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1.
A detailed Raman study on thin single-wall carbon nanotubes prepared by the HiPCO process 总被引:2,自引:0,他引:2
A. Kukovecz Ch. Kramberger V. Georgakilas M. Prato H. Kuzmany 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):223-230
The Raman spectrum of single wall carbon nanotubes (SWNTs) prepared by high pressure CO decomposition (HiPCO process) has
been recorded at nine excitation laser energies ranging from 1.83 eV to 2.71 eV. The characteristic nanotubes features: G
band, D band and radial breathing mode (RBM) have been analyzed and compared to those of an arc discharge SWNT material of
similar diameter. A strong Breit-Wigner-Fano type (metallic) contribution to the G band was found in the spectra measured
with green lasers, while spectra measured with red lasers indicate resonances of semiconducting SWNTs. Analysis of the energy
dependence of the position of the D band revealed sinusoid oscillations superimposed on a linear trend. The validity of full
DOS calculations for HiPCO materials has been confirmed by a match found between the estimated spectral contribution of metallic
SWNTs as calculated from the components of the measured G band and as predicted by the (n, m) indexes of the major scatterers of DOS simulations. The RBM region of the HiPCO spectrum is more complex than usually observed
for SWNTs. The analysis performed with a Gaussian distribution and improved fitting parameters leads to a mean diameter and
variance of 1.05 nm and 0.15 nm, respectively. A bimodal Gaussian distribution had little influence on the error sum but reduced
the standard error slightly. The major spectral features of the RBM could be interpreted using available resonance Raman theory.
Received 5 February 2002 / Received in final form 3 April 2002 Published online 19 July 2002 相似文献
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G. S. N. Eliel H. B. Ribeiro K. Sato R. Saito Chun-Chieh Lu Po-Wen Chiu C. Fantini A. Righi M. A. Pimenta 《Brazilian Journal of Physics》2017,47(6):589-593
A resonant Raman study of twisted bilayer graphene (TBG) samples with different twisting angles using many different laser lines in the visible range is presented. The samples were fabricated by CVD technique and transferred to Si/SiO2 substrates. The Raman excitation profiles of the huge enhancement of the G-band intensity for a group of different TBG flakes were obtained experimentally, and the analysis of the profiles using a theoretical expression for the Raman intensities allowed us to obtain the energies of the van Hove singularities generated by the Moiré patterns and the lifetimes of the excited state of the Raman process. Our results exhibit a good agreement between experimental and calculated energies for van Hove singularities and show that the lifetime of photoexcited carrier does not depend significantly on the twisting angle in the range intermediate angles (?? between 10° and 15°). We observed that the width of the resonance window (Γ ≈ 250 meV) is much larger than the REP of the Raman modes of carbon nanotubes, which are also enhanced by resonances with van Hove singularities. 相似文献
4.
Shigehiro Komura T. Takeda Y. Kawabata S.K. Ghosh H. Seto M. Nagao 《The European physical journal. E, Soft matter》2001,5(3):329-336
Dynamical fluctuations of microemulsion and lamellar structures in a ternary amphiphilic system C12E 5/water/n-octane are studied by means of neutron spin echo spectrometry. The decay rate of the time correlation of the concentration
was analyzed in terms of a theory (M. Nonomura, T. Ohta, J. Chem. Phys. 110, 7516 (1999)), in which both van Hove and hydrodynamic interactions are considered. The result shows that the time correlation
function is expressed mostly by a single exponential determined exclusively by hydrodynamic interactions.
Received 1 December 1999 and Received in final form 12 March 2001 相似文献
5.
M.G. Donato G. Faggio M. Marinelli G. Messina E. Milani A. Paoletti S. Santangelo A. Tucciarone G. Verona Rinati 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):133-139
High quality synthetic diamonds were grown on single-crystal silicon by microwave plasma enhanced chemical vapour deposition
(CVD). A careful optimisation of both the experimental setup and the growth parameters was necessary before that the achievement
of the best results was made possible. The films were deposited using a CH4-H2 gas mixture at methane concentrations variable in the range 0.6-2.2%, while the substrate temperature was fixed at 750 °C. Raman spectroscopy and photoluminescence (PL) were utilised to monitor the quality of the deposited films and to study
the spatial distribution of defects, respectively. Micro-Raman analysis shows that linewidths of the diamond peak lower than
2.4 cm-1 can be easily measured at the growth surface, indicating that the crystalline quality of individual grains is comparable
to that of the best natural diamonds. The excellent phase purity of the diamond microcrystals at the growth surface is witnessed
by the complete absence of any non-diamond carbon feature and by a very weak luminescence background in the 1.6-2.4 eV spectral
range. A worsening of the quality of the diamond particles is found moving from the growth surface towards the film-substrate
interface. A photoluminescence feature at about 1.68 eV, commonly associated to Si impurities, is distinctly observed as the
exciting laser beam is focused close to the interface. A progressive degradation of the global quality of the films is found
with increasing methane concentration in the gas mixture, as witnessed by an increased PL background in the films grown at
higher methane concentrations.
