共查询到20条相似文献,搜索用时 15 毫秒
1.
Daohua Song Feng Wang Gordana Dukovic Ming Zheng E. D. Semke Louis E. Brus Tony F. Heinz 《Applied Physics A: Materials Science & Processing》2009,96(2):283-287
A strong optical Stark effect has been observed in (6,5) semiconducting single-walled carbon nanotubes by femtosecond pump-probe
spectroscopy. The response is characterized by an instantaneous blueshift of the excitonic resonance upon application of pump
radiation at photon energy well below the band gap. The large Stark effect is attributed to the enhanced Coulomb interactions
present in these one-dimensional materials. 相似文献
2.
M. Combescot O. Betbeder-Matibet 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(1):33-46
This paper contains a detailed calculation of the photoinduced current density at third order in the coupling between a semiconductor
and a multifrequency photon field, starting from its standard textbook expression which reads in terms of a triple commutator.
Due to a major intrinsic problem linked to this triple commutator, such a derivation has been made possible quite recently
only, thanks to the tools developed in the composite-boson many-body theory we have recently constructed. The photoinduced
current density is shown to ultimately read in a compact form, in terms of the “Pauli scatterings” and “Coulomb scatterings”
for exciton-exciton interactions introduced in this theory. Representation of this third order response in Shiva diagrams,
which visualize interactions between excitons, is also given to better grasp the physics of the various contributions. 相似文献
3.
W. Pogosov M. Combescot 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(2):183-192
By using the composite many-body theory for Frenkel excitons we have recently developed, we here derive the ground state energy
of N Frenkel excitons in the Born approximation through the Hamiltonian mean value in a state made of N identical Q = 0 excitons. While this quantity reads as a density expansion in the case of Wannier excitons, due to many-body effects induced
by fermion exchanges between N composite particles, we show that the Hamiltonian mean value for N Frenkel excitons only contains
a first order term in density, just as for elementary bosons. Such a simple result comes from a subtle balance, difficult
to guess a priori, between fermion exchanges for two or more Frenkel excitons appearing in Coulomb term and the ones appearing
in the N exciton normalization factor – the cancellation being exact within terms in 1/Ns where Ns is the number of atomic sites in the sample. This result could make us naively believe that, due to the tight binding approximation
on which Frenkel excitons are based, these excitons are just bare elementary bosons while their composite nature definitely
appears at various stages in the precise calculation of the Hamiltonian mean value. 相似文献
4.
S. Schulz S. Schumacher G. Czycholl 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(1):51-60
We present an sp
3 tight-binding model for the calculation of the electronic and optical properties of wurtzite semiconductor quantum dots (QDs).
The tight-binding model takes into account strain, piezoelectricity, spin-orbit coupling and crystal-field splitting. Excitonic
absorption spectra are calculated using the configuration interaction scheme. We study the electronic and optical properties
of InN/GaN QDs and their dependence on structural properties, crystal-field splitting, and spin-orbit coupling. 相似文献
5.
InSe:Ho single crystal was grown by Bridgman-Stockberger method. Electric field effects on the absorption measurements have
been investigated as a function of temperature in InSe:Ho single crystal. The absorption edge shifted towards longer wavelengths
and a decrease of intensity in absorption spectra occurred under an electric field of 7.5 kV/cm. Using absorption measurements,
steepness parameter and Urbach energy were calculated under electric field. Applied electric field caused an increase in the
Urbach energy. At 10 K and 320 K, the first exciton energies were calculated as 1.322 and 1.301 eV for zero voltage and 1.245
and 1.232 eV for applied electric field, respectively. 相似文献
6.
Mathias Steiner Marcus Freitag James C. Tsang Vasili Perebeinos Ageeth A. Bol Antonio V. Failla Phaedon Avouris 《Applied Physics A: Materials Science & Processing》2009,96(2):271-282
We study the optical properties of a single, semiconducting single-walled carbon nanotube (CNT) that is partially suspended
across a trench and partially supported by a SiO2-substrate. By tuning the laser excitation energy across the E
33 excitonic resonance of the suspended CNT segment, the scattering intensities of the principal Raman transitions, the radial
breathing mode (RBM), the D mode and the G mode show strong resonance enhancement of up to three orders of magnitude. In the
supported part of the CNT, despite a loss of Raman scattering intensity of up to two orders of magnitude, we recover the E
33 excitonic resonance suffering a substrate-induced red shift of 50 meV. The peak intensity ratio between G band and D band
is highly sensitive to the presence of the substrate and varies by one order of magnitude, demonstrating the much higher defect
density in the supported CNT segments. By comparing the E
33 resonance spectra measured by Raman excitation spectroscopy and photoluminescence (PL) excitation spectroscopy in the suspended
CNT segment, we observe that the peak energy in the PL excitation spectrum is red-shifted by 40 meV. This shift is associated
with the energy difference between the localized exciton dominating the PL excitation spectrum and the free exciton giving
rise to the Raman excitation spectrum. High-resolution Raman spectra reveal substrate-induced symmetry breaking, as evidenced
by the appearance of additional peaks in the strongly broadened Raman G band. Laser-induced line shifts of RBM and G band
measured on the suspended CNT segment are both linear as a function of the laser excitation power. Stokes/anti-Stokes measurements,
however, reveal an increase of the G phonon population while the RBM phonon population is rather independent of the laser
excitation power. 相似文献
7.
