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Kikuo Harigaya - One of the best experts on this subject based on the ideXlab platform.

  • Possible Charge-Ordered States in Boron?Nitride and Boron?Carbon?Nitride Nanotubes and Nanoribbons
    Japanese Journal of Applied Physics, 2006
    Co-Authors: Kikuo Harigaya
    Abstract:

    Electronic states in boron–nitride and boron–carbon–nitride nanoribbons with zigzag edges are studied using the extended Hubbard model with nearest-neighbor Coulomb interactions. Charge- and spin-polarized states are considered, and the phase diagram between two states is obtained. Next, Electric Capacitance is calculated to examine the nanofunctionalities of the system. Owing to the presence of strong site energies, the charge polarized state overcomes the spin polarized state, yielding a large difference in the phase diagram compared with that of a graphite system. Electronic structures are always like that of semiconductors. Capacitance is inversely proportional to ribbon width, owing to the presence of the charge excitation energy gap.

  • Electric Capacitance as nanocondensers in zigzag nanographite ribbons
    Japanese Journal of Applied Physics, 2005
    Co-Authors: Kikuo Harigaya
    Abstract:

    Electronic states in nanographite ribbons with zigzag edges are studied using the extended Hubbard model with nearest neighbor Coulomb interactions. The nearest Coulomb interactions stabilize electronic states with the opposite Electric charges separated and localized along both edges. Such states are analogous as nanocondensers. Therefore, Electric Capacitance, defined using a relation of polarizability, is calculated to examine nano functionalities. We find that the behavior of the Capacitance is widely different depending on whether the system is in the magnetic or charge polarized phases. In the magnetic phase, the Capacitance is dominated by the presence of the edge states while the ribbon width is small. As the ribbon becomes wider, the Capacitance remains with large magnitudes as the system develops into metallic zigzag nanotubes. It is proportional to the inverse of the width, when the system corresponds to the semiconducting nanotubes and the system is in the charge polarized phase also. The latter behavior could be understood by the presence of an energy gap for charge excitations.

  • Magnetic vs. charge ordered states, and Electric Capacitance in zigzag nanographite ribbons
    Synthetic Metals, 2005
    Co-Authors: Kikuo Harigaya, Atsushi Yamashiro, Yukihiro Shimoi, Katsunori Wakabayashi
    Abstract:

    Nanographite materials show novel electronic properties: spin glass like behaviors [1], the on/off switching of magnetism with molecule adsorptions [2], and so on. Here, we study electronic states in nanographite ribbons with zigzag edges. Effects of the nearest neighbor Coulomb interactions are investigated using the extended Hubbard model. The nearest Coulomb interactions stabilize a novel electronic state with the opposite Electric charges separated and localized along both edges, resulting in a finite Electric dipole moment pointing from one edge to the other. Next, Electric Capacitance is calculated to examine nano functionalities. We find that the behavior of the Capacitance is widely different depending on whether the system is in the magnetic or charge polarized phases. In the magnetic phase, the Capacitance is dominated by the presence of the edge states while the ribbon width is small. As the ribbon becomes wider, the Capacitance remains with large magnitudes as the system develops into metallic zigzag nanotubes. It is proportional to the inverse of the width, when the system corresponds to the semiconducting nanotubes and the system is in the charge polarized phase also. The latter behavior could be understood by the presence of an energy gap for charge excitations.

  • Calculations of Electric Capacitance in carbon and BN nanotubes, and zigzag nanographite (BN, BCN) ribbons
    Physica E: Low-dimensional Systems and Nanostructures, 2005
    Co-Authors: Kikuo Harigaya
    Abstract:

    Electronic states in nanographite ribbons with zigzag edges are studied using the extended Hubbard model with nearest neighbor Coulomb interactions. The electronic states with the opposite Electric charges separated along both edges are analogous as nanocondensers. Therefore, Electric Capacitance, defined using a relation of polarizability, is calculated to examine nano-functionalities. We find that the behavior of the Capacitance is widely different depending on whether the system is in the magnetic or charge polarized phases. In the magnetic phase, the Capacitance is dominated by the presence of the edge states while the ribbon width is small. As the ribbon becomes wider, the Capacitance remains with large magnitudes as the system develops into metallic zigzag nanotubes. It is proportional to the inverse of the width, when the system corresponds to the semiconducting nanotubes and the system is in the charge polarized phase also. The latter behavior could be understood by the presence of an energy gap for charge excitations. In the BN (BCN) nanotubes and ribbons, the electronic structure is always like that of semiconductors. The calculated Capacitance is inversely proportional to the distance between the positive and negative electrodes.

Katsunori Wakabayashi - One of the best experts on this subject based on the ideXlab platform.

