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.     

Identification of oxygen vacancy types from Raman spectra of SnO2 nanocrystals

Raman spectra acquired from spherical SnO₂ nanocrystals prepared by pulsed laser ablation and hydrothermal synthesis exhibit three oxygen‐vacancy‐related Raman modes at 234, 573, and 618 cm⁻¹. The peak location and intensity vary with annealing temperature under O₂ finally approaching those of bulk materials. Density functional calculation discloses that the three Raman modes stem from subbridging, in‐plane, and bridging oxygen vacancies, respectively. Raman spectra can thus be used to discern different types of oxygen vacancies in SnO₂ nanocrystals. Copyright © 2012 John Wiley & Sons, Ltd.     

Raman spectra of CdS nanocrystals in Nafion: longitudinal optical and confined acoustic phonon modes

Quantum confinement effects on the longitudinal optical and acoustic phonons in CdS nanocrystals in the strongly confined regime in the polymer matrix Nafion are studied using Raman spectroscopy. The LO-phonon modes show size-dependent asymmetric broadening though the broadening and asymmetry are less than those predicted by the phonon confinement models. Two types of confined acoustic modes corresponding to n=1, l=0 and n=1, l=2 spheroidal vibrations are observed. Softening of the spheroidal modes is observed in the strongly confined regime.     

偏磷酸钙玻璃陶瓷的Raman光谱分析

测量了Ca/P摩尔比为0.45的偏磷酸钙玻璃及其在300~700℃下结晶化处理获得玻璃陶瓷的拉曼光谱,对谱峰的振动模式进行了指认,利用拉曼振动频率计算了P—O键长。光谱分析发现偏磷酸钙玻璃在300℃已经开始了结晶相变,不同温度下,sν(PO2)和sν(POP)谱带的振动频率基本不变,随着温度提高,谱峰强度增加,并出现了精细的指纹结构;玻璃陶瓷的表面和内部的结构不同,表面结晶化程度高于内部;结晶过程中,P—O键平均键长会发生变化,随着结晶化程度的提高,骨架上(POP)的P—O键平均键长减小,由159.96 pm变为158.27 pm,侧链(PO2)上的P—O键长增大,由147.90 pm变为149.02 pm。     

Mode-locking of neodymium lasers by glasses doped with PbS nanocrystals

Nonlinear optical absorption properties of silicate glasses doped by the PbS nanocrystals were investigated by means of the picosecond pump-probe absorption spectroscopy and absorption bleaching technique. The glass samples were used as saturable absorbers for passive mode-locking of Nd:YAG and Nd:glass lasers. Application of the PbS doped glass together with the active mode-locking and laser cavity quality control enabled the stable of generation of 28 ps and 5 ps duration pulses in Nd:YAG and Nd:glass lasers respectively. PACS 42.60.Fc; 42.70.Hj; 78.47.+p     

Absorption spectra of germanium nanocrystals

Absorption spectra of hydrogenated germanium nanocrystals are calculated in real space using ab initio pseudopotentials constructed within the local density approximation. Nanocrystals with over 800 atoms are considered. We find the calculated spectra are essentially bulk-like for systems with ∼250 atoms or more. The energy positions for the E₁ and E₂ reflectivity peaks are blue-shifted with respect to their bulk values owing to quantum confinement. Comparisons with available experimental data reveal good agreement for the energies of the E₁ peak, whereas the energy position of the E₂ peak is underestimated by a constant shift, which is independent of the nanocrystal size. This shift is consistent with local density calculations for bulk germanium.     