F. Morales M. Monteverde M. Núñez-Regueiro 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(4):511-514
We measure electrical transport on networks of single wall nanotube of different origin as a function of temperature T, voltage V
and pressure P. We observe Luttinger liquid (LL) behavior, a conductance ∝Tα and a dynamic conductance ∝Vα. We observe a sample dependent P variation of the α parameters, interpreted as Fermi level changes due to pressure induced
charge transfer. We show how, through standard four-leads and crossed configuration methods, it is possible to determine αbulk and αend, respectively. We study and discuss the pressure and doping level dependences of the number of channels N, the LL parameter g
and the intra-rope tube-tube coupling constant U within a phenomenological model. 相似文献
8.
Y. Jia G. Yu J. Dong 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(4):433-439
The binding energies and sizes of excitons, and energy splitting of
the bright-dark excitons in single-walled carbon nanotubes have been
calculated using the nonorthogonal tight-binding model, supplemented
by the long-range Coulomb interaction. It is found that the binding
energies and the sizes of excitons not only depend on tube's
diameter d, but also its chirality. However, the splitting of the
bright-dark excitons mostly depends on 1/d2. Our obtained
results show that the curvature effect is very important for the
exciton excitations in the SWNTs, especially in the smaller diameter
ones. 相似文献
9.
The binding energy of excitonium negative ion for the ground1,3S-states in bulk semiconductors GaAs and ZnO in the hyperspherical coordinate method was found. Angular and radial correlations
between electrons in gerade and ungerade states were taken into account by channel functions, that are the eigenfunctions
of Hamiltonian on the surface of the sphere in the three-dimensional configuration space. Energy values were calculated using
the adiabatic and Born-Oppenheimer approximations. The obtained energy values are in agreement with those obtained using variational
method. 相似文献
10.
Takeshi Yasuda Masatoshi Saito Hiroaki Nakamura Tetsuo Tsutsui 《Applied Physics A: Materials Science & Processing》2009,95(1):179-183
We have studied the electronic excitations of fluorinated copper phthalocyanine, CuPcF16, thin films using electron energy-loss spectroscopy in transmission. This allowed for the derivation of the dielectric function
in a wide energy range. Furthermore, we have analyzed the lowest excitation feature using a Lorentz model, which enabled the
determination of the dielectric background in the energy range of the gap excitation, and an analysis of the momentum dependence
of the spectral intensities at low energies. 相似文献
11.
Cumulative and continuous laser vaporization synthesis of single wall carbon nanotubes and nanohorns
A. A. Puretzky D. J. Styers-Barnett C. M. Rouleau H. Hu B. Zhao I. N. Ivanov D. B. Geohegan 《Applied Physics A: Materials Science & Processing》2008,93(4):849-855
The conditions for the scaled synthesis of single wall carbon nanotubes (SWNTs) and single wall carbon nanohorns (SWNHs) by
laser vaporization at high temperatures are investigated and compared using in situ diagnostics. An industrial Nd:YAG laser
(600 W, 1–500 Hz repetition rate) with tunable pulse widths (0.5–50 ms) is utilized to explore conditions for high-yield production.
High-speed videography (50000 frames/s) of the laser plume and pyrometry of the target surface are correlated with ex situ
high resolution transmission electron microscopy analysis of the products for pure carbon targets and carbon/catalyst targets
to understand the effects of the processing conditions on the resulting nanostructures. Carbon is shown to self-assemble into
single-wall nanohorn structures at rates of ∼1 nm/ms, which is comparable to the catalyst-assisted SWNT growth rates. Two
regimes of laser ablation, cumulative ablation by multiple pulses and continuous ablation by individual pulses, were explored. Cumulative ablation with spatially overlapping 0.5-ms pulses is favorable for
the high yield and production rate of SWNTs at ∼6 g/h while continuous ablation by individual long laser pulses (∼20 ms) at
high temperatures results in the highest yield of SWNHs at ∼10 g/h. Adjustment of the laser pulse width is shown to control
SWNH morphology. 相似文献
12.
