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1.
We have investigated one phonon resonant Raman scattering in GaN nanowires (NWs) with ring geometry. We consider the Fröhlich electron–phonon interaction in the framework of the dielectric continuum approach. The selection rules are studied. For the GaN NWs with small radius, results reveal that the main contribution to the differential cross-section (DCS) stems from the surface optical (SO) phonons especially from the high-frequency of SO phonons, with a minor contribution from the longitudinal optical (LO) phonons. Meanwhile, dispersions of the two branches of the SO phonon modes are obvious when the wire is thin. Moreover, compared to GaAs NWs, the GaN NWs make more contribution to the DCS in the small quantum size. 相似文献
2.
Santanu Bhattacharya Anindya Datta Sandip Dhara Dipankar Chakravorty 《Journal of Raman spectroscopy : JRS》2011,42(3):429-433
Raman scattering studies were performed in GaN nanoribbons grown along [1 0 0]. These samples were prepared inside Na‐4 mica nanochannels by the ion‐exchange technique and subsequent annealing in NH3 ambient. Detailed morphological and structural studies including the crystalline orientation were performed by analyzing the vibrational properties in these GaN nanoribbons. Pressure in the embedded structure was calculated from the blue shift of the E2(high) phonon mode of GaN. Possible red shift of optical phonon modes due to the quantum confinement is also discussed. In addition to the optical phonons allowed by symmetry, two additional Raman peaks were also observed at ∼633 and 678 cm−1 for these nanoribbons. Calculations for the wavenumbers of the surface optical (SO) phonon modes in GaN in Na‐4 mica yielded values close to those of the new Raman modes. The SO phonon modes were calculated in the slab (applicable to belt‐like nanoribbon) mode, as the wavenumber and intensity of these modes depend on the size and the shape of the nanostructures. The effect of surface‐modulation‐assisted electron–SO phonon scattering is suggested to be responsible for the pronounced appearance of SO phonon modes. A scaling factor is also estimated for the interacting surface potential influencing the observed SO Raman scattering intensities. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
3.
The progress on anti‐Stokes photoluminescence and Stokes and anti‐Stokes Raman scattering in GaN single crystals and GaN/AlN heterostructures is reviewed. Anti‐Stokes photoluminescence investigated in the past was primarily attributed to two‐photon absorption, three‐photon absorption, and phonon‐assisted absorption. On the other hand, anti‐Stokes Raman scattering was used to determine electron‐phonon scattering time and decay time constant for longitudinal‐optical phonons. In a typical high electron mobility transistor based on GaN/AlN heterostructures, strong resonances were reached for first‐order and second‐order Raman scattering processes. Therefore, both Stokes and anti‐Stokes Raman intensities were dramatically enhanced. The feasibility of laser cooling of a nitride structure has been demonstrated. Anti‐Stokes photoluminescence and Raman scattering have potential applications in upconversion lasers and laser cooling of nitride ultrafast electronic and optoelectronic devices. 相似文献
4.
5.
First-order Raman scattering from phonons in the magnetic phases of the europium chalcogenides is analyzed in terms of symmetry for both electric-dipole and electric-quadrupole virtual electronic transitions. The magnetic ordering increases the size of the unit cell and lowers the point group symmetry of the various phases. The magnetic symmetry is used to derive the allowed Raman transitions and polarization selection rules. A phonon dispersion curve for EuSe along the [111] axis is inferred from recent experimental data by applying the selection rules derived on the basis of the magnetic symmetry. 相似文献
6.
We demonstrate for the first time that excitation of silver containing rare gas matrices at 406.74 nm results in resonance Raman spectra which show low energy localized and resonant modes. As they combine with the Ag2 stretching vibration and its overtones, they can unambiguously be attributed to the Ag2 molecule. In Xe-matrices the coupling of lattice phonons and impurity vibrations is documented by side bands which resemble the phonon density of states of the host lattice. Two trapping sites are observed in Kr-matrices. 相似文献
7.
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
8.
Xiaming Zhu Huizhen Wu Zijian Yuan Jinfang Kong Wenzhong Shen 《Journal of Raman spectroscopy : JRS》2009,40(12):2155-2161
Multiphonon resonant Raman scattering in N‐doped ZnO films was studied, and an enhancement of the resonant Raman scattering process as well as longitudinal optical (LO) phonon overtones up to the sixth order were observed at room temperature. The resonant Raman scattering intensity of the 1LO phonon in N‐doped ZnO appears three times as strong as that of undoped ZnO, which mainly arises from the defect‐induced Raman scattering caused by N‐doping. The nature of the 1LO phonon at 578 cm−1 is interpreted as a quasimode with mixed A1 and E1 symmetry because of the defects formed in the ZnO lattice. In addition, the previously neglected impurity‐induced two‐LO‐phonon scattering process was clearly observed in N‐doped ZnO. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
9.
