Nd:LuVO_4晶体的拉曼光谱研究

采用不同的几何配置测量了Nd:LuVO4晶体的室温拉曼光谱,根据群论对称性分类计算了该晶体的红外和拉曼活性振动模并与实验结果做了比较,指认了测定的特征谱线。测量并分析了Nd:LuVO4晶体A1g全对称类的高温拉曼光谱,讨论了拉曼频移随温度变化的关系,认为晶体的热膨胀是引起拉曼频移变化的主要原因。     

Shell model lattice dynamics of transition metal oxides

The lattice dynamics of transition metal oxides has been investigated in detail with threebody force shell model which is a successful extension of the shell model and includes the effect of electron shell displacements as well as deformations. The phonon dispersion relations along three principal symmetry directions obtained from this model have been compared with neutron data and found to give better agreement as compared to other models. The complete phonon spectra have also been computed and used to derive the temperature dependence of Debye temperature, and the second-order Raman and infrared spectra. The derived data agree fairly well with the observed ones wherever available.     

光学声子色散关系对多孔硅喇曼谱的影响

测量了多孔硅的喇曼光谱,观察到谱峰有明显的红移和非对称性展宽效应。用微晶模型对此现象进行了解释:认为谱峰的这种变化不完全是由尺寸的空间限制效应和多孔硅的应变造成的,更主要的是多孔硅的色散关系发生了变化。采用不同的色散关系对谱峰进行了拟合,发现色散关系对喇曼谱的拟合有较大的影响。     

Temperature dependent phonon confinement in silicon nanostructures

Temperature dependent variation in Raman line-shape from silicon (Si) nanostructures (NSs) is studied here. Asymmetry and red-shift in room temperature Raman spectrum is attributed to phonon confinement effect. Raman spectra recorded at higher temperatures show increase in FWHM and decrease in asymmetry ratio with respect to its room temperature counterpart. Theoretical Raman line-shape analyses of temperature dependence of phonon confinement is done by incorporating the temperature dependence of phonon dispersion relation. Experimental and theoretical temperature dependent Raman spectra are in good agreement.     

用拉曼散射光谱估算纳米Ge晶粒平均尺寸

用射频共溅射技术和真空退火方法制备了埋入ＳｉＯ２基底中的纳米Ｇｅ复合膜（ｎｃ－Ｇｅ／ＳｉＯ２）测量了不同温度退火后该复合膜的拉曼散射光谱，其结果与晶体Ｇｅ的拉曼谱相比，纳米Ｇｅ的拉曼峰红移峰形变宽，用拉曼谱的参数计算了纳米Ｇｅ晶粒的平均尺寸，所得结果与声子限域理论模型符合。     

Temperature‐dependent Raman scattering study of multiferroic MnWO4

We have measured polarized Raman spectra of MnWO₄ single crystals at low temperatures, and studied the temperature dependence of the various phonon modes. From our Raman studies of the MnWO₄, a new transition temperature, ∼180 K, was found. We have completely assigned the symmetries of the 18 observed Raman modes of the MnWO₄, as expected from a group theoretical analysis. These Raman modes have been classified into three groups according to weak, intermediate and strong temperature dependence of the modes in each group. Six internal modes have been identified by their weak temperature dependence of the Raman wavenumbers. The temperature dependence of the wavenumbers of the B_g modes in Mg O bonds, modes of intermediate temperature dependence group, shows an anomalous behavior under 50 K. The phonon modes of strong temperature dependence show an anomalous change at ∼180 K in the linewidths. This is believed to be a new transition temperature which involves the changes in the inter‐WO₆ octahedra structure. Copyright © 2009 John Wiley & Sons, Ltd.     

纳米结构和薄膜材料的拉曼 布里渊研究(英文)

在过去三十年中,对多种纳米结构和薄膜材料进行了拉曼 布里渊散射的研究.得到一些特征量的变化,如半高宽,峰位的改变;由此可得系列微结构参量.由于纳米(含薄膜)结构的基本特征:小,大,多,断和(相)移;即小的尺度,大的体表比,多的界面,断裂的波矢和相位的偏移的特证,在非弹性光散射谱中得到明显的展示:多种无序结构特征;三叉晶界特征;波矢断裂引发的折迭,由此形成的频隙;光学声子的带隙;相位偏移或失配在谱中的表现为过阻尼特征等.此外,本文还给出了该领域中非弹性光散射的某些概念.     

