Structural refinement, growth process, photoluminescence and photocatalytic properties of (Ba1-xPr2x/3)WO4 crystals synthesized by the coprecipitation method

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

Nucleation and crystallization of titania nanoparticles in silica titania planar waveguides: A study by low frequency Raman scattering

SiO2 (1-x) - TiO2 (x) waveguides, with the mole fraction x in the range 0.07 - 0.20 and thickness of about 0.4 μm, were deposited on silica substrates by a dip-coating technique. The thermal treatments at 700-900°C, used to fully densify the xerogels, produce nucleation of TiO2 nanocrystals even for the lowest TiO2 content. The nucleation of TiO2 nanocrystals and their growth by thermal annealing up to 1300°C were studied by waveguide Raman spectroscopy, for the SiO2 (0.8) - TiO2 (0.2) composition. By increasing the annealing temperature, the Raman spectrum evolves from that typical of the silica-titania glass to that of anatase, but brookite phase is dominant at intermediate temperatures. In the low. frequency region (5-50 cm-1) of the Raman spectra, acoustic vibrations of the nanocrystals are observed. From the measured line shapes, we can deduce the size distribution of the particles. The results are compared with those obtained from the line widths in the X-ray diffraction patterns. Nanocrystals with a mean size in the range 4-20 nm are obtained, by thermal annealing in a corresponding range of 800-1300°C.

Release of Cyanopyridine from a Ruthenium Complex Adsorbed on Gold: Surface-Enhanced Raman Scattering, Electrochemistry, and Density Functional Theory Analyses

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

Analysis of experimental tendinitis in rats treated with laser and platelet-rich plasma therapies by Raman spectroscopy and histometry

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

Surface-enhanced Raman spectroscopy studies of organophosphorous model molecules and pesticides

This work reports the analytical application of surface-enhanced Raman spectroscopy (SERS) in the trace analysis of organophosphorous pesticides (trichlorfon and glyphosate) and model organophosphorous compounds (dimethyl methylphosphonate and o-ethyl methylphosphonothioate) bearing different functional groups. SERS measurements were carried out using Ag nanocubes with an edge square dimension of ca. 100 nm as substrates. Density functional theory (DFT) with the B3LYP functional was used for the optimization of ground state geometries and simulation of Raman spectra of the organophosphorous compounds and their silver complexes. Adsorption geometries and marker bands were identified for each of the investigated compound. Results indicate the usefulness of SERS methodology for the sensitive analyses of organophosphorous compounds through the use of vibrational spectroscopy.

Functionalization of gold and silver nanoparticles with diphenyl dichalcogenides probed by surface enhanced Raman scattering

This paper describes a surface-enhanced Raman scattering (SERS) systematic investigation regarding the functionalization of gold (Au) and silver (Ag) nanoparticles with diphenyl dichalcogenides, i.e. diphenyl disulfide, diphenyl diselenide, and diphenyl ditelluride. Our results showed that, in all cases, functionalization took place with the cleavage of the chalcogenchalcogen bond on the surface of the metal. According to our density functional theory calculations, the molecules assumed a tilted orientation with respect to the metal surface for both Au and Ag, in which the angle of the phenyl ring relative to the metallic surface decreased as the mass of the chalcogen atom increased. The detected differences in the ordinary Raman and SERS spectra were assigned to the distinct stretching frequencies of the carbonchalcogen bond and its relative contribution to the ring vibrational modes. In addition, the SERS spectra showed that there was no significant interaction between the phenyl ring and the surface, in agreement with the tilted orientation observed from our density functional theory calculations. The results described herein indicate that diphenyl dichalcogenides can be successfully employed as starting materials for the functionalization of Au nanoparticles with organosulfur, organoselenium, and organotellurium compounds. On the other hand, diphenyl disulfide and diphenyl diselenide could be employed for the functionalization of Ag nanoparticles, while the partial oxidation of the organotellurium unit could be detected on the Ag surface. Copyright (C) 2011 John Wiley & Sons, Ltd.

