共查询到20条相似文献,搜索用时 31 毫秒
1.
《Physics Reports》2005,409(2):47-99
The use of Raman spectroscopy to reveal the remarkable structure and the unusual electronic and phonon properties of single wall carbon nanotubes (SWNTs) is reviewed comprehensively. The various types of Raman scattering processes relevant to carbon nanotubes are reviewed, and the theoretical foundations for these topics are presented. The most common experimental techniques used to probe carbon nanotubes are summarized, followed by a review of the novel experimental findings for each of the features in the first order and second order Raman spectra for single wall carbon nanotubes. These results are presented and discussed in connection with theoretical considerations. Raman spectra for bundles of SWNTs, for SWNTs surrounded by various common wrapping agents, and for isolated SWNTs at the single nanotube level are reviewed. Some of the current research challenges facing the field are briefly summarized. 相似文献
2.
Wang F Liu W Wu Y Sfeir MY Huang L Hone J O'Brien S Brus LE Heinz TF Shen YR 《Physical review letters》2007,98(4):047402
Combinations of up to 6 zone-edge and zone-center optical phonons are observed in the Raman spectra of individual single-walled carbon nanotubes (SWNTs). These multiphonon Raman modes exhibit distinct signatures of the one-dimensional nature of SWNTs and provide information on the phonon structure, exciton-phonon coupling, and excitonic transitions in nanotubes. 相似文献
3.
Song D Wang F Dukovic G Zheng M Semke ED Brus LE Heinz TF 《Physical review letters》2008,100(22):225503
Time-resolved anti-Stokes Raman spectroscopy has been applied to probe the dynamics of optical phonons created in single-walled carbon nanotubes by femtosecond laser excitation. From measurement of the decay of the anti-Stokes Raman signal in semiconducting nanotubes of (6,5) chiral index, a room-temperature lifetime for G-mode phonons of 1.1+/-0.2 ps has been determined. This lifetime, which reflects the anharmonic coupling of the G-mode phonons to lower-frequency phonons, is important in assessing the role of nonequilibrium phonon populations in high-field transport phenomena. 相似文献
4.
Gate-modulated low-temperature Raman spectra reveal that the electric field effect (EFE), pervasive in contemporary electronics, has marked impacts on long-wavelength optical phonons of graphene. The EFE in this two-dimensional honeycomb lattice of carbon atoms creates large density modulations of carriers with linear dispersion (known as Dirac fermions). Our EFE Raman spectra display the interactions of lattice vibrations with these unusual carriers. The changes of phonon frequency and linewidth demonstrate optically the particle-hole symmetry about the charge-neutral Dirac point. The linear dependence of the phonon frequency on the EFE-modulated Fermi energy is explained as the electron-phonon coupling of massless Dirac fermions. 相似文献
5.
S. Piscanec M. Lazzeri F. Mauri A. C. Ferrari 《The European physical journal. Special topics》2007,148(1):159-170
We review the optical phonon dispersions of graphene. In
particular, we focus on the presence of two Kohn anomalies in the
highest optical phonon branch at the
and
points
of the Brillouin zone. We then show how graphene can be used as a
model for the calculation of phonons in carbon nanotubes. Finally,
we present the beyond Born-Oppenheimer corrections to their phonon
dispersions. These are experimentally revealed in the Raman spectra
of doped samples. 相似文献
6.
Properties of phonons-quanta of the crystal lattice vibrations-in graphene have recently attracted significant attention from the physics and engineering communities. Acoustic phonons are the main heat carriers in graphene near room temperature, while optical phonons are used for counting the number of atomic planes in Raman experiments with few-layer graphene. It was shown both theoretically and experimentally that transport properties of phonons, i.e. energy dispersion and scattering rates, are substantially different in a quasi-two-dimensional system such as graphene compared to the basal planes in graphite or three-dimensional bulk crystals. The unique nature of two-dimensional phonon transport translates into unusual heat conduction in graphene and related materials. In this review, we outline different theoretical approaches developed for phonon transport in graphene, discuss contributions of the in-plane and cross-plane phonon modes, and provide comparison with available experimental thermal conductivity data. Particular attention is given to analysis of recent results for the phonon thermal conductivity of single-layer graphene and few-layer graphene, and the effects of the strain, defects, and isotopes on phonon transport in these systems. 相似文献
7.
