Resonant Raman spectroscopic study of biphenyl glutarate diacetylene polymer

The resonantly enhanced Raman spectra of biphenyl glutarate diacetylene polymer chains in fully radiation polymerized and partially thermally polymerized samples are reported. Details of the resonant enhancement in the region of the polymer electronic absorption were studied in partially polymerized samples. The role of defects in producing fluorescent emission and in broadening the optical absorption for radiation polymerized samples is briefly discussed.     

Raman spectroscopic study on boron-doped silicon nanoparticles

Raman analyses were performed on thin films prepared from B-doped Si nanoparticles with an average diameter of 15 nm using the spin-coating method. The resulting spectrum exhibited a broad band with a peak near 520 cm⁻¹. The band was decomposed into three bands corresponding to the crystalline, grain boundary (GB), and amorphous regions by the least-squares band-fitting method based on the three Voigt bands. The fractions of the crystalline, GB, and amorphous regions were 37%, 35%, and 28%, respectively. A spherical particle exhibited an ordered crystalline core surrounded by a disordered shell in a transmission electron microscope (TEM) image. The crystalline fraction of the 15-nm B-doped Si nanoparticle film was much lower than that of the 19-nm P-doped Si nanoparticle film. This result suggested that the B-doping mechanism was different from that of P-doping. The temperature of the sample was estimated from the ratio of the peak intensities of anti-Stokes to Stokes Raman bands (I^AS/I^S) observed near 520 cm⁻¹. The temperature of the B-doped Si nanoparticle film upon irradiation at a power density of 4.6 kW/cm² was 298 °C, whereas the temperature of the P-doped Si nanoparticle film was 92 °C. The B-doped Si nanoparticle films were capable of producing light-induced heat.     

Raman spectroscopic study of bacterial endospores

Endospores and endospore-forming bacteria were studied by Raman spectroscopy. Raman spectra were recorded from Bacillus licheniformis LMG 7634 at different steps during growth and spore formation, and from spore suspensions obtained from diverse Bacillus and Paenibacillus strains cultured in different conditions (growth media, temperature, peroxide treatment). Raman bands of calcium dipicolinate and amino acids such as phenylalanine and tyrosine are more intense in the spectra of sporulating bacteria compared with those of bacteria from earlier phases of growth. Raman spectroscopy can thus be used to detect sporulation of cells by a characteristic band at 1,018 cm^–1 from calcium dipicolinate. The increase in amino acids could possibly be explained by the formation of small acid-soluble proteins that saturate the endospore DNA. Large variations in Raman spectra of endospore suspensions of different strains or different culturing conditions were observed. Next to calcium dipicolinate, tyrosine and phenylalanine, band differences at 527 and 638 cm^–1 were observed in the spectra of some of the B. sporothermodurans spore suspensions. These bands were assigned to the incorporation of cysteine residues in spore coat proteins. In conclusion, Raman spectroscopy is a fast technique to provide useful information about several spore components. Figure A difference spectrum between Raman spectra of B. licheniformis LMG 7634 cultured for 6 days and 1 day, together with the reference Raman spectrum of calcium dipicolinate     

Low frequency polarization of ferroelectric liquid crystals

The possibility of the separation of free charge carriers in ferroelectric liquid crystals has been investigated in terms of the kinetic equation for the charge density. The non-uniformity of the charge distribution leads to an additional term in the free energy of the system, which can be essential for low-frequency external fields. The corresponding correction to the dielectric response of the system is proportional to the spontaneous polarization of the sample and thus has an anomalous temperature dependence near the phase transition.     

Raman spectroscopic study on classification of cervical cell specimens

Cervix-cancer is the third most common female cancer worldwide. Papanicolaou (Pap) test, a well-recognized screening tool, is labor intensive, time consuming and prone to subjective interpretations. Optical spectroscopic methods, sensitive to molecular changes are being pursued as potential diagnostics tool. In this study we have explored Raman spectroscopic approach to differentiate exfoliated cell pellets using 94 cervical cell specimens (45-normal and 49-abnormal specimens). Study was carried out by two approaches. In the first approach, spectral data from 37 cell specimens were acquired and analyzed by Principal Component-Linear Discriminant Analysis (PC-LDA), which yielded classification efficiencies of 86% and 84% for normal and abnormal specimens, respectively. Mean and difference spectra suggest presence of blood in abnormal specimen as a major cause of discrimination. However, as tumor is vascular, bleeding was observed during abnormal sample collection. Hence, spectra of abnormal specimens show heme and fibrin features, and this can lead to false interpretations, as bleeding also occur in several non-cancerous conditions. Therefore, remaining 57 specimens were treated with Red Blood Corpuscles (RBC) lysis buffer in order to remove the RBC influence. PC-LDA resulted classification efficiency of about 79% and 78% for normal and abnormal smear, respectively – comparable to Pap test. Thus finding of the study suggests feasibility of Raman spectroscopic classification of normal and cancerous exfoliated cervical cell specimens.     