Structural refinement, growth process, photoluminescence and photocatalytic properties of (Ba1-xPr2x/3)WO4 crystals synthesized by the coprecipitation method

Barium praseodymium tungstate (Ba1-xPr2x/3)WO4 crystals with (x = 0, 0.01, and 0.02) were prepared by the coprecipitation method. These crystals were structurally characterized by X-ray diffraction (XRD), Rietveld refinements, Fourier-transform Raman (FT-Raman) and Fourier-transform infrared (FT-IR) spectroscopies. The shape and size of these crystals were observed by field emission scanning electron microcopy (FE-SEM). Their optical properties were investigated by ultraviolet visible (UV-vis) absorption and photoluminescence (PL) measurements. Moreover, we have studied the photocatalytic (PC) activity of crystals for degradation of rhodamine B (RhB) dye. XRD patterns, Rietveld refinements data, FT-Raman and FT-IR spectroscopies indicate that all crystals exhibit a tetragonal structure without deleterious phases. FT-Raman spectra exhibited 13 Raman-active modes in a range from 50 to 1000 cm(-1), while FT-IR spectra have 8 infrared active modes in a range from 200 to 1050 cm(-1). FE-SEM images showed different shapes (bonbon-, spindle-, rice-and flake-like) as well as a reduction in the crystal size with an increase in Pr3+ ions. A possible growth process was proposed for these crystals. UV-vis absorption measurements revealed a decrease in optical band gap values with an increase of Pr3+ into the matrix. An intense green PL emission was noted for (Ba1-xPr2x/3)WO4 crystals (x = 0), while crystals with (x = 0.01 and 0.02) produced a reduction in the wide band PL emission and the narrow band PL emission which is related to f-f transitions from Pr3+ ions. High photocatalytic efficiency was verified for the bonbon-like BaWO4 crystals as a catalyst in the degradation of the RhB dye after 25 min under UV-light. Finally, we discuss possible mechanisms for PL and PC properties of these crystals.

Internal characteristics, chemical compounds and spectroscopy of sapphire as single crystals

In this study more than 450 natural sapphire samples (most of basaltic type) collected from 19 different areas were examined. They are from Dak Nong, Dak Lak, Quy Chau, two unknown sources from the north (Vietnam); Bo Ploi, Khao Ploi Waen (Thailand); Ban Huay Sai (Laos); Australia; Shandong (China); Andapa, Antsirabe, Nosibe (Madagascar); Ballapana (Sri Lanka); Brazil; Russia; Colombia; Tansania and Malawi. rnThe samples were studied on internal characteristics, chemical compositions, Raman-, luminescence-, Fourier transform infrared (FTIR)-, and ultraviolet-visible-near infrared (UV-Vis-NIR)- spectroscopy. The internal features of these sapphire samples were observed and identified by gemological microscope, con focal micro Raman and FTIR spectroscopy. The major and minor elements of the samples were determined by electron probe microanalysis (EPMA) and the trace elements by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). rnThe structural spectra of sapphire were investigated by con focal Raman spectroscopy. The FTIR spectroscopy was used to study the vibration modes of OH-groups and also to determine hydrous mineral inclusions in sapphire. The UV-Vis-NIR absorption spectroscopy was used to analyze the cause of sapphire color. rnNatural sapphires contain many types of mineral inclusions. Typically, they are iron-containing inclusions like goethite, ilmenite, hematite, magnetite or silicate minerals commonly feldspar, and often observed in sapphires from Asia countries, like Dak Nong, Dak Lak in the south of Vietnam, Ban Huay Sai (Laos), Khao Ploi Waen and Bo Ploi (Thailand) or Shandong (China). Meanwhile, CO2-diaspore inclusions are normally found in sapphires from Tansania, Colombia, or the north of Vietnam like Quy Chau. rnIron is the most dominant element in sapphire, up to 1.95 wt.% Fe2O3 measured by EPMA and it affects spectral characteristics of sapphire.rnThe Raman spectra of sapphire contain seven peaks (2A1g + 5Eg). Two peaks at about 418.3 cm-1 and 577.7 cm-1 are influenced by high iron content. These two peaks shift towards smaller wavenumbers corresponding to increasing iron content. This shift is showed by two equations y(418.3)=418.29-0.53x andy(577.7)=577.96-0.75x, in which y is peak position (cm-1) and x is Fe2O3 content (wt.%). By exploiting two these equations one can estimate the Fe2O3 contents of sapphire or corundum by identifying the respective Raman peak positions. Determining the Fe2O3 content in sapphire can help to distinguish sapphires from different origins, e.g. magmatic and metamorphic sapphire. rnThe luminescence of sapphire is characterized by two R-lines: R1 at about 694 nm and R2 at about 692 nm. This characteristic is also influenced by high iron content. The peak positions of two R-lines shift towards to smaller wavelengths corresponding to increasing of iron content. This correlation is showed by two equations y(R_2 )=692.86-0.049x and y(R_1 )=694.29-0.047x, in which y is peak position (nm) of respective R-lines and x is Fe2O3 content (wt.%). Two these equations can be applied to estimate the Fe2O3 content of sapphire and help to separate sapphires from different origins. The luminescence is also applied for determination of the remnant pressure or stress around inclusions in Cr3+-containing corundum by calibrating a 0-pressure position in experimental techniques.rnThe infrared spectra show the presence of vibrations originating from OH-groups and hydrous mineral inclusions in the range of 2500-4000 cm-1. Iron has also an effect upon the main and strongest peak at about 3310 cm-1. The 3310 cm-1 peak is shifted to higher wavenumber when iron content increases. This relationship is expressed by the equation y(3310)=0.92x+3309.17, in which y is peak position of the 3310 cm-1 and x is Fe2O3 content (wt.%). Similar to the obtained results in Raman and luminescence spectra, this expression can be used to estimate the Fe2O3 content and separate sapphires from different origins. rnThe UV-Vis-NIR absorption spectra point out the strong and sharp peaks at about 377, 387, and 450 nm related to dispersed Fe3+, a broad band around 557 and 600 nm related to intervalence charge transfer (IVCT) Fe2+/Ti4+, and a broader band around 863 nm related to IVCT of Fe2+/Fe3+. rnGenerally, sapphires from different localities were completely investigated on internal features, chemical compounds, and solid spectral characteristics. The results in each part contribute for identifying the iron content and separate sapphires from different localities order origins. rn

