分子束外延PbTe单晶薄膜的反常拉曼光谱研究

采用分子束外延(MBE)方法在BaF₂(111)衬底上生长了高质量的PbTe单晶薄膜， 拉曼光谱测量观察到了表面氧化物的振动模、布里渊区中心(q≈0)纵光学(LO)声子振动模以 及声子-等离子激元耦合模振动.随着显微拉曼光谱仪激光光斑聚焦深度的改变，各拉曼散射 峰的峰位、积分强度、半高宽等都表现出不同的变化趋势. 随着激光光斑聚焦位置从样品表 面上方3μm处变化到表面下方3μm处，PbTe外延薄膜的LO声子频率从119cm^-1移 动到124cm^{-1关键词： PbTe外延薄膜 拉曼散射 纵光学声子}     

压电晶体拉曼散射的统一量子论

发展了拉曼散射的一个广义量子理论，它能同时说明非极性模和极性模的作用.在场论中， 光被纵光学和横光学模的拉曼散射能在一个统一的理论框架内描述. 关键词： 拉曼散射 声子 量子场论     

MOCVD生长的GaN和GaN:Mg薄膜的拉曼散射

通过显微拉曼散射对用金属有机化学气相沉积(MOCVD)法在Al2O3衬底上生长的六方相CaN和掺Mg的P型GaN薄膜进行了研究。在两个样品的拉曼散射谱中同时观察到位于640,660cm^-1附近的两个峰。640cm^-1的峰归因于布里渊区边界(L点)最高声学声子的二倍频,而660cm^-1的峰为布里渊区边界的光学声子支或缺陷诱导的局域振动模。掺Mg的GaN在该处的峰型变宽是Mg诱导的缺陷引起的加宽或Mg的局域模与上述两峰叠加的结果。在掺Mg的样品中还观察到276,376cm^-1几个局域模并给予了解释。同时掺Mg的GaN中出现了应力弛豫的现象,掺Mg引起的失配位错和电子-声子相互作用都有可能对E2模的频率产生影响。     

单壁BC3纳米管晶格动力学研究

基于力常数模型计算了一系列扶手椅型、锯齿型和手性单壁BC₃纳米管的声子色散关系.描述了单壁BC₃纳米管结构的表征方式,比较详细地给出了其结构、对称性和晶格动力学分析.基于数值计算结果,讨论了拉曼活性模和红外活性振动模的频率与管径的关系.由分析结果做出推断,BC₃纳米管的拉曼光谱和红外光谱比单壁碳纳米管更为复杂. 关键词： 3纳米管')" href="#">BC₃纳米管 声子色散关系 晶格动力学     

BaBPO5晶体晶格振动光谱研究与第一性原理计算

通过偏振拉曼光谱和第一性原理计算对非线性光学晶体BaBPO₅的 晶格振动模式进行了研究. 实验得到了不同几何配置下、在100–1600 cm^-1范围内的晶体偏振拉曼光 谱与傅里叶变换红外吸收谱, 结合因子群分析方法研究了晶体的外振动与内振动模式特征. 分析表明拉曼振动主要来自于PO₄四面体和BO₄四面体的振动, 且PO₄基团振动具有较强的拉曼与红外活性. 此外,根据第一性原理对晶体拉曼振动进行了数值模拟, 进一步明确了拉曼峰与晶体中原子振动的对应关系, 计算表明拉曼光谱中位于672 cm^-1峰位来自晶体中B–O–P键的伸缩振动, 这是晶体中PO₄四面体和BO₄四面体共顶点连接的特征结构在光谱中的体现.     