First-principles study for transport properties of defective carbon nanotubes with oxygen adsorption
Z. Li C.-Y. Wang S.-H. Ke W. Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(3):375-382
Oxygen gas usually presents in carbon nanotube (CNT) based devices and can affect
their transport properties. Here, we perform simulations for
O2 adsorption on a (5, 5) CNT with a double vacancy. We first use
first-principles plane-wave calculation to optimize the structures
and then use single-particle Green function method to study their
transport properties. It is found that an O2 can be either
physisorbed or chemisorbed on the defective CNT. The physisorption has
only minor effects on the transport while the chemisorption can
improve it and the resulting conductance is affected by the orientation of the O2 bonding. 相似文献
13.
M. Combescot 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(3):289-303
We reconsider the procedure
developed for atoms a few decades ago by Girardeau, in the light of
the composite-boson many-body theory we recently proposed. The
Girardeau's procedure makes use of a so called “unitary Fock-Tani
operator” which in an exact way transforms one composite bound
atom into one bosonic “ideal” atom. When used to transform the
Hamiltonian of interacting atoms, this operator generates an extremely
complex set of effective scatterings between ideal bosonic atoms and free
fermions which makes the transformed Hamiltonian impossible to write
explicitly, in this way forcing to some truncation. The scatterings
restricted to the ideal-atom subspace are shown to read rather simply in
terms of the two elementary scatterings of the composite-boson many-body
theory, namely, the energy-like direct interaction scatterings
— which describe fermion interactions without fermion exchange — and
the dimensionless Pauli scatterings — which describe fermion exchanges
without fermion interaction. We here show
that, due to a fundamental difference in the scalar products of
elementary and composite bosons, the Hamiltonian expectation
value for N ground state atoms
obtained by staying in the ideal-atom subspace and working
with boson operators only, differ from the exact ones even for N = 2 and
a mapping to the ideal-atom subspace performed, as advocated, from
the fully antisymmetrical atomic state, i.e., the state which obeys the
so-called “subsidiary condition”. This shows that, within this
Girardeau's procedure too, we cannot completely forget the underlying
fermionic components of the particles if we want to correctly describe
their interactions. 相似文献
14.
M. Zimbone G. Litrico M. Barbera G. A. Baratta G. Foti 《Applied physics. B, Lasers and optics》2009,94(1):29-32
The defects produced in 4H-SiC epitaxial layers by irradiation with 200-keV H+ were characterized by low-temperature photoluminescence. These defects induce sharp luminescent lines, the so-called alphabet
lines. Their intensity shows an evolution under UV-laser irradiation not previously observed. By monitoring the change in
the resulting photoluminescence spectra versus time, we distinguish two original ‘families’ of peaks called PB1 and PB2. They display a different, and opposite, behaviour with laser irradiation but they are strongly correlated. In particular,
the recovering rate of the PB1 family and the growth rate of the PB2 family are the same, indicating a structural rearrangement of defects. 相似文献
15.
Vjekoslav Sajfert Jovan Šetrajčić Bratislav Tošić Rajka Djajić 《Czechoslovak Journal of Physics》2004,54(9):975-988
The analyses of exciton diffusion in thin molecular films have shown that the diagonal elements of the diffusion tensor, usually
called diffusion coefficients, depend on the layer index labeling layers in the direction of disturbed symmetry. The particular
analysis was done for a thin film having four layers. In this structure only two layers are occupied by optical excitations.
It means that in the four layer film two films occur in which optical excitations can travel. The subfilm contains a boundary
layer that noticeably differs from the subfilm with internal layers. If the subfilm contains the boundary layer, the diffusion
coefficient of this layer differs from the diffusion coefficient of any internal layer. If the subfilm contains two internal
layers, the diffusion coefficient of these layers are equal, expectably from the viewpoint of physics. The exciton diffusion
is very low due to the high exciton energies.
This work was supported by the Serbian Ministry of Science and Technology: Grant No 1895. 相似文献
16.
Finite element simulation for estimating the mechanical properties of multi-walled carbon nanotubes 总被引:2,自引:0,他引:2
C. W. Fan Y. Y. Liu Chyanbin Hwu 《Applied Physics A: Materials Science & Processing》2009,95(3):819-831
A finite element simulation technique for estimating the mechanical properties of multi-walled carbon nanotubes is developed.
