著者

Ishikawa Atsushi Nakashima Hiroyuki Nakatsuji Hiroshi

出版者

American Institute of Physics

雑誌

JOURNAL OF CHEMICAL PHYSICS (ISSN:00219606)

巻号頁・発行日

vol.128, no.12, 2008-03-28

被引用文献数

29

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The nonrelativistic Schrödinger equation and the relativistic four-component Dirac equation of H2+ were solved accurately in an analytical expansion form by the free iterative complement interaction (ICI) method combined with the variational principle. In the nonrelativistic case, we compared the free ICI wave function with the so-called "exact" wave function as two different expansions converging to the unique exact wave function and found that the free ICI method is much more efficient than the exact method. In the relativistic case, we first used the inverse Hamiltonian to guarantee Ritz-type variational principle and obtained accurate result. We also showed that the ordinary variational calculation also gives a nice convergence when the g function is appropriately chosen, since then the free ICI calculation guarantees a correct relationship between the large and small components of each adjacent order, which we call ICI balance. This is the first application of the relativistic free ICI method to molecule. We calculated both ground and excited states in good convergence, and not only the upper bound but also the lower bound of the ground-state energy. The error bound analysis has assured that the present result is highly accurate.

著者

Natori Kenji Kimura Yoji Shimizu Tomo

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.97, no.3, pp.034306, 2005-02

被引用文献数

94

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A general expression of the current-voltage characteristics of a ballistic nanowire field-effect transistor (FET) is derived. At T=0, the conductance, which is equal to the quantum conductance multiplied by the number of channels at zero bias, decreases stepwise toward current saturation as the drain bias is increased. The current-voltage characteristics of a single-wall carbon nanotube FET in ballistic conduction are discussed based on the band structure of the nanotube. When both the gate overdrive and the drain bias are equal to 1 V, the device made of a (19,0) nanotube and a 2-nm high-k gate insulator (epsilon=40epsilon(0)) flows a current of 183 muA, which amounts to a current density 48 times as large as the counterpart of a silicon device. The high performance originates from a high carrier density due to the enhanced gate capacitance, and a large carrier velocity caused by the large group velocity of the original graphene band. Quantum capacitance also plays an important role in the device's characteristics.

著者

Tanaka Masanori Sawai Shinya Sengoku Masaya Kato Manabu Masumoto Yasuaki 舛本 泰章

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.87, no.12, pp.8535-8540, 2000-06

被引用文献数

30

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Nanocrystalline particles of ZnS:(Ag, Al) semiconductor phosphor, whose sizes are mostly 3–5 nm in diameter, are prepared by the gas-evaporation method with cw CO2 laser heating. The Raman scattering spectrum as well as the transmission electron microscope observation demonstrates that the crystallization of the nanoparticles was caused successfully through the gas-phase condensation. Under irradiation of ultraviolet light, the nanoparticles exhibit blue luminescence, as in the case of the starting material of ZnS:(Ag, Al) bulk powder. The peak of the luminescence spectrum of the nanoparticles shifts to lower energy with increasing delay time and also with decreasing excitation intensity, showing that the luminescence originates from the donor–acceptor pair recombination. However, it is concluded that the luminescence of the nanoparticles is not ascribed to the blue Ag luminescence mechanism responsible for the luminescence of the bulk powder, by taking into account the spatial confinement of an electron trapped at the donor and a hole at the acceptor. It is argued that the luminescence mechanism of the nanoparticles is the so called self-activated luminescence, which involves zinc vacancies.

著者

Susuki Yoshihiko Yokoi Yuuichi Hikihara Takashi

出版者

American Institute of Physics

雑誌

CHAOS: An Interdisciplinary Journal of Nonlinear Science (ISSN:10541500)

巻号頁・発行日

vol.17, pp.023108, 2007-06

被引用文献数

7

---

This paper analyzes frequency entrainment described by van der Pol and phase-locked loop (PLL) equations. The PLL equation represents the dynamics of a PLL circuit that appear in typical phase-locking phenomena. These two equations describe frequency entrainment by a periodic force. The entrainment originates from two different types of limit cycles: libration for the van der Pol equation and rotation for the PLL one. To explore the relationship between the geometry of limit cycles and the mechanism of entrainment, we investigate the entrainment using an energy balance relation. This relation is equivalent to the energy conservation law of dynamical systems with dissipation and input terms. We show response curves for the dc component, harmonic amplitude, phase difference, and energy supplied by a periodic force. The obtained curves indicate that the entrainments for the two equations have different features of supplied energy, and that the entrainment for the PLL equation possibly has the same mechanism as does the regulation of the phase difference for the van der Pol equation.

