Electron states and electron Raman scattering in semiconductor double cylindrical quantum well wire

The differential cross section for an electron Raman scattering process in a semiconductor GaAs/AlGaAs double quantum well wire is calculated,and expressions for the electronic states are presented.The system is modeled by considering T = 0 K and also with a single parabolic conduction band,which is split into a subband system due to the confinement.The gain and differential cross-section for an electron Raman scattering process are obtained.In addition,the emission spectra for several scattering configurations are discussed,and interpretations of the singularities found in the spectra are given.The electron Raman scattering studied here can be used to provide direct information about the efficiency of the lasers.     

Interplay between phonon confinement effect and anharmonicity in silicon nanowires

Getting light out of silicon is a difficult task since the bulk silicon has an indirect energy electronic band gap structure. It is expected that this problem can be circumvented by silicon nanostructuring, since the quantum confinement effect may cause the increase of the silicon band gap and shift the photoluminescence into the visible energy range. The increase in resulting structural disorder also causes the phonon confinement effect, which can be analyzed with a Raman spectroscopy. The large phonon softening and broadening, observed in silicon nanowires, are compared with calculated spectra obtained by taking into account the anharmonicity, which is incorporated through the three and four phonon decay processes into Raman scattering cross-section. This analysis clearly shows that the strong shift and broadening of the Raman peak are dominated by the anharmonic effects originating from the laser heating, while confinement plays a secondary role.     

Quantum confinement effect in the vibrational spectrum of CdSxSe1−x quantum dots in a fluorophosphate glass matrix

The vibrational spectra of mixed cadmium sulfoselenide nanocrystals in a fluorophosphate glass matrix are investigated by Raman spectroscopy. The asymmetry of the lines of the fundamental modes of nanocrystals is experimentally observed in the region of lattice vibrations, which is interpreted as a quantum confinement effect. In the framework of the model of confined phonons, the contribution of the band states to the Raman scattering spectrum is calculated and the size of nanocrystalline regions is estimated. The results obtained are in good agreement with the data on the low-frequency Raman scattering in these objects.     

The nonlinear optical properties of a magneto-exciton in a strained Ga_(0.2)In_(0.8)As/GaAs quantum dot

The magnetic field-dependent heavy hole excitonic states in a strained Ga0.2In0.8As/GaAs quantum dot are investigated by taking into account the anisotropy,non-parabolicity of the conduction band,and the geometrical confinement.The strained quantum dot is considered as a parabolic dot of InAs embedded in a GaAs barrier material.The dependence of the effective excitonic g-factor as a function of dot radius and the magnetic field strength is numerically measured.The interband optical transition energy as a function of geometrical confinement is computed in the presence of a magnetic field.The magnetic field-dependent oscillator strength of interband transition under the geometrical confinement is studied.The exchange enhancements as a function of dot radius are observed for various magnetic field strengths in a strained Ga0.2In0.8As/GaAs quantum dot.Heavy hole excitonic absorption spectra,the changes in refractive index,and the third-order susceptibility of third-order harmonic generation are investigated in the Ga0.2In0.8As/GaAs quantum dot.The result shows that the effect of magnetic field strength is more strongly dependent on the nonlinear optical property in a low-dimensional semiconductor system.     

Low frequency Raman scattering of anatase titanium dioxide nanocrystals

TiO₂ nanoparticle of size 7.8 nm are synthesized by wet chemical route and characterized by low-frequency Raman scattering (LFRS), transmission electron microscopy (TEM) and X-ray diffraction. The low frequency peaks in the Raman spectra have been explained using the Lamb's theory that predicts the vibrational frequencies of a homogeneous elastic body of spherical shape. Our results show that the observed low-frequency Raman scattering originates from the spherical (l=0) and quadrupolar vibrations (l=2) of the spheriodal mode due to the confinement of acoustic vibrations in TiO₂ nanoparticles. In addition to the low-frequency peak due to the vibrational quadrupolar and spheriodal modes, a band is also observed, which is assigned to the Raman forbidden torsional l=2 mode originating from the near spherical shape of the TiO₂ nanoparticles. The size distribution is also obtained from LFRS, which is in good agreement with TEM.     

Cascade processes in inelastic light scattering in ZnSe nanowire structures

The resonance Raman scattering of light in MBE-grown structures with ZnSe nanowires (10–20 nm in diameter) with an Au film deposited on the substrate used as a catalyst was investigated. The thicknesses of the Au layers were 2, 10, and 100 Å. The photon energy of the He-Cd pump laser (λ = 441.6 nm) was in excess of the band gap of bulk ZnSe, and the measurements were conducted at room temperature. Under these conditions, the Raman spectra are defined by a cascade process in which the electron interacting with a longitudinal optical phonon transfers between real band states with a certain probability of radiative recombination at each step. The blue shift of the luminescence maximum associated with the quantum confinement of carriers in the nanowire has been observed. The average nanowire diameter derived from the magnitude of this shift agrees well with electron microscopy measurements.     

