Structure, stability, depolarized light scattering, and vibrational spectra of fullerenols from all-electron density-functional-theory calculations

We have investigated the stability, electronic properties, Rayleigh (elastic), and Raman (inelastic) depolarization ratios, infrared and Raman absorption vibrational spectra of fullerenols [C(60)(OH)(n)] with different degrees of hydroxylation by using all-electron density-functional-theory (DFT) methods. Stable arrangements of these molecules were found by means of full geometry optimizations using Becke's three-parameter exchange functional with the Lee, Yang, and Parr correlation functional. This DFT level has been combined with the 6-31G(d,p) Gaussian-type basis set, as a compromise between accuracy and capability to treat highly hydroxylated fullerenes, e.g., C(60)(OH)(36). Thus, the molecular properties of fullerenols were systematically analyzed for structures with n=1, 2, 3, 4, 8, 10, 16, 18, 24, 32, and 36. From the electronic structure analysis of these molecules, we have evidenced an important effect related to the weak chemical reactivity of a possible C(60)(OH)(24) isomer. To investigate Raman scattering and the vibrational spectra of the different fullerenols, frequency calculations are carried out within the harmonic approximation. In this case a systematic study is only performed for n=1-4, 8, 10, 16, 18, and 24. Our results give good agreements with the expected changes in the spectral absorptions due to the hydroxylation of fullerenes.

Raman microprobe characterization of electrodeposited S-rich CuIn(S,Se)2 for photovoltaic applications: Microstructural analysis

This article reports a detailed Raman scattering and microstructural characterization of S-rich CuIn(S,Se)2 absorbers produced by electrodeposition of nanocrystalline CuInSe2 precursors and subsequent reactive annealing under sulfurizing conditions. Surface and in-depth resolved Raman microprobe measurements have been correlated with the analysis of the layers by optical and scanning electron microscopy, x-ray diffraction, and in-depth Auger electron spectroscopy. This has allowed corroboration of the high crystalline quality of the sulfurized layers. The sulfurizing conditions used also lead to the formation of a relatively thick MoS2 intermediate layer between the absorber and the Mo back contact. The analysis of the absorbers has also allowed identification of the presence of In-rich secondary phases, which are likely related to the coexistence in the electrodeposited precursors of ordered vacancy compound domains with the main chalcopyrite phase, in spite of the Cu-rich conditions used in the growth. This points out the higher complexity of the electrodeposition and sulfurization processes in relation to those based in vacuum deposition techniques.

Raman microstructural analysis of silicon-on-insulator formed by high dose oxygen ion implantation: As-implanted structures

A microstructural analysis of silicon-on-insulator samples obtained by high dose oxygen ion implantation was performed by Raman scattering. The samples analyzed were obtained under different conditions thus leading to different concentrations of defects in the top Si layer. The samples were implanted with the surface covered with SiO2 capping layers of different thicknesses. The spectra measured from the as-implanted samples were fitted to a correlation length model taking into account the possible presence of stress effects in the spectra. This allowed quantification of both disorder effects, which are determined by structural defects, and residual stress in the top Si layer before annealing. These data were correlated to the density of dislocations remaining in the layer after annealing. The analysis performed corroborates the existence of two mechanisms that generate defects in the top Si layer that are related to surface conditions during implantation and the proximity of the top Si/buried oxide layer interface to the surface before annealing.

Polymorphous Si thin films from radio frequency plasmas of SiH4 diluted in Ar: A study by transmission electron microscopy and Raman spectroscopy

In this study, we present a detailed structural characterization by means of transmission electron microscopy and Raman spectroscopy of polymorphous silicon (pm-Si:H) thin films deposited using radio-frequency dust-forming plasmas of SiH4 diluted in Ar. Square-wave modulation of the plasma and gas temperature was varied to obtain films with different nanostructures. Transmission electron microscopy and electron diffraction have shown the presence of Si crystallites of around 2 nm in the pm-Si:H films, which are related to the nanoparticles formed in the plasma gas phase coming from their different growth stages, named particle nucleation and coagulation. Raman scattering has proved the role of the film nanostructure in the crystallization process induced ¿in situ¿ by laser heating.

Uma Demonstração Sobre o Espalhamento Inelástico de Luz: Repetindo o Experimento de Raman

An adaptation of the Raman experiment is presented as a very convenient, simple and easily made demonstration about inelastic light scattering. The procedure involves an overhead projector, a rectangular and transparent cell, complementary filters and solvent. Alternatively a spectrofluorimeter can he used to evaluate how weak Raman scattering is.