Si and SixGe1-x NWs studied by Raman spectroscopy

Group IV nanostructures have attracted a great deal of attention because of their potential applications in optoelectronics and nanodevices. Raman spectroscopy has been extensively used to characterize nanostructures since it provides non destructive information about their size, by the adequate modeling of the phonon confinement effect. The Raman spectrum is also sensitive to other factors, as stress and temperature, which can mix with the size effects borrowing the interpretation of the Raman spectrum. We present herein an analysis of the Raman spectra obtained for Si and SiGe nanowires; the influence of the excitation conditions and the heat dissipation media are discussed in order to optimize the experimental conditions for reliable spectra acquisition and interpretation.

Interaction between a laser beam and semiconductor nanowires: application to the raman spectrum of Si nanowires

One presents in this work the study of the interaction between a focused laser beam and Si nanowires (NWs). The NWs heating induced by the laser beam is studied by solving the heat transfer equation by finite element methods (fem). This analysis permits to establish the temperature distribution inside the NW when it is excited by the laser beam. The overheating is dependent on the dimensions of the NW, both the diameter and the length. When performing optical characterization of the NWs using focused laser beams, one has to consider the temperature increase introduced by the laser beam. An important issue concerns the fact that the NWs diameter has subwavelength dimensions, and is also smaller than the focused laser beam. The analysis of the thermal behaviour of the NWs under the excitation with the laser beam permits the interpretation of the Raman spectra of Si NWs, where it is demonstrated that temperature induced by the laser beam play a major role in shaping the Raman spectrum of Si NWs

Detection and quantification of peanut traces in wheat flour by near infrared hyperspectral imaging spectroscopy using principal-component analysis

The use of a common environment for processing different powder foods in the industry has increased the risk of finding peanut traces in powder foods. The analytical methods commonly used for detection of peanut such as enzyme-linked immunosorbent assay (ELISA) and real-time polymerase chain reaction (RT-PCR) represent high specificity and sensitivity but are destructive and time-consuming, and require highly skilled experimenters. The feasibility of NIR hyperspectral imaging (HSI) is studied for the detection of peanut traces down to 0.01% by weight. A principal-component analysis (PCA) was carried out on a dataset of peanut and flour spectra. The obtained loadings were applied to the HSI images of adulterated wheat flour samples with peanut traces. As a result, HSI images were reduced to score images with enhanced contrast between peanut and flour particles. Finally, a threshold was fixed in score images to obtain a binary classification image, and the percentage of peanut adulteration was compared with the percentage of pixels identified as peanut particles. This study allowed the detection of traces of peanut down to 0.01% and quantification of peanut adulteration from 10% to 0.1% with a coefficient of determination (r2) of 0.946. These results show the feasibility of using HSI systems for the detection of peanut traces in conjunction with chemical procedures, such as RT-PCR and ELISA to facilitate enhanced quality-control surveillance on food-product processing lines.