自受激拉曼晶体Nd3+:SrMoO4的光谱性质研究

通过拉曼散射光谱，吸收光谱，荧光发射寿命和808 nm LD激发下的红外荧光光谱的实验测量，系统研究了Nd³⁺:SrMoO₄晶体的自受激拉曼光谱性质.分析指认了拉曼散射光谱中各拉曼峰所对应的晶格振动模式，得出了其SRS活性最强的声子频率约为898 cm^-1，对应于(MoO^2-₄)离子团的完全对称光学伸缩振动A_g模；通过J-O理论对晶体的吸收谱进行了全面的光谱参数计算，得出⁴F_3/2→⁴I_11/2跃迁的积分发射截面达0.57×10^-18 cm²，自发辐射概率为141.06 s^-1；同时，实验测得该跃迁的荧光发射寿命约为0.2 ms.最后，结合808 nm LD激发下的红外波段荧光光谱，论证了SrMoO₄晶体中Nd³⁺离子1068 nm发射通过拉曼频移获得1180 nm一级斯托克斯激光发射的可能性，为Nd³⁺:SrMoO₄晶体的自受激拉曼激光器研究提供了理论依据. 关键词： 3+离子')" href="#">d³⁺离子 4 晶体')" href="#">SrMoO₄ 晶体 自受激拉曼散射     

非对称耦合量子阱ZnCdSe/ZnSe的荧光光谱与拉曼散射谱

本文研究了非对称Ⅱ -Ⅳ族耦合多量子阱Zn1-xCdxSe/ZnSe的荧光光谱和拉曼散射谱特性。实验中观察到了比较明显的量子阱荧光峰 ;在拉曼散射谱中观察到了分别对应于与ZnCdSe窄阱和宽阱的一级限制光学模LOL 和LOW 及对应于ZnSe/GaAs界面的声子和等离子体的耦合模 ,并对它们进行了简单分析。     

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     

NH4H2PO4和ND4D2PO4晶体微结构的拉曼光谱研究

本文利用偏振拉曼光谱和第一性原理, 对磷酸二氢铵(NH₄H₂PO₄, ADP)和不同氘含量磷酸二氢铵DADP晶体的晶格振动模式进行了研究. 实验测得了不同几何配置、200–4000 cm^-1范围的偏振拉曼光谱, 分析在不同氘含量条件下921 cm^-1和3000 cm^-1附近拉曼峰的变化. 在ADP晶体中, 基于基本结构单元NH₄⁺ 和H₂PO₄^-基团的振动模, 用第一性原理进行了数值模拟, 进一步明确拉曼峰与晶体中原子振动的对应关系; 通过洛伦兹拟合不同氘含量DADP晶体的拉曼光谱中2000–2600 cm^-1处各峰的变化讨论了DADP 晶体的氘化过程, 结果表明氘化顺序是先NH₄⁺ 基团后H₂PO₄^-基团, 研究结果为今后此类材料的生长和性能优化奠定了基础.     

CH4分子ν1模拉曼诱导克尔效应谱与受激拉曼光声光谱峰形的比较

以气相甲烷分子ν₁模Q支的拉曼光谱为例，采用拉曼诱导克尔效应谱(RIKES)进行峰形测量，并将其与同时测量的受激拉曼光声光谱(PARS)的峰形进行了比较.结果表明，在pump光和Stokes光均为线偏振的情况下，两者存在着差异；在拉曼共振峰的低频端，RIKES谱强度略高；而高频端则恰好相反.从信号产生机制出发，对此进行了合理解释. 关键词： 拉曼诱导克尔效应谱 受激拉曼光声光谱 峰形     

Raman Spectroscopic Characterization of Graphene

Abstract

The recent progress using Raman spectroscopy and imaging of graphene is reviewed. The intensity of the G band increases with increased graphene layers, and the shape of 2D band evolves into four peaks of bilayer graphene from a single peak of monolayer graphene. The G band will blue shift and become narrow with both electron and hole doping, whereas the 2D band will blue shift with hole doping and red shift with electron doping. Frequencies of the G and 2D band will downshift with increasing temperature. Under compressed strain, the upshift of the G and 2D bands can be found. Moreover, the strong Raman signal of monolayer graphene is explained by interference enhancement effect. As for epitaxial graphene, Raman spectroscopy can be used to identify the superior and inferior carrier mobility. The edge chirality of graphene can be determined by using polarized Raman spectroscopy. All results mentioned here are closely relevant to the basic theory of graphene and application in nanodevices.     