Raman analysis of amorphous silicon ruthenium thin films embedded with nanocrystals

We report the Raman analysis of both as‐deposited and annealed amorphous silicon ruthenium thin films embedded with nanocrystals. In the Raman spectra of as‐deposited films, variations of TO peak indicate a short‐range disorder of a‐Si network with an increase of Ru concentration. The substitutional Ru atoms lower the concentration of Si―Si bonds and suppress the intensity of TO peak, but have less effect on TA, LA and LO peaks. In the Raman spectra of annealed films, characteristic parameters confirm the upgrade of a‐Si network at a low annealing temperature and the emergence of both ruthenium silicide and silicon nanocrystals at 700 °C. Although ruthenium silicide nanocrystals present no Raman peaks in the Raman spectra of as‐deposited samples, the non‐linear variations of intensity ratios I_{LA + LO}/I_TO and I_TA/I_TO still suggest their existence, and these nanocrystals are subsequently verified by high‐resolution transmission electron microscopy. Copyright © 2015 John Wiley & Sons, Ltd.     

天然、合成红宝石的拉曼光谱分析

天然与合成宝石一直是宝石鉴定中的难题,而拉曼光谱的半高宽,即声子寿命可提供宝石是天然或合成的信息。论文利用BTR111-785微型近红外拉曼光谱仪对天然、合成红宝石进行测试分析,研究表明天然红宝石的半高宽均在10cm-1以上,合成红宝石的半高宽均低于10cm-1。     

Vibrational Raman spectra of CdSx Se1‐x magic‐size nanocrystals

Resonant Raman scattering spectra of ultrasmall (<2 nm) magic‐size nanocrystals (NCs) are reported. The spectra of CdS and CdS_x Se_1‐x NCs, resonantly excited with 325 nm and 442 nm laser lines, correspondingly, reveal broad features in the range of bulk optical phonons. The relatively large width, ～50 cm^‐1, and downward shift, ～20 cm^‐1, of the Raman bands with respect to the longitudinal optical phonon in bulk crystals and large NCs are discussed based on the breaking of the translational symmetry and bond distortion in these ultrasmall NCs. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Raman investigation of defective SiC nanocrystals

Phonon confinement effect and surface optical mode in SiC nanocrystal have been investigated through Raman spectroscopy. Considering high density of stacking faults in SiC grains, the correlation length of RWL (proposed by Richter, Wang, Li to explain phonon confinement in nano silicon) model is determined as a distance between nearby stacking faults. Thus, homogeneous region becomes thin slices in cylindrical SiC grains, which redefines weighting function. Effect of anisotropy of phonon dispersion curve is also analyzed during calculation. The additional 875‐cm⁻¹ band is attributed to defects and amorphous SiC, which is confirmed by transmission electron microscopy. SiC grains are approximated as column array with grain boundary substances regarded as surrounding medium, which explains surface optical phonon mode at 915 cm⁻¹. Copyright © 2015 John Wiley & Sons, Ltd.     

Quantum mechanical analysis of resonance Raman spectra of thymine

A direct quantum mechanical calculation of the relative intensities of lines in resonance Raman (RR) spectra of thymine was performed. The method of calculation is based on the adiabatic model in the Herzberg-Teller approximation. It is shown that the basic features of the intensity distribution in the spectra can be explained only by taking into account the vibronic mixing of electronic states and the contribution to the components of the scattering tensor from excited electronic states located close to the resonance state. The calculated results agree satisfactorily with experimental RR spectra of thymine excited by laser radiation at 266, 240, 218, and 200 nm. A comparative analysis of the intensity distribution in the RR spectra of thymine and uracil is carried out.     

PbS及其光致氧化产物的显微成像拉曼散射研究

使用高数值孔径的物镜通过显微拉曼扫描成像的方法获得了方铅矿结晶体的空间分辨的分子信息。实验中包括不同尺寸大小的晶体和不同强度的激发光功率。从逐点扫描(步长为0.5μm)的显微探针成像方法获得的光谱数据分析,得到了化学组分的空间分布。多变量数据分析处理得到PbS及其退化产物的特征光谱。在非破坏性激发条件下,PbS的特征谱线很弱。在强激光的光化作用下,在微米尺度大的样品点上产生完全不可逆的氧化反应,把PbS氧化为α-PbO。对于大尺度的PbS晶体,通过拉曼扫描成像光谱在照明点附近还发现了铅的氧硫酸盐包括4PbO.PbSO4,3PbO.PbSO4和PbO.PbSO4。     