Vibrational dynamics and structure of natural feldspars

The present study gives a contribution to the knowledge on the Na-feldspar and plagioclases, extending the database of the Raman spectra of plagioclases with different chemical compositions and structural orders. This information may be used for the future planetary explorations by “rovers”, for the investigation of ceramics nanocrystal materials and for the mineralogical phase identification in sediments. Na-feldspar and plagioclase solid solution have been investigated by Raman spectroscopy in order to determine the relationships between the vibrational changes and the plagioclase crystal chemistry and structure. We focused on the Raman micro-spectroscopy technique, being a non-destructive method, suited for contactless analysis with high spatial resolution. Chemical and structural analyses have been performed on natural samples to test the usefulness of Raman spectroscopy as a tool in the study of the pressure-induced structural deformations, the disordering processes due to change in the Al-Si distribution in the tetrahedral sites and, finally, in the determination of the anorthitic content (Anx) in plagioclase minerals. All the predicted 39 Ag Raman active modes have been identified and assigned to specific patterns of atomic vibrational motion. A detailed comparison between experimental and computed Raman spectra has been performed and previous assignments have been revised, solving some discrepancies reported in recent literature. The ab initio calculation at the hybrid HF/DFT level with the WC1LYP Hamiltonian has proven to give excellent agreement between calculated and experimentally measured Raman wavenumbers and intensities in triclinic minerals. A short digression on the 36 infrared active modes of Na-feldspar has been done too. The identification of all 39 computed Raman modes in the experimentally measured spectra of the fully ordered Na-feldspar, known as low albite, along with the detailed description of each vibrational mode, has been essential to extend the comparative analysis to the high pressure and high temperature structural forms of albite, which reflect the physical–chemical conditions of the hosting rocks. The understanding of feldspar structure response to pressure and temperature is crucial in order to constrain crustal behaviour. The compressional behaviour of the Na-feldspar has been investigated for the first time by Raman spectroscopy. The absence of phase transitions and the occurrence of two secondary compression mechanisms acting at different pressures have been confirmed. Moreover, Raman data suggest that the internal structural changes are confined to a small pressure interval, localized around 6 GPa, not spread out from 4 to 8 GPa as suggested by previous X-rays studies on elasticity. The dominant compression mechanisms act via tetrahedral tilting, while the T-O bond lengths remain nearly constant at moderate compressional regimes. At the spectroscopic level, this leads to the strong pressure dependencies of T-O-T bending modes, as found for the four modes at 478, 508, 578 and 815 cm-1. The Al-Si distribution in the tetrahedral sites affects also the Raman spectrum of Na-feldspar. In particular, peak broadening is more sensitive than peak position to changes in the degree of order. Raman spectroscopy is found to be a good probe for local ordering, in particular being sensitive to the first annealing steps, when the macroscopic order parameter is still high. Even though Raman data are scattered and there are outliers in the estimated values of the degree of order, the average peak linewidths of the Na-feldspar characteristic doublet band, labelled here as υa and υb, as a function of the order parameter Qod show interesting trends: both peak linewidths linearly increase until saturation. From Qod values lower than 0.6, peak broadening is no more affected by the Al-Si distribution. Moreover, the disordering process is found to be heterogeneous. SC-XRD and Raman data have suggested an inter-crystalline inhomogeneity of the samples, i.e., the presence of regions with different defect density on the micrometric scale. Finally, the influence of Ca-Na substitution in the plagioclase Raman spectra has been investigated. Raman spectra have been collected on a series of well characterized natural, low structural plagioclases. The variations of the Raman modes as a function of the chemical composition and the structural order have been determined. The number of the observed Raman bands at each composition gives information about the unit-cell symmetry: moving away from the C1 structures, the number of the Raman bands enhances, as the number of formula units in the unit cell increases. The modification from an “albite-like” Raman spectrum to a more “anorthite-like” spectrum occurs from sample An78 onwards, which coincides with the appearance of c reflections in the diffraction patterns of the samples. The evolution of the Raman bands υa and υb displays two changes in slope at ~An45 and ~An75: the first one occurs between e2 and e1 plagioclases, the latter separates e1 and I1 plagioclases with only b reflections in their diffraction patterns from I1 and P1 samples having b and c reflections too. The first variation represents exactly the e2→e1 phase transitions, whereas the second one corresponds in good approximation to the C1→I1 transition, which has been determined at ~An70 by previous works. The I1→P1 phase transition in the anorthite-rich side of the solid solution is not highlighted in the collected Raman spectra. Variations in peak broadening provide insights into the behaviour of the order parameter on a local scale, suggesting an increase in the structural disorder within the solid solution, as the structures have to incorporate more Al atoms to balance the change from monovalent to divalent cations. All the information acquired on these natural plagioclases has been used to produce a protocol able to give a preliminary estimation of the chemical composition of an unknown plagioclase from its Raman spectrum. Two calibration curves, one for albite-rich plagioclases and the other one for the anorthite-rich plagioclases, have been proposed by relating the peak linewidth of the most intense Raman band υa and the An content. It has been pointed out that the dependence of the composition from the linewidth can be obtained only for low structural plagioclases with a degree of order not far away from the references. The proposed tool has been tested on three mineralogical samples, two of meteoric origin and one of volcanic origin. Chemical compositions by Raman spectroscopy compare well, within an error of about 10%, with those obtained by elemental techniques. Further analyses on plagioclases with unknown composition will be necessary to validate the suggested method and introduce it as routine tool for the determination of the chemical composition from Raman data in planetary missions.

IRAS 00183-7111: ALMA and X-ray view of an ultra luminous infrared galaxy

The aim of this Thesis work is to study the multi-frequency properties of the Ultra Luminous Infrared Galaxy (ULIRG) IRAS 00183-7111 (I00183) at z = 0.327, connecting ALMA sub-mm/mm observations with those at high energies in order to place constraints on the properties of its central power source and verify whether the gas traced by the CO may be responsible for the obscuration observed in X-rays. I00183 was selected from the so-called Spoon diagnostic diagram (Spoon et al. 2007) for mid-infrared spectra of infrared galaxies based on the equivalent width of the 6.2 μm Polycyclic Aromatic Hydrocarbon (PAH) emission feature versus the 9.7 μm silicate strength. Such features are a powerful tool to investigate the contribution of star formation and AGN activity in this class of objects. I00183 was selected from the top-left region of the plot where the most obscured sources, characterized by a strong Si absorption feature, are located. To link the sub-mm/mm to the X-ray properties of I00183, ALMA archival Cycle 0 data in Band 3 (87 GHz) and Band 6 (270 GHz) have been calibrated and analyzed, using CASA software. ALMA Cycle 0 was the Early Science program for which data reprocessing is strongly suggested. The main work of this Thesis consisted in reprocessing raw data to provide an improvement with respect to the available archival products and results, which were obtained using standard procedures. The high-energy data consists of Chandra, XMM-Newton and NuSTAR observations which provide a broad coverage of the spectrum in the energy range 0.5 − 30 keV. Chandra and XMM archival data were used, with an exposure time of 22 and 22.2 ks, respectively; their reduction was carried out using CIAO and SAS software. The 100 ks NuSTAR are still private and the spectra were obtained by courtesy of the PI (K. Iwasawa). A detailed spectral analysis was done using XSPEC software; the spectral shape was reproduced starting from simple phenomenological models, and then more physical models were introduced to account for the complex mechanisms that involve this source. In Chapter 1, an overview of the scientific background is discussed, with a focus on the target, I00183, and the Spoon diagnostic diagram, from which it was originally selected. In Chapter 2, the basic principles of interferometry are briefly introduced, with a description of the calibration theory applied to interferometric observations. In Chapter 3, ALMA and its capabilities, both current and future, are shown, explaining also the complex structure of the ALMA archive. In Chapter 4, the calibration of ALMA data is presented and discussed, showing also the obtained imaging products. In Chapter 5, the analysis and discussion of the main results obtained from ALMA data is presented. In Chapter 6, the X-ray observations, data reduction and spectral analysis are reported, with a brief introduction to the basic principle of X-ray astronomy and the instruments from which the observations were carried out. Finally, the overall work is summarized, with particular emphasis on the main obtained results and the possible future perspectives.

Desenvolvimento de um algoritmo para identificação e correção de spikes em espectroscopia Raman de imagem

Raman imaging spectroscopy is a highly useful analytical tool that provides spatial and spectral information on a sample. However, CCD detectors used in dispersive instruments present the drawback of being sensitive to cosmic rays, giving rise to spikes in Raman spectra. Spikes influence variance structures and must be removed prior to the use of multivariate techniques. A new algorithm for correction of spikes in Raman imaging was developed using an approach based on comparison of nearest neighbor pixels. The algorithm showed characteristics including simplicity, rapidity, selectivity and high quality in spike removal from hyperspectral images.

Numerical comparison between conventional dispersion compensating fibers and photonic crystal fibers as lumped Raman amplifiers

In this paper we discuss the use of photonic crystal fibers (PCFs) as discrete devices for simultaneous wideband dispersion compensation and Raman amplification. The performance of the PCFs in terms of gain, ripple, optical signal-to-noise ratio (OSNR) and required fiber length for complete dispersion compensation is compared with conventional dispersion compensating fibers (DCFs). The main goal is to determine the minimum PCF loss beyond which its performance surpasses a state-of-the-art DCF and justifies practical use in telecommunication systems. (C) 2009 Optical Society of America