Surface‐enhanced Raman scattering from polystyrene on gold clusters

Surface‐enhanced Raman scattering (SERS) constitutes a spectroscopic method of rapidly growing importance, and polystyrene is a widely used compound of great industrial importance. In this work, SERS data were obtained from polystyrene samples prepared by vapor deposition of gold and plasma‐induced polymerization of styrene gas. A thorough examination of this data is presented. The relationships between sample preparation parameters, gold‐cluster morphology, and SERS intensity were elucidated. Using Wilson's notation, vibrations were assigned to all bands between 250 and 1750 cm⁻¹ in the ordinary Raman and SERS spectra of polystyrene. The correct assignment of these bands would be a significant achievement because they have been controversial in the literature for ∼30 years. Our assignments were made by reviewing the literature and comparing the assignments found there to spectral data acquired during this study; they were confirmed using density functional theory (DFT) calculations performed on the styrene monomer. The orientation of polystyrene's phenyl ring, relative to the gold surface, was determined. It has been suggested that reactions involving silver catalyze polystyrene degradation during SERS, but we found that silver is not necessary for the degradation to occur. Copyright © 2009 John Wiley & Sons, Ltd.     

Understanding tip‐enhanced Raman spectra of biological molecules: a combined Raman,SERS and TERS study

Although conventional Raman, surface‐enhanced Raman (SERS) and tip‐enhanced Raman spectroscopy (TERS) have been known for a long time, a direct, thorough comparison of these three methods has never been carried out. In this paper, spectra that were obtained by conventional Raman, SERS (on gold and silver substrates) and TERS (in ‘gap mode’ with silver tips and gold substrates) are compared to learn from their differences and similarities. Because the investigation of biological samples by TERS has recently become a hot topic, this work focuses on biologically relevant substances. Starting from the TER spectra of bovine serum albumin as an example for a protein, the dipeptides Phe–Phe and Tyr–Tyr and the tripeptide Tyr–Tyr–Tyr were investigated. The major findings were as follows. (1) We show that the widely used assumption that spectral bands do not shift when comparing SER, TER and conventional Raman spectra (except due to binding to the metal surface in SERS or TERS) is valid. However, band intensity ratios can differ significantly between these three methods. (2) Marker bands can be assigned, which should allow one to identify and localize proteins in complex biological environments in future investigations. From our results, general guidelines for the interpretation of TER spectra are proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

Infrared Spectra of Morfolonium (mpH)2Mo2Cl6(H20)2(I),(mpH)2Mo2ClxBr6-x(H2O)2(II)/ (mpH)2Mo2Br6(H2O)2(III) and the Pyridinium (PyH)2Mo2I6(H2O)2(IV)Hexahalo-di(aquo): dimolybdate(II) Complexes,Containing Quadruple Metal-Metal Bounds

Abstract

The electronic (800–400 nm), infrared (4000–200,400–20 cm^?1), ordinary Raman (400–200 cm^?1) spectra of morpholinium and the pyridium hexahalo-di(aquo) dimolybdate(II) complexes, containing quadruple metal-metal bonds were investigated. The electronic spectra of the solid compounds at various temperatures (25,100 and 300K) demonstrate intense and structured bands in the visible region (510–582 nm) attributed to the expected δ→δ? transitions.

From the infrared and Raman spectra, the skeletal stretching modes in these complexes have been localized, and the charectenstic bands of these ions were observed in the expected regions.

Finally, the ionic interections were relatively weak, but the existance of phenomena was perceptible and the result was obtained in agreement with X-ray data.     

Dielectric response of SrTiO<Subscript>3</Subscript>–SrMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript> solid solutions in the terahertz–infrared range

The reflection and transmission spectra of ceramic samples of SrTiO₃–SrMg_1/3Nb_2/3O₃ solid solutions have been measured in the frequency range of 5–5000 cm^–1 and in the temperature range of 5–370 K. Based on these spectra, the spectra of the real ε'(ν) and imaginary ε''(ν) parts of the complex permittivity ε*(ν) have been simulated by the method of dispersion analysis. It has been found that the temperature evolution of the dielectric constant is entirely determined by the behavior of the soft mode.     

