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Starting from the extended SSH model that includes an external Coulomb potential arising from interchain charged solitons and counterions, the intrachain e-e interaction and the next neighbor hopping interactions, eight localized vibrational modes around the soliton lattice have been found for the doping levels from 3.33 at.% to 13.33 at.%. Among them three are infrared active and they can be used to interpret the three observed infrared absorption lines at 487, 1284 and 1362 cm–1. Furthermore, the frequencies of localized modes are decreased and their localizations are weakened when the dopant concentrations increase. 相似文献
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Using force constants which have been obtained for the first time from semi-empirical self-consistent-field calculations on various cluster models of periodic trans-polyacetylene and of neutral and charged soliton and polaron defects the infrared and Raman spectrum of undoped and doped trans-polyacetylene is analyzed and interpreted. 相似文献
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Dynamical formation processes of self-localized excitations
induced by charge injection or photoexcitations in a polyacene
chain are investigated by a nonadiabatic dynamic method. The
polyacene chain is treated as two alternatively coupled
polyacetylene chains. The initial lattice configuration is taken
as the pristine polyacene chain. It contains an interchain-coupled
neutral soliton as a consequence of odd-number sites in each of
the two chains. The nonadiabatic dynamical processes are carefully
investigated in the following physical cases: (1) electron
injection; (2) electron transition from the highest occupied
molecular orbital (HOMO) to the lowest unoccupied molecular
orbital (LUMO); (3) electron transition from HOMO to the localized
soliton level, and (4) electron-hole pair excited at the continuum
absorbtion edge for light polarized parallel to the chain. It is
interestingly found that the centers of the electron and the hole
excited by light polarized parallel to the chain are separated.
Therefore, the photogenerated charge carriers should be favorable
in polyacene, which is remarkably different from those found in a
single polyacetylene chain. 相似文献
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TWO-DIMENSIONAL LOCALIZED VIBRATIONAL MODES AROUND A POLARON WITH THE NEXT-NEAREST-NEIGHBOR HOPPING INTERACTIONS 下载免费PDF全文
We have calculated the vibrational modes around a polaron to test the effects of the next-nearest-neighbor hopping interactions on the localized medes within a framework of the two-dimensional mode. The results show that: (1) For a negative polaron, eleven localized modes have been found, compared with ten modes obtained on a previous work without non-nearest neighbor hopping. (2) For a positive polaron, two additional localized modes occur. (3) The localization of localized modes are strengthened and their frequencies move after turning on the next-nearest-neighbor hopping interactions. 相似文献
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Photoexcitation of a neutral soliton will create a polaron and a charged soliton.According to a tight-binding model and a nonadiabatic method,we investigate the dynamical process of these two photogenerated charge carriers in an external electric field.It is found that the polaron and the soliton can pass through each other,which excludes the possibility of carrier recombination that usually occurs in existing organic solar cells.The results indicate a more efficient way to realize the optoelectric conversion by photoexciting polymer materials with soliton defects.On the other hand,it is found that solitons take on greater stability than polarons during collision. 相似文献
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In consideration of the effects of the square term of the electron-lattice interaction and the bond-bending term, the energy spectra and the localized vibrational modes around a bipolaron of the polythiophene are investigated based on the one-dimensional and two-dimensional extension SSH model. The results show that, with the influence of the square term, the energy gap increases, the frequencies of all the localized vibrational modes around a bipolaron decrease and their localizations also shift. It is noted that, an even-parity mode has been found which corresponds to absorption peak at 1220 cm−1. When the bond-bending term is considered, the frequencies of the localized modes increase and five new localized modes appear. Among them, one Raman active mode and three infrared active modes may correspond the observed RRS absorption peaks at 1047 cm−1 and three infrared absorption peaks at 370, 1020, 1120 cm−1 in the experiments. 相似文献
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掺镜钒酸钇晶体是一种很有应用前景的晶体材料,由于它适合于半导体激光器泵浦的全固态激光器的要求而受到人们的普遍关注。拉曼光谱是研究材料的声子能谱分布的方法。本文根据群论对称性分类,计算了掺镜钒酸钇晶体的拉曼和红外活性振动模。选择不同几何配置的拉曼光谱,获得了不同的晶格振动模并计算了不同晶格振动模的散射效率。实验证明最强的振动模来自钒氧四面体的振动。 相似文献
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A. G. Milekhin L. L. Sveshnikova S. M. Repinskii A. K. Gutakovskii M. Friedrich D. R. T. Zahn 《Physics of the Solid State》2002,44(10):1976-1980
The structures with CdS, PbS, and ZnS quantum dots produced using the Langmuir-Blodgett method are investigated by infrared (IR) spectroscopy, Raman scattering, and ultraviolet (UV) spectroscopy. The quantum dot size estimated from the UV spectra and high-resolution transmission electron microscopy (HRTEM) falls in the range 2–6 nm. The longitudinal optical (LO) phonons localized in quantum dots and the surface optical vibration modes are revealed in the IR reflection and Raman scattering spectra of the structures under investigation. The frequencies of the surface optical modes are adequately described with allowance made for the effect of localizing optical phonons in the quantum dots. 相似文献
