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Journal Articles

Microscopic origin of the spin-reorientation transition in the kagome topological magnet TbMn$$_{6}$$Sn$$_{6}$$

Huang, Z.*; Wang, W.*; Ye, H.*; Bao, S.*; Shangguan, Y.*; Liao, J.*; Cao, S.*; Kajimoto, Ryoichi; Ikeuchi, Kazuhiko*; Deng, G.*; et al.

Physical Review B, 109(1), p.014434_1 - 014434_9, 2024/01

Journal Articles

Pressure-modulated magnetism and negative thermal expansion in the Ho$$_2$$Fe$$_{17}$$ intermetallic compound

Cao, Y.*; Zhou, H.*; Khmelevskyi, S.*; Lin, K.*; Avdeev, M.*; Wang, C.-W.*; Wang, B.*; Hu, F.*; Kato, Kenichi*; Hattori, Takanori; et al.

Chemistry of Materials, 35(8), p.3249 - 3255, 2023/04

 Times Cited Count:0 Percentile:0(Chemistry, Physical)

Hydrostatic and chemical pressure are efficient stimuli to alter the crystal structure and are commonly used for tuning electronic and magnetic properties in materials science. However, chemical pressure is difficult to quantify and a clear correspondence between these two types of pressure is still lacking. Here, we study intermetallic candidates for a permanent magnet with a negative thermal expansion (NTE). Based on in situ synchrotron X-ray diffraction, negative chemical pressure is revealed in Ho$$_2$$Fe$$_{17}$$ on Al doping and quantitatively evaluated by using temperature and pressure dependence of unit cell volume. A combination of magnetization and neutron diffraction measurements also allowed one to compare the effect of chemical pressure on magnetic ordering with that of hydrostatic pressure. Intriguingly, pressure can be used to control suppression and enhancement of NTE. Electronic structure calculations indicate that pressure affected the top of the majority band with respect to the Fermi level, which has implications for the magnetic stability, which in turn plays a critical role in modulating magnetism and NTE. This work presents a good example of understanding the effect of pressure and utilizing it to control properties of functional materials.

Journal Articles

Experimental study on interfacial area transport of two-phase bubbly flow in a vertical large-diameter square duct

Shen, X.*; Sun, Haomin; Deng, B.*; Hibiki, Takashi*; Nakamura, Hideo

International Journal of Heat and Fluid Flow, 67(Part A), p.168 - 184, 2017/10

 Times Cited Count:15 Percentile:62.93(Thermodynamics)

An experimental study on upward bubbly air-water flows in a vertical large-diameter square duct have been performed by mainly using four-sensor probes. Local measurements of interfacial area concentration (IAC), void fraction, 3D bubble velocity vector and bubble diameter at 3 axial positions were conducted. Although the interfacial area transport equation (IATE) and its bubble coalescence and breakup models have already played an important role in predicting the IAC in general two-phase flow fields, they are mainly developed based on the two-phase flow experimental data taken in round pipes or small diameter channels. To confirm their usability in large-diameter square duct, this study has evaluated the 1D one-group IATE with its 6 sets of bubble coalescence and breakup models with the presently-obtained database. It was found the relative error between the best prediction and the database was 25%.

Journal Articles

Axial flow characteristics of bubbly flow in a vertical large-diameter square duct

Shen, X.*; Sun, Haomin; Deng, B.*; Hibiki, Takashi*; Nakamura, Hideo

Proceedings of 17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-17) (USB Flash Drive), 14 Pages, 2017/09

An experimental study on the upward bubbly air-water flows in a vertical large-diameter square duct have been performed by using four-sensor probes. The four-sensor probe were applied in the local measurements at 3 axial positions along the flow direction to obtain interfacial area concentration, 3-D bubble velocity vector and bubble diameter. The obtained void fraction, interfacial area concentration, 3-D bubble velocity vector and bubble diameter provided valuable insight into the flow structure and will serve as a valuable database to develop the mechanistic models for interfacial area transport equation sources and sinks.

