Raman Dispersion Research Articles

Heterodyne Raman dispersion spectroscopy with harmonic demodulation for hydrogen detection

A heterodyne scheme for stimulated Raman dispersion gas spectroscopy with phase-sensitive harmonic measurement is demonstrated. It is accomplished by optically manipulating the Raman transition through pump modulation and harmonically extracting the associated change on the beatnote generated by the sidebands of a Stokes beam. Theoretical formulation describing the spectral signal is developed and verified experimentally. Experiments on a 5-cm-long, 700-nm-diameter optical nanofiber have demonstrated a noise equivalent concentration of 24 ppm with 99 s integration time and a dynamic range of four orders of magnitude for hydrogen detection. This new approach provides a sensitive spectroscopic tool with the potential for widespread gas sensing applications.

Biomass characterization and solvent extraction as tools to promote phenol production from urban pruning

Nowadays, leaves, bark, and branches are generated from the tree-pruning process in urban places, where their management is a problem because of the necessity of disposal. These wastes are lignocellulosic biomasses with poor properties for use in biofuel production, but with interesting projections for building block products such as phenol compounds. Therefore, extensive biomass characterization of urban pruning from Liquidambar styraciflua L. was developed to evaluate its composition as a tool for phenol production through thermal processing, in which solvent extraction is a complementary tool for selectivity improvement. The results showed high lignin content in bark and leaves at 45 and 28 %, respectively, compared with that in branches (14 %). Additionally, high extractives in leaves (14 %) could be an additional source of phenols. The lignin units were analyzed by Raman dispersion, revealing p–hydroxyphenyl (H) units in the bark, guaiacyl (G) units in the bark and leaves, and syringyl (S) units only in the branches. Furthermore, the micropyrolysis coupled with gas chromatography/mass spectrometry assay realized at 600 °C showed high presence of phenolic compounds in the three biomass investigated, where a high phenol concentration was identified in leaves, probably due to the S unit degradation during pyrolysis. With these results, an assay for bio-oil production was performed in a low-temperature pyrolysis reactor using leaves as feedstock, reaching a low bio-oil yield with high water content favored for the high inorganic content of leaves (13 %). The produced bio-oil was used for liquid–liquid extraction evaluation, where 1-octanol and methyl isobutyl ketone were identified as interesting solvents for catechol and phenol extraction, respectively. This article presents the challenge of characterizing each part of urban trees, which could be a tool to promote the use of urban pruning by studying the thermal degradation mechanism to implement processes for high-value products, such as phenols produced from L. styraciflua L.

Mechanical Reinforcement of ABS with Optimized Nano Titanium Nitride Content for Material Extrusion 3D Printing.

Acrylonitrile Butadiene Styrene (ABS) nanocomposites were developed using Material Extrusion (MEX) Additive Manufacturing (AM) and Fused Filament Fabrication (FFF) methods. A range of mechanical tests was conducted on the produced 3D-printed structures to investigate the effect of Titanium Nitride (TiN) nanoparticles on the mechanical response of thermoplastic polymers. Detailed morphological characterization of the produced filaments and 3D-printed specimens was carried out using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). High-magnification images revealed a direct impact of the TiN concentration on the surface characteristics of the nanocomposites, indicating a strong correlation with their mechanical performance. The chemical compositions of the raw and nanocomposite materials were thoroughly investigated by conducting Raman and Energy Dispersive Spectroscopy (EDS) measurements. Most of the mechanical properties were improved with the inclusion of TiN nanoparticles with a content of 6 wt. % to reach the optimum mechanical response overall. ABS/TiN 6 wt. % exhibits remarkable increases in flexural modulus of elasticity (42.3%) and toughness (54.0%) in comparison with pure ABS. The development of ABS/TiN nanocomposites with reinforced mechanical properties is a successful example that validates the feasibility and powerful abilities of MEX 3D printing in AM.

