Publications (28)12.39 Total impact
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Article: Optical properties of simple hexagonal and rhombohedral few-layer graphenes in an electric field
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ABSTRACT: The influence of a perpendicular electric field ( F ) on the optical properties of simple hexagonal and rhombohedral few-layer graphenes is studied through the tight-binding model. The electric-field-modulated absorption spectra depend on the stacking sequence. The low-energy absorption spectra of simple hexagonal few-layer graphenes exhibit the jumping structures in the absence or presence of an electric field. On the other hand, absorption spectra of rhombohedral few-layer graphenes show discontinuities and sharp peaks at F =0 . Besides, the application of F affects the absorption spectra, generates new peaks, and changes peak position and peak height. The frequency of the peak is predicted to be closely associated with the stacking sequences and the field strength. Above all, the predicted absorption spectra could be verified by optical measurements.Journal of Applied Physics 06/2008; · 2.17 Impact Factor -
Article: Electronic structures of finite double-walled carbon nanotubes in a magnetic field
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ABSTRACT: The discrete electronic states of finite double-walled armchair carbon nanotubes are obtained in a magnetic field by using the Peierls tight-binding model. State energy, wavefunction, energy gap, and density of states are investigated in detail. Electronic properties strongly depend on the intertube atomic interactions, magnitude and direction of the magnetic field, boundary structure, length, and Zeeman splitting. The intertube atomic interactions result in an asymmetric energy spectrum about the Fermi level, a drastic change in energy gap, and obvious energy shifts. The magnetic field could lead to state crossing, alter the hybridization of the inner and outer tight-binding functions, destroy state degeneracy, increase more low-energy states, and induce complete energy-gap modulations (CEGMs). The different atomic positions along the tube axis make the C5 system differ from the D5h or S5 systems. According to the lengths Nl = 3i, 3i+1, and 3i+2 (i an integer), there exist three types of magnetic-flux-dependent state energies. The Zeeman effect causes CEGMs to happen at weaker magnetic fields. The main features of quantized electronic states are directly reflected in the density of states. The predicted magneto-electronic properties could be examined by the transport and optical measurements.Journal of Physics Condensed Matter 01/2008; 20(7):075213. · 2.55 Impact Factor -
Article: Deformation effect on electronic and optical properties of nanographite ribbons
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ABSTRACT: The electronic structures of deformed nanographite ribbons are calculated from the Huckel tight-binding model. They strongly depend on the uniaxial strain and the ribbon geometry (edge structure and width). The uniaxial strain significantly affects the subband spacings and the energy dispersions. A monotonous relation between the uniaxial strain and the state energies is absent. For armchair ribbons, the uniaxial strain drastically changes the energy gap and thus leads to the semiconductor-metal transition. The dependence of energy gap on strain is determined by the ribbon width. The large strain could also induce the subband crossing. On the other hand, zigzag ribbons remain metallic during the variation of the strain. Armchair and zigzag ribbons, respectively, behave as zigzag and armchair nanotubes. The calculated absorption spectrum exhibits rich peak structures, mainly owing to the divergent density of states of the one-dimensional subbands. The uniaxial-strain effects on optical excitations are strong for armchair ribbons, but weak for zigzag ribbons.Journal of Applied Physics 04/2007; · 2.17 Impact Factor -
Article: Electronic and optical properties of finite carbon nanotubes in an electric field.