Polarized Infrared and Raman Spectra and Ab-initio Calculations of Benzotriazole

Abstract

The i. r. spectra of benzotriazole have been measured from 4000 to 60 cm^?1: polarized spectra of single crystals have been also obtained. The Raman spectra of polycrystalline samples and solutions have been investigated. The structural parameters and vibrational frequencies have been determined from ab-initio Hartree-Fock gradient calculations using the 6–31G* basis set. A detailed arsignment of most of the observed bands has been proposed on the basis of the i. r. dichroism, Raman polarization data and frequency calculations.

     

Investigation of the structure and luminescence properties of CdF2-CaF2 : Eu superlattices on Si(111)

A complex investigation of CdF₂-CaF₂ : Eu superlattices with different bilayer thicknesses (2.0–17.5 nm) grown by molecular beam epitaxy on Si(111) has been carried out. The structural perfection of the layers and interfaces of the superlattices have been estimated from the X-ray diffractometry and reflectometry data. The possibility of producing short-period pseudomorphic superlattices with a period of approximately 2 nm has been established. It has been shown that these superlattices are characterized by a larger root-mean-square roughness amplitude of the interfaces as compared to the long-period superlattices. The specific features of cathodoluminescence spectra have been analyzed as a function of the superlattice period. It has been revealed that, with a decrease in the superlattice period, the intrinsic luminescence intensity of fluorides increases in comparison with the intensity of the luminescence associated with the emission of Eu²⁺ impurity ions; in this case, several Eu³⁺ luminescence bands appear in the spectrum. The possibilities of electron probe microanalysis for determining the ratio of thicknesses of individual layers in short-period superlattices have been demonstrated.     

Infrared reflection spectra of the one-dimensional ionic conductor K— and RbAl priderites

The reflection spectra of the one-dimensional ionic conductors K_1.6Al_1.6Ti_6.4O₁₆ and Rb_1.49Al_1.65Ti_6.35O_15.92 have been measured for the polarizations E ∥ c (channel direction) and E 6 c in the frequency region 60–2000 cm^-1. The spectra of these two compounds are very similar with their features and have the same number of bands. The vibrational mode frequencies are obtained from a Kramers-Kronig analysis for each polarized reflectivity spectrum. A comparison of the corresponding mode frequencies for both priderites shows that only the lowest frequency mode observed in the E 6 c spectra is strongly associated with the alkali ion, while the others are not. The effect due to the non-stoichiometry is not found in the infrared reflection spectra.     

Raman Spectra of <Emphasis Type="Italic">n</Emphasis>-Butane,Isobutane, <Emphasis Type="Italic">n</Emphasis>-Pentane,and Isopentane in a Methane Environment

We have studied the particular features of the Raman spectra of gaseous n-butane, isobutane, n-pentane, and isopentane in a methane medium at a pressure of 25 atm. It has been found that, under these conditions, changes in the conformational equilibria of these molecules are negligible, and most significant changes in the spectra are observed in the range of 2850–3000 cm^–1, in which bands corresponding to the stretching vibrations of CH₂ and CH₃ groups shift to lower frequencies. The data obtained will be usefull in determining the composition of natural gas using Raman spectroscopy.     

Far infrared absorption of amorphous GaAs and Ge

Far infrared reflection spectra of amorphous GaAs and Ge have been obtained in the frequency region from 30–600 cm^?1. For each material, curves of ω?₂ vs frequency have been obtained whose corresponding reflectivity curves give a best fit to the data. The peak value of the abdorption coefficient is about 4000 cm^?1 for GaAs and 160 cm^?1 for Ge. The results are compared with Raman spectra and with theoretical calculations.     

Gamma ray interactions with MoO3-doped lead phosphate glasses

The UV–Visible, Fourier transform infrared (FTIR) and Raman and electron spin resonance (ESR) spectra of undoped lead phosphate and MoO₃-doped glassy samples have been investigated. The UV–VIS absorption spectra were re-measured after successive gamma irradiation. Before irradiation, undoped sample exhibited strong ultraviolet absorption, which was attributed to co-absorption due to trace iron impurities (mainly Fe³⁺ ions) and lead Pb²⁺ ions. With the introduction of MoO₃ in progressive amounts, extra visible bands were recorded at about 400–440, 540, 750 and 870?nm. These bands are most likely correlated with the presence of Mo³⁺, Mo⁴⁺ and Mo⁵⁺ ions in the host glass. In the undoped specimen, gamma irradiation produced UV absorption bands that increased slightly with irradiation but no visible bands were recorded. Samples containing high MoO₃ content showed some resistance to irradiation with no bands in the visible region being observed. FTIR absorption spectra of the undoped and MoO₃-doped samples revealed the formation of metaphosphate and pyrophosphate structural units. Highly MoO₃-doped samples exhibited additional bands due to molybdate groups. Raman and ESR spectra were in agreement with UV–VIS and IR data, indicating the presence of molybdenum ions in lead phosphate glass, as Mo³⁺, Mo⁴⁺ and Mo⁶⁺ with different ratios. However, such glassy systems favor the trivalent species.     

