共查询到20条相似文献，搜索用时 15 毫秒
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Hui Wang Jinghan You Lin Wang Min Feng Yufang Wang 《Journal of Raman spectroscopy : JRS》2010,41(2):125-129
A double‐resonance process gives rise to the 2D band in the Raman spectra of monolayer and bilayer graphene. Based on the electronic and vibrational dispersion energies of graphene, the wavenumbers of the 2D band were calculated under different laser excitation energies (from 1.0 to 4.4 eV). Calculated results are in good agreement with experimental data and reproduce the experimental dispersion slope of the 2D band very well. The calculated wavenumbers of the 2D band do not show a linear dependence on the laser excitation energies. Moreover, it is explained that the lowest wavenumber peak of the 2D band of the bilayer graphene, which is composed of four components, has the largest slope with laser excitation energy. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Ying Ying Wang Jie Jiang Chuan Wei Gao Hai Yan Nan Zhen Hua Ni Dong Wang Bo Zhong Guang Wu Wen 《Journal of Raman spectroscopy : JRS》2016,47(6):668-673
We present a systematic Raman study of twisted tetralayer graphene (t(2 + 2)LG), under excitation of two laser lines. In t(2 + 2)LG samples, top Bernal stacked bilayer graphene (2LG stands for Bernal‐stacked bilayer graphene) twists different angle relative to bottom 2LG. It is found that 2D and 2D′ peaks of t(2 + 2)LG show positive wavenumber shift relative to those of 2LG. We propose a simplified electronic band structure for t(2 + 2)LG; interlayer interaction‐induced changing in electronic band structure can be used to understand the aforementioned spectral features. The electronic structures of t(2 + 2)LG samples are then probed from resonant Raman studies of 2D and 2D′ peaks using two laser lines; electronic dispersions in t(2 + 2)LG samples are given. Our study facilitates understanding of twist angle‐dependent electronic properties of tetralayer graphene superlattice. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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We review the key aspects of Raman spectroscopy of graphite and graphene, focusing on the double resonant Raman modes such as the D, D* (also known as G' or 2D), and D' bands. We discuss the practical significance of Raman spectroscopy for the study of single‐ and multi‐layer graphene. 相似文献
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利用拉曼散射技术对N型4H-SiC单晶材料进行了30～300 K温度范围的光谱测量。实验结果表明,随着温度的升高,N型4H-SiC单晶材料的拉曼峰峰位向低波数方向移动,峰宽逐渐增宽。分析认为,晶格振动随着温度的升高而随之加剧,其振动恢复力会逐渐减小,使振动频率降低;原子相对运动会随温度的升高而加剧,使得原子之间及晶胞之间的相互作用减弱,致使声学模和光学模皆出现红移现象。随着温度的升高,峰宽逐渐增宽。这是由于随着温度的升高声子数逐渐增加,增加的声子进一步增加了散射概率,从而降低了声子的平均寿命,而声子的平均寿命与峰宽成反比,因此随着温度的升高峰宽逐渐增宽。声子模强度随温度升高呈现不同规律,E2(LA),E2(TA),E1(TA)和A1(LA)声子模随着温度升高强度单调增加,而E2(TO),E1(TO)和A1(LO)声子模强度出现了先增后减的明显变化,在138 K强度出现极大值。分析认为造成原因是由于当温度高于138 K时,高能量的声子分裂成多个具有更低能量的声子所致。 相似文献
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A first-principles plane wave self-consistent method with the Ultrasoftpseudopotential scheme in the framework of density functional theory is performed to study the high pressure structural, electronic and vibrational properties of InX (X = N, P) for the zinc-blende (ZnS/B3), rock-salt (NaCl/B1) and cesium-chloride (CsCl/B2) phases. We also calculate the phase transition pressures among these different phases. Conclusions based on electronic energy band structure, phonon dispersion and phonon density of states at high pressure phases along phase transition regions are outlined. 相似文献
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应用线性响应的线性糕模轨道方法计算AlB2型结构的新超导体CaAlSi的电子能带、声子谱及电子-声子耦合常数，并讨论了它们的超导电性．通过比较两种结构模型的计算结果可以看出：若CaAISi中Al，si原子沿c轴方向以-Al-Al-A1-,（或-Si-Si-Si-）排列，低频B1g模式的声子频率沿A-L方向出现虚频，使得这种结构处于不稳定状态，电子-声子耦合表现异常增大；若Al，si原子沿c轴方向以-Al-si-A1-排列，声子振动模式的增加消除了低频声子的异常软化,由此计算得到的声子对数平均频率增大为147K，电子-声子耦合常数A=0．80,用中等耦合强度的Bardeen-Cooper-Schrieffer理论可合理解释其超导电性。 相似文献
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应用全势线性缀加平面波方法计算新超导体CaAlSi的电子能带结构,用带心冻结声子法计算了声子频率及电声子耦合常数,并讨论了它们的超导电性.考虑到Al,Si原子分布的无序性和完全等价性,我们采用了双层超格子原胞模型,并考虑了低频B1g1声子频率的非谐性效应.由此计算得到稳定的低频B1g1声子频率为110cm-1,对超导电性有较大的贡献的Cad态电子与B1g1振动模式间的电声子耦合常数为0.37.我们的结果与用虚晶近似的结果是一致的.并证明CaAlSi的超导电性可由中等耦合的BCS理论来解释. 相似文献
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We have presented a theoretical calculation of the differential cross section (DCS) for the electron Raman scattering (ERS) process associated with surface optical (SO) phonon modes in a semiconductor quantized spherical film. We consider the Fröhlich electron–phonon interaction in the framework of the dielectric continuum approach. We study the selection rules for the processes. Singularities are found to be size-dependent and by varying the size of the QDs, it is possible to control the frequency shift in the Raman spectrum. A discussion of the phonon behavior for the films with large and small size is presented. The numerical results are also compared with that of experiments. 相似文献