  • Magnetic vs. charge ordered states, and Electric Capacitance in zigzag nanographite ribbons
    Synthetic Metals, 2005
    Co-Authors: Kikuo Harigaya, Atsushi Yamashiro, Yukihiro Shimoi, Katsunori Wakabayashi
    Abstract:

    Nanographite materials show novel electronic properties: spin glass like behaviors [1], the on/off switching of magnetism with molecule adsorptions [2], and so on. Here, we study electronic states in nanographite ribbons with zigzag edges. Effects of the nearest neighbor Coulomb interactions are investigated using the extended Hubbard model. The nearest Coulomb interactions stabilize a novel electronic state with the opposite Electric charges separated and localized along both edges, resulting in a finite Electric dipole moment pointing from one edge to the other. Next, Electric Capacitance is calculated to examine nano functionalities. We find that the behavior of the Capacitance is widely different depending on whether the system is in the magnetic or charge polarized phases. In the magnetic phase, the Capacitance is dominated by the presence of the edge states while the ribbon width is small. As the ribbon becomes wider, the Capacitance remains with large magnitudes as the system develops into metallic zigzag nanotubes. It is proportional to the inverse of the width, when the system corresponds to the semiconducting nanotubes and the system is in the charge polarized phase also. The latter behavior could be understood by the presence of an energy gap for charge excitations.

Koji Fukao - One of the best experts on this subject based on the ideXlab platform.

  • A Kinetic Study on the Response of the Relaxation Time of the α Process to Quick Temperature Change around the Glass Transition
    Journal of the Physical Society of Japan, 2012
    Co-Authors: Akihiro Harada, Koji Fukao, Takashi Oikawa, Haruhiko Yao, Yasuo Saruyama
    Abstract:

    Glass transition is characterized by the relaxation time of the process ( ) which increases abruptly on cooling towards the glass transition temperature. Temperature dependence of has been studied extensively. 1) In experimental studies is measured after the sample temperature reaches the aimed value and becomes stable. In order to avoid temperature disturbance temperature is controlled slowly. On the other hand in this study sample temperature was changed quickly in order to investigate whether or not changed with retardation to the temperature change. It seems to be natural to consider that retardation should be observed because the atomic scale structure, on which is dependent, changes with retardation to the quick temperature change near the glass transition temperature. We carried out experiments to measure the retardation of and confirmed existence of it. However, it should have been noted that the retardation time of to the quick temperature change, written as below, exhibited temperature dependence notably different from that of . This result suggested that the origin of was different from that of . The experimental technique is briefly explained below. A new technique called temperature modulated diElectric measurement (TM-diElectric measurement) has been developed in the authors’ laboratory. Conventional Wheatstone bridge was utilized to measure the Electric Capacitance of the sample. In TM-diElectric measurement the sample temperature was modulated sinusoidally with time. A schematic diagram of the experimental system is shown in Fig. 1. According to the temperature modulation the value of , on which the complex Electric Capacitance of the sample was dependent, changed sinusoidally at the angular frequency of the temperature modulation, !T . This led to nonlinear relationship between the voltage applied to the Electric capacitor including the sample and the Electric current passing through it. Consequently although the voltage applied to the Wheatstone bridge was purely sinusoidal with the frequency of !V , the voltage measured with the lock-in amplifier in Fig. 1 was composed of three Fourier components with the frequencies of !V , !V þ !T and !V !T with the first order approximation. The !V component was the ordinary linear response. The nonlinear components with the frequencies of !V þ !T and !V !T provided the information about the response of to the temperature modulation. The complex amplitude of the measured voltage with the frequency of !V þ !T is written as A þ below. The nonlinear complex Electric Capacitance of the sample, C þ, is defined by the ratio of the complex amplitude of the !V þ !T component of the charge on the electrode to that of the purely sinusoidal voltage with the frequency of !V applied to the electrode. The next equation is derived through analysis of the Electric circuit of Fig. 1:

  • Application of new treatment methods for “reading” of the complex Capacitance: A quantitative description of the aging phenomenon in polymer glasses
    Communications in Nonlinear Science and Numerical Simulation, 2010
    Co-Authors: Raoul R. Nigmatullin, Daisuke Tahara, Hideyuki Nakanishi, Qui Tran-cong-miyata, Koji Fukao
    Abstract:

    Abstract The glassy dynamics have been investigated using Electric Capacitance measurements for thin films of poly(2-chlorostyrene). The observed relaxation behavior of the Electric Capacitance has been analyzed using a new smoothing procedure for the noisy curves and the eigen-coordinates method for the fitting trends obtained in the results of the smoothing procedure. Such analysis has given us a fascinating relaxation function related to the glassy dynamics. New aging curve will give us a chance to understand a proper physical mechanism (related to a possible formation of dynamical self-similar interacting clusters) that can describe this interesting phenomenon. Physical consequences for the recognized relaxation function are discussed.

  • Glassy dynamics in thin films of polystyrene.
    Physical review. E Statistical nonlinear and soft matter physics, 2008
    Co-Authors: Koji Fukao, Hiroki Koizumi
    Abstract:

    Glassy dynamics was investigated for thin films of atactic polystyrene by complex Electric Capacitance measurements using diElectric relaxation spectroscopy. During the isothermal aging process the real part of the Electric Capacitance increased with time, whereas the imaginary part decreased with time. It follows that the aging time dependences of real and imaginary parts of the Electric Capacitance were primarily associated with change in volume (film thickness) and diElectric permittivity, respectively. Further, diElectric permittivity showed memory and rejuvenation effects in a similar manner to those observed for poly(methyl methacrylate) thin films. On the other hand, volume did not show a strong rejuvenation effect.