Applying an improved phonon confinement model to the analysis of Raman spectra of germanium nanocrystals

The improved phonon confinement model developed previously [11] is applied for definition of germanium nanocrystal sizes from the analysis of its Raman scattering spectra. The calculations based on the model allow determining the sizes of germanium nanocrystals more precisely from the analysis of their Raman spectra. In some cases, the comparative analysis of Raman data and electron microscopy data is carried out, and good agreement is observed.     

GaN直纳米线的光学性能

对 Ga N直纳米线的拉曼光谱及光致发光光谱进行了研究。拉曼光谱表明 ,与计算值相比 ,E2 ( high)声子频率在 560 cm- 1有 -9cm- 1的移动 ,这种声子频率显示出向低能带频移及带变宽的特征 ,是由于纳米尺寸效应所引起的结果。体系的光致发光光谱在 3 44 .8nm附近的近带隙发光 ,与文献报道的 Ga N体材料的数值3 65nm相比有一蓝移 ,这是由于量子限制效应造成的     

若干低维材料的拉曼光谱学研究--2004年度国家自然科学二等奖获奖项目介绍

文章扼要介绍了2004年国家自然科学二等奖获奖项目：《若干低维材料的拉曼光谱学研究》．用拉曼光谱研究低维纳米材料,必须对传统拉曼光谱学进行改造,创建新的“低维拉曼光谱学”．该项目通过若干低维材料的研究,为创建低维拉曼光谱学作出了系统的创新性贡献,如最先鉴认出典型低维材料的拉曼指纹谱,发现拉曼光谱的两个基本特征出现“反常”,但证明拉曼散射基本原理在低维体系中依然成立．通过低维拉曼光谱和光发射谱的应用研究,发现了材料的许多新奇物性,如发现超晶格和碳纳米管是类缺陷结构,和极性半导体纳米晶材料具有非晶特性,并提出了多孔硅的“量子限制电化学”形成和“多源量子阱”光发射模型,促进了低维材料和半导体器件的制备．     

利用Raman散射光谱研究铜铟镓硒薄膜表面的掺杂调节作用

主要研究了采用溅射后硒化方法制备CIGS(铜铟镓硒)薄膜太阳电池的吸收体材料中的表面层掺杂调节问题。并利用Raman散射谱分析研究了样品表面层特征峰的移用,研究结果表明: CIGS薄膜表面层由富In表面层调节为富CuGa表面层后,Raman特征峰位向高波数移动,表明薄膜表面的Ga含量随之变化,并导致表面能带的相应改变,经计算证实了富CuGa表面层样品较之富In表面层样品具有更高的表面能带,从而改善了以此材料为吸收层的太阳电池器件性能, V_oc提高了74 mV,填充因子上升8％,最终使器件转换效率η相应提高了约2％。提高了V_oc与FF。同时表明Raman散射谱作为一种灵敏的表面表征手段,在研究太阳电池吸收层表面状态时十分有力。     

Theory of Raman light scattering by nanocrystal acoustic vibrations

A theory of Raman scattering of light by acoustic phonons in spherical nanocrystals of zinc-blende and wurtzite semiconductors has been developed with the inclusion of the complex structure of the valence band. The deformation-potential approximation was used to describe the exciton-phonon interaction. It is shown that this approximation allows only Raman scattering processes involving spheroidal acoustic phonons with a total angular momentum F=0 or 2. The effect of phonon quantum confinement on linewidth in Raman scattering spectra and scattered polarization is analyzed. An expression for the shape of the spectral line corresponding to nonresonant scattering from F=0 phonons was obtained. Fiz. Tverd. Tela (St. Petersburg) 41, 1473–1483 (August 1999)     

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。     

外场对π电子能隙调制C==C，C-C伸缩振动的影响

共振拉曼光谱是研究线性多烯分子的主要分子光谱技术。该技术完美地表征了π电子能隙对C==C,C-C伸缩振动的调制规律。这种调制是通过电子-声子耦合完成的。改变外界环境,能隙调制作用将受到影响。测量了溶剂中β-胡萝卜素分子在温度、压力、溶剂效应、相变等不同环境影响下的吸收光谱、共振拉曼光谱,研究了不同外场对π电子能隙调制C==C,C-C伸缩振动的影响机理及规律。结果表明,在外场影响下,体系的能量降低,π电子能隙(π-π*)减小会使调制增强。即电子-声子耦合增强,使拉曼强度增加,谱线红移。对理解共振拉曼物理过程,认识线性多烯分子的结构,性能有重要意义,对研制优质光电器件也有参考价值。     

Size effects on phonon localization and Raman enhancement in silicon nanotips

Silicon nanotip arrays exhibit a wide variety of interesting optical and electronic properties associated with their dimensionality. We here investigate the effect of size‐induced changes on phonon localization and explain the enhanced Raman response. The occurrence of normally forbidden transitions in the photoluminescence spectra provides evidence for the predicted localization effect. Spatially resolved Raman spectroscopy reveals a continuous change of the silicon Raman peak position and peak width along the nanotip that is attributed to a smooth change between bulk properties at the base to size‐induced phonon confinement in the apex of the nanotip. This approach allows to exclude heating effects that normally overwhelm the phonon confinement signature. The Raman spectra are in excellent agreement with the spatial correlation model and the extracted correlation length is comparable to the tip dimensions. The observed phonon confinement coincides with an enhancement of the Raman scattering efficiency at the tip apex and results in a 40‐fold increase of the sample's Raman intensity compared with bulk silicon. These results provide a step toward the integration of Si based optoelectronic devices. Copyright © 2012 John Wiley & Sons, Ltd.     