Received 24 November 2000 相似文献
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A. Avella F. Mancini D. Villani H. Matsumoto 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(3):303-311
The addition to the Hubbard Hamiltonian of a t' diagonal hopping term, which is considered to be material dependent for high-T
c cuprate superconductors, is generally suggested to obtain a model capable to describe the physics of high-T
c cuprate materials. In this line of thinking, the two-dimensional t-t'-U model has been studied by means of the Composite Operator Method, which allows to determine the dynamics in a fully self-consistent
way by use of symmetry requirements, as the ones coming from the Pauli principle. At first, some local quantities have been
calculated to be compared with quantum Monte Carlo data. Then, the structure of the energy bands, the shape of the Fermi surface
and the position of the van Hove singularity have been computed as functions of the model parameters and studied by the light
of the available experimental data. The results of our study show that there exists two sets of parameters that allows the
model to describe the relevant features of the 1-layer compounds Nd2-xCexCuO4 and La2-xSrxCuO4. On the other hand, for the 2-layer compound YBa2Cu3O 7 - δ is not possible to find a reasonable set of parameters which could reproduce the position of the van Hove singularity as
predicted by ARPES experiments. Hence, it results questionable the existence of an unique model that could properly describe
the variety of cuprate superconductors, as the two-dimensional t-t'-U model was thought to be.
Received 29 March 2000 and Received in final form 10 August 2000 相似文献
8.
M. Leone A. Vázquez A. Vespignani R. Zecchina 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):191-197
We present a detailed study of the phase diagram of the Ising model in random graphs with arbitrary degree distribution. By
using the replica method we compute exactly the value of the critical temperature and the associated critical exponents as
a function of the moments of the degree distribution. Two regimes of the degree distribution are of particular interest. In
the case of a divergent second moment, the system is ferromagnetic at all temperatures. In the case of a finite second moment
and a divergent fourth moment, there is a ferromagnetic transition characterized by non-trivial critical exponents. Finally,
if the fourth moment is finite we recover the mean field exponents. These results are analyzed in detail for power-law distributed
random graphs.
Received 4 April 2002 Published online 19 July 2002 相似文献
9.
S. Chattopadhyay W.A. Kanner J. Chakrabarti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):393-398
The evolution in coding DNA sequences brings new flexibility and freedom to the codon words, even as the underlying nucleotides
get significantly ordered. These curious contra-rules of gene organisation are observed from the distribution of words and
the second moments of the nucleotide letters. We apply these statistical data to determine the relative positions of a few
bacterial groups as per their divergence in the geological timescale.
Received 3 January 2002 相似文献
10.
Fluid and plastic flow dynamics of the critical state for a strongly pinned 2D superconductor 总被引:2,自引:0,他引:2
D. Monier L. Fruchter 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(2):201-205
The frequency of the Raman active A1g radial breathing mode has been widely used as a tool to estimate the distribution of diameters of single wall carbon nanotubes
(SWNT). However, the relation between frequency and diameter is not straightforward and results are model-dependent. Because
most of the experiments are performed on bundles and not on isolated tubes, the model should especially take into account
the van der Waals intertube interactions. Here, we use a pair-potential approach to account for such interactions and we derive
a nonlinear relation between the SWNT diameter and the frequency of the A1g radial breathing modes. We demonstrate a good agreement between calculations and the diameters derived from diffraction experiments
on the same samples.
Received 22 December 1999 and Received in final form 17 July 2000 相似文献
11.
G.J. Rodgers K. Darby-Dowman 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(2):267-271
We study a number of properties of a simple random growing directed network which can be used to model real directed networks
such as the world-wide web and call graphs. We confirm numerically that the distributions of in- and out-degree are consistent
with a power law, in agreement with previous analytical results and with empirical measurements from real graphs. We study
the distribution and mean of the minimum path length, the high degree nodes, the appearance and size of the giant component
and the topology of the nodes outside the giant component. These properties are compared with empirical studies of the world-wide
web.
Received 15 June 2001 and Received in final form 12 July 2001 相似文献
12.
The hopping motion of a classical bounded pair of two particles along a chain is investigated. It is shown that in the asymmetric
case of the system dynamics including excited states which differ from the respective ground states by the barrier to be overcome
by one of the two particles, the over- and underpopulation of these excited states leads to a directed motion of the particle
pair. Thereby, overpopulation results in one direction of motion, whereas underpopulation results in the opposite direction,
and the mean velocity is determined by the amount of over-resp. underpopulation. For small deviations from equilibrium, the
system exhibits linear response well known from other ratchet-type models. Possible generalizations and applications are discussed.
