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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:66 Percentile:92.87(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

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:137 Percentile:93.89(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:2.14(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:5 Percentile:27.24(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:53.93

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:33.03(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:5.72(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

Oral presentation

Sulfur-metal interface behavior studied by S K-edge NEXAFS

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

no journal, , 

no abstracts in English

Oral presentation

Chemical-state selective mapping of Si compounds by micro-XAFS using soft X-rays from synchrotron light source

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

no journal, , 

no abstracts in English

Oral presentation

Metal-intereface bond behavior of amino acid on solid surface

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

no journal, , 

no abstracts in English

Oral presentation

Chemical-state-selective mapping at nanometer scale using synchrotron radiation and photoelectron emission microscopy

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

no journal, , 

no abstracts in English

Oral presentation

Chemical-state mapping by photoelectron emission microscopy using soft X-rays from synchrotron light source

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

no journal, , 

no abstracts in English

Oral presentation

Observation of electronic structures at nanometer scale for silicon compounds by SR-excited PEEM

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

no journal, , 

Photoelectron emission microscopy (PEEM) excited by soft X-rays from synchrotron light source has been applied to the nano-scaled observations on electronic structures for silicon compounds. The lateral spacial resolution of the PEEM was about 40 nm. For organic silicon compounds, silicon phthalocyanine dichloride (SiPcCl$$_{2}$$) molecules were deposited on the gold surface using a mask. At room temperature, periodic bright-and-dark PEEM images were clearly observed by the excitation at the Si K-edge. The brightnesses of the bright and dark regions were plotted as a function of the photon energy. In comparison with the X-ray absorption spectrum of SiPcCl$$_{2}$$ molecules, the electronic structure of each domain in the PEEM image was elucidated at nanometer scale. When we annealed the sample, the lateral diffusion of the deposited layer was in-situ observed at real time.

Oral presentation

Organic thin films probed by synchrotron radiation

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

no journal, , 

no abstracts in English

28 (Records 1-20 displayed on this page)