Lattice Dynamics and Electronic Properties of a BaGa2GeS6 Nonlinear Crystal: Raman Scattering,IR Reflection,and ab initio Calculations

Optics and Spectroscopy - We have measured the polarized Raman scattering and IR reflection spectra of a BaGa2GeS6 crystal, the Ga and Ge atoms of which are disordered, randomly occupying...     

Titanium dioxide synthesized using titanium chloride: size effect study using Raman spectroscopy and photoluminescence

Titanium dioxide nanocrystals were prepared by the wet chemical method and characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), Raman scattering (RS) and photoluminescence techniques. The XRD pattern shows the formation of single phase anatase structure of average sizes ∼7 nm (sample A) and ∼15 nm (sample B) for two samples. Additionally, TEM and RS were used to confirm the anatase crystal structure for both samples. The PL spectra show that the intensity of the sample A is more than that of sample B, which has been attributed to defect(s) and particle size variation. A modified phonon confinement model incorporating particle size distribution function and averaged dispersion curves for two most dispersive phonon branch (Γ‐X direction) have been used to interpret the size effect in Raman spectra. The obtained Raman peak shift and full width at half‐maximum agree well with the experimental data. Our observations suggest that the phonon confinement effects are responsible for a significant shift and broadening for the Raman peaks. Copyright © 2009 John Wiley & Sons, Ltd.     

紫金山金铜矿明矾石的拉曼光谱特征

紫金山金铜矿是我国大陆首例高硫化型浅成低温热液型矿床。矿床上金下铜,金矿主要赋存在潜水面以上,与强硅化有关;铜矿主要赋存于潜水面之下,与明矾石化有关。明矾石有四种产出状态,分别为蚀变岩型、与铜硫化物共生型、后期脉状、粉末状。不同产出状态的明矾石具有不同的拉曼光谱特征和荧光散射背景。明矾石流体包裹体激光拉曼谱图显示：(1)从蚀变岩型、与铜硫矿化物共生型到后期脉状明矾石均具有明矾石特征性的谱带,只是受荧光散射影响逐渐减弱;粉末状明矾石具有与前三者不同的谱带特性,各谱带强度均较弱,荧光散射较强烈。(2)100～700 cm-1区间谱带可作为明矾石分子结构中阳离子类质同象置换的“指纹谱带”。蚀变岩型明矾石,161和234 cm-1峰变化明显,具有较广泛的Na对K的类质同象置换;与铜硫化物共生的明矾石,381和484 cm-1峰变化明显,指示Cu和Ga等阳离子对Al离子的类质同象置换;后期脉状明矾石,161, 234,484,508 cm-1峰值均比较稳定,Na对K和Si对Al的类质同象置换较少;潜水面附近的粉末状明矾石因荧光散射强烈,各个谱带强度均较弱。(3)明矾石的激光拉曼光谱和红外光谱配合使用,可为明矾石矿物研究提供完整的分子振动光谱特征,为明矾石的成因提供结构信息。在岩相学、矿相学、矿床地质、矿床地球化学、区域地质特征研究的基础上,通过明矾石的激光拉曼光谱(结合荧光散射背景)可进一步为紫金山金铜矿这个典型的高硫化型浅成低温热液矿床的形成机制提供演化进程信息。     

Raman spectroscopy for study of interplay between phonon confinement and Fano effect in silicon nanowires

A combined effect of doping (type and species) and size on Raman scattering from silicon (Si) nanowires (NWs) has been presented here to study interplay between quantum confinement and Fano effects. The SiNWs prepared from low doping Si wafers show only confinement effect, as evident from the asymmetry in the Raman line‐shape, irrespective of the doping type. On the other hand SiNWs prepared from wafer with high doping shows the presence of electron–phonon interaction in addition to the phonon confinement effect as revealed from the presence of asymmetry and antiresonence in the corresponding Raman spectra. This combined effect induces an extra asymmetry in the lower energy side of Raman peak for n‐type SiNWs whereas the asymmetry flips from lower energy side to the higher energy side of the Raman peak in p‐type SiNWs. Such an interplay can be represented by considering a general Fano‐Raman line‐shape equation to take care of the combined effect in SiNWs. Copyright © 2015 John Wiley & Sons, Ltd.