n-SiC拉曼散射光谱的温度特性

测量了采用离子注入法得到掺N的n-SiC晶体从100—450 K的拉曼光谱. 研究了SiC一级拉曼谱、电子拉曼散射谱及二级拉曼谱的温度效应. 实验结果表明,大部分SiC一级拉曼峰会随温度升高向低波数方向移动,但声学模红移(峰值位置向低频方向移动)的幅度较光学模小. 重掺杂4H-SiC的纵光学声子等离子体激元耦合(LOPC)模频率随温度升高表现出先蓝移(峰值位置向高频方向移动)后红移的变化趋势,表明LOPC模的温度特性不仅会受到非简谐效应的影响,还与实际已离化杂质浓度有关. 电子拉曼散射峰线宽随温度升高而增 关键词： 碳化硅 温度 纵光学声子等离子体激元耦合模 电子拉曼散射     

一种基于荧光材料的聚合物白光发光二极管

制备了一种基于荧光聚合物共混的单发光层聚合物白光发光二极管.器件结构为铟锡氧化物/苯磺酸掺杂聚乙烯基二氧噻吩/发光层/ 1,3,5-三(N-苯基-2-苯并咪唑-2)苯41/Ba/Al,蓝光材料芴-氟化喹喔啉共聚物(PF-BPFQ5)、绿光材料苯基取代的聚对苯乙炔(P-PPV)和红光材料聚(2-甲氧基-5-(2′-乙基己氧基)-1,4-对苯乙炔)(MEH-PPV)共混为发光层.当PF-BPFQ5,P-PPV,MEH-PPV的质量比例为100∶06∶06时,获得标准的白光,色坐标为（033 关键词： 聚合物发光二极管 白光 共混     

Raman scattering from CuBr and CuI

Detailed temperature-dependent Raman spectra of CuI and CuBr are reported for the first time. Spectra have been recorded between room temperature and 6K. Peaks arising from scattering by the zone-center optic phonon modes have been identified and their frequencies compared with those determined by neutron scattering and infrared measurements. The LO phonon energy in CuBr is found to reflect the negative thermal expansion at low temperatures while the TO phonon frequency does not follow this behavior. Second-order features of the CuI spectrum are identified using available phonon dispersion curves.     

用硅离子注入方法制备的纳米硅的拉曼散射研究

在直角散射配置下测量了纳米硅样品的拉曼散射谱及其退火温度的关系。结果表明,在８００℃以下退火的样品只观察到单晶硅衬底的光学声子模,在９００℃以上退火,才观察到纳米硅的特征拉曼散射峰。在１２００℃下退火后,纳米硅的特征拉曼散射峰消失,观察到类似于非晶硅的光学声子特征峰,可能表示纳米硅不能承受这样的高温热退火。这些结果进一步证实了光致发光谱的结果。     

Critical-point analysis of the two-phonon Raman spectrum of silicon

Two-phonon Raman spectrum of silicon has been measured in back-scattering configuration at room temperature using Argon ion laser. It reveals many critical points and consists mainly of two-phonon overtone states. The agreement between the calculated density of states from neutron diffraction data and the present Raman spectrum is excellent except the region where combination spectrum appears. Polarization measurement shows that the structure centered at 300 cm^?1 is not the one-phonon fine structure, predicted by Cowley and observed in part and identified as such by Wright and Mooradian, but the two-phonon overtone spectrum of acoustic phonons. Critical-point analysis has been done on the two-phonon overtone and combination spectra, and phonon frequencies of points of high symmetry in the Brillouin zone are determined and compared with other experimental results. In contrast to the Raman spectrum of diamond, no peak was observed near twice the frequency of zone-center optical phonon. This fact is explained by the difference of phonon dispersion relation between diamond and silicon.     

Two phonon density of states of partially disordered crystal NH4I

Two phonon density of states of NH₄ have been computed with the help of deformation dipole model at room temperature. The results have been compared with the available experimental Raman Spectrum and peak position. It has been shown that in addition to single phonon process which is dominant, the two-phonon density of states also contribute to the Raman Intensity in a partially disordered crystal.     