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ABSTRACT: The effects, caused by the geometric structure and an electric field (E), on the electronic and optical properties of quasi-zero-dimensional finite carbon nanotubes are explored by employing the tight-binding model coupled with curvature effects. Electronic properties (state energies, symmetry of electronic states, energy spacing and state degeneracy) are significantly affected by the magnitude and the direction of the electric field and the geometric structure (radius, length and chirality). The electric field, by lowering the symmetry of finite carbon nanotubes, modifies the electronic properties. Thus, the optical excitation spectra, excited by electric polarization parallel to the nanotube axis, exhibit rich delta-function-like peaks, which reveal the characteristics of the electronic properties. Therefore it follows that geometric structure and E influence the low-energy absorption spectra, i.e. the change of frequency of the first peak, the alternation of the peak height and the production of the new peaks. There are more absorption peaks when E is oriented closer to the cross-section plane. Moreover, the very complicated optical absorption spectra are characteristic for the individual chiral carbon nanotube due to its specific geometric structure. Above all, the predicted absorption spectra and the associated electronic properties could be verified by optical measurements.Nanotechnology 02/2007; 18(7):075704. · 3.98 Impact Factor -
Article: Electronic structures of finite carbon nanotubes under external fields
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ABSTRACT: The electronic states of finite carbon nanotubes in the presence of electric and magnetic fields are calculated by the tight-binding model. Electronic properties such as state energy, energy gap, and density of states are mainly determined by the transverse electric field, the magnetic field, the Zeeman splitting, and the nanotube length, as well as the transverse geometric structure. The electric field could induce the destruction of state degeneracy, produce more low-energy states, and lead to significant changes in energy spacing. Complete energy-gap modulations exist during the variation of the electric field. Such effects are enhanced by the magnetic field.J. Phys.: Condens. Matter. 01/2006; 18:9427-9434. -
Article: Magnetic Moment of Armchair Carbon Tori
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ABSTRACT: Magnetoband structures of armchair carbon tori are studied from the tight-binding model. They strongly depend on the agnitude and the direction of the magnetic field ( B). There exist metal-semiconductor (MS) transition as B varies. They happen more frequently when B is relatively close to the toroid axis. The characteristics of band structure are directly reflected in magnetic properties. The magnetic moment exhibit special jump structures at T=0, mainly owing to the MS transition. Paramagnetism or diamagnetism is mainly determined by the toroid radius (R) and the angle α) between the magnetic field and the toroid axis. Most of armchair carbon tori are paramagnetic for α > 30rc. The temperature dependence is strong at α = 0rc, but weak at α=90rc.02/2004; -1:1116. -
Article: Magnetoelectronic excitations in single-walled carbon nanotubes
Physical Review B. 04/2003; 67(16):165421. -
Article: Magnetoelectronic and optical properties of carbon nanotubes
Physical Review B. 01/2003; 67(4):045405. -
Article: Novel magnetoplasmons in armchair carbon nanotubes
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ABSTRACT: The low-frequency magnetoplasmons of armchair carbon nanotubes are investigated by the random phase approximation. The dependence on the magnetic flux (φ), the direction (α) of magnetic field, and the temperature (T) is novel. Each nanotube exhibits one interband magnetoplasmon at low temperature, when the magnetic field is not perpendicular to the nanotube axis. The plasmon frequency decreases (increases) with α (φ), while the strength of plasmon exhibits the opposite behavior. One interband and intraband magnetoplasmon can exist at α = 90 • , and it is almost the same with that in the absence of φ. The temperature can induce one intraband magnetoplasmon and reduce the frequency of the interband magnetoplasmon. The new plasmon is absent at low T , or at high T and large α. The T -dependence is negligible for the interband and intraband magnetoplasmon at α = 90 • or the plasmon at φ = 0. 2003 Elsevier Science B.V. All rights reserved.Physics Letters A. 01/2003; 311:53-59. -
Article: Optical properties of well-aligned multiwalled carbon nanotube bundles
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ABSTRACT: The optical properties of well-aligned multiwalled carbon nanotube bundles are studied within the gradient approximation. The imaginary (real) part of the transverse dielectric function exhibits a special peak (dip) at frequency ω∼2γ0 (γ0 is the nearest-neighbor overlap integral). Consequently the loss function shows a prominent π-plasmon peak at ω>2γ0. The π plasmon also induces a strong and abrupt edge in the reflectance spectrum. These features are similar to those of graphite. The optical properties are hardly affected by the chiral angle of carbon nanotube; moreover, they are insensitive to small variation in the radius of carbon nanotube. On the other hand, the optical properties strongly depend on the polarization direction of an external electric field. The well-aligned multiwalled carbon nanotubes with high radius uniformity, which were recently reported by Fan et al. [Science 283, 512 (1999)], could be used to verify the predicted optical properties.Phys. Rev. B. 05/2000; 61(20). -
Article: Uniaxial-stress effects on electronic structures of nanographite ribbons
