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Search Results: 1 - 10 of 117979 matches for " T. Kawazoe "
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Native point defects in few-layer phosphorene
V. Wang,Y. Kawazoe,W. T. Geng
Physics , 2014, DOI: 10.1103/PhysRevB.91.045433
Abstract: Using hybrid density functional theory combined with a semiempirical van der Waals dispersion correction, we have investigated the structural and electronic properties of vacancies and self-interstitials in defective few-layer phosphorene. We find that both a vacancy and a self-interstitial defect are more stable in the outer layer than in the inner layer. The formation energy and transition energy of both a vacancy and a self-interstitial P defect decrease with increasing film thickness, mainly due to the upward shift of the host valence band maximum in reference to the vacuum level. Consequently, both vacancies and self-interstitials could act as shallow acceptors, and this well explains the experimentally observed p-type conductivity in few-layer phosphorene. On the other hand, since these native point defects have moderate formation energies and are stable in negatively charged states, they could also serve as electron compensating centers in n-type few-layer phosphorene.
Effect of Uniaxial Stress for Pressure-Induced Superconductor SrFe_2As_2
H. Kotegawa,T. Kawazoe,H. Sugawara,K. Murata,H. Tou
Physics , 2009, DOI: 10.1143/JPSJ.78.083702
Abstract: We report that the pressure-temperature phase diagram of single-crystalline SrFe$_2$As$_2$ is easily affected by the hydrostaticity of a pressure-transmitting medium. For all of the three mediums we used, superconductivity with zero resistance appears, accompanied by the suppression of an antiferromagnetic (orthorhombic) phase, but the critical pressure $P_c$ was found to depend on the type of medium. $P_c$ was estimated to be 4.4 GPa under almost hydrostatic condition, but it decreased to $3.4-3.7$ GPa with the use of the medium already solidified at room temperature. The uniaxial stress along the c-axis is suggested to aid in the suppression of the antiferromagnetic (orthorhombic) phase. The pressure effect of BaFe$_2$As$_2$ is also reported.
Statics and dynamics of phase segregation in multicomponent fermion gas
K. Esfarjani,S. T. Chui,V. Kumar,Y. Kawazoe
Physics , 2001, DOI: 10.1140/epjd/e2002-00197-8
Abstract: We investigate the statics and dynamics of spatial phase segregation process of a mixture of fermion atoms in a harmonic trap using the density functional theory. The kinetic energy of the fermion gas is written in terms of the density and its gradients. Several cases have been studied by neglecting the gradient terms (the Thomas-Fermi limit) which are then compared with the Monte-Carlo results using the full gradient corrected kinetic energy. A linear instability analysis has been performed using the random-phase approximation. Near the onset of instability, the fastest unstable mode for spinodal decomposition is found to occur at $q=0$. However, in the strong coupling limit, many more modes with $q\approx K_F$ decay with comparable time scales.
Nature and evolution of the band-edge states in few-layer phosphorene
V. Wang,Y. C. Liu,Y. Kawazoe,W. T. Geng
Physics , 2015,
Abstract: Using first-principles calculations, we have investigated the evolution of band-edge states of few-layer phosphorene as a function of the number of P layers. Our results predict that the valence band edge of monolayer phosphorene is extremely sensitive to strain. Its band gap could undergo an indirect-direct transition under a lattice expansion as small as 1%. A semi-empirical interlayer coupling model is proposed, which can well reproduce the evolution of valence band-edges obtained by first-principles calculations. We conclude that the interlayer coupling plays a predominant role in the evolution of the band-edge states. The analysis of the orbital-decomposed band structure provides a better understanding of the upward shift of valence band maximum surpassing that of conduction band minimum.
Alguns aspectos da biologia de Biomphalaria glabrata (Say, 1818) e Biomphalaria tenagophila (D'Orbigny, 1835) (Pulmonata, planorbidae): II - Fecundidade e fertilidade
Revista de Saúde Pública , 1977, DOI: 10.1590/S0034-89101977000100005
Abstract: the fecundity (ratio egg-masses per snail, eggs per snail and eggs per egg-mass) and the fertility (hatchability and viability of eggs) of biomphalaria glabrata and biomphalaria tenagophila were compared during one year, in the laboratory. the average of eggs per egg-mass was significantly higher in b. glabrata (19.9) than in b. tenagophila (16.2) and both species showed highest fecundity during april. the influence of temperature was very small. the fecundity defined as egg-mass per snail per day was greater in b. glabrata (0.65) than in b. tenagophila (0.56). the same was verified in the ratio eggs per snail per day: the average was 13.4 in b. glabrata and 9.9 in b. tenagophila. considering the fertility as percentage of snail hatchability, b. glabrata showed an average of 95.8 and b. tenagophila 90.5%, the difference being significant, at the 5% level. the greatest hatchability rate in b. glabrata was observed during november-january (98.0); in b. tenagophila, during october-november (95.0%). seasonal rhythm and influence of seasonal variation of temperature were not observed.
Alguns aspectos da biologia de Biomphalaria glabrata (Say, 1818) e Biomphalaria tenagophila (D'Orbigny, 1835) (Pulmonata, Planorbidae): I - Dura??o do período embrionário
Revista de Saúde Pública , 1976, DOI: 10.1590/S0034-89101976000100005
Abstract: the incubation periods of biomphalaria glabrata and biomphalaria tenagophila were compared during one year, in the laboratory. the average time for eggs hatching was 7,6 and 8,0 days for biomphalaria glabrata and biomphalaria tenagophila, respectively; the difference was not significant at the 5% level. the fastest development of the eggs was verified in the summer when the average water temperature was approximately 28°c. the analysis of the correlation coeficient showed that the influence of temperature on the egg development period was not strong: biomphalaria glabrata showed best correlation with minimum air temperature (36,2%) and with water temperature (36,0%), while biomphalaria tenagophila correlated best with minimum air temperature (27,0%).