著者

Max Jammer

出版者

American Institute of Physics

巻号頁・発行日

1989

著者

Suzuki Akio Konno Hidetoshi

出版者

American Institute of Physics

雑誌

AIP Advances (ISSN:21583226)

巻号頁・発行日

vol.1, no.3, pp.032103, 2011-07

被引用文献数

9

---

The dynamics of ventricular fibrillation (VF) has been studied extensively, and the initiation mechanism of VF has been elucidated to some extent. However, the stochastic dynamical nature of sustained VF remains unclear so far due to the complexity of high dimensional chaos in a heterogeneous system. In this paper, various statistical mechanical properties of sustained VF are studied numerically in 2D Beeler-Reuter-Drouhard-Roberge (BRDR) model with normal and modified ionic current conductance. The nature of sustained VF is analyzed by measuring various fluctuations of spatial phase singularity (PS) such as velocity, lifetime, the rates of birth and death. It is found that the probability density function (pdf) for lifetime of PSs is independent of system size. It is also found that the hyper-Gamma distribution serves as a universal pdf for the counting number of PSs for various system sizes and various parameters of our model tissue under VF. Further, it is demonstrated that the nonlinear Langevin equation associated with a hyper-Gamma process can mimic the pdf and temporal variation of the number of PSs in the 2D BRDR model.

出版者

American Institute of Physics

雑誌

Journal of Chemical Physics (ISSN:00219606)

巻号頁・発行日

vol.125, no.11, 2006-09-21

被引用文献数

14

---

The accurate first principles description of the correlations between electrons has been a topic of interest in molecular physics. We have reported in our previous paper [J. Chem. Phys. 123, 144112 (2005)] that the T matrix, which is the ladder diagrams up to the infinite order, can accurately represent the short-range electron correlations while calculating the double ionization energy spectra of atoms and molecules. In this paper, we calculate the two-electron distribution functions of real systems (Ar, CO, CO2, and C2H2) from the eigenvalue equation associated with the Bethe-Salpeter equation for the T matrix by beginning with the local density approximation of the density functional theory and the GW approximation. We found that when the interelectron distance is very small, the Coulomb hole appears between antiparallel spin electrons due to the short-range repulsive Coulomb interaction. The resulting two-electron distribution functions clearly show the Coulomb hole. (c) 2006 American Institute of Physics.

著者

Hara K. O. Usami N. Toh K. Baba M. Toko K. Suemasu T.

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.112, no.08, pp.083108, 2012-10

被引用文献数

83

---

Excess-carrier recombination mechanisms in undoped BaSi2 epitaxial films grown by molecular beam epitaxy on n-type silicon substrates have been studied by the microwave-detected photoconductivity decay measurement. The measured excess-carrier decay is multiexponential, and we divided it into three parts in terms of the decay rate. Measurement with various excitation laser intensities indicates that initial rapid decay is due to Auger recombination, while the second decay mode with approximately constant decay to Shockley-Read-Hall recombination. Slow decay of the third decay mode is attributed to the carrier trapping effect. To analyze Shockley-Read-Hall recombination, the formulae are developed to calculate the effective lifetime (time constant of decay) from average carrier concentration. The measurement on the films with the thickness of 50–600 nm shows that the decay due to Shockley-Read-Hall recombination is the slower in the thicker films, which is consistent with the formulae. By fitting the calculated effective lifetime to experimental ones, the recombination probability is extracted. The recombination probability is found to be positively correlated with the full width at half-maximum of the X-ray rocking curves, suggesting that dislocations are acting as recombination centers.