Dark soliton solutions of the cubic-quintic complex Ginzburg–Landau equation with high-order terms and potential barriers in normal-dispersion fiber lasers

In this paper, we numerically study dark solitons in normal-dispersion optical fibers described by the cubic-quintic complex Ginzburg–Landau equation. The effects of the third-order dispersion, self-steepening, stimulated Raman dispersion, and external potentials are also considered. The existence, chaotic content and interactions of these objects are analyzed, as well as the tunneling through a potential barrier and the formation of dark breathers aside from dark solitons in two dimensions and their mutual interactions as well as with periodic potentials. Furthermore, the homogeneous solutions of the model and the conditions for their stability are also analytically obtained.

Resonance Raman characterization of poly(benzidine) in different oxidation states

In this paper, the structure of poly(benzidine) (PBZ) in different oxidation and protonation states is investigated by Raman spectroscopy (resonance Raman and FT-Raman) at several laser lines. In addition, all vibrational data is supported by DFT calculations. The resonance Raman spectra of doped and undoped PBZ show similar set of bands, however the doped PBZ show an increase of bands related to protonated segments (dications and radical cations) at 1147, 1332 and 1598 cm−1. The UV–vis-NIR and Raman confirm the formation of reduced form of PBZ, where the azo groups dominate. For all PBZ forms is not seen changes of the band position with the laser line (Raman dispersion). Probably, this is an indication of low conjugation between the segments in the polymeric backbone and justify the lower conductivity observed for PBZ than measured for polyaniline (PANI), a similar conducting polymer. Finally, the oxidation of PBZ with strong oxidants probably destroy the azo and phenazine units into PBZ backbone.

Synthesis and structural analysis of zinc oxide nano particle by chemical method

Abstract Nanoparticles of zinc oxides are synthesised by chemical methods taking as 1:4 M ratios ZnSO4.7H20 and NaOH. X-ray diffraction (XRD) and Raman Spectroscopy present the structural, chemical and optical properties of zinc oxide nanoparticles. Patterns from XRD show that the ZnO nanoparticles with a mean size 25 nm are made from a Wurtzite structure. Raman dispersion displays a sharp, strong E2 pitch, with a maximum of nearly 439 cm, which also lends a rootstock structure to nano-zinc oxide. It also adds nanoparticles (NPs) to their inherent toxicity, which is either totally overlooked or poorly investigated. The result of analysis shows a comparison of toxins and dangers derived from ZnO's chemical, physical and biological processes. In addition, the focus should be on developing environmentally compatible ZnO synthesis techniques, particularly organic approaches that remain relatively less dangerous then required to be enhanced with check of response situations in order to achieve the anticipated results and features.

Talbot effect based on a Raman-induced grating

We theoretically study the Talbot effect resulting from Raman-induced grating based on periodic spatial modulation of the Raman gain and dispersion in the field of a standing pump wave. Features of integer and fractional Talbot effects are demonstrated for one- and two-dimensional (1D and 2D) Raman-induced gratings. It is shown that the intensity of diffraction images can increase due to Raman amplification in the grating. Glass-shaped diffraction patterns are demonstrated for 2D gratings. It is also shown that in the vicinity of the Talbot planes there are planes in which the diffraction patterns are spatially compressed and the intensity becomes greater. The results expand the possibility of using the Talbot effect in various applications.

Chemical bonding mechanism in SERS effect of pyridine by CuO nanoparticles

AbstractThis article reports the theoretical and experimental study of nonresonant mechanisms (CHEM) of surface‐enhanced Raman spectroscopy (SERS) of pyridine (Py). An improvement in the Raman dispersion intensity of Py is determined after the chemical absorption on CuO nanoparticles synthesized in NaCl. The density functional theory predicts the formation of new electronic states as result of the chemical bond (CB) established between the Py molecule and the (CuO)n clusters. This study is focused on the study of the most intense vibrational modes of Py before and after chemical adsorption. The CHEM by CB mechanisms is found as responsible for the SERS effect in Py.

