Main Raman Peak Research Articles

Theoretical and Experimental Raman Investigation of Mechanical Strain and Electric Field Effects on Conductive Polymers.

Mechanical strain and electric field affect the performance of conductive polymer devices, for which the underlying mechanism should be investigated at the molecular level. This study combines theoretical and experimental Raman approaches to explore the changes in the molecular structure of poly(3-hexylthiophene) (P3