We have developed a new theoretical formalism for phonon transport in nanostructures using the nonequilibrium phonon Green's function technique and have applied it to thermal conduction in defective carbon nanotubes. The universal quantization of low-temperature thermal conductance in carbon nanotubes can be observed even in the presence of local structural defects such as vacancies and Stone-Wales defects, since the long wavelength acoustic phonons are not scattered by local defects. At room temperature, however, thermal conductance is critically affected by defect scattering since incident phonons are scattered by localized phonons around the defects. We find a remarkable change from quantum to classical features for the thermal transport through defective carbon nanotubes with increasing temperature. 相似文献
8.
ZnSe-ZnS应变超晶格的Raman散射 总被引:1,自引:1,他引:0
本文报导了Znse—ZnS应变超晶格的Raman光学声子谱.我们观测到,随着应变大小的改变,ZnSe和ZnS的纵向光学声子发生频移.ZnSe层中纵向光学声子可发生较大的蓝移,也可发生较小的红移;ZnS层中的纵向光学声子发生较大的红移.这些现象为“应变场下的光学模理论”所解释.文中还报导了在波数为110cm-1处观测到一很强的散射峰,并把它归结为超晶格表面层单斜Se所引起的散射;在其它地方还观测到非晶态Se、三角Se引起的散射峰. 相似文献
9.
We investigated the phonon scattering effects on the transport properties of carbon nanotube devices with micron-order lengths at room temperature, using the time-dependent wave-packet approach based on the Kubo formula within a tight-binding approximation. We studied the scattering effects of both the longitudinal acoustic and the optical phonons on the transport properties. The conductance of semiconducting nanotubes is decreased by the acoustic phonon, instead of the optical phonon. Furthermore, we clarified how the electron mobilities of the devices are affected by the acoustic phonon. 相似文献
10.
Phonon sideband optical spectroscopy determines the energy of the dark K-momentum exciton for (6,5) carbon nanotubes. One-phonon sidebands appear in absorption and emission, split by two zone-boundary (K-point) phonons. Their average energy locates the E11 K-momentum exciton 36 meV above the E11 bright level, higher than available theoretical estimates. A model for exciton-phonon coupling shows the absorbance sideband depends sensitively on the K-momentum exciton effective mass and has minimal contributions from zone-center phonons, which dominate the Raman spectra of carbon nanotubes. 相似文献
11.
Synthesis of nitrogen-doped single-walled carbon nanotubes and monitoring of doping by Raman spectroscopy 下载免费PDF全文
Nitrogen-doped single-walled carbon nanotubes (CNx-SWNTs) with tunable dopant concentrations were synthesized by chemical vapor deposition (CVD), and their structure and elemental composition were characterized by using transmission electron microscopy (TEM) in combination with electron energy loss spectroscopy (EELS). By comparing the Raman spectra of pristine and doped nanotubes, we observed the doping-induced Raman G band phonon stiffening and 2D band phonon softening, both of which reflect doping-induced renormalization of the electron and phonon energies in the nan- otubes and behave as expected in accord with the n-type doping effect. On the basis of first principles calculations of the distribution of delocalized carrier density in both the pristine and doped nanotubes, we show how the n-type doping occurs when nitrogen heteroatoms are substitutionally incorporated into the honeycomb tube-shell carbon lattice. 相似文献
12.
A. B. Talochkin 《Journal of Experimental and Theoretical Physics》2010,111(6):1003-1009
The spectra of Raman scattering by folded acoustic phonons in Si/Ge superlattices with pseudomorphic layers of Ge quantum
dots (QDs) grown by low-temperature (T = 250°C) molecular beam epitaxy are studied. New features of the folded phonon lines related to the resonant enhancement
and unusual intensity ratio of the doublet lines that cannot be explained by the existing theory have been observed. The observed
modes are shown to be related to the vibrations localized to the QDs and induced by the folded phonons of the Si spacer layers.
The calculations performed in the model of a one-dimensional chain of atoms have allowed the nature of the localization of
acoustic phonons attributable to a modification of the phonon spectrum of a thin QD layer to be explained. The observed intensity
ratio of the folded phonon doublet lines is caused by asymmetry of the relief of the QD layers. 相似文献
13.