Realization of an ultra-high magnetic field on a nano-scale
S. T. Chui,J. -T. Wang,Li Zhou,K. Esfarjani,Y. Kawazoe
Physics , 2000,
Abstract: In tunnel junctions of which at least one side is a ferromagnet, very large magnetic polarization change ($\approx 0.1 \mu_B$) and splitting of the spin up and spin down Fermi energy ($\approx 0.1 eV$) can be created under steady state finite current conditions (bias voltage $\approx$ 1 volt). This is {\bf much higher} than can be created by the highest magnetic field on earth. We illustrate this with a specific calculation of a recently observed very large Hall effect in the Al side of a Co-I-Al tunnel junction. Other recent experiments that support this idea are discussed.
Contrasting Pressure Effects in Sr2VFeAsO3 and Sr2ScFePO3
H. Kotegawa,T. Kawazoe,H. Tou,K. Murata,H. Ogino,K. Kishio,J. Shimoyama
Physics , 2009, DOI: 10.1143/JPSJ.78.123707
Abstract: We report the resistivity measurements under pressure of two Fe-based superconductors with a thick perovskite oxide layer, Sr2VFeAsO3 and Sr2ScFePO3. The superconducting transition temperature Tc of Sr2VFeAsO3 markedly increases with increasing pressure. Its onset value, which was Tc{onset}=36.4 K at ambient pressure, increases to Tc{onset}=46.0 K at ~4 GPa, ensuring the potential of the "21113" system as a high-Tc material. However, the superconductivity of Sr2ScFePO3 is strongly suppressed under pressure. The Tc{onset} of ~16 K decreases to ~5 K at ~4 GPa, and the zero-resistance state is almost lost. We discuss the factor that induces this contrasting pressure effect.
Hysteretic current-voltage characteristics and resistance switching at an epitaxial oxide Schottky junction SrRuO$_{3}$/SrTi$_{0.99}$Nb$_{0.01}$O$_{3}$
T. Fujii,M. Kawasaki,A. Sawa,H. Akoh,Y. Kawazoe,Y. Tokura
Physics , 2004, DOI: 10.1063/1.1845598
Abstract: Transport properties have been studied for a perovskite heterojunction consisting of SrRuO$_{3}$ (SRO) film epitaxially grown on SrTi$_{0.99}$Nb$_{0.01}$O$_{3}$ (Nb:STO) substrate. The SRO/Nb:STO interface exhibits rectifying current-voltage ($I$-$V$) characteristics agreeing with those of a Schottky junction composed of a deep work-function metal (SRO) and an $n$-type semiconductor (Nb:STO). A hysteresis appears in the $I$-$V$ characteristics, where high resistance and low resistance states are induced by reverse and forward bias stresses, respectively. The resistance switching is also triggered by applying short voltage pulses of 1 $\mu$s - 10 ms duration.
Chemical Functionalization of Graphene Nanoribbons
Narjes Gorjizadeh,Yoshiyuki Kawazoe
Journal of Nanomaterials , 2010, DOI: 10.1155/2010/513501
Abstract: We review the electronic properties of graphene nanoribbons functionalized by various elements and functional groups. Graphene nanoribbons are strips of graphene, the honeycomb lattice of carbon with hybridization. Basically nanoribbons can be classified into two categories, according to the geometry of their edge, armchair, and zigzag, which determine their electronic structure. Due to their fascinating electronic and magnetic properties many applications has been suggested for these materials. One of the major methods to use graphene nanoribbons in future applications is chemical functionalization of these materials to make an engineering on their band gap. In this review, we introduce various types of modifying graphene nanoribbons to meet their promising applications. 1. Introduction After discovery of graphene [1], it has been considered as basic material for the future nanoelectronic devices. Its unique properties, such as massless Dirac fermion behavior [2–4], half-integer quantum Hall effect [2, 5], and high-carrier mobility [2] make it a promising candidate for application in nanoelectronics and spintronics devices [2, 5–9]. Graphene nanoribbons can be constructed as strips of graphene, with quasi1D structures. So far, Nanoribbons with widths up to 2?nm have been fabricated experimentally [10–12]. Geometrically, two main types of nanoribbons with two edge shapes can be cut from a hexagonal lattice of graphene: zigzag edge and armchair edge [13–16]. Different types of ribbons are specified by their edge geometry and width. The width is labeled by an integer which counts the number of carbon chains between the two edges. Figure 1 shows the two types of ribbons with their width indices. The two ribbon characteristics, that is, edge geometry and width, are the key parameters which determine the electronic properties of the ribbons [7, 17–19]. Figure 1: Graphene nanoribbons with armchair (a) and zigzag (b) edges. In each case, index denotes the width of the ribbon, and ribbon axis is the vertical direction. The earliest theoretical studies of graphene nanoribbons, using a simple tight-binding method, predicted that of the armchair nanoribbons, whose width index satisfies ( is an integer), are metallic [17], and another are semiconductor with band gaps depending on their width, while all zigzag nanoribbons are metallic, a similar behavior as carbon nanotubes (CNTs). A characteristic peak in the density of states (DOS) of zigzag nanoribbons near and slightly below Fermi energy is also predicted [16, 20]. But recently the first principle studies based
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