Journal Articles

Gas-liquid bubbly flow structure in a vertical large-diameter square duct

Shen, X.*; Sun, Haomin; Deng, B.*; Hibiki, Takashi*; Nakamura, Hideo

Progress in Nuclear Energy, 89, p.140 - 158, 2016/05

 Times Cited Count:20 Percentile:88.97(Nuclear Science & Technology)

An experimental study was performed on the local structure of upward air-water two-phase flow in a vertical large diameter square duct by using a four-sensor probe. The four-sensor probe method classifying spherical and non-spherical bubbles was applied as a key measurement way to obtain local parameters such as 3-D bubble velocity vector, bubble diameter and interfacial area concentration. Both the local void fraction and interfacial area concentration indicated radial core-peak and wall-peak distributions at low and high liquid flow rates respectively. The 2 components of the bubble velocity vector in the cross-section revealed that there exists a rotating secondary flow in the octant symmetric triangular area and the magnitude of the rotating secondary flow increases with the liquid flow rate. Some of constitutive correlations of drift-flux model and interfacial area concentration are reviewed to study their predictabilities against the present data.

Journal Articles

Diluted ferromagnetic semiconductor Li(Zn,Mn)P with decoupled charge and spin doping

Deng, Z.*; Zhao, K.*; Gu, B.; Han, W.*; Zhu, J. L.*; Wang, X. C.*; Li, X.*; Liu, Q. Q.*; Yu, R. C.*; Goko, Tatsuo*; et al.

Physical Review B, 88(8), p.081203_1 - 081203_5, 2013/08

 Times Cited Count:71 Percentile:91.9(Materials Science, Multidisciplinary)

Journal Articles

Orientation of silicon phthalocyanine thin films revealed using polarized X-ray absorption spectroscopy

Sekiguchi, Tetsuhiro; Baba, Yuji; Shimoyama, Iwao; Hirao, Norie; Honda, Mitsunori; Deng, J.*

Photon Factory Activity Report 2012, Part B, P. 68, 2013/00

The orientation of organic semiconducting molecules on surfaces plays a crucial role in improving the properties of electronic devices. We prepared thin films of silicon phthalocyanine dichroride (SiPcCl$$_{2}$$) on graphite spin-cast followed by heating to 350$$^{circ}$$C at ambient condition. We investigate the molecular orientation of the films using angle-dependent near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy. Si 1s NEXAFS spectra for the thin films after annealing are very different each other, indicating that the corresponding reactions thus the structures of final products are different. The structures of the reaction products are estimated with the help of ab initio molecular orbital calculations that fit the observed NEXAFS spectra.

Journal Articles

Nonlinear simulation of energetic particle modes in JT-60U

Bierwage, A.; Aiba, Nobuyuki; Shinohara, Koji; Todo, Yasushi*; Deng, W.*; Ishikawa, Masao; Matsunaga, Go; Yagi, Masatoshi

Proceedings of 24th IAEA Fusion Energy Conference (FEC 2012) (CD-ROM), 8 Pages, 2012/10

Journal Articles

Nonlinear simulation of energetic particle modes in high-beta tokamak plasma

Bierwage, A.; Aiba, Nobuyuki; Todo, Yasushi*; Deng, W.*; Ishikawa, Masao; Matsunaga, Go; Shinohara, Koji; Yagi, Masatoshi

Plasma and Fusion Research (Internet), 7(Sp.1), p.2403081_1 - 2403081_4, 2012/07

Journal Articles

Li(Zn,Mn)As as a new generation ferromagnet based on a I-II-V semiconductor

Deng, Z.*; Jin, C. Q.*; Liu, Q. Q.*; Wang, X. C.*; Zhu, J. L.*; Feng, S. M.*; Chen, L. C.*; Yu, R. C.*; Arguello, C.*; Goko, Tatsuo*; et al.