In the present modeling concept, individual carbon nanotube is simulated as a frame-like structure and the primary bonds between
two nearest-neighboring atoms are treated as beam elements, the beam element properties are determined via the concept of
energy equivalence between molecular dynamics and structural mechanics. As to the simulation of the interlayer van der Waals
force which has intrinsic nonlinearity and complicated applying region, a simplifying method is proposed that the interlayer
pressure caused by van der Waals force instead of the force itself is to be considered, and we make use of the linear part
of the interlayer pressure near the equilibrium condition to avoid the nonlinearity in problem, then linear spring elements
whose stiffness is determined by equivalent force concept can be utilized to simulate the interlayer van der Waals force such
that significant modeling and computing effort is saved in performing the finite element analysis. Numerical examples for
estimating the mechanical properties of nanotubes, such as axial and radial Young’s modulus, shear modulus, natural frequency,
buckling load, etc., are presented to illustrate the accuracy of this simulation technique. By comparing to the results found
in the literature and the possible analytical solutions, it shows that the obtained mechanical properties of nanotubes by
the present method agree well with their comparable results. In addition, the relations between these mechanical properties
and the nanotube size are also discussed. 相似文献
17.
G. Hartung J. Hult R. Balachandran M. R. Mackley C. F. Kaminski 《Applied physics. B, Lasers and optics》2009,96(4):843-862
This paper describes the simultaneous application of time-sequenced laser-induced fluorescence imaging of OH radicals and
stereoscopic particle image velocimetry for measurements of the flame front dynamics in lean and premixed LP turbulent flames.
The studied flames could be acoustically driven, to simulate phenomena important in LP combustion technologies. In combination
with novel image post processing techniques we show how the data obtained can be used to track the flame front contour in
a plane defined by the illuminating laser sheets. We consider effects of chemistry and convective fluid motion on the dynamics
of the observed displacements and analyse the influence of turbulence and acoustic forcing on the observed contour velocity,
a quantity we term as s
d
2D. We show that this quantity is a valuable and sensitive indicator of flame turbulence interactions, as (a) it is measurable
with existing experimental methodologies, and (b) because computational data, e.g. from large eddy simulations, can be post
processed in an identical fashion. s
d
2D is related (to a two-dimensional projection) of the three-dimensional flame displacement speed s
d
, but artifacts due to out of plane convective motion of the flame surface and the uncertainty in the angle of the flame surface
normal have to be carefully considered. Monte Carlo simulations were performed to estimate such effects for several distributions
of flame front angle distributions, and it is shown conclusively that s
d
2D is a sensitive indicator of a quantity related to s
d
in the flames we study. s
d
2D was shown to increase linearly both with turbulent intensity and with the amplitude of acousting forcing for the range of
conditions studied. 相似文献
18.
P. Thiyagarajan Brajesh Tiwari M. Kottaisamy N. Rama M. S. Ramachandra?Rao 《Applied Physics A: Materials Science & Processing》2009,94(3):607-612
Cool white light was realized in Y2−x−y
Gd
x
SiO5: Ce
y
phosphor under near UV excitation, due to the occupation Ce3+ in Y3+ 1st and 2nd site, synthesized using solid state carbothermal reduction route. SEM with elemental analysis show the existence
of Gd in Y2SiO5:Ce enhances the particles size in comparison to Y2SiO5:Ce phosphors alone. Gd3+ (0.00≤x≤0.75) and Ce3+ (0.02≤y≤0.10) concentration was optimized to 0.50 and 0.08 in Y2SiO5, respectively. The CIE chromaticity color coordinates (0.24, 0.20) are close to cool white light value which could be useful
for the fabrication of cool white LED. 相似文献
19.
S. E. Muraviev B. A. Tulupov M. G. Urin 《Zeitschrift für Physik A Hadrons and Nuclei》1992,341(4):383-393
A method to describe quantitatively the one-quasiparticle strength functions is proposed which takes approximately into account the coupling of one-quasiparticle states to many-phonon configurations. The method is used to interpret the appropriate experimental data for medium-heavy spherical nuclei. The results are compared with the calculations made in different theoretical approaches. 相似文献
20.
S. Allende J. Escrig D. Altbir E. Salcedo M. Bahiana 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(1):37-40
The angular dependence of the
transverse and vortex modes in a magnetic nanotube is investigated as a function of the tube
geometry, by means of analytical calculations and numerical
simulations. A critical
radius defining the transition between vortex and transverse reversal modes is determined,
leading to low or high coercivity
modes just by varying the direction of the external field, in a fixed nanotube. 相似文献