著者

Ogawa Kyohei Nakamura Takashi Terada Yasuhiko Kose Katsumi Haishi Tomoyuki

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.98, no.23, pp.234101, 2011-06

被引用文献数

81 12

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We have developed the first magnetic resonance (MR) microscope using a high critical-temperature superconducting bulk magnet. The bulk magnet comprises six annular bulk superconductors (60 mm outer diameter, 28 mm inner diameter, 20 mm high) made of c-axis oriented single-domain EuBa2Cu3Oy crystals. The magnet was energized using a superconducting NMR magnet operating at 4.7 T. The inhomogeneity of the trapped magnetic field measured with MR imaging was 3.1 ppm (rms) in the ϕ6.2 mm×9.1 mm cylindrical region. Three-dimensional MR images of a chemically fixed mouse embryo acquired with voxels of (50 μm)3 demonstrated the potential of our system.

著者

Matsuda Tadashi Sakakibara Jun

出版者

American Institute of Physics

雑誌

Physics of fluids (ISSN:10706631)

巻号頁・発行日

vol.17, no.2, pp.025106, 2005-01

被引用文献数

48 41

---

Turbulent vortical structures in a round free jet of water were experimentally visualized by using stereo particle image velocimetry (PIV). A laser light sheet illuminated a cross-sectional plane normal to the axis of the jet, and two charge-coupled device cameras captured particle images in the same region of interest but from different directions. The stereo-PIV algorithm had been applied to obtain two-dimensional, three-component (2D-3C) velocity distributions on various cross-sectional planes along the axis downstream. All nine components of the velocity gradient tensor were reconstructed from time-dependent 2D-3C velocity data by locally assuming Taylor's frozen field hypothesis based on the convective velocity evaluated from the mean flow profile. Isosurfaces of the swirling strength lambdai revealed that the existence of a group of hairpinlike vortex structures was quite evident around the rim of the shear layer of the jet. The center of curvature of the head of the hairpin was typically observed around r/b = 1.5, and the azimuthal spacing between the legs of the hairpin was roughly 0.9b. A similar hairpin structure was estimated by linear stochastic estimation. The typical spacing between the legs of the estimated hairpin was 0.65b, which is generally constant over the range of Re = 1500–5000.

著者

Hattori Toshiaki

出版者

American Institute of Physics

雑誌

The journal of chemical physics (ISSN:00219606)

巻号頁・発行日

vol.133, no.20, pp.204503, 2010-11

被引用文献数

9

---

A general theoretical framework of two-dimensional time-domain second-order and third-order terahertz spectroscopy has been presented. The theoretical treatment is based on a classical and phenomenological model with weak nonlinearities. Three types of nonlinearity sources, anharmonicity, nonlinear coupling, and nonlinear damping, were considered. The second-order THz spectroscopy has an exact correspondence to fifth-order off-resonance Raman spectroscopy, and it has been shown that the present treatment gives exactly the same results as of the quantum mechanical theory under the weak nonlinearity condition. General expressions for the nonlinear signal have been obtained for a single-mode system, and numerical calculations for delta-function incident terahertz pulses were shown. For the third-order signal, two-level systems were also considered for comparison. Contributions of two types of incident pulse sequences have been studied separately in the third-order signals. Profiles of the two-dimensional signals were found to depend on the origin and order of the nonlinearity and also on the pulse sequence. The results of the present study show that the two-dimensional signal features of second- and third-order nonlinear terahertz spectroscopy can clarify the nature of the system which is not accessible using linear spectroscopy.