Raman spectroscopy to probe residual stress in ZnO nanowire

Raman spectroscopic studies are performed to probe the stress along the length of a bent ZnO nanowire. The zone‐centre E₂^high optical phonon shows a systematic red shift as the junction point of the two arms of the nanowire is approached. The mechanism of the red shift is discussed on the basis of the tensile strain. From the red shift of the phonon peak position, the strain at different regions on the nanowire is estimated. Stress in the bent nanowire is also investigated using photoluminescence (PL) spectroscopy. Results of both Raman and PL study confirm that the bent nanowire is under tensile strain. Copyright © 2011 John Wiley & Sons, Ltd.     

Steric hindrance in cationic and neutral rhodamine 6 G molecules adsorbed on Au nanoparticles

The adsorption of cationic and neutral R6G molecules on Au nanoparticles was elucidated by surface enhanced Raman scattering (SERS). The steric hindrance at hydroethyl amino (‐N(H)Et) groups in R6G was evidenced by the observation that R6G⁺ adsorb on as‐prepared gold nanoparticles (AuNPs) only with electrostatic forces, in contrast to the electrostatic and chemical adsorption of R123⁺ with dihydro amino (‐NH₂) groups on as‐prepared AuNPs. Large steric hindrance at the amino groups in R6G yielded saturated coverage of 700 molecules/AuNP for R6G⁺ significantly fewer than 1000 molecules/AuNP for R123⁺. In addition, neutral R6G⁰ on AuNPs showed markedly enhanced peaks at 1200–1600 cm⁻¹, which were not observed in Raman spectra of R6G⁰ in bulk solution, and also in SERS of R6G⁺ on AuNPs. These bands are attributed to vibrational modes of an outer phenyl ring and ethyl amino groups, which are vertical to a xanthene plane, on the basis of theoretical analysis of molecular vibrations. Thus, Raman scattering of these bands is enhanced under an inclined orientation of R6G⁰ molecules chemisorbed on AuNPs via lone pair electrons at amino groups. Copyright © 2013 John Wiley & Sons, Ltd.     

Study of porous silicon structure by Raman scattering

In this paper, the effect of etching time on light emitting porous silicon has been studied by using Raman scattering. Enhancement of Raman intensity by increasing the porosity is observed. Also there is a red shift, about 4 cm⁻¹, from the Raman peak of crystalline silicon to that of porous silicon. The phonon confinement model suggests the existence of spherical nanocrystalline silicon with diameter around 7 nm. But SEM images show that the samples have a sheetlike structure that confines phonons in one dimension. This should not cause any shift in their Raman spectra. It is suggested that the observed Raman peak shift is due to the spherical nanocrystals on the surface of these sheets.     

Raman spectroscopic studies of pulsed laser‐induced defect evolution in graphene

Raman spectra were obtained for graphene after irradiating the samples by pulsed laser (λ = 248 nm). Changes in the spectra were observed as the pulse laser energy density (PLED) was varied from 0.1 to 0.25 J/cm². Changes in bilayer graphene were accompanied by the appearance of the D peak and the broadening of the G peak. Changes in multilayer graphene are more profound as the Raman spectra changes from a multilayer to bilayer and subsequently to monolayer graphene in response to a slow increase in the PLED. The threshold PLED was found to be dependent on the number of graphene layers. We also irradiate graphene with very high PLED (much above the threshold), and the Raman spectra were found to be significantly changed. The G‐band became broader, and red shifted, while the intensity of the 2D‐band was drastically reduced and an intense defect‐related D peak appeared at about 1350 cm⁻¹. The laser ablation of graphene, both with low‐ and high‐energy intensity, is consistent with the reported theoretical predictions. Copyright © 2013 John Wiley & Sons, Ltd.     