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A systematic study on lattice dynamics of Mn + 1AlCn (n = 1–3) phases using first‐principle calculations is reported, where the Raman‐active and infrared‐active (IR) modes are emphasized. The highest phonon wavenumber is related to the vibration of C atoms. The ‘imaginary wavenumber’ in the phonon spectrum of Nb3AlC2 contributes to the composition gap in Nb‐Al‐C system (Nb2AlC and Nb4AlC3 do appear in experiments, but there are no experimental reports on Nb3AlC2). The full set of Raman‐active and IR‐active modes in the 211, 312, and 413 Mn + 1AXn phases is identified, with the corresponding Raman and IR wavenumbers. The 211, 312, and 413 Mn + 1AXn phases have 4, 6, and 8 IR‐active modes, respectively. There is no distinct difference among the wavenumber ranges of IR‐active modes for 211, 312, and 413 phases, with the highest wavenumber of 780 cm−1 in Ta4AlC3. The Raman wavenumbers of M2AlC phases all decrease with increasing the d‐electron shell number of transition metal M. However, this case is valid only for the Raman‐active modes with low wavenumbers of M3AlC2 and M4AlC3. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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In the present work, vibrational and thermodynamic properties of XBi(X = B, Al, Ga, In) compounds are compared and investigated. The calculation is carried out using density functional theory(DFT) within the generalized gradient approximation(GGA) in a plane wave basis, with ultrasoft pseudopotentials. The lattice dynamical properties are calculated using density functional perturbation theory(DFPT) as implemented in Quantum ESPRESSO(QE) code. Thermodynamic properties involving phonon density of states(DOS) and specific heat at constant volume are investigated using quasiharmonic approximation(QHA) package within QE. The phonon dispersion diagrams for InBi, GaBi, BBi, and AlBi indicate that there is no imaginary phonon frequency in the entire Brillouin zone, which proves the dynamical stability of these materials. BBi has the highest thermal conductivity and InBi has the lowest thermal conductivity. AlBi has the largest and GaBi has the smallest reststrahlen band which somehow suggests the polar property of XBi materials. The phonon gaps for InBi, GaBi, BBi and AlBi are about 160 cm~(-1), 150 cm~(-1), 300 cm~(-1), and 150 cm~(-1), respectively. For all compounds,the three acoustic modes near the gamma point have a linear behavior. C_V is a function of T~3 at low temperatures while for higher temperatures it asymptotically tends to a constant as expected. 相似文献
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Surface optical phonon—assisted electron Raman scattering in a semiconductor quantum disc 总被引：2，自引：0，他引：2 
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下载免费PDF全文 We have carried out a theoretical calculation of the differential cross section for the electron Raman scattering process associated with the surface optical phonon modes in a semiconductor quantum disc.electron states are considered to be confined within a quantum disc with infinite potential barriers.The optical phonon modes we have adopted are the slab phonon modes by taking into consideration the Frohlich interaction between an electron and a phonon.The selection rules for the Raman process are given.Numerical results and a discussion are also presented for various radii and thicknesses of the disc,and different incident radiation energies. 相似文献
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Rohit Narula Nicola Bonini Nicola Marzari Stephanie Reich 《physica status solidi b》2011,248(11):2635-2638
We investigate the dominant phonon wavevectors q * and the associated dominant phonon‐assisted electronic transitions implied by the 2D Raman mode of graphene by combining ab initio calculations with a full two‐dimensional integration over the graphene Brillouin zone. We find that q * are highly anisotropic and rotate with the polarizer:analyzer condition, providing access to the entire angular extent around K . The resonant electronic transitions do not lie along the line and can be transformed from being apparently “inner” to “outer” with the addition of a reciprocal lattice vector, showing that both are equivalent. We thus invalidate the notion of “inner” and “outer” processes completely. 相似文献