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The localized vibrational modes of Be in ZnS and ZnSe are observed by using the infrared absorption and Raman scattering. The concentration dependent shift of local mode line is found in ZnS: Be. For these systems, anharmonic potential constants are calculated up to the 4th order. Fundamental local mode of ZnTe: Be is also measured. 相似文献
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《Physics Reports》1987,151(1):1-92
Results of experimental study of hyper-Raman scattering by phonons and polaritons in centrosymmetric and noncentrosymmetric crystals, inorganic oxide glasses and molecular liquids are discussed. Experimental techniques developed for investigation of this weak scattered light are described. We discuss a number of interesting results such as (a) detection of silent modes forbidden in Raman scattering and infrared absorption, (b) determination of the soft mode frequency damping at various temperatures, (c) the study of vibrational polaritons and their resonances with vibrational excitations in centrosymmetrical media, and (d) existence of the vibrational spectra dependence on both value and orientation of momentum transferred to vibrational system in the scattering process in glasses and liquids. 相似文献
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G. Lucazeau 《Solid State Communications》1976,18(7):917-922
The Raman and infrared active long wavelength phonons of a GaS single crystal were studied at different temperatures in the 10–600 cm?1 range. Properly polarized Raman spectra could be obtained with the 4880 Å exciting line and the previous assignment of the E1g modes controversed recently could be confirmed. Infrared spectra were recorded in the 30–600 cm?1 region. The vibrational frequencies of the crystal were also calculated using a method developed by Wieting and six new frequencies corresponding to infrared and Raman inactive modes have been proposed.We have observed that the degree of leakage of scattered intensity in unallowed polarizations increases when the wavelength of the exciting line moves off the exciton absorption front. The phonon at 74 cm?1 was particularly sensitive and the question of the antiresonant behaviour of this compound is raised. 相似文献
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Gadolinium manganese sulfide solid solutions are investigated by infrared and Raman spectroscopy. Longitudinal optical–transverse optical splitting of the manganese–sulfur bond vibration is observed in the vibrational spectra. The Raman spectra contain modes that are prohibited in the crystal structure of the alpha phase of manganese sulfide, which are associated with activation of the phonons from both the Brillouin zone center and its X and L points. The concentration dependence of transverse optical and longitudinal optical modes’ frequencies is calculated within the frame of the modified random-element-isodisplacement model, being in good agreement with the experimental results. Both theory and experiment show that the solid solution under study exhibits a “one-mode” behavior. 相似文献
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The vibrational properties and Raman spectra of graphene nanoribbons with six different edges have been studied by using the first-principles calculations. It is found that edge reconstruction leads to the emergence of localized vibrational modes and new topological defect modes, making the different edges identified by polarized Raman spectra. The radial breathing-like modes are found to be independent of the edge structures, while the G-band-related modes are affected by different edge structures. Our results suggest that the polarized Raman spectrum could be a powerful experimental tool for distinguishing the GNRs with different edge structures due to their different vibrational properties. 相似文献
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Z. V. Popović C. Thomsen M. Cardona R. Liu G. Stanišić W. König 《Zeitschrift für Physik B Condensed Matter》1988,72(1):13-16
We report both Raman and infrared reflectivity spectra of M2Cu2O5 (M=Y, Ho) at room temperature in the spectral range of 30–1000 cm–1.37 (31) ir and 18 (15) Raman active modes of Y2Cu2O5 (Ho2Cu2O5) are observed. A factor group analysis has been performed to identify the symmetries of the observed modes. Comparing the vibrational spectra of these compounds we conclude that the phonons above 300 cm–1 originate from the Cu–O vibrations and those under 300 cm–1 from M–O vibrations.Alexander von Humboldt Foundation fellow 相似文献
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A short‐range force constant model has been applied to investigate the Raman and the infrared wavenumbers in R2BaNiO5 (R = Y, Gd) in their orthorhombic phase of space group Immm. Calculations of zone‐center phonons are made with seven stretching and four bending force constants. The force constants are evaluated by fitting nine Raman and two infrared modes. Two Raman modes are reassigned on the basis of group theoretical calculations. The calculated Raman and infrared modes show good agreement with the observed values. The infrared values are assigned for the first time in these oxides. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献