$^{30}$$Si can be transmuted into $$^{31}$$P by thermal neutron (Neutron Transmutation Doping, NTD). NTD of nanostructure fabricated from $$^{30}$$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, $$^{30}$$Si-enriched thin film has been fabricated in order to demonstrate the local NTD. The $$^{30}$$Si-enriched film with thickness of 100 nm was deposited on the Si(100) substrate by plasma enhanced chemical vapor deposition using $$^{30}$$Si-enriched SiF$$_{4}$$ as the source gases. The film contains 7.1 % of $$^{30}$$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.

Journal Articles

Photoluminescence characterization of $$beta$$-FeSi$$_{2}$$ prepared by ion beam sputter deposition (IBSD) method

Zhuravlev, A. V.; Yamamoto, Hiroyuki; Shimura, Kenichiro*; Yamaguchi, Kenji; Shamoto, Shinichi; Hojo, Kiichi; Terai, Takayuki*

Thin Solid Films, 515(22), p.8149 - 8153, 2007/08

 Times Cited Count:2 Percentile:86.28(Materials Science, Multidisciplinary)

A semiconducting silicide, $$beta$$-FeSi$$_{2}$$, formed on a Si substrate, is known to exhibit strong photoluminescence (PL) peak at around 0.8 eV when it is annealed at high temperature (1073-1173 K). On the other hand, dislocation-related band of Si has intensity maxima at 0.81 eV. In the present study, the PL spectra were taken at the various stages of IBSD in order to understand the processes that are responsible for the observed PL enhancement. We observed a strong PL peak at around 0.8 eV in IBSD-grown $$beta$$-FeSi$$_{2}$$ film on Si substrate, as well as in substrate itself, upon thermal annealing in air at 1153 K. The most pronounced peak at 0.8 eV was observed when Si substrates were sputter etched by Ne$$^{+}$$, prior to the thermal annealing in air. However, the temperature dependence of peak intensity of $$beta$$-FeSi$$_{2}$$ was different from that of SE-treated Si, where thermal quenching appeared to occur at slightly lower temperature in the former.

Journal Articles

Crystal nucleation behavior caused by annealing of SiC irradiated with Ne at liquid nitrogen temperature or at 573K

Aihara, Jun; Hojo, Kiichi; Furuno, Shigemi*; Hojo, Tomohiro; Sawa, Kazuhiro; Yamamoto, Hiroyuki; Motohashi, Yoshinobu*

Materials Transactions, 48(7), p.1896 - 1900, 2007/07

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

Silicon carbide(SiC) TEM specimens were annealed, in-situ, at 1273K for 30 minutes after amorphization with 30keV Ne$$^{+}$$ irradiation to the fluence of 1.9 or 2.3$$times$$10$$^{20}$$Ne$$^{+}$$/m$$^{2}$$ at 573K or about 98K. The crystal nucleation and bubble coalescence accompanied by recrystallization were observed in both specimens with the annealing after the irradiations. 2.3$$times$$10$$^{20}$$Ne$$^{+}$$/m$$^{2}$$ irradiations in both specimens. The Debye-Sherrer rings of the nucleated crystals well fitted the net pattern of the matrix, even though no ring corresponding to (200) of $$beta$$-SiC appeared. Dependence of the crystal nucleation behavior on irradiation temperature was not observed within the present experimental range.

Journal Articles

Sputter etching effect of the substrate on the microstructure of $$beta$$-FeSi$$_{2}$$ thin film prepared by ion beam sputter deposition method

Sasase, Masato*; Shimura, Kenichiro*; Yamaguchi, Kenji; Yamamoto, Hiroyuki; Shamoto, Shinichi; Hojo, Kiichi

Nuclear Instruments and Methods in Physics Research B, 257(1-2), p.186 - 189, 2007/04

 Times Cited Count:5 Percentile:56.5(Instruments & Instrumentation)

Beta iron disilicide ($$beta$$-FeSi$$_{2}$$) is one of the candidate materials for a compound semiconductor. We have employed ion beam sputter deposition method to grow highly oriented $$beta$$-FeSi$$_{2}$$ film on a single crystal Si(100) substrate. In the present study, sputter etching effect of the substrate is investigated by the cross-sectional transmission electron microscope (TEM) observation in order to observe nanostructural changes as a function of Ne$$^{+}$$ energy. The observed TEM images show that the 1 keV sputtering provides uniform films with few defects and smooth interface. The number of the produced defects rapidly increases with the energy. The obtained $$beta$$-FeSi$$_{2}$$ tends to form small grains at the higher energy. Quite rough surface is also observed in this condition. Higher energies produce excessive amount of damages for the substrate to form epitaxially grown film. These results imply that a certain fluence is required for better quality of the deposited film.