Low frequency dielectric spectroscopy on mixtures containing ferroelectric liquid crystals

Abstract

Dielectric spectroscopy (frequency range 10 ^?1 Hz to 10⁵ Hz, temperature range 300 K to 370 K) was employed to investigate the Goldstone mode in ferroelectric liquid-crystalline mixtures of chiral and achiral compounds. While the spontaneous polarization decreases with increasing fraction of the achiral molecules the Goldstone mode remains constant in its oscillatory strength. As expected the Goldstone mode frequency shifts to lower values with increasing amount of achiral molecules in the ferroelectric liquid-crystalline mixture.     

Low frequency dielectric spectroscopy on mixtures containing ferroelectric liquid crystals

Dielectric spectroscopy (frequency range 10 ^-1 Hz to 10⁵ Hz, temperature range 300 K to 370 K) was employed to investigate the Goldstone mode in ferroelectric liquid-crystalline mixtures of chiral and achiral compounds. While the spontaneous polarization decreases with increasing fraction of the achiral molecules the Goldstone mode remains constant in its oscillatory strength. As expected the Goldstone mode frequency shifts to lower values with increasing amount of achiral molecules in the ferroelectric liquid-crystalline mixture.     

Raman spectroscopic study of vanadium oxide nanotubes

Raman-scattering measurements have been used to study the microstructure of vanadium oxide nanotubes (VO_x-NTs). The Raman spectra of VO_x-NTs reflect the various (group) vibrations of V-O type and lattice vibration of the layered structure as well as organic group vibration of the residual organic template. Moreover, it is confirmed that the residual organic template can be removed by irradiation of laser under the preservation of the tubular morphology, which provides the possibility for favoring the scaling-up of removing the residual organic template in the structure of VO_x-NTs.     

Raman spectroscopic study of mixed carbonate materials

The main parameters for precipitation of mixed carbonate materials have been studied by Raman microscopy. These carbonates are compounds of barium, strontium and calcium. It has been shown that the Raman spectrum of a sample is exclusively controlled by its composition, the precipitation parameters do not affect the crystal structure. Even at relatively low levels, the calcium content of a sample can dominate the vibrational frequencies as measured by Raman spectroscopy. Calcium contents greater than 17% show this effect to a considerable degree, and give the broadest or two Raman peaks and thus the least uniform unit cells. The analysis of the lattice modes demonstrates that each Raman shift observed for a mixed carbonate sample corresponds to a specific crystal structure. Some peaks lie within two or three shifts that are observed for different crystal structures.     

A Raman spectroscopic study of synthetic giniite

The mineral giniite has been synthesised and characterised by XRD, SEM and Raman and infrared spectroscopy. SEM images of the olive-green giniite display a very unusual image of pseudo-spheres with roughened surfaces of around 1-10microm in size. The face to face contact of the spheres suggests that the spheres are colloidal and carry a surface charge. Raman spectroscopy proves the (PO4)3- units are reduced in symmetry and in all probability more than one type of phosphate unit is found in the structure. Raman bands at 77K are observed at 3380 and 3186cm-1 with an additional sharp band at 3100cm-1. The first two bands are assigned to water stretching vibrations and the latter to an OH stretching band. Intense Raman bands observed at 396, 346 and 234cm-1are attributed to the FeO stretching vibrations. The giniite phosphate units are characterised by two Raman bands at 1023 and 948cm-1 assigned to symmetric stretching mode of the (PO4)3- units. A complex band is observed at 460.5cm-1 with additional components at 486.8 and 445.7cm-1 attributed to the nu(2) bending modes suggesting a reduction of symmetry of the (PO4)3- units.     

The intermediate frequency modes of single- and double-walled carbon nanotubes: a Raman spectroscopic and in situ Raman spectroelectrochemical study

The intermediate frequency modes (IFM) of single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs) were analyzed by Raman spectroscopy and in situ Raman spectroelectrochemistry. The inner and outer tubes of DWCNTs manifested themselves as distinct bands in the IFM region. This confirmed the diameter dependence of IFM frequencies. Furthermore, the analysis of inner tubes of DWCNTs allowed a more-precise assignment of the bands in the IFM region to features intrinsic for carbon nanotubes. Although the inner tubes in DWCNTs are assumed to be structurally perfect, the role of defects on IFM was discussed. The dependence of IFM on electrochemical charging was also studied. In situ spectroelectrochemical data provide a means to distinguish the bands of the outer and inner tubes.     

NMR spectroscopic study of phosphorus-containing polymer sorbent

The nature and distribution of functional groups in the polymer matrix, as well as the nature of the spatial network in the phosphorus-containing polymeric sorbent was studied by the method of NMR spectroscopy.     