A. G. Milekhin A. I. Toropov A. K. Bakarov S. Schulze D. R. T. Zahn 《JETP Letters》2006,83(11):505-508
Raman scattering by optical phonons in InxGa1 ? x As/AlAs nanostructures with quantum dots has been studied experimentally for compositions corresponding to x = 0.3?1 under out-resonance conditions. Features due to scattering by GaAs-and InAs-like optical phonons in quantum dots have been detected, and the phonon frequencies have been determined as a function of the dot composition. With increasing excitation energy, a red shift is observed in the frequency of the GaAs-like phonon in quantum dots, which testifies to Raman scattering selective by the size of quantum dots. Under resonant conditions, multiphonon light scattering by optical and interface phonons is observed up to the third order, including overtones of the first-order phonons of InGaAs and AlAs materials and their combinations. 相似文献
10.
Hui Wang Xuewei Cao Min Feng Qinghua Jin Datong Ding Guoxiang Lan 《Journal of Physics and Chemistry of Solids》2009,70(1):8-14
The phonon dispersions of single-wall BC3 nanotubes with any chirality are calculated within a symmetry-based force constant model of the lattice dynamics. Based on the non-symmorphic symmetry group of the BC3 tubes, the symmetries and number of the Raman- and infrared-active modes at Γ point of the one-dimensional Brillouin zone are given. The neighbor atom-atomic interaction force constants are recalculated by fitting them to the experimental phonon energy-dispersion curves of honeycomb BC3 sheet. The frequencies of the optically active modes are presented as the function of diameters and chiralities for BC3 tubes. The obtained phonon density-of-states spectra, phonon dispersion relations, and vibrational patterns of the zone-center phonons are presented and discussed in detail. The calculated frequencies of infrared-active modes are compared with the experimental values reported in the literature. The results provide comprehensive information about the vibrational properties of the BC3 tubes and shed light on the interpretation of Raman scattering and infrared spectroscopies. 相似文献
11.
在经典的物理学理论中,声子广泛地被认为是线极化的、不具有角动量的.最近的理论研究发现,在具有自旋声子相互作用的磁性体系(时间反演对称性破缺)中,声子可以携带非零的角动量,在零温时声子除了具有零点能以外还带有零点角动量;非零的声子角动量将会修正通过爱因斯坦-德哈斯效应测量的回磁比.在非磁性材料中,总的声子角动量为零,但是在空间反演对称性破缺的六角晶格体系中,其倒格子空间的高对称点上声子具有角动量,并具有确定的手性;三重旋转对称操作给予声子量子化的赝角动量,赝角动量的守恒将决定电子谷间散射的选择定则;此外还理论预测了谷声子霍尔效应. 相似文献
12.
M.J. Seong S. Francoeur S. Yoon A. Mascarenhas S. Tixier M. Adamcyk T. Tiedje 《Superlattices and Microstructures》2005,37(6):394-400
We have studied GaAs1−xBix (up to x3%) using Raman scattering with two different polarization configurations. Two Bi-induced phonon modes are observed at 186 cm−1 and 214 cm−1 with increasing Raman intensity as the Bi concentration increases. By comparing Raman selection rules for the observed Bi-induced phonon modes with those for the substitutional N vibrational mode (GaN mode) in GaAsN, the phonon mode at 214 cm−1 is identified as originating from substitutional Bi at the As site in GaAsBi. 相似文献
13.
The symmetry properties of the normal modes of the chalcopyrite lattice are analyzed. The phonon spectra of chalcopyrite and sphalerite are compared. There is a discussion of the intensity of the IR absorption lines due to single-phonon processes. Selection rules are found for direct and indirect transitions. Carrier scattering by phonons is analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 10, pp. 42–48, October, 1970. 相似文献
14.
A combination of studies on photoluminescence and resonant Raman scattering in N-doped ZnO thin films were carried out at room temperature. In the photoluminescence spectra, a transformation of radiative recombination mechanism from free-exciton to donor-acceptor-pair transition was observed. An enhancement of resonant Raman scattering processes as well as longitudinal optical (LO) phonon overtones up to the sixth order were observed in the Raman spectra. Also, the nature of the 1LO phonon underwent a transformation from a pure A1(LO) mode to a quasimode with mixed A1 and E1 symmetry. The underlying mechanisms accounting for the influences of N doping on the optical properties of ZnO were related to the incorporation of extrinsic defects in the crystal lattice. 相似文献
15.
Within an extended Su-Schrieffer-Heeger model, we made a lattice
vibrational analysis of polyacene. In a singly-charged polyacene,
the ground state contains an interchain-coupled polaron of
quasi-D2h symmetry, around which we found thirteen localized
modes in total. Among these localized modes, five (three B2u
and two B3u) are infrared active, six (four Ag and two
B1g) modes are Raman active, and the other two localized
modes are asymmetric, which are both infrared active and Raman
active. For the case a charged polaron is coupled with a neutral
soliton in a finite polyacene chain, the vibrational modes are
also calculated to display the coupling effect between
self-trapping excitations on phonons. It is found that the
localized phonons are determined mainly by the charged polaron,
but the number and frequencies of the localized modes are
influenced by the existence of the neutral soliton. 相似文献
16.