Two-dimensional phonon transport in graphene

Properties of phonons-quanta of the crystal lattice vibrations-in graphene have recently attracted significant attention from the physics and engineering communities. Acoustic phonons are the main heat carriers in graphene near room temperature, while optical phonons are used for counting the number of atomic planes in Raman experiments with few-layer graphene. It was shown both theoretically and experimentally that transport properties of phonons, i.e. energy dispersion and scattering rates, are substantially different in a quasi-two-dimensional system such as graphene compared to the basal planes in graphite or three-dimensional bulk crystals. The unique nature of two-dimensional phonon transport translates into unusual heat conduction in graphene and related materials. In this review, we outline different theoretical approaches developed for phonon transport in graphene, discuss contributions of the in-plane and cross-plane phonon modes, and provide comparison with available experimental thermal conductivity data. Particular attention is given to analysis of recent results for the phonon thermal conductivity of single-layer graphene and few-layer graphene, and the effects of the strain, defects, and isotopes on phonon transport in these systems.     

Observation of low‐wavenumber out‐of‐plane optical phonon in few‐layer graphene

Few‐layer graphene grown by chemical vapor deposition has been studied by Raman and ultrafast laser spectroscopy. A low‐wavenumber Raman peak of ~120 cm⁻¹ and a phonon‐induced oscillation in the kinetic curve of electron–phonon relaxation process have been observed, respectively. The Raman peak is assigned to the low‐wavenumber out‐of‐plane optical mode in the few‐layer graphene. The phonon band shows an asymmetric shape, a consequence of so‐called Breit‐Wigner‐Fano resonance, resulting from the coupling between the low‐wavenumber phonon and electron transitions. The obtained oscillation wavenumber from the kinetic curve is consistent with the detected low‐wavenumber phonon by Raman scattering. The origin of this oscillation is attributed to the generation of coherent phonons and their interactions with photoinduced electrons. Copyright © 2012 John Wiley & Sons, Ltd.     

Signatures of epitaxial graphene grown on Si-terminated 6H-SiC (0 0 0 1)

Epitaxial graphene layers thermally grown on Si-terminated 6H-SiC (0 0 0 1) have been probed using Auger electron spectroscopy, Raman microspectroscopy, and scanning tunneling microscopy (STM). The average multilayer graphene thickness is determined by attenuation of the Si (L₂₃VV) and C (KVV) Auger electron signals. Systematic changes in the Raman spectra are observed as the film thickness increases from one to three layers. The most striking observation is a large increase in the intensity of the Raman 2D-band (overtone of the D-band and also known as the G′-band) for samples with a mean thickness of more than ∼1.5 graphene layers. Correlating this information with STM images, we show that the first graphene layer imaged by STM produces very little 2D intensity, but the second imaged layer shows a single-Lorentzian 2D peak near 2750 cm⁻¹, similar to spectra acquired from single-layer micromechanically cleaved graphene (CG). The 4-10 cm⁻¹ higher frequency shift of the G peak relative to CG can be associated with charge exchange with the underlying SiC substrate and the formation of finite size domains of graphene. The much greater (41-50 cm⁻¹) blue shift observed for the 2D-band may be correlated with these domains and compressive strain.     

Manipulation of optical properties of Ag/Cu alloy nanowire arrays embedded in anodic alumina membranes

Arrays of Ag/Cu alloy nanowires embedded in anodic alumina membranes (AAMs) were synthesized by directly electrodepositing from a mixing electrolyte solution containing Ag⁺ and Cu²⁺ ions. Manipulations of optical properties of the resulting samples were successfully achieved by tuning the molar ratio of Ag⁺ and Cu²⁺ ions in the starting materials. When the ratio is less than 2:20, two surface plasma resonance (SPR) peaks corresponding to Ag and Cu appear, respectively. After annealing treatment, the SPR peak corresponding to Cu disappears, and that of Ag presents a red shift. Furthermore, this red shift can be up to 85 nm when the molar ratio of Ag⁺ and Cu²⁺ reduce to 1:20, which is attributed to the transferable electrons from Cu atoms.