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ABSTRACT: The uniaxial-stress effects on the low-energy electronic properties of nanographite ribbons are studied by the tight-binding model. The dependence on the strain, the edge structure, the ribbon width, and the stacking sequence is strong. The strain could induce the alternation of energy dispersions, the destruction of state degeneracy, the variation of energy gap, the semiconductor–metal transition, and the change of special structures in density of states. The effects of strain are important for the AB- and AA-stacked armchair ribbons. However, they are negligible for the AB- and AA-stacked zigzag ribbons. Armchair ribbons could exhibit the semiconductor–metal transition. Such transition is mainly determined by the strain and the ribbon–ribbon interactions.Physica E: Low-dimensional Systems and Nanostructures. -
Article: Optical excitations of finite carbon nanotubes
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ABSTRACT: Optical excitations of finite carbon nanotubes by the cross polarized light are studied within the gradient approximation. They are dominated by the quantum size effects. The absorption spectra exhibit rich absorption peaks, mainly owing to many zero-dimensional discrete states. They strongly depend on the length, the radius, the chiral angles, and the magnetic flux. The absorption peaks gradually group together as the length increases. The threshold excitation energy (ωth) decreases in the increasing of radius. The dependence of ωth on length is monotonous for zigzag nanotubes, while it is oscillatory for armchair nanotubes. The threshold excitation energy is constant for the sufficiently long carbon nanotubes. Chiral carbon nanotubes exhibit very complicated optical spectra, compared with achiral carbon nanotubes. The magnetic flux reduces the threshold excitation energy and increases the number of absorption peaks.Carbon. -
Article: Influence of an electric field on the optical properties of few-layer graphene with AB stacking
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ABSTRACT: The effect of perpendicular electric field F on optical properties of the AB-stacked few-layer graphene, made up of two, three, or four graphite sheets, is explored through the gradient approximation. In contrast to the featureless optical spectra of graphene, the low-energy absorption spectra of few-layer graphene with AB stacking exhibit many jumping structures, which result from the band-edge states caused by the stacking effect, in the absence of an electric field. Remarkably, F causes the subband anticrossing, changes the subband spacing, produces the oscillating bands, and increases the band-edge states. It, therefore, follows that the field-modulating spectra with sharp peaks are generated. Moreover, the frequency of peak, which is strongly dependent on the layer number and the field strength, is predicted. Above all, the predicted absorption spectra and the associated electronic properties could be verified by the optical measurements.20. -
Article: Electron energy loss spectra of finite carbon nanotubes
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ABSTRACT: The sp 3 tight-binding model and the gradient approximation are, respectively, used to calculate electronic states and the loss function of finite carbon nanotubes. The study results show that the loss spectra of finite carbon nanotubes are strongly dependent on the nanotube geometric structure length, radius, and chiral angle and the magnetic flux. The prominent peaks at 4 0 0 is the nearest-neighbor overlap integral mainly result from the states, while the peaks at 4 0 result from the + states. For 4 0 , most loss spectra contain four peaks in the different finite carbon nanotubes CNTs systems. The peak energy versus length graph is a monotonous curve for zigzag nanotubes, while the one for armchair nanotubes is oscillatory. Prominent peak energies are almost independent of length for sufficiently long CNTs. These results illustrate the quasi-zero-dimensional character. Moreover, finite armchair CNTs reveal dominating and + plasmon peaks at 2 0 6 eV and 6.5 0 18 eV, respectively. Yet, for finite zigzag CNTs plasmon peaks exist at 2.15 0 and 6.6 0 , due to special localized states at the outermost zigzag positions. The predicted loss spectra and the plasmon frequencies could be verified by electron energy loss spectra. © 2007 American Institute of Physics. -
Article: Dielectric response of an electron-gas nanotube superlattice
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ABSTRACT: The dielectric function of an electron-gas nanotube superlattice is calculated within the linear response. The intertube Coulomb interactions play an important role on the excitation properties. The electronic excitations of the nanotube superlattice are the superposition of those of the individual nanotubes. However, the collective plasma oscillations of these two systems quite differ from each other. A nanotube superlattice exhibits two-dimensional characteristics and is highly anisotropic.Physics Letters A. 253:88-92. -
Article: Persistent currents in finite zigzag carbon nanotubes
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ABSTRACT: Magnetic properties of finite zigzag carbon nanotubes are studied within the tight-binding model. The spin–B interaction (Zeeman splitting) causes the metal–semiconductor transition and thus produces a large persistent current (J) with special jump structures. This effect makes all zigzag carbon nanotubes exhibit a gigantic paramagnetism. It also destroys the periodicity of magnetic properties. The dependence on the magnetic flux, the length (w), the radius (r), the temperature (T), and the chirality (zigzag or armchair) is strong. The amplitude of J quickly decreases with increasing of (w, r, T). Zigzag carbon nanotubes differ significantly from armchair carbon nanotubes (or infinite zigzag carbon nanotubes) in features such as magnetic susceptibility and in special structures in J.Carbon. 42(14):2873-2878. -