Journal Articles

Structure of beam tracks induced by swift heavy ions in Bi$$_{2}$$Sr$$_{2}$$CaCu$$_{2}$$O$$_{8}$$ superconductors

Sasase, Masato*; Okayasu, Satoru; Yamamoto, Hiroyuki; Kurata, Hiroki*; Hojo, Kiichi

Japanese Journal of Applied Physics, Part 1, 46(2), p.783 - 786, 2007/02

Columnar defects are produced in semiconducting and insulating materials by swift heavy ion irradiation. In the present study, we investigate the columnar defects produced in the Bi$$_{2}$$Sr$$_{2}$$CaCu$$_{2}$$O$$_{8}$$ superconductor by the heavy ion irradiation (Au$$^{+}$$, I$$^{+}$$, Br$$^{+}$$, Ni$$^{+}$$) in the energy range of 60-600 MeV. On the basis of the transmission electron microscopy, it is shown that the diameters of columnar defects become smaller and their distributions become narrower with the ion velocity. These facts are explained as the effect of nuclear collision by calculating the mean free path for the irradiated ions. Present results imply the nuclear collisions strongly affect the columnar defect formations even for the swift heavy ion irradiation.

Journal Articles

Structure of beam tracks induced by swift heavy ions in Bi$$_2$$Sr$$_2$$CaCu$$_2$$O$$_8$$ superconductors

Sasase, Masato*; Okayasu, Satoru; Yamamoto, Hiroyuki; Kurata, Hiroki*; Hojo, Kiichi

Japanese Journal of Applied Physics, Part 1, 46(2), p.783 - 786, 2007/02

 Times Cited Count:1 Percentile:94.11(Physics, Applied)

Columnar defects are produced in semiconductor and insulator materials by swift heavy ion irradiation. It has been considered that the electronic stopping power of irradiating ions is the dominant factor in the formation of defects. However, our recent results suggest that ion-velocity is also an important parameter for use in describing this phenomenon. We investigate the columnar defects produced in Bi$$_2$$Sr$$_2$$CaCu$$_2$$O$$_8$$ (Bi-2212) superconductor by heavy ion irradiation (Au$$^{8+,12+}$$, I$$^{8+,29+}$$, Br$$^{12+}$$, and Ni$$^{11+}$$) in the energy range of 60-600MeV. From tansmission electron microscopy, it is shown that the diameters of columnar defects become smaller and their distribution become narrower with an increase in ion velocity. This is explained as an effect of nuclear collision by calculation of the mean free path for the irradiated ions. The present results imply that nuclear collisions strongly affect the formation of columnar defects, even for swift heavy ion irradiation.

Journal Articles

Radiation effects on MgAl$$_{2}$$O$$_{4}$$-yttria stabilized ZrO$$_{2}$$ composite material irradiated with Ne$$^{+}$$ ions at high temperatures

Hojo, Tomohiro*; Yamamoto, Hiroyuki; Aihara, Jun; Furuno, Shigemi*; Sawa, Kazuhiro; Sakuma, Takashi*; Hojo, Kiichi

Nuclear Instruments and Methods in Physics Research B, 250(1-2), p.123 - 127, 2006/09

 Times Cited Count:2 Percentile:77.4(Instruments & Instrumentation)

Spinel and yttria stabilized zirconia (YSZ) are candidates for fuel materials for use in nuclear reactors and the optical and insulating materials for fusion reactors. In the present study, the damage evolution process of polycrystalline spinel-YSZ composite materials has been studied by in situ transmission electron microscope observation during ion irradiation. The irradiation was performed with 30 keV Ne$$^{+}$$ at a flux of 5 $$times$$ 10$$^{13}$$ ions/cm$$^{2}$$ per second at 923 K and 1473 K, respectively. At 923 K, defect clusters and bubbles were formed homogeneously in YSZ grains. On the other hand, at 1473 K, only bubble formation was observed. The bubbles grew remarkably with increasing ion fluence in both grains. Even though the growth of the bubbles was observed in both grains, the average diameter of grown bubbles in spinel grains was larger than those in YSZ ones. The bubbles tended to form along the grain boundary at both temperatures.