Multipeak fitting analysis of Raman spectra on DLCH film

The hydrogenated diamond‐like carbon (DLCH) film with 1‐µm thickness is deposited by direct hydrocarbon gas ion beam method on silicon wafer and annealed at 400 °C. Detailed Raman spectra feature are fitted from nine sets of different peak fitting functions, including Gaussian, Lorentzian and Breit‐Wigner‐Fano (BWF) functions. These fitting results obtained from a two‐peak combination show some specific variances on the G peak position, FWHM_G and I_D/I_G ratio for as‐deposited and as‐annealed DLCH films. The most popular two‐peak fitting method with full Gaussian function tends to exhibit a higher ratio of the G peak position shift and higher I_D/I_G ratio than others fitting methods, the drastic difference among the most popular G (G) & G (D) and B (G) & L (D) schemes also have brought out in I_D/I_G ratio. However, for a more complex four‐peak Gaussian function fitting Raman spectra, the I_D/I_G ratio is close to that of a two‐peak fitting function with a mixture functions of BWF (G) and L (D). Furthermore, a series of systematic peak fitting procedures and comparisons of Raman spectra have been discussed in this study. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectra of fosterite

The normal modes of the Raman-active phonons in the center of the Brillouin zone in a natural monocrystal of Mg₂SiO₄ were measured by using Raman scattering. All of the modes predicted by group theory were observed and measured. Some deviations from previously published values in synthetic samples were observed for the low energy phonons.     

Two-photon-excited luminescence spectra in diamond nanocrystals

Two-photon-excited luminescence (TEL) spectra have been recorded in the blue (400–500 nm) and near-ultraviolet (300–400 nm) ranges for diamond particles with 4 nm average size, which were obtained by detonation synthesis from explosives. The observed TEL bands are attributed, by comparing the obtained spectra with the impurity luminescence spectra in large diamond crystals, to N2 and N3 defects associated with the presence of nitrogen impurities in diamond. The TEL spectra presented are found to have certain distinguishing features: short-wavelength shift of the maximum and changes in the shape and width of the spectral bands for ultradispersed diamond compared with the spectrum in bulk crystals. Fiz. Tverd. Tela (St. Petersburg) 41, 1110–1112 (June 1999)     

Excitonic luminescence spectra of hexagonal CuBr nanocrystals

The structure of low-temperature excitonic luminescence spectra of CuBr nanocrystals of hexagonal modification is studied. It is shown that the observed spectral structure can be explained assuming the formation of exciton-phonon complexes with their subsequent annihilation and radiative recombination of the exciton. Fiz. Tverd. Tela (St. Petersburg) 39, 1657–1658 (August 1997)     

Raman and infrared spectra of tere-phthalaldehyde

The laser Raman spectrum of tere-phthalaldehyde powder has been recorded on a Jobin Yvonhg 2S spectrophotometer with a~100 mW Argon-Ion laser. The infrared spectrum of the solid substance has been recorded on a Perkin-Elmer 621 spectrophotometer in the region 300–4000 cm^-1 using KBr and nujol mull techniques. The observed frequencies have been assigned in terms of the fundamentals, overtones and combinations assumingD _2h point-group symmetry.     

苏氨酸的太赫兹及拉曼光谱研究

采用太赫兹时域光谱和拉曼光谱法对L-苏氨酸多晶粉末进行测试研究,获得了样品在0.2—2.8 THz（6.7—93.2 cm^-1）波段的特征吸收和10—4000 cm^－1波段的拉曼散射谱;分别在6.7—93.2 cm^－1和400—4000 cm^－1两个波段进行了吸收光谱与拉曼散射光谱的对比,根据晶胞分子所属的空间群,对隶属于分子的极性和非极性振动模式（A, B₁, 关键词： 太赫兹光谱 拉曼散射 氨基酸