Raman spectroscopic investigations on transition‐metal dichalcogenides MX2 (M = Mo,W; X = S,Se) at high pressures and low temperature

Transition‐metal dichalcogenides have been investigated using Raman spectroscopy both being off‐resonance and in resonance. The first‐order Raman spectra of MoS₂, MoSe₂, WS₂ and WSe₂ single crystal synthesized by vapor transport technique have been studied as a function of hydrostatic pressure (0–20 GPa) and temperature (80–300 K). Isobaric and isothermal mode‐Grüneisen parameters have been determined from the temperature and pressure‐dependent Raman spectra. The pressure dependence of the chalcogen–chalcogen and metal–chalcogen force constant has been obtained using a central force model. Separation of the temperature dependence of Raman mode wavenumbers into quasi‐harmonic and purely anharmonic contributions using measured high‐pressure Raman data allows us to extract the changes in the phonon wavenumbers arising exclusively due to anharmonic interactions. Copyright © 2014 John Wiley & Sons, Ltd.     

Low-frequency optical phonons in silica

Measurements of low_frequency Raman spectra of silica fibers under longitudinal tensions as a function of temperature have been correlated with the measurements of FIR spectra of bulk silica in reflection and transmission. The results indicate existence of an LO-TO pair of a low-frequency optical phonon branch in amorphous silica.     

锐钛矿二氧化钛超细纳米晶的三声子互作用

本文通过对粒径为2.2-25.5nm的锐钛矿二氧化钛超细纳米晶在83-293 K温度范围内的变温拉曼光谱的研究,得到了三声子互作用对拉曼频率和线宽的贡献随粒径的变化关系。结果表明锐钛矿二氧化钛超细纳米晶的三声子相互作用随粒径减小而加强。     

P型半导体氧化锌薄膜的Raman光谱研究

本文主要对超声喷雾热解方法生长在本征Si衬底上的N－In共掺的p型ZnO薄膜的Raman光谱进行了研究。通过洛仑兹(Lorentz)模型和等离子激元与纵光学声子耦合模理论模型拟合不同浓度下的室温Raman光谱, 我们对样品的Raman峰进行了指认; 同时也得到了样品的空穴浓度和迁移率, 结果和霍耳测量得到的空穴浓度和迁移率符合的较好, 证明了霍耳测量p型ZnO薄膜得到的电学参数是可信的。随后我们又对不同浓度的p型ZnO薄膜的变温Raman光谱进行研究,运用一个详细的模型(考虑了晶格热膨胀、残余应力、和三声子、四声子衰变)描述不同浓度下各个样品Raman光谱中的等离子激元与纵光学声子耦合模随温度变化的情况。分析拟合参数, 可以清楚地了解随着浓度的增加耦合模参数随温度的衰变行为。     

High temperature Raman scattering and phase transition in EuAlO3

Polarized Raman spectra of EuAlO₃ have been obtained at various temperatures from 77–1500 K. Three phonon modes are observed to soften in frequency with increasing temperature. Discontinuity in the frequency temperature dependence appears at 1420 K. This result is consistent with a first order phase transition. Analysis of the Raman data shows evidence of a coupling between the soft mode of Bg(XY) symmetry and one mode of same symmetry.     

Enhanced Fröhlich interaction of semiconductor cuprous oxide films determined by temperature‐dependent Raman scattering and spectral transmittance

Anomalous low temperature behaviors in cuprous oxide (Cu₂O) film grown on quartz substrate have been investigated by temperature‐dependent Raman and transmittance spectra. The longitudinal optical components of two Γ₁₅‐ phonon modes become sharper and more intense at a low temperature. It can be found that the highest‐order electronic transition located at 6.4 eV exhibits a minimum transmittance near 200 K. Correspondingly, the variations from phonon intensity ratios reveal obvious anomalies with the decreasing temperature, indicating the existence of strong electron–phonon coupling mediated by Fröhlich interaction in the Cu₂O films below the temperature of 200 K. Copyright © 2012 John Wiley & Sons, Ltd.     

Possible interplay between a two phonon mode and high energy magnetic excitations in BiFeO<Subscript>3</Subscript>

We have performed Raman measurements on high energy excitations in BiFeO₃ single crystals as a function of both temperature and laser excitation lines. A strong feature observed at 1250 cm^-1 in the Raman spectra has been previously assigned to two phonon overtone. This peak exhibits an unusual frequency shift with the laser lines and the temperature dependence of its Fano lineshape shows two singularities at 150 K and 200 K which can be related to magnetic excitations. In the same energy range, we have also identified the two-magnon excitation with a temperature dependence very similar to the one measured for the one-magnon modes.