基于支持向量机的假酒近红外光谱识别分类研究

一般的检测假酒中甲醇的化学方法虽然结果较准确,但操作复杂、费用昂贵且对实验的环境条件要求严格.为此,提出了一种基于支持向量机对掺甲醇的假酒光谱进行识别与分类的方法.采用ASD FieldSpec 3光谱仪测量了样品溶液的反射光谱;通过对反射光谱进行平滑、导数等预处理并进行相关性分析和单变量回归分析,得出假酒中甲醇光谱不被乙醇光谱掩盖的特征峰作为特征谱带;最后用特征谱带训练分类模型并得到分类结果.结果表明:以甲醇含量小于等于3%为真酒的总体分类准确度为85%,以甲醇含量小于等于5%为真酒的总体分类准确度为97.5%;证明该方法是可行的且具有较高的分类准确度.     

CdxHg1-xTe混晶的远红外反射光谱和多振子模型

在温度4.2—300K和波数15—450cm^-1范围内研究了x=0.18到0.45的不同组份的Cd_xHg_1-xTe样品的远红外反射光谱。实验观察到了类CdTe光学声子反射带的精细结构和低组份样品类HgTe反射带的复杂结构,研究了这些结构对组份和温度的关系,并用多振子模型讨论了反射光谱的这种精细结构。对实验反射光谱用经典的振子匹配方法进行了拟合计算,并从这种拟合运算获得了Cd_(x^-)Hg_1-xTe的远红外介电函数谱及其它光学常数和频率的关系。 关键词：     

Infrared absorption spectra of polyarylenealkyl compounds. Polychlorophenyleneethyl

The absorption spectra of polychlorophenyleneethyl have been obtained and interpreted over the range 680–3100 cm^?1. The type of substitution in the monomer unit of the polymer has been established by examining a number of spectral regions, and its structural formula is given. A number of bands have been assigned to definite types of vibrations.     

Thin film polymer photonics: Spin cast distributed Bragg reflectors and chirped polymer structures

Polymer based photonic structures were produced by spin coating up to 50 alternating layers of polystyrene (PS) and poly(vinylpyrrolidone) (PVP) from mutually exclusive (orthogonal) solvents. The resulting thin film multi-layer structures were studied using a simple optical reflectivity apparatus and were shown to have narrow (10-20nm wide) reflectance bands in the visible region. The position of the reflectance bands was controlled by varying the spin speed used during production of the multi-layers and peak reflectance values of 55% were obtained for samples containing 50 layers. The results were shown to be in agreement with modified optical transfer matrix method calculations which include the effects of diffuse polymer interfaces. This modelling approach revealed that the width of the polymer/polymer interfaces formed by spin coating was in the range 15-20nm. Data and calculations were also obtained for chirped polymer photonic structures. These results were also shown to be in good agreement. These experiments demonstrate that simple processing methods such as spin coating can be used to produce organic photonic structures with tailored optical properties.     

Infrared reflectivity and Raman scattering of lithium oxide single crystals

Infrared reflection and Raman spectra of single crystals of lithium oxide have been measured at room temperature. The reflection spectra have been analyzed by means of a fit with a classical dispersion formula. The result gives the frequencies of the fundamental transverse and longitudinal optical modes as 425 and 737 cm^?1, respectively. The frequency of the Raman active fundamental mode is also established at 523 cm^?1. From these frequencies an effective charge of lithium ion and effective force constants are obtained on the basis of lattice dynamical models.     