Cálculo ab initio de intensidades Raman dinâmicas utilizando a teoria da resposta linear

In this paper a methodology for the computation of Raman scattering cross-sections and depolarization ratios within the Placzek Polarizability Theory is described. The polarizability gradients are derived from the values of the dynamic polarizabilities computed at the excitation frequencies using ab initio Linear Response Theory. A sample application of the computational program, at the HF, MP2 and CCSD levels of theory, is presented for H2O and NH3. The results show that high correlated levels of theory are needed to achieve good agreement with experimental data.

Efeito do tratamento térmico na microestrutura, turbostraticidade e superfície de carbono vítreo reticulado analisado por XPS, espalhamento Raman e voltametria cíclica

The structural and surface properties of reticulated vitreous carbon (RVC) were discussed as a function of its heat treatment temperature (HTT), for samples produced in the range from 700 to 2000 ºC, using the furfuryl precursor resin. The samples were analyzed by x-ray photoelectron spectroscopy, first and second order Raman scattering as well as electrochemical response. Exploring the material turbostraticity concept, the interdependence between the RVC chemical surface variation and its defects were demonstrated. The influence of heteroatom presence was discussed in the material ordering for HTT lower than 1300 ºC while the graphitization process evolution was also pointed out for HTT higher than 1500 ºC.

Two-dimensional atom localization and Raman cooling of tripod-type atoms

Both atom localization and Raman cooling, considered in the thesis, reflect recent progress in the area of all-optical methods. We focus on twodimensional (2D) case, using a four-level tripod-type atomic scheme for atom localization within the optical half-wavelength as well as for efficient subrecoil Raman cooling. In the first part, we discuss the principles of 1D atom localization, accompanying by an example of the measurement of a spontaneously-emitted photon. Modifying this example, one archives sub-wavelength localization of a three-level -type atom, measuring the population in its upper state. We go further and obtain 2D sub-wavelength localization for a four-level tripod-type atom. The upper-state population is classified according to the spatial distribution, which in turn forms such structures as spikes, craters and waves. The second part of the thesis is devoted to Raman cooling. The cooling process is controlled by a sequence of velocity-selective transfers from one to another ground state. So far, 1D deep subrecoil cooling has been carried out with the sequence of square or Blackman pulses, applied to -type atoms. In turn, we discuss the transfer of atoms by stimulated Raman adiabatic passage (STIRAP), which provides robustness against the pulse duration if the cooling time is not in any critical role. A tripod-type atomic scheme is used for the purpose of 2D Raman cooling, allowing one to increase the efficiency and simplify the realization of the cooling.

Détection de protéines par diffusion Raman exaltée par effet de pointe (TERS)

La concentration locale des messagers chimiques sécrétés par les cellules peut être mesurée afin de mieux comprendre les mécanismes moléculaires liés à diverses maladies, dont les métastases du cancer. De nouvelles techniques analytiques sont requises pour effectuer ces mesures locales de marqueurs biologiques à proximité des cellules. Ce mémoire présentera le développement d’une nouvelle technique basée sur la réponse plasmonique sur des leviers AFM, permettant d’étudier les réactions chimiques et biologiques à la surface des leviers grâce au phénomène de résonance des plasmons de surface (SPR), ainsi qu’à la diffusion Raman exaltée par effet de pointe (TERS). En effet, il est possible de localiser l’amplification du signal Raman à la pointe d’un levier AFM, tout comme le principe de la diffusion Raman exaltée par effet de surface (SERS) basée sur la diffusion de la lumière par des nanoparticules métalliques, et permettant une large amplification du signal Raman. La surface du levier est recouverte d’une nano-couche métallique d’or, suivi par des réactions biologiques pour l’immobilisation d’un récepteur moléculaire, créant ainsi un biocapteur sur la pointe du levier. Une détection secondaire utilisant des nanoparticules d’or conjuguées à un anticorps secondaire permet également une amplification du signal SPR et Raman lors de la détection d’antigène. Ce mémoire démontrera le développement et la validation de la détection de l’immunoglobuline G (IgG) sur la pointe du levier AFM.Dans des projets futurs, cette nouvelle technique d’instrumentation et d’imagerie sera optimisée grâce à la création d’un micro-détecteur protéique généralement adapté pour l’étude de la communication cellulaire. En intégrant le signal SPR à la microscopie AFM, il sera alors possible de développer des biocapteurs SPR couplés à une sonde à balayage, ce qui permettra d’effectuer une analyse topographique et de l’environnement chimique d’échantillons cellulaires en temps réel, pour la mesure des messagers moléculaires sécrétés dans la matrice extracellulaire, lors de la communication cellulaire.