著者

Ishizuka Shogo Yamada Akimasa Islam Muhammad Monirul Shibata Hajime Fons Paul Sakurai Takeaki Akimoto Katsuhiro Niki Shigeru

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.106, no.3, pp.034908, 2009-08

被引用文献数

144 57

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The systematic variations in the structural, optical, and electrical properties of polycrystalline Cu(In,Ga)Se2 (CIGS) thin films with Na doping level were investigated. Precise control of the Na concentration in CIGS films was demonstrated using alkali-silicate glass thin layers of various thicknesses deposited on substrates prior to CIGS growth. The CIGS grain size was observed to decrease with increasing Na concentration, although the surface morphology became smoother and exhibited a stronger (112) texture, which has been demonstrated consequence of larger grain size. The Ga composition gradient in the CIGS films was found to become large due to the presence of Na during growth, which in turn led to a decrease in the nominal band gap energy. Variations in the photoluminescence spectra and electrical properties suggested that the formation of an acceptor energy state, which may originate from OSe point defects, was enhanced in the presence of Na. This result suggests that not only Na, but also the presence of O in combination with Na contributes to the compensation of point defects and enhances p-type conductivity in CIGS films.

著者

Lee J. D. Gomi H. Hase Muneaki

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.106, no.8, pp.083501, 2009-10-16

被引用文献数

1 3

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Using the nonperturbative many-body time-dependent approach, we investigate the nonequilibrium dynamics of the coherent longitudinal optical phonon-plasmon coupled (LOPC) modes in a polar semiconductor and explore their coherent optical control and eventually the carrier mobility of the semiconductor. The basic idea for a control of the carrier mobility is to manipulate the ultrafast dephasing of the coherent carrier-relevant LOPC mode. We theoretically propose two possible options to realize the idea and reach the final goal. One is to optimize a semiconductor by finely balancing two kinds of carrier densities by chemical doping and optical doping (or photodoping), where the relaxation of the coherent carrier-relevant LOPC mode would respond in a (weak) singular way. It is found that, in this way, the carrier mobility could be enhanced by a few tens of percent. The other is to optimize the optical pumping laser. In this option, the pulse train creating pure virtual carriers through the below-band-gap excitation would be incorporated for an optical pumping, which can make possible the dephasing-free dynamics of the coherent carrier-relevant LOPC mode. The carrier mobility can then be efficiently controlled and dramatically enhanced by synchronizing the pulse train with its coherent oscillation. This might imply one of ultimate ways to control the carrier mobility of the semiconductor

著者

Otani Minoru Takagi Yoshiteru Koshino Mikito Okada Susumu

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.96, no.24, pp.242504, 2010-06

被引用文献数

25

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Based on first-principle total-energy calculations, we have found that by applying an external electric field it is possible to control the magnetic state of graphite thin film with the rhombohedral stacking arrangement. When exposed to a moderate electric field normal to the film, the surface of a thin film of rhombohedral graphite undergoes a magnetic phase transition from the antiferromagnetic state to the ferromagnetic state. The polarized electron spin is primarily distributed in the bottommost layer of the film, which forms the interface with the negative electrode. The amount of polarized electron spin is calculated to be 0.067 μB/nm2. The ferromagnetic ordering with the characteristic distribution of the polarized electron spin opens the possibility of using graphite thin films in electronic devices with spin degree of freedom.

著者

Natori Kenji

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.76, no.8, pp.4879-4890, 1994-10

被引用文献数

28 516

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Experiments on ultra-small metal-oxide-semiconductor field effect transistors (MOSFETs) less than 100 nm have been widely reported recently. The frequency of carrier scattering events in these ultra-small devices is diminished, so that further suppression of carrier scattering may bring these devices close to the regime of ballistic transport. Carrier scattering is suppressed by constructing their channel regions with intrinsic Si and also by low temperature operation. This article proposes the ballistic transport of carriers in MOSFETs, and presents the current-voltage characteristics of the ballistic n-channel MOSFET. The current is expressed with the elementary parameters without depending on the carrier mobility. It is independent of the channel length and is proportional to the channel width. The current value saturates as the drain voltage is increased and the triode and the pentode operation are specified as in the conventional MOSFET. Similar current-voltage characteristics in the ballistic transport regime are also investigated for the p-channel MOSFET, the dual gate ultra-thin silicon on insulator MOSFET, and the high electron mobility transistor device. The obtained current gives the maximum current limitation of each field effect transistor geometry. The current control mechanism of ballistic MOSFETs is discussed. The current value is governed by the product of the carrier density near the source edge in the channel, and the velocity with which carriers are injected from the source into the channel.Influence of optical phonon emission to the transport is discussed. It is suggested that if the device is operated with relatively low carrier density at low temperatures, and if the scattering processes other than the optical phonon emission are suppressed so as to attain the ballistic transport, the optical phonon emission is also suppressed and ballistic transport is sustained. A convenient figure of merit to show the ballisticity of carrier transport in an experimental MOSFET is proposed. Its value is estimated for some examples of the recent ultra-small MOSFET experiment. The proposed current voltage characteristics are evaluated for a dual gate silicon on insulator MOSFET geometry. The result is compared with the recently reported elaborate Monte Carlo simulation with satisfactory agreement.