  • Aging Phenomena in Thin Polymer Films Observed through Volume and DiElectric Susceptibility
    AIP Conference Proceedings, 2008
    Co-Authors: Koji Fukao, Daisuke Tahara
    Abstract:

    Glassy dynamics was investigated for thin films of poly(2‐chlorostyrene) (P2CS) through complex Electric Capacitance measurements using diElectric relaxation spectroscopy. During the isothermal aging process the real part of the Electric Capacitance increased with time, whereas the imaginary part decreased with time. This results are similar to those observed in thin films of atactic polystyrene (a‐PS), although the glass transition temperature is by 20 K higher in P2CS than in a‐PS. The aging behavior is discussed in terms of the change in volume and diElectric susceptibility during the aging process.

  • Aging phenomena in polystyrene thin films
    The European Physical Journal Special Topics, 2007
    Co-Authors: Koji Fukao, Hiroki Koizumi
    Abstract:

    The aging behavior is investigated for thin films of atactic polystyrene through measurements of complex Electric Capacitance. During isothermal aging process the real part of the Electric Capacitance increases with aging time, while the imaginary part decreases with aging time. This result suggests that the aging time dependence of the real and imaginary parts are mainly associated with change in thickness and diElectric permittivity, respectively. In thin films, the thickness depends on thermal history of aging even above the glass transition. Memory and `rejuvenation' effects are also observed in the thin films.

Yukio Sakabe - One of the best experts on this subject based on the ideXlab platform.

  • A study of a diElectric thermometer for a microcalorimeter
    2004
    Co-Authors: Tetsuya Ariyoshi, Takumi Yamauchi, Keisuke Maehata, Kenji Ishibashi, Nobuyuki Wada, Yukio Sakabe, Hiroki Tanaka, Takahiro Umeno
    Abstract:

    The permissivity temperature dependence below 100mK of some diElectric materials expects to be utilized for a sensitive thermometer. We have investigated the SrTiO{sub 3} diElectric containing 1.0% of SrTa{sub 2}O{sub 6} and measured the Electric Capacitance with different nonstoichiometric ratio between SrO and TiO{sub 2} site in the temperature range from 50mK to 100mK. In addition, we manufactured a prototype of a diElectric microcalorimeter with sapphire absorber. (T. Tanaka)

  • A Study of Microcalorimeter with DiElectric Thermomete
    Journal of Nuclear Science and Technology, 2004
    Co-Authors: Tetsuya Ariyoshi, Hirok Tanaka, Akihi Hora, Takumi Yamauchi, Keisuke Maehata, Kenji Ishibashi, Nobuyuki Wada, Yukio Sakabe
    Abstract:

    The microcalorimeter detects a single particle of radiation by means of the temperature rise in the absorber kept at low temperature below IK. A sensitive thermometer measuring the temperature rise is an important component in the microcalorimeter. DiElectric materials whose Electric Capacitances depend on temperature at low temperature can be utilized for the sensitive thermometer of the microcalorimeter. The temperature dependence of the Electric Capacitance d(ln Cd)/dT is an important parameter for the diElectric thermometer. We have studied the diElectric thermometer made of SrTiO3 based material and carried out measurement of the Electric Capacitance in the temperature range from 50mK to 120mK. By using experimental values of d(ln Cd)/dT an output signal of the diElectric microcalorimeter was estimated in the detection of a 5.5 MeV α-partice.

Slobodan Zumer - One of the best experts on this subject based on the ideXlab platform.

  • Nematics with dispersed polymer fibrils: a Monte Carlo study of the external-field-induced switching.
    Physical Review E, 2003
    Co-Authors: Cesare Chiccoli, Paolo Pasini, Gregor Skačej, Claudio Zannoni, Slobodan Zumer
    Abstract:

    We present a Monte Carlo study of molecular ordering in nematics with dispersed regular and random arrays of straight and distorted polymer fibrils. We focus on the collective molecular reorientation--the switching--resulting from the competing aligning effects of fibrils and of a progressively applied transversal external field, and for straight fibrils identify structural Freedericksz and saturation transitions. The role of fibril topography in the switching is monitored by simulating Electric Capacitance Slightly distorted fibrils are shown to give a sharper switching at a lower threshold.

  • Nematics with dispersed polymer fibrils: a Monte Carlo study of the external-field-induced switching.
    Physical review. E Statistical nonlinear and soft matter physics, 2003
    Co-Authors: Cesare Chiccoli, Paolo Pasini, Gregor Skačej, Claudio Zannoni, Slobodan Zumer
    Abstract:

    We present a Monte Carlo study of molecular ordering in nematics with dispersed regular and random arrays of straight and distorted polymer fibrils. We focus on the collective molecular reorientation--the switching--resulting from the competing aligning effects of fibrils and of a progressively applied transversal external field, and for straight fibrils identify structural Fréedericksz and saturation transitions. The role of fibril topography in the switching is monitored by simulating Electric Capacitance Slightly distorted fibrils are shown to give a sharper switching at a lower threshold.