Synthesis of reduced graphene oxide/Co3O4 nanocomposite electrode material for sensor application

A sensitive electrochemical sensor has been developed based on reduced graphene oxide/Co3O4 (rGO/Co3O4) nanocomposites (NCs) synthesized by a facile solvothermal method. The developed sensor was used to determine the Dopamine Acid (DA) and Uric Acid (UA). The structure, morphology, band gap and composition of NCs was characterized by powder X-ray diffraction, scanning electron microscope, UV–Vis-Diffuse reflectance, FT-IR, Raman and Energy Dispersive Spectroscopy. rGO/Co3O4 NCs exhibited better electrocatalytic activity for the oxidation of DA and UA in solution with phosphate buffer at pH 7.0. For individual determination, the oxidation peak currents were linearly increased with the concentration of DA and UA in the ranges of 0.5–10 μM and 100 μM–1 mM, respectively. The detection limit of DA and UA was estimated to be 0.176 μM and 1.31 μM, respectively, with (S/N = 3). The fabricated modified electrode displayed an excellent anti-interference ability against 100-fold higher concentration of potential interferent species and metal ions with good stability and reproducibility. Results show that the developed sensor has a potential to determine the target analytes in real samples with satisfactory efficiency.

Structural and chemical homogeneity of chalcogenide glass prepared by melt-rocking.

The chemical and structural homogeneity of selenide glasses produced by mechanical homogenization of the melt in a rocking furnace is investigated by Raman and Energy Dispersive Spectroscopy (EDS). Both techniques demonstrate that the glass is macroscopically homogeneous along the entire length of a 6 cm rod. EDS imaging performed over four orders of magnitude in scale further confirms that the glass is homogeneous down to the sub-micron scale. An estimate of the diffusion coefficient from experimental viscosity data shows that the diffusion length is far larger than the resolution of EDS and therefore confirms that the glass is homogeneous at any length scale. In order to investigate a systematic mismatch in physical properties reported in the literature for glasses produced by extended static homogenization, two germanium selenide samples are produced under the same conditions except for the homogenization step: one in a rocking furnace for 10 h and the other in a static furnace for 192 h. No difference in physical properties is found between the two glasses. The properties of an ultra-high purity glass are also found to be identical. The origin of the systematic deviation reported in the literature for germanium selenide glasses is therefore still unknown, but the present results demonstrate that homogeneity or dryness does not have a significant contribution in contrast to previous suggestions. The implications of glass homogeneity for technological applications and industrial production are discussed.

Temperature dependence of the Raman dispersion of Sr2Nb2O7: Influence of an electric field during the synthesis

AbstractWe report on the preparation and structural characterization of powder samples of the perovskite‐slab layered polycrystalline Sr2Nb2O7 (hereafter named SNO) ferroelectric compound. Comparison is performed on samples grown without (SNO) and with an applied electric field of 3.34 kV/cm (SNOE). The Raman effect produced by these samples as a function of temperature, from 27°C (room temperature) to 400°C is presented and discussed. Significant differences are observed and discussed among SNO and SNOE. The electric field promotes the growth of platelets, preferentially oriented along the (0b0) planes. The temperature coefficients of 35 phonon wavenumbers were determined for both samples. A majority of the phonons exhibit monotonic wavenumber softening's with increasing temperatures, but a significant number of them show discontinuities on the wavenumber temperature slopes at two temperatures 215°C and 307 ± 5°C. The first temperature corresponds to the well‐known incommensurate phase to the ferroelectric phase transition (Phases III to II). The second temperature is indicative of an unreported phase transition for both the SNO and SNOE samples. For the sample SNOE, a phonon f7 (at 121 cm−1 at room temperature) displays a behavior that may be indicative of the existence of another ordering parameter that vanishes at 488 ± 5°C in the SNOE sample, induced by the electric field applied during the growth. The phonon broadenings with temperature are explained in terms of the Klemens model, which considers that the broadenings are due to the thermal expansion of the lattice, with a substantial contribution in magnitude from anharmonic phonon–phonon interactions.

One- and two-dimensional Raman-induced diffraction gratings in atomic media

We propose and analyze an efficient scheme for the one- and two-dimensional atomic gratings based on periodic spatial modulation of the Raman gain and dispersion, which we name the Raman-induced diffraction gratings (RIDGs). There are fundamentally different from those based on electromagnetically induced transparency. As the probe field propagates along the direction normal to the standing pump wave, it can be effectively diffracted into high-order directions. The grating is a hybrid grating, i.e. it represents a mixture of amplitude and phase gratings. We identify the conditions when all high-order diffractions are amplified. In addition, we also show that diffraction of a probe field could be dynamically controlled using an additional laser field. With its help, it is possible to suppress or amplify diffraction beams. The RIDGs can be considered as all-optical multibeam splitters with amplification.