Nature Communications (Internet), 2, p.1425_1 - 1425_5, 2011/08

 Times Cited Count:150 Percentile:93.71(Multidisciplinary Sciences)

In a prototypical ferromagnet (Ga,Mn)As based on a III-V semiconductor, substitution of divalent Mn atoms into trivalent Ga sites leads to severely limited chemical solubility and metastable specimens available only as thin films. The doping of hole carriers via (Ga,Mn) substitution also prohibits electron doping. To overcome these difficulties, Masek et al. theoretically proposed systems based on a I-II-V semiconductor LiZnAs, where isovalent (Zn,Mn) substitution is decoupled from carrier doping with excess/deficient Li concentrations. Here we show successful synthesis of Li$$_{1+y}$$(Zn$$_{1-x}$$Mn$$_x$$)As in bulk materials. We reported that ferromagnetism with a critical temperature of up to 50 K is observed in nominally Li-excess compounds, which have p-type carriers.

Journal Articles

Orientation of Si phthalocyanine investigated by X-ray absorption spectroscopy and molecular orbital calculation

Sekiguchi, Tetsuhiro; Baba, Yuji; Shimoyama, Iwao; Honda, Mitsunori; Hirao, Norie; Narita, Ayumi; Deng, J.*

Surface and Interface Analysis, 42(6-7), p.863 - 868, 2010/06

 Times Cited Count:1 Percentile:1.76(Chemistry, Physical)

Metal phthalocyanines (Pc) have attracted growing attention due to potential application as organic semiconductors or light emitters. Recently it has been pointed out that orientation of Pc molecules is one of key properties that improve the career mobility. We studied orientation property of Si-phthalocyanine thin films using synchrotron radiation. We report on following topics: (1) Orientation analysis using polarized X-rays, (2) Effect of metal substrates and annealing on orientation, (3) Analysis aided by molecular orbital method, and (4) New method to observe chemical-bond directions in nanometer scale using combined techniques of polarized X-ray absorption fine structure (XAFS) spectroscopy and photoelectron emission microscopy (PEEM).

Journal Articles

Real-time observation on surface diffusion and molecular orientations for phthalocyanine thin films at nanometer spacial resolution

Baba, Yuji; Sekiguchi, Tetsuhiro; Shimoyama, Iwao; Honda, Mitsunori; Hirao, Norie; Narita, Ayumi; Deng, J.

Surface Science, 603(16), p.2612 - 2618, 2009/08

 Times Cited Count:6 Percentile:29.57(Chemistry, Physical)

The morphology, electronic structure and ordering for micropatterns of silicon phthalocyanine thin films on gold have been investigated at nanometer scale by photoelectron emission microscopy (PEEM) excited by polarized soft X-rays from synchrotron light source. The incident angle dependences of the X-ray absorption fine structure (XANES) spectra at the silicon K-edge revealed that the molecules of 5-layered films are lying nearly flat on the surface. Clear image of the micropattern was observed by PEEM at room temperature, while the surface diffusion was observed upon heating. On the basis of the photon-energy dependences of the brightnesses in the PEEM images, it was found that the molecules diffusing to the fresh gold surface rather stand-up at 240$$^{circ}$$C. The observed changes in the molecular orientations at nanometer domains are discussed on the basis of the strengths of the molecular-molecular and molecular-surface interactions.

Journal Articles

Chemical-state-selective observations on Si-SiO$$_{rm x}$$ at nanometer scale by photoelectron emission microscopy combined with synchrotron radiation

Baba, Yuji; Sekiguchi, Tetsuhiro; Shimoyama, Iwao; Honda, Mitsunori; Hirao, Norie*; Deng, J.; Narita, Ayumi

Journal of Physics; Conference Series, 100, p.012015_1 - 012015_4, 2008/00

 Times Cited Count:1 Percentile:51.89

Chemical-state-selective mapping of micro-patterns for silicon compounds has been demonstrated using photoelectron emission microscopy excited by soft X-rays from synchrotron light source. The samples investigated were micro-patterns of silicon oxides, silicon nitrides, and organic silicon compounds. By scanning the X-ray energy around the Si $$K$$-edge, we succeeded in observing the sub-micron images depending on the valence states. When we annealed the sample, the lateral diffusion was observed from 700$$^{circ}$$C. During the annealing, however, no intermediate valence states were observed at the Si-SiO$$_{2}$$ interfaces. It was elucidated that the diffusion of oxygen induced the sudden changes of the Si valence states from Si$$^{0}$$ to Si$$^{4+}$$ without any intermediate valence states. The results for the chemical-state-selective mappings and lateral diffusions are also presented for organic silicon compounds.