澳大利亚烟煤热解的拉曼光谱研究

采用拉曼光谱考察了澳大利亚烟煤在常压、温度为298~1 473 K条件下,不同热解气氛(Ar和N2)下的热解性能。结合AD/Aall、AG/Aall、WG以及PG-PD等表征参数分析发现,澳大利亚烟煤的热解可以分为三个阶段:298~873 K为固有小分子和大分子键能较弱处断裂分解产生的小分子化合物的析出沉积和挥发;873~1 273 K为大分子化合物裂解挥发和炭化;1 273~1 473 K为焦炭的石墨化。在N2和Ar气氛经1 473 K热处理后,焦炭的不同杂化结构的碳相对含量呈现明显差异。不同保温时间下,其煤焦碳结构演变趋势相似,但保温时间越长,越有利于小分子挥发分在较低温度的挥发。     

A Raman spectroscopic study of photochromic benzothiazolium dyes

Resonance Raman spectra using several excitation wavelengths have been obtained in the region 300–1750 cm⁻¹ for two photochromic benzothiazolium dyes containing a crown ether ring. Bands arising from both cis- and trans-isomers have been distinguished by comparing the spectra observed at different resonances and under different sample conditions. Preliminary assignments of the bands have been made, allowing insight into the changes in structure and bonding which occur on photoisomerization.     

The pH dependent Raman spectroscopic study of caffeine

First of all the surface enhanced Raman spectroscopy (SERS) and normal Raman spectra of caffeine aqueous solution were obtained at different pH values. In order to obtain the detailed vibrational assignments of the Raman spectroscopy, the geometry of caffeine molecule was optimized by density functional theory (DFT) calculation. By comparing the SERS of caffeine with its normal spectra at different pH values; it is concluded that pH value can dramatically affect the SERS of caffeine, but barely affect the normal Raman spectrum of caffeine aqueous solution. It can essentially affect the reorientation of caffeine molecule to the Ag colloid surface, but cannot impact the vibration of functional groups and chemical bonds in caffeine molecule.     

Raman spectroscopic study of the rare earth sesquisulfides

Raman spectra have been measured on carefully synthesized and characterized sesquisulfides of the rare earth ions plus yttrium and scandium. Six structure-types are represented. The Raman spectra are diagnostic of the structure-types. Raman line widths indicate structural disorder only in the defect gamma-type structure. High wavenumber bands shift with ionic radius of the rare earths and only slightly with cation coordination number.     

A Raman spectroscopic study of N,N-dimethylacrylamide

A comprehensive Raman spectroscopic study of N,N-dimethylacrylamide has been carried out to produce new vibrational assignments for the molecule. The provision of polarization data for the first time has enabled the correction of several assignments for the normal modes previously reported in the literature to be made.     

Aurichalcite – An SEM and Raman spectroscopic study

Raman spectroscopy complimented with supplementary infrared spectroscopy has been used to characterise the vibrational spectrum of aurichalcite a zinc/copper hydroxy carbonate (Zn,Cu²⁺)₅(CO₃)₂(OH)₆. XRD patterns of all specimens show high orientation and indicate the presence of some impurities such as rosasite and hydrozincite. However, the diffraction patterns for all samples are well correlated to the standard reference patterns. SEM images show highly crystalline and ordered structures in the form of micron long fibres and plates. EDAX analyses indicate variations in chemical composition of Cu/Zn ratios ranging from 1/1.06 to 1/2.87. The symmetry of the carbonate anion in aurichalcite is C_s and is composition dependent. This symmetry reduction results in multiple bands in both the symmetric stretching and bending regions. The intense band at 1072 cm⁻¹ is assigned to the ν₁(CO₃)²⁻ symmetric stretching mode. Three Raman bands assigned to the ν₃(CO₃)²⁻ antisymmetric stretching modes are observed for aurichalcite at 1506, 1485 and 1337 cm⁻¹. Multiple Raman bands are observed in 800–850 cm⁻¹ and 720–750 cm⁻¹ regions and are attributed to ν₂ and ν₄ bending modes confirming the reduction of the carbonate anion symmetry in the aurichalcite structure. An intense Raman band at 1060 cm⁻¹ is attributed to the δ OH deformation mode.     

A Raman spectroscopic study of indolinium steryl dyes

Resonance Raman spectra have been obtained in the region 400–1700 cm⁻¹ for several indolinium steryl dyes under various experimental conditions. The changes in vibrational frequencies have been correlated with changes in the UV—vis absorption maxima observed previously and which are due to solvent polarity variations, the complexation of the dye molecules containing a crown ether ring with Mg²⁺, and the variations in molecular structure. Preliminary assignments of the observed bands to particular vibrations are made.     

A Raman spectroscopic study of selected natural jarosites

Raman spectroscopy has been used to characterise the jarosite group of minerals of formula Mn(Fe3+)6(SO4)4(OH)12 where M may be K, (NH4)+, Na, Ag or Pb and where n = 2 for monovalent cations and 1 for the divalent cations. Raman spectroscopy proved useful for mineral identification especially where closely related minerals crystallise out from solutions where paragenetic relationships exist between the minerals. The band position of the SO4(2-) symmetric stretching mode proved to be a function of the ionic radius of the cation. The bending modes show a slight dependence. The spectra of the natural samples can be complex. This complexity is attributed to the incorporation of low levels of other cations into the structure.