Micro Far-Infrared Reflectivity of CaNb(2)O(6) Single Crystal Fibers Grown by the Laser-Heated Pedestal Growth Technique

CaNb(2)O(6) single crystal fibers were grown by the laser-heated pedestal growth technique, directly from the starting reagents. Optically transparent fibers were obtained in the form of rods with elliptical cross-section, free from cracks, impurities, and secondary phases, with an average diameter of 0.4 mm and about 20 mm of length. The fibers grew within the orthorhombic Pbcn columbite structure, with the growth axis nearly parallel to the crystallographic a-direction. The parameters b and c were parallel to the shorter and larger ellipsis axes. A special setup using a microscope was developed to obtain the far-infrared reflectivity spectra of these micrometer-sized fibers, allowing the identification and assignment of 34 of the 38 polar phonons foreseen for the material. From these phonons, the intrinsic dielectric constant ( = 18.2) and quality factor ( of 185 THz) could be estimated, showing the potential of the material for applications in microwave circuitry. These results, along with previous polarized Raman data (Cryst. Growth Des. 2010, 10, 1569), allow us to present a comprehensive set of optical phonon modes and to discuss the potential use of designed CaNb(2)O(6) microcrystals in compact optical devices.

Studies on the resonance Raman spectra of polyaniline obtained with near-IR excitation

The effects of near-IR (NIR) laser power over the Raman spectra of poly(aniline) emeraldine salt (PANIES) and base (PANI-EB) were investigated. The reasons for the existence of several bands from 1324 to 1500 cm-1 in the Raman spectra of poly(aniline) obtained at NIR region were also studied. The bands from 1324 to 1375 cm-` were associated to vC-N of polarons with different conjugation lengths and the bands from 1450 to 1500 cm-1 in Raman spectra of PANI emeraldine and pernigraniline base forms were correlated to vC=N modes associated with quinoid units having different conjugation lengths. The increase of laser power at 1064.0 run causes the deprotonation of PANI-ES and the formation of cross-linking segments having phenazine and/or oxazine rings. For PANI-EB only a small spectral change is observed when the laser power is increased, owing to the low absorption of this form in the NIR region. Copyright (c) 2007 John Wiley & Sons, Ltd.

FT-Raman, FTIR and density functional theory studies of a hydrogen-bonded formamide: pyridine complex

Raman and IR experiments have been carried out on formamide (FA) and pyridine (Py) mixtures at different compositions. The appearance of a new Raman band at 996 cm(-1) (nu(1) region of Py), whose intensity depends on the FA concentration, is assigned to an FA: Py adduct and this result is in excellent agreement with those of other authors who employed noisy light-based coherent Raman scattering spectroscopy (I((2)) CARS). Another band at 1587 cm(-1) (nu(8) region of Py) has been observed for the first time by using Raman and IR spectroscopies. Its intensity shows the same dependence on the FA concentration and this fact allows us to also attribute it to an FA: Py adduct. The good relationship between the Raman and IR data demonstrates the potential of the vibrational spectroscopy for this kind of study. Owing to higher absolute Raman scattering cross section, the nu(1) region of Py has been chosen for the quantitative analysis and a stoichiometry of 1 : 1 FA: Py is reported. The experimental data are very well supported by the density functional theory (OFT) calculation, which was employed for the first time to the present system. Furthermore, the actual investigation shows an excellent agreement with those reported from computational calculations for similar systems. A comparison with our previous studies confirms that: the solvent dielectric constant determines the stoichiometry of a given Lewis acid-base adduct in the infinite dilution limit. Copyright (C) 2009 John Wiley & Sons, Ltd.

Investigation in SrTiO3-CaTiO3-PbTiO3 ternary thin films by dielectric proprieties and Raman spectroscopy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Resonant excitation of Mn local vibrational modes in the higher order Raman spectra of nanocrystalline Ga(1-x)Mn(x)N films

The effect of manganese on the vibrational properties of Ga(1-x)Mn(x)N (0 <= x <= 0.18) films has been investigated by Raman scattering using 488.0 and 632.8 nm photon excitations. The first-order transverse and longitudinal optical GaN vibrational bands were observed in the whole composition range using both excitations, while the corresponding overtones, as well as a prominent peak located in 1238 cm(-1) (153.5 meV) were only observed in the Mn-containing films under 488.0 nm excitation. We propose that the peak observed at 1238 cm(-1) is due to resonant Mn local vibrational modes, the excitation process being related to electronic transitions involving the Mn acceptor band.

Diagnosis of inflammatory lesions by high-wavenumber FT-Raman spectroscopy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)