V. N. Kamenshchikov V. A. Stefanovich Z. P. Gad’mashi V. I. Sideĭ L. M. Suslikov 《Physics of the Solid State》2007,49(2):351-355
Raman scattering of light in a PbGa2S4 crystal is studied. The phonon spectrum of this crystal is calculated using factor group analysis for the first time. The number of active modes in the Raman spectrum, their symmetry, and the selection rules are determined. The modes observed in the Raman spectra are identified with the vibrations of the atoms comprising the crystal lattice of the PbGa2S4 compound. 相似文献
17.
Indirect electronic transitions in alkali halate crystals-I (sodium and potassium chlorate crystals)
S.B.S. Sastry R.B. Tripathi C. Ramasastry 《Journal of Physics and Chemistry of Solids》1973,34(3):473-479
The long wavelength tail of the fundamental absorption in NaClO3 and KClO3 crystals has been analysed based on the theory of band to band transitions of Bardeen et al.[8] developed in the case of semi-conducting crystals. Evidence of phonon involvement in the transitions giving an indirect band gap is observed. The energies of the phonons involved in the process are the same for both the crystals, and agree well with combinations of prinicple frequencies of ClO3? ion, their overtones and also lattice phonons. The indirect band gap in these crystals varies with temperature more or less linearly and the rate of variation is ?3·8 × 10?4 eV/K and ?5·0 × 10?4 eV/K for sodium chlorate and potassium chlorate respectively. 相似文献
18.
N. Esser 《Applied Physics A: Materials Science & Processing》1999,69(5):507-518
Only recently Raman spectroscopy (RS) has advanced into the study of surface phonons from clean and adsorbate-covered semiconductor
surfaces. RS allows the determination of eigenfrequencies as well as symmetry selection rules of surface phonons, by k-conservation limited to the Brillouin zone-center, and offers a significantly higher spectral resolution than standard surface
science techniques such as high-resolution electron energy loss spectroscopy. Moreover, surface electronic states become accessible
via electron–phonon coupling. In this article the fundamentals of Raman scattering from surface phonons are discussed and
its potential illustrated by considering two examples, namely Sb-monolayer-terminated and clean InP(110) surfaces. Both are
very well understood with respect to their atomic and electronic structure and thus may be regarded as model systems for heteroterminated
and clean semiconductor surfaces. In both cases, localized surface phonons as well as surface resonances are detected by Raman
spectroscopy. The experimental results are compared with surface modes predicted by theoretical calculations. On InP(110),
due to the high spectral resolution of Raman spectroscopy, several surface modes predicted by theory can be experimentally
verified. Surface electronic transitions are detected by changing the energy of the exciting laser light indicating resonances
in the RS cross section.
Received: 7 April 1999 / Accepted: 25 June 1999 / Published online: 16 September 1999 相似文献
19.
S. Issing F. Fuchs C. Ziereis E. Batke A. Pimenov Y. Vu. Ivanov A. A. Mukhin J. Geurts 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,73(3):353-360
A systematic and detailed study of Raman and infrared active lattice excitations in the orthorhombic multiferroic manganite
Eu1−xYxMnO3 (0 ≤ x ≤ 0.5) was carried out at room temperature. For the infrared active phonon modes the eigenfrequencies, damping constants
and oscillator strengths were analyzed by Fourier-Transform Infrared Spectroscopy in the far infrared frequency range. For
the Raman active phonons the same analysis for eigenfrequencies and damping constants was carried out using Raman spectroscopy
in the range from 200 cm−1 to 700 cm−1. Y doping leads to mode-dependent phonon frequency shifts up to 8%. These are interpreted in terms of the interplay between
the decrease of the reduced ion masses and the axis-dependent change of bond lengths. The latter leads to a bond softening
along the a-axis and a strengthening along the c-axis, for which the highest phonon frequency increase is observed. The application
of both Raman and Infrared Spectroscopy gives us sensitivity not only to symmetry properties via the selection rules but also
to the involvement of different ion types within the unit cell. It is clearly shown that the disorder induced effects are
of minor impact on the lattice properties and solely detected on the rare earth sites. The MnO6 octahedra remain unaffected and show the same behavior as in the stochiometric RMnO3 making Eu1−xYxMnO3 an excellent model system for a quasi-continuous fine-tuning of the lattice parameters relevant for the appearance of multiferroicity. 相似文献
20.
A symmetry analysis of the crystal structure and the phonon spectrum during continuous topochemical conversion of silicon into silicon carbide has been carried out. The transformation of the symmetry of phonons at high-symmetry points of the Brillouin zone upon the transition from the initial cubic structure of silicon (diamond) through an intermediate cubic structure of silicon carbide to the trigonal structure of SiC has been determined. The selection rules for the infrared and Raman spectra of all the three phases under investigation have been established. 相似文献