Journal Articles

Loop formation by ion irradiation in yttria stabilized zirconia

Hojo, Tomohiro*; Yamamoto, Hiroyuki; Aihara, Jun; Furuno, Shigemi*; Sawa, Kazuhiro; Sakuma, Takashi*; Hojo, Kiichi

Nuclear Instruments and Methods in Physics Research B, 250(1-2), p.101 - 105, 2006/09

 Times Cited Count:5 Percentile:63.98(Instruments & Instrumentation)

Yttria stabilized zirconia (YSZ) is a candidate material focused as optical and insulating materials in nuclear reactors. Therefore, it is useful to investigate defect formation during irradiation, in order to assess YSZ resistance to radiation damage. In the present study, in situ transmission electron microscopy (TEM) observations were performed on YSZ during 30 keV Ne$$^{+}$$ irradiation in the temperature range of 723-1123 K. For irradiations below 1023 K, defect clusters and bubbles were formed simultaneously. On the other hand, at 1123 K, only bubbles were formed in the initial stage of irradiation. Loops formed later following the bubble formation. It was also observed that, in the early stage of irradiation above 923 K, larger bubbles were formed along the loop planes compared with other areas. TEM observations indicated that dislocation loops formed on three kinds of crystallographic planes: namely, (100), (111) and (112) planes.

Journal Articles

Cross-sectional transmission electron microscopy of interface structure of $$beta$$-FeSi$$_2$$/Si(100) prepared by ion beam sputter deposition

Sasase, Masato*; Shimura, Kenichiro*; Yamamoto, Hiroyuki; Yamaguchi, Kenji; Shamoto, Shinichi; Hojo, Kiichi

Japanese Journal of Applied Physics, Part 1, 45(6A), p.4929 - 4933, 2006/06

 Times Cited Count:9 Percentile:63.03(Physics, Applied)

no abstracts in English

Journal Articles

Effect of thermal annealing on the photoluminescence from $$beta$$-FeSi$$_2$$ films on Si substrate

Yamaguchi, Kenji; Shimura, Kenichiro; Udono, Haruhiko*; Sasase, Masato*; Yamamoto, Hiroyuki; Shamoto, Shinichi; Hojo, Kiichi

Thin Solid Films, 508(1-2), p.367 - 370, 2006/06

 Times Cited Count:12 Percentile:50.07(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Local oxidation induced by inhomogeneous stress on blistered Si surface

Igarashi, Shinichi*; Itakura, Akiko*; Kitajima, Masahiro*; Nakano, Shinsuke*; Muto, Shunsuke*; Tanabe, Tetsuo*; Yamamoto, Hiroyuki; Hojo, Kiichi

Japanese Journal of Applied Physics, Part 1, 45(5A), p.4179 - 4182, 2006/05

 Times Cited Count:3 Percentile:85.81(Physics, Applied)

By utilizing surface stress to modify surface reaction potential and increase surface reactivity, a technique for the twodimensional patterning of surface chemical reactions may be realized by surface stress modulation. A blister is a local protrusion on a solid surface induced by gas ion irradiation, and is considered to create local stress on surface layers. Si(100) substrate was irradiated with H$$^{+}$$ (incident energy: 10 keV, fluence: 1$$times$$10$$^{22}$$ ions) at an angle of 30 to the surface normal. Blisters of 1-5 mm in diameter at the base were formed. After the ion irradiation, the substrate was oxidized. Scanning Auger electron microscopy revealed that, compared with the flat surface, the perimeters of the blisters had a higher oxygen intensity whereas the blister tops had a lower oxygen intensity. The stress distribution of the blister was calculated using the finite element method. It was found that the surface layers were stretched laterally at the blisters tops and compressed at theperimeters, relative to the flat surface. There was a clear correspondence between the O distribution and the stress distribution on the surface. Our results indicate that the patterned oxidation of the Si surface can be governed by the application of surface stress.

175 (Records 1-20 displayed on this page)