Luminescence spectra of lead-doped NaCl,KCl and KBr

The luminescence spectra of lead-doped NaCl, KCl and KBr have been systematically investigated. Special attention has been paid to the effects of concentration and thermal history of the crystals. In the three systems, the emission spectra for A and C band excitation consists mainly of two well-defined emission bands whose energy separation is ～0.7 eV. It has been concluded that none of the bands can be attributed to a single type of lead center but are both typical of Pb²⁺ luminescence. In fact, their behavior can be correlated with that found for most monovalent ions and interpreted in a similar way. The excitation spectra for the two emissions have shown that the A-band is complex. One of the components appearing in very low doped and quenched samples is ascribed to dipoles, whereas additional side bands are attributed to complexes or small aggregates involving Pb²⁺ ions.     

Intracavity Electronic Absorption Spectra of MoO and WO Molecules in the Visible Region

Absorption electronic spectra of MoO and WO molecules have been investigated by a intracavity laser technique in the region 550–800 run. New features have been discovered.

As for MoO molecule the rotational analysis of the four bands have been carried out for the first time. Two of these bands were referred to 0–0 transitions arisen from the new (probable triplet) low-lying electronic state, two other bands were referred to transitions arisen from excited components of X⁵II ground state.

As for WO molecule the rotational analysis of 0–0 and 1–0 bands represented A-X and B-X systems have been carried out for the first time. The new band has been discovered which has been referred to new electronic transition.

Molecular constants of new states of both molecules studied have been evaluated.     

Optical and Structural Modifications in Heavy Ion Irradiated Polystyrene

Samples of polystyrene (PS) have been irradiated with ⁶⁴Cu (50 and 120 MeV) and ¹²C (70 MeV) ion beams (fluence=10¹¹ to 10¹³ ions cm^?2) in order to study the induced modifications using UV‐VIS and FTIR spectroscopy. UV spectra of irradiated samples reveal that the optical band gap decreases from 4.36 to 1.46 eV in PS. The decrease in optical band gap is more pronounced with the Cu‐ion beam due to high electronic energy loss as compared to the C ion beam. The effect of low energy (50 MeV) Cu ions on the optical properties of PS is larger than that due to high energy (120 MeV) Cu ions. The correlation between the optical band gap and the number of six member carbon rings inside the largest carbon clusters embedded in the network of polystyrene is discussed. FTIR spectra reveal the formation of hydroxyl, alkene, and alkyne groups in the Cu‐ion irradiated PS. Changes in the intensity of the absorption bands on irradiation with C‐ion relative to pristine samples have also been observed and are discussed.     

Polarized Infrared and Raman Spectra and Ab-Initio Calculations of 2-(Methylthio)Benzothiazole

Abstract

The infrared spectra of 2-(methylthio)benzothiazole have been measured from 4000 to 180 cm^?1 for liquid and polycrystalline samples, polarized spectra of oriented films have also been obtained. the Raman spectra of polycrystalline and liquid samples have been investigated. the structural parameters, energies and vibrational frequencies have been calculated from ab-initio RHF calculations using the 6-31G?? basis set for various conformations. a detailed assignment of most of the observed bands has been proposed on the basis of the infrared dichroism, Raman polarization data and frequency calculations.     

Luminescence spectroscopy of Eu3+ and Mn2+ ions in MgGa2O4 spinel

Photoluminescence and excitation spectra of the spinel-type MgGa₂O₄ with 0.5 mol. % Mn²⁺ ions and Eu³⁺ content from 0 to 8 mol. % have been investigated in this work at room temperature. Polycrystalline samples were synthesized via high-temperature solid-state reaction method. Photoluminescence spectra of all samples exhibit host emission presented by a broad “blue” band peaking ∼430 nm, which consists of at least three elementary bands that correspond to different host defects. Excitation of the host luminescence showed the broad band with a maximum at 360 nm. Characteristic bands of d–d transitions of Mn²⁺ ions and f–f transitions of Eu³⁺ ions together with charge-transfer bands (CTB) of these ions were also found on the excitation spectra. Mn²⁺ and Eu³⁺ co-doped samples emit in green and red spectral regions. Mn²⁺ ions are responsible for the green emission band at 505 nm (⁴Т₁→⁶А₁ transition). The studies of photoluminescence spectra of activated samples with different Eu³⁺ ions content show characteristic f–f luminesecence of Eu³⁺ ions. The maximum of Eu³⁺ emission was found at 618 nm (⁵D₀→⁷F₂) and optimal concentration of activator ions was around 4 mol. %.