V. S. Vinogradov G. Karczewski I. V. Kucherenko N. N. Mel’nik P. Fernandez 《Physics of the Solid State》2008,50(1):164-167
Quantum-dot structures based on the CdTe, ZnTe, and CdSe semiconductors are prepared by molecular-beam epitaxy, colloid chemistry methods, and ball milling, and their Raman spectra are studied. Localized longitudinal phonons are observed in all spectra. The dependence of the localized phonon frequency on the thickness of the ZnTe barrier in CdTe/ZnTe quantum-dot superlattices is used to derive the dispersion relation for longitudinal phonons in ZnTe. The Raman spectra of ensembles of colloidal quantum dots differ from the spectra of the other objects by the absence of tellurium bands and a strong intensity of the longitudinal phonon band of CdTe. It is revealed that the spectra depend on the technology employed to prepare quantum-dot structures. 相似文献
14.
We have measured the Raman spectra of intermediate valent (IV) SmB6 and compared it to LaB6 and EuB6. Beside the three high energy Raman active phonons we found additional features in the spectra. Most prominent is a peak at 172 cm-1 for SmB6, at 214 cm-1 for LaB6 and at ~220 cm-1 for EuB6. The spectra are analysed in terms of defect induced phonon excitations yielding a weighted phonon density of states. The softening of the line in IV SmB6 compared to the other hexaborides is unusual since even in the trivalent MB6 compounds the Raman active phonon modes normally are at lower frequencies than in semiconducting, divalent samples. This phonon softening is explained in analogy with the phonon anomalies in other IV compounds like Sm1?xYxS and TmSe. 相似文献
15.
G. Xu S. K. Tripathy X. Mu Y. J. Ding K. Wang Yu. Cao D. Jena J. B. Khurgin 《Laser Physics》2009,19(4):745-751
We review our recent results obtained on an AlN/GaN-based high-electron-mobility transistor. The temperature of the electrons drifting under a relatively-high electric field is significantly higher than the lattice temperature (i.e., the hot electrons are generated). These hot electrons are produced through the Fröhlich interaction between the drifting electrons and long-lived longitudinal-optical phonons. By fitting electric field vs. electron temperature deduced from the measurements of photoluminescence spectra to a theoretical model, we have deduced the longitudinal-optical-phonon emission time for each electron is to be on the order of 100 fs. We have also measured the decay time constant for LO phonons to be about 4.2 ps. An electric field present in a GaN/AlN heterostructure can bring both the first-order and second-order Raman scattering processes into strong resonances. The resonant Stokes and anti-Stokes Raman scattering results in the increase and decrease of non-equilibrium longitudinal-optical phonon temperatures, respectively. Moreover, the phonon temperature measured from the Raman scattering is increased with an applied electric field at a much higher rate than the lattice temperature due to the presence of field-induced non-equilibrium longitudinal-optical phonons. 相似文献
16.
17.
The Raman light scattering from optical phonons of Ge quantum dots grown by molecular beam epitaxy on a Si(111) surface is studied. A series of Raman lines related to the quantization of phonon spectrum is observed. It is shown that phonon frequencies are adequately described in terms of the elastic properties and the dispersion of the optical phonons of bulk Ge. The strain experienced by the Ge quantum dots is estimated. 相似文献
18.
19.
YVO4晶体及其掺Nd的喇曼光谱 总被引:1,自引:0,他引:1
本文报道了对YVO4晶体及其掺Nd的喇曼光谱的测量结果,用这些结果可以了解到这种材料的声子能谱情况,在与其它基质材料比较中可以看出它的特点是:分立的低声子在500-800cm^-1之间有一个间隙,主要部分分布在800-900cm^-1附近,根据群论分析可以得出各喇曼谱线相应的对称性,而且可看出这些喇曼谱线主要来源于VO4^3-的振动,对这种不均匀分布的声子能变对于其光谱性能可能产生的影响也作了分析讨论,测量结果还发现掺杂能抑制原有的高能声子。 相似文献
20.
碳纳米管的拉曼光谱及其温度效应 总被引:3,自引:2,他引:1
在室温下首次观察到碳纳米管的四级拉曼光谱,并且发现碳纳米管的D峰和D*峰的斯托克斯线和反斯托克斯线频率不一致。此外,还发现碳纳米管的拉曼特征峰频率严重依赖样品的温度,随着温度增加,碳纳米管拉曼特征峰频率下移,频移与温度变化成线性关系。 相似文献