Tunable Raman gain in mid-IR waveguides

By means of theoretical analysis and numerical simulations, we show a tunable Raman gain which may find applications in a variety of fields, ranging from mid-IR fiber Raman lasers and supercontinuum generation to ultra-wideband slow-light Raman-based devices. In particular, by analyzing the interplay among Raman gain, dispersion, and self-steeping (SE) in a full model of modulation instability (MI) in waveguides, we show that there exists a range of pump powers where the gain spectrum is not only dominated by the Raman contribution, but also, most strikingly, it can be fine-tuned at will. We present analytical and numerical results, in excellent agreement, confirming this observation.

The solvation inhomogeneity of sulfur dioxide in 1‐butyl‐3‐methylimidazolium thiocyanate ionic liquid probed by Raman spectroscopy

AbstractThe different solvation states of SO2 in 1‐butyl‐3‐methylimidazolium thiocyanate ionic liquid were probed by the detailed analysis of the SO2 symmetric stretching mode, νs(SO2). The band position and linewidth were monitored in function of gas molar fraction, excitation wavelength, and temperature. As expected, the decreasing of the SO2 molar fraction, XSO2, from approximately 0.8 to 0.2, leads to a gradual downshift of the νs(SO2) band, attributed to a more effective charge transfer interaction from thiocyanate anion to SO2. Interestingly, at high gas concentrations (XSO2 = 0.8), a gradual downshift of the νs(SO2) band was noticed as the Raman excitation energy increases, an unexpected behavior because the change in the excitation wavelength in Raman spectroscopy should affect only the band intensities. Such νs(SO2) Raman dispersion can be understood as a consequence of the distinct charge transfer electronic transition energies associated to different SO2 solvation states, whose relative band intensities are modulated by resonance Raman conditions. Moreover, the lowering from room temperature to 100 K showed an increasing in the Raman dispersion effect. The temperature dependence was attributed to the strengthening of the cation–anion interaction, responsible for the increasing of SO2 solvation states distribution. The vibrational spectroscopic data regarding the SO2 solvation inhomogeneity in ionic liquids are showed for the first time, and it may contribute in the understanding of why such liquids are promising solvents for SO2 capture.

Raman and Energy Dispersive Spectroscopy (EDS) Analyses of a Microsubstance Adhering to a Fiber of the Turin Shroud.

The Raman spectrum of a microsubstance, smeared on a fiber coming from the Shroud of Turin, was compared with numerous spectra published for old or modern pigment dyes, whole bloods, dried bloods, red blood cells, albumin, very ancient blood stains, and various "degradation" products of heme. Within the wavenumber measure accuracy, it is shown that all Raman lines detected above background could correspond to vibration frequencies found in biliverdin-derived compounds except a weak line that we tentatively attributed to amide I. Biliverdin is known as an oxidative ring cleavage product of the heme of blood. Energy dispersive spectroscopy (EDS) analysis of the sample confirms an elemental composition fully compatible with this hypothesis. Therefore, it is very likely that this microsubstance contains products of heme including heme/biliverdin-derived compounds and protein traces (amide I). Nevertheless, other measures will be necessary to confirm it. This method of identification, adding EDS to Raman spectrometry can be applied to nondestructive testing (NDT) of many other microsamples.

Raman dispersion in polyaniline nanofibers

In this work the Raman dispersion observed for the polyaniline (PANI) nanofibers was investigated. PANI nanofibers were prepared by interfacial polymerization using HCl or HClO4 acids as dopant. The use of different acids in the aniline polymerization can produce PANI fibers with different diameters. The polymers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), small angle X-ray scattering (SAXS), UV–VIS-NIR and resonance Raman (RR). By using several laser lines (from 1.16 to 3.05eV) the dependency of νCN band frequencies, related to the quinoid rings, with the laser lines was investigated. The Raman dispersion of νCN frequencies was analyzed using Amplitude Mode Model (AMM). Excitation photon energy versus ∏n(ωnRωn0)2 curves were linear in region of the electronic absorption transition. The Raman dispersion of PANI nanofibers with smaller diameter (d≈30nm) shows lower dispersion D rate (slope of ∏n(ωnRωn0)2 versus laser line energies) and as consequence higher torsion of Cring-N-Cring segments. Hence, for PANI with higher morphological organization has more stacking between quinoid rings (higher torsion angles) and more electronic homogeneity (lower D rate) compared to other samples.