Article: Electric-field-tunable electronic properties of graphene quantum dots
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ABSTRACT: The tight-binding method is employed to investigate the electronic properties of a square graphene quantum dot subject to an in-plane electric field (F). The electronic properties are strongly modified by tuning the field strength or altering the field direction. F will change state energies, alter energy gaps, and induce energy gap modulations. State energies show oscillatory behavior with the change of the field strength. The oscillating amplitude and period are further modulated by the change of the field direction. The field-orientation-dependent electronic properties originate in the geometrical anisotropy of the square graphene quantum dot. Moreover, the density of states (DOS), exhibiting many discrete peaks, directly reveals the characteristic of the electric-field-tunable electronic properties. The number and frequencies of DOS peaks are significantly dependent on the field strength and direction.Physica E Low-dimensional Systems and Nanostructures 42(10):2812-2815. · 1.53 Impact Factor -
Article: Electron decay rates in a zero-gap graphite layer
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ABSTRACT: A 2D monolayer graphite exhibits rich Coulomb excitations and deexcitations, mainly owing to the zero-gap characteristic. The low-frequency electronic excitations include interband e–h excitations, intraband e–h excitations, and plasmon. The two latters are purely caused by temperature. The Coulomb decay rate strongly depends on temperature and wave vector (or energy), and the analytic formulas between them are absent. The Coulomb decay rate of the Fermi-momentum state only comes from the intraband e–h excitations. It grows quickly as temperature increases. Its value is close to the measured results of the layered graphite. As to other states, three kinds of electronic excitations make important contributions to the Coulomb decay rates and cause the novel dependence on wave vector. The Coulomb decay rate is much faster than the electron–phonon scattering rate. A 2D monolayer graphite quite differs from a 2D electron gas or a 1D gapless carbon nanotube in electronic excitations and deexcitations.Physics Letters A. 357:401-406. -
Article: Influence of modulated fields on the Landau level properties of graphene
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ABSTRACT: The influences of modulated electric fields and modulated magnetic fields on low-energy Landau levels (LL’s) of monolayer graphene are investigated by the tight-binding model. The ratio of the uniform magnetic-field strength to the modulated field strength is arbitrarily chosen for discussions. Both modulated fields cause the LL’s to split into two twofold parabolic subbands; these subbands exhibit periodic oscillations and two kinds of band-edge states. However, the subband dispersions and oscillation amplitudes associated with electric and magnetic modulated fields behave differently. The main features of the electronic structure are reflected in the density of states, which presents pairlike and square-root divergent structures for both modulated field cases. The LL wave functions are strongly affected by both modulated fields, such as the broken symmetry, displacement of the center location, and alteration of the amplitude strength. These changes in the LL wave functions should be reflected in other physical properties, e.g., the optical selection rules. Furthermore, the dependence of the LL properties on the modulation strength and modulation period is also discussed in detail.Phys. Rev. B. 83(19). -
Article: Magnetization of armchair carbon tori
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ABSTRACT: Magnetoelectronic states of armchair carbon tori are studied by the tight-binding model. They strongly depend on the magnitude and the direction of the magnetic field (B). B induces the destruction of state degeneracy, the change of energy spacing, and the semiconductor-metal transition (SMT). SMT’s happen more frequently when B is relatively close to the toroid axis. Such characteristics are directly reflected in magnetic properties. Magnetization (M) exhibits special jump structures at T=0, mainly owing to SMT’s. Magnitude of M and magnetism are mainly determined by the toroid radius (R), the temperature, the angle (α) between the magnetic field and the symmetry axis, and the chirality. The dependence of M on radius (temperature) is strong at α=0°, but weak at α=90°. Most of armchair carbon tori are paramagnetic for α>30°. The critical angle in determining magnetism is αc≃30°. Armchair carbon tori quite differ from carbon tori near zigzag configuration (or armchair carbon nanotubes) in magnetoelectronic structures and magnetism.Phys. Rev. B. 70(7).
Top co-authors
Top Journals
Institutions
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2007–2008
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Tainan University of Technology
Tainan, Taiwan, Taiwan
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2006–2008
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National Kaohsiung Marine University
Kaohsiung, Kaohsiung, Taiwan -
Kun Shan University
Kaohsiung, Kaohsiung, Taiwan
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2000
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Yung Ta Institute Of Technology & Commerce
Pingtung, Taiwan, Taiwan
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