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Swayam Kesari Rekha Rao Mayanak K. Gupta R. Mittal Geetha Balakrishnan 《Journal of Raman spectroscopy : JRS》2019,50(4):587-594
Knowledge of symmetries of vibrational modes is essential for understanding the mechanism of structural transitions and spin-phonon coupling in multiferroics where phonons play a vital role. Using polarized Raman spectroscopy, we have identified and assigned symmetries of 30 out of the 36 expected Raman active modes in Ni3V2O8. The zone-centred phonon mode wavenumbers are calculated using ab initio calculations. The gerade mode wavenumbers are compared with our polarized Raman data whereas ungerade mode wavenumbers are compared with the reported infrared measurements and a good agreement was observed between the experimentally measured wavenumbers and the calculated wavenumbers. The displacements of different types of vibrations calculated and visualized using ab initio phonon calculation are presented. These assignments will be useful for visualization of Raman modes that may be sensitive to different magnetic states and to explore spin–lattice coupling across magnetic transitions. 相似文献
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The structural phase transition and electronic properties at ambient (B 1-phase) and high pressure (B 2-phase) of heavy rare earth monoantimonides (RESb; RE?=?Ho, Er, and Tm) have been studied theoretically using the self-consistent tight binding linear muffin tin orbital method. These compounds show metallic behavior under ambient condition and undergo a structural phase transition to the B 2 phase at high pressure. We predict a structural phase transition from the B 1 to B 2 phase in the pressure range 30.0–35.0?GPa. Apart from this, the ground state properties, such as lattice parameter and bulk modulus are calculated and compared with the available theoretical and experimental results. 相似文献
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We have extensively studied the phonon, magnon and magnetic properties of copper (Cu)-doped nanocrystalline nickel(II) oxide (NiO) using room-temperature Raman spectroscopy. The required nanomaterials were synthesized using a simple sol–gel method. The phonon modes of NiO nanoparticles have been observed in a large background of magnon excitations, and the wavenumbers of phonon modes were deviated from the theoretical predictions due to the phonon–magnon interaction. The variations of magnon excitations with the Cu doping concentrations were investigated based on reduced spin correlation length and superexchange interaction. The two-magnon (2M) excitations were suppressed and blue shifted with Cu doping concentration indicating the variations in the magnetic behaviour. The modification of antiferromagnetic nature and the formation of multiphase magnetic properties of NiO nanoparticles were investigated using a vibrating sample magnetometer (VSM) and discussed in detail. The variations in the phonon and magnon excitations can be used to probe the magnetic nature and spintronic applications of NiO nanoparticles. 相似文献
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Poonam Singh 《光谱学快报》2013,46(6):444-446
ABSTRACTPerovskite structured mixed metal fluorides containing manganese/sodium or potassium have been synthesized in pure form by a greener precipitation route and characterized by high-resolution powder X-ray diffraction and Raman spectroscopy techniques. While all the reflections in the powder X-ray diffraction pattern of potassium manganese fluoride could be indexed in cubic symmetry with a = 4.1889 Å, sodium manganese fluoride showed reflections at positions typical of orthorhombic symmetry (Pnma space group) with a = 5.751, b = 8.008, and c = 5.548 Å. Potassium manganese fluoride in powder form showed bands at 209, 291, 386, 558, 621, and 733 cm?1 in the Raman spectrum at room temperature. All these bands disappeared and second-order band at 1151 and 1298 cm?1 emerged when the powders were compacted under pressure ranging between 1 and 4 tons (uniaxial). A similar change was noticed for sodium manganese fluoride in which bands at 1099, 1149, 1203, and 1286 cm?1 were observed for the compacted samples. The response of the vibrational modes of these compounds to uniaxial pressure revealed the existence of large structural disorder in them. Additionally, the need for the extreme care to collect and interpret Raman data of polycrystalline samples of these systems has been illustrated through this study. 相似文献