聚噻吩中双电子极化子附近的二维局域振动模

将聚噻吩的一维SSH孤子模型推广到二维平面,研究了聚噻吩双电子极化子附近的二维局域振动模.计算结果表明双电子极化子附近存在15个局域振动模,其中4个奇宇称模与4条强红外吸收谱线1020,1120,1200,1323cm^-1相对应,4个偶宇称模恰与4条Raman吸收峰700,1047,1175,1220cm^-1一致. 关键词：     

The vibrational modes around the soliton lattice with next neighbor hopping interactions in highly doped trans-(CH) x

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.     

The infrared and Raman spectrum of trans-polyacetylene: A self-consistent-field study

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.     

Dynamics of self-localized excitations in a polyacene chain

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.     

TWO-DIMENSIONAL LOCALIZED VIBRATIONAL MODES AROUND A POLARON WITH THE NEXT-NEAREST-NEIGHBOR HOPPING INTERACTIONS

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.     

A new perspective on optoelectric conversion in conjugated polymers

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.     

Nonlinear electron-lattice interaction on excited states in polythiophene

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.     

扰动对一维局域模的影响

在紧束缚模型基础上，考虑到缺陷、温度、掺杂等外界因素的影响，用方形随机分布模拟了格点原子扰动对一维局域模的影响.给出了不同扰动参数σ下，孤子和极化子中各个局域模的变化情况.计算发现，由于孤子g₁模的钉扎效应，扰动后，弱模g₄定域性会得到加强，还会产生两个新定域模g′₁和g′₂，它们与相应的g₁和g₂模有相同的节点和宇称 ；极化子的g₇模在畸变较大时将 关键词： 扰动 局域模 聚合物     

掺镱钒酸钇晶体的晶格振动光谱

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。     

气相外延GaN的拉曼散射

测量了在蓝宝石衬底上气相外延生长GaN的拉曼散射谱.除观察到已被确认的两个E2,一个A1(TO)和一个E1(TO)声于振动以外,在734±3cm-1处观察到一个散射峰且从实验上确认其为GaN的纵向光学声子模E1(LO).而且发现其强度与外延层晶体质量密切相关.A1(TO)和高频E2散射峰相对强度变化显示不同生长条件引起的外延层质量的变化.     

Optical vibration modes in (Cd,Pb, Zn)S quantum dots in the Langmuir-Blodgett matrix

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.     

非对称量子点中极化子的声子平均数

采用线性组合算符和幺正变换方法研究非对称量子点中强、弱耦合极化子的声子平均数的性质,导出了量子点中强、弱耦合极化子的声子平均数和振动频率随量子点的横向和纵向受限强度、电子-声子耦合强度的变化关系。对RbCl晶体进行数值计算,结果表明非对称量子点中强耦合极化子的振动频率和声子平均数随量子点的横向和纵向的受限强度的增强而迅速增大,随电子-声子耦合强度的增强而增大。     

Infrared absorption and Raman scattering due to localized vibrational mode of Be in zinc-chalcogenides

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.     

Vibrational spectra of a GaS single crystal

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 E_1g 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.     

Raman and infrared characterization of gadolinium-doped manganese sulfide

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.     

Infrared and Raman spectra of M2Cu2O5 (M=Y,Ho)

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     

Vibrational properties and Raman spectra of different edge graphene nanoribbons,studied by first-principles calculations

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.     

Binding energy of a polaron in asymmetric polar semiconductor heterostructures

By using a modified Lee-Low-Pines variational method, we have investigated the ground-state binding energy of a polaron confined in asymmetric single and step quantum wells (QWs) due to interface phonons, confined bulk-like LO phonons, and half-space LO phonons. The relative importance of the different phonon modes is analysed in detail. Our results show that the asymmetry and the well width of the QWs have a significant influence on the polaron energy. The polaron binding energy has an intimate relation to the potential parameters of QWs. The subband nonparabolicity has a little influence to the polaron binding energy. Comparing with the results calculated with perturbation theory, a good agreement is found.     

Lattice dynamic investigation of the Raman and infrared wavenumbers of orthorhombic R2BaNiO5 (R = Y,Gd) oxides in Immm structure

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.     

一维极化子的定域振动模

本文研究了一维电子-晶格耦合系统中极化子的晶格振动,发现了两个新的定域振动模g₆和g′₆,它们分别在一定的耦合参量λ的范围内存在。本文还给出了各个定域振动模的频率和位形随λ的变化情况。 关键词：