著者

Koga T. Cronin S. B. Dresselhaus M. S. Liu J. L. Wang K. L.

出版者

American Institute of Physics

雑誌

Applied Physics Letters (ISSN:00036951)

巻号頁・発行日

vol.77, no.10, pp.1490-1492, 2000-09-04

被引用文献数

162

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An experimental proof-of-principle of an enhanced Z3DT (thermoelectric figure of merit) is demonstrated using (001) oriented Si/Ge superlattices. The highest value of the experimental Z3DT at 300 K for a (001) oriented Si(20 Å)/Ge(20 Å) superlattice is 0.1 using κ = 5 Wm−1 K−1, for the in-plane thermal conductivity, which is a factor of seven enhancement relative to the estimated value of Z3DT = 0.014 for bulk Si. The good agreement between experiment and theory validates our modeling approach (denoted as “carrier pocket engineering”) to design superlattices with enhanced values of Z3DT. Proposals are made to enhance the experimental values of Z3DT for Si/Ge superlattices even further. © 2000 American Institute of Physics.

著者

Takashi Ida

出版者

American Institute of Physics

雑誌

REVIEW OF SCIENTIFIC INSTRUMENTS (ISSN:00346748)

巻号頁・発行日

vol.69, no.11, pp.3837-3839, 1998-11

---

An efficient method for evaluating asymmetric diffraction peak profile functions based on the convolution of the Lorentzian or Gaussian function with any asymmetric window function is proposed. When this method is applied to approximate the convolution with the Howard’s window function [J. Appl. Crystallogr. 15, 615 (1982)], only a few terms of numerical integration give satisfactory results, even if the asymmetry is very strong.

著者

長谷川 浩司

出版者

American Institute of Physics

雑誌

Journal of mathematical physics (ISSN:00222488)

巻号頁・発行日

vol.35, no.11, pp.6158-6171, 1994

被引用文献数

20

著者

Yoshida Toshiyuki Hashizume Tamotsu

出版者

American Institute of Physics

雑誌

Applied Physics Letters (ISSN:00036951)

巻号頁・発行日

vol.101, no.12, pp.122102, 2012-09-17

被引用文献数

5

---

The air-gap capacitance-voltage characteristics of InGaAs surfaces were measured after 1-, 2-, 6-, 9-, and 17-cycle atomic layer deposition (ALD) Al2O3 processing. A high density of mid-gap states was found to be generated and increased during these ALD process steps, while the native oxide component was reduced. On the other hand, the mid-gap state density was drastically reduced after the usual annealing process. The generation of the mid-gap states seemed to be relevant to a non-stoichiometric Al-oxide component associated with a deficit in oxygen atoms, which became re-oxidized during the annealing process.

著者

Murakami Katsuhisa Kadowaki Takuya Fujita Jun-ichi

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.102, no.4, pp.043111, 2013-01

被引用文献数

29 2

---

From the analysis of the ratio of D peak intensity to G peak intensity in Raman spectroscopy, electron beam irradiation with energies of 100 eV was found to induce damage in single-layer graphene. The damage becomes larger with decreasing electron beam energy. Internal strain in graphene induced by damage under irradiation is further evaluated based on G peak shifts. The dose-dependent internal strain was approximately 2.22% cm2/mC at 100 eV and 2.65 × 10−2% cm2/mC at 500 eV. The strain induced by the irradiation showed strong dependence on electron energy.