Received 17 August 2001 and Received in final form 11 October 2001 相似文献
13.
The thermodynamic properties of a crystal lattice in the harmonic approximation are expressed in terms of a dispersion function conjugate to the spectral distribution of normal-mode vibrations. Frequency moments of the normal-mode distribution provide the necessary and sufficient information for construction of accurate bounds on the dispersion function and on the associated thermodynamic properties. This clarifies the successful employment of moment expansions and approximate frequency spectra in determinations of thermodynamic properties, and establishes the equivalence of recently devised continued-fraction and moment-theory techniques for investigating crystal lattice vibrations. When sufficient numbers of frequency moments are available, accurate histogram approximations to the normal-mode distribution, which correctly image band gaps and van Hove singularities, are obtained from Stieltjes inversion of the dispersion function, thereby providing an alternative to the more customary root-sampling techniques. 相似文献
14.
The spatial confinement of a fluctuation spectrum leads to forces at the confining boundaries. While electromagnetic (EM)
fluctuations lead to the well-known dispersion forces, the acoustic analogy has widely been neglected. We show that the strength
of the forces resulting from confined acoustic modes may be of the same order of magnitude as van der Waals forces. Additionally,
the predicted scaling behavior is identical to the non-retarded case of the EM fluctuations. Our results suggest that dewetting
experiments using polymer films are strongly influenced by the acoustic dispersion forces.
Received 5 March 2002 and Received in final form 21 May 2002 相似文献
15.
A. Bielski D. Lisak R.S. Trawiński J. Szudy 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):217-222
Using a laser-induced fluorescence method a detailed analysis of profiles of the 114Cd 326.1 nm line perturbed by N2 and CH4 was performed which revealed deviations from the ordinary Voigt profile. These deviations are shown to be consistent with
fits of experimental profiles to an asymmetric Voigt profile. Coefficients of the pressure broadening, shift and collision-time
asymmetry are determined and compared with those calculated for van der Waals interaction potential.
Received 29 November 2001 / Received in final form 12 July 2002 Published online 4 February 2003 相似文献
16.
N. Petit V. Garnier V. Ta Phuoc R. Caillard A.-M. Frelin A. Ruyter I. Laffez J.-C. Soret A. Maignan F. Gervais 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):423-429
The reflectivity spectra of an oriented ceramic of Bi-2223 has been investigated by polarized infrared reflectivity spectroscopy
in the energy range 0.005-2.2 eV. It is shown that the data for the polarization parallel to the c axis cannot be fitted with a one-component Drude or extended-Drude model. The conductivity spectrum is then obtained from
the best fit of a “double-damping Drude” model to reflectivity spectra, itself derived from the factorized form of the dielectric
function, and by a Kramers-Kronig inversion as well. The data and their analysis give a new insight of the 2D character of
the system.
Received 26 April 2001 and Received in final form 28 August 2001 相似文献
17.
D. Dantchev J. Rudnick 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(2):251-268
We study the behavior of systems in which the interaction contains a long-range component that does not dominate the critical
behavior. Such a component is exemplified by the van der Waals force between molecules in a simple liquid-vapor system. In
the context of the mean spherical model with periodic boundary conditions we are able to identify, for temperatures close
above T
c, finite-size contributions due to the subleading term in the interaction that are dominant in this region decaying algebraically as a function of L. This mechanism goes beyond the standard formulation of the finite-size scaling but is to be expected in real physical systems.
We also discuss other ways in which critical point behavior is modified that are of relevance for analysis of Monte Carlo
simulations of such systems.
Received 21 November 2000 and Received in final form 28 February 2001 相似文献
18.
A.V. Volotka V.M. Shabaev G. Plunien G. Soff 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(1):51-56
The finite nuclear size effect on the hyperfine splitting of low-Z hydrogen-like atoms is studied in the external field approximation. A simple non-relativistic formula is proposed which expresses
the nuclear size correction to the hyperfine splitting in terms of moments of the nuclear charge and magnetization distribution.
The numerical results obtained via this formula are compared with corresponding results derived by means of the Zemach formula. A relativistic formula for the
nuclear size correction to the hyperfine splitting is also derived.
Received 18 March 2002 / Received in final form 14 November 2002 Published online 28 January 2003
RID="a"
ID="a"e-mail: plunien@physik.tu-dresden.de 相似文献
19.
N. Breuer 《Zeitschrift für Physik A Hadrons and Nuclei》1974,271(3):289-293
As proposed by Bredovet al. [2, 3] the phonon spectrum can be obtained approximately from coherent neutron scattering by polycrystals if suitable averages over scattering angles are considered. The accuracy of this method is estimated by comparison with analytical results for simple lattice models (discussed here in particular for Aluminium). The errors are about 5% for low order moments and about 50% near van Hove singularities for “cold” neutrons (wavelength of the order of the nearest-neighbour-distance). 相似文献