Journal Articles

Effect of substrates on the molecular orientation of silicon phthalocyanine dichloride thin films

Deng, J.; Baba, Yuji; Sekiguchi, Tetsuhiro; Hirao, Norie*; Honda, Mitsunori

Journal of Physics; Condensed Matter, 19(19), p.196205_1 - 196205_11, 2007/05

 Times Cited Count:6 Percentile:31.38(Physics, Condensed Matter)

Molecular orientations of silicon phthalocyanine dichloride (SiPcCl$$_{2}$$) thin films deposited on three different substrates have been measured by near edge X-ray absorption fine structure (NEXAFS) spectroscopy. For thin films about 5 monolayers, the polarization dependences of the Si K-edge NEXAFS spectra showed that the molecular planes of SiPcCl$$_{2}$$ on three substrates were nearly parallel to the surface. Quantitative analyses of the polarization dependences revealed that the tilted angle on HOPG was only 2 degree, which is interpreted by the perfect flatness of HOPG surface. While the tilted angle on indium tin oxide (ITO) was 26$$^{circ}$$. It is concluded that the morphology of the top surface layer of the substrate affects the molecular orientation of SiPcCl$$_{2}$$ molecules not only for mono-layered adsorbates but also multi-layered thin films.

Journal Articles

Orientation of thin films synthesized from silicon phthalocyanine dichloride on a highly oriented pyrolytic graphite investigated using near edge X-ray absorption fine structure

Deng, J.; Sekiguchi, Tetsuhiro; Baba, Yuji; Hirao, Norie*; Honda, Mitsunori

Japanese Journal of Applied Physics, Part 1, 46(2), p.770 - 773, 2007/02

 Times Cited Count:1 Percentile:5.43(Physics, Applied)

Molecular orientation of thin films of silicon phthalocyanine (SiPc) compounds on highly oriented pyrolytic graphite (HOPG) was investigated by near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS). The films were prepared by a casting method using solution of SiPc dichloride. XPS results showed that the chlorine atoms in SiPc dichloride were substituted by oxygen atoms when the film was heated in the air. The orientation of the molecules with respect to the substrate plane was investigated by the polarization dependences of the Si $$K$$ edge NEXAFS spectra. For the sample heated in the air, two clear peaks appeared in the NEXAFS spectra at around 1847.2 and 1852.4 eV, which were assigned to the resonant excitation form Si 1s to $$sigma$$* orbitals around the Si-N bonds and those around the Si-O bonds, respectively. The intensities of the resonance peaks showed strong polarization dependence. A quantitative analysis of the polarization dependences revealed that the Si-N bond was lying down while the Si-O bond was out of the plane.

Oral presentation

Synchrotron radiation studies of the orientation of thin silicon phthalocyanine dichloride film on HOPG substrate

Deng, J.; Sekiguchi, Tetsuhiro; Baba, Yuji; Hirao, Norie*

no journal, , 

no abstracts in English

Oral presentation

Chemical-state-selective mappings for silicon compounds by PEEM combined with synchrotron soft X-ray excitation at the Si K-edge

Baba, Yuji; Sekiguchi, Tetsuhiro; Shimoyama, Iwao; Hirao, Norie*; Deng, J.

no journal, , 

no abstracts in English

Oral presentation

Chemisorption of amino acid monolayer on gold substrate

Honda, Mitsunori; Baba, Yuji; Hirao, Norie*; Deng, J.; Sekiguchi, Tetsuhiro

no journal, , 

no abstracts in English

Oral presentation

Chemical-state mapping of Si-SiO$$_{2}$$ by photoelectron emission microscopy

Hirao, Norie*; Baba, Yuji; Sekiguchi, Tetsuhiro; Shimoyama, Iwao; Honda, Mitsunori; Deng, J.

no journal, , 

no abstracts in English

Oral presentation

Amino acid adsorption on solid surface

Honda, Mitsunori; Baba, Yuji; Hirao, Norie*; Deng, J.; Sekiguchi, Tetsuhiro

no journal, , 

no abstracts in English

37 (Records 1-20 displayed on this page)