Exploring molecular and spin interactions of Tellurium adatom in reduced graphene oxide

The transport of spin information fundamentally requires favourable molecular architecture and tunable spin moments to make the medium pertinent for spintronic. We report on achieving coherent molecular-spin parameters for rGO due to Tellurium (Te) adatom. Initially, GO prepared using graphite, was modified into rGO by in situ incorporation of 1 (w/w)% of Te. Both the systems were subjected to ESCA, FTIR, Raman dispersion, ESR spectroscopy, and electron microscopy. Analysis revealed that, Te substantially reacted with epoxides, carbonyl, and carboxylate groups that improved C-to-O ratio by twice. However, the spin splitting character, between Te and C, seems to be quenched. Moreover, Te altered the dynamical force constant between CC and CC that generated the mechanical stress within rGO network. The layer conjugation, nature of folding, symmetry, and electronic states of the edges were also affected by precipitation and entrapment of Te. The calculated dynamic molecular Raman and ESR spin parameters indicated that, Te acted as a bridging element for long range spin transport. This is particularly due to, the p-orbital moments of Te contributing, vectorially, to spin relaxation process operative at broken inversion symmetry sites. Our study suggests that, facile addition of Te in rGO is useful to achieve favourable spintronic properties.

Dynamics of Dispersive Wave Generation in Gas-Filled Photonic Crystal Fiber with the Normal Dispersion

The absence of Raman and unique pressure-tunable dispersion is the characteristic feature of gas-filled photonic crystal fiber (PCF), and its zero dispersion points can be extended to the near-infrared by increasing gas pressure. The generation of dispersive wave (DW) in the normal group velocity dispersion (GVD) region of PCF is investigated. It is demonstrated that considering the self-steepening (SS) and introducing the chirp of the initial input pulse are two suitable means to control the DW generation. The SS enhances the relative average intensity of blue-shift DW while weakening that of red-shift DW. The required propagation distance of DW emission is markedly varied by introducing the frequency chirp. Manipulating DW generation in gas-filled PCF by the combined effects of either SS or chirp and three-order dispersion (TOD) provides a method for a concentrated transfer of energy into the targeted wavelengths.

Solitons and frequency combs in silica microring resonators: Interplay of the Raman and higher-order dispersion effects

The influence of Raman scattering and higher order dispersions on solitons and frequency comb generation in silica microring resonators is investigated. The Raman effect introduces a threshold value in the resonator quality factor above which the frequency locked solitons can not exist and, instead, a rich dynamics characterized by generation of self-frequency shift- ing solitons and dispersive waves is observed. A mechanism of broadening of the Cherenkov radiation through Hopf instability of the frequency locked solitons is also reported.

Co-occurrence of bacteria and fungi and spatial partitioning during photographic materials biodeterioration

The microbial spoilage and correlated surface changes of a cellulose nitrate negative film, a gelatine–silver positive print, a cardboard frame and a cellulosic envelope dated back to 1938–1940 was assessed by means of molecular methods and scanning electron microscopy (SEM). Materials characterisation was obtained with Raman, Infrared and Electronic dispersion spectroscopies. DNA was extracted from bacteria and fungi, amplified through PCR oriented to bacterial 16S rRNA gene and fungal internal transcribed spacer (ITS), and clone libraries were constructed for each investigated material. The ITS fungal cloning was able to detect a bigger spectrum of species respect to bacterial one. Correspondence between molecular results and SEM observations was used to address the cause of biodeterioration to single species, and to map the presence of different organisms in separate niches. This investigation highlighted a co-occurrence of both bacteria and fungi on most of the substrata, and a spatial partitioning according to the different photographic materials. Moreover, for the first time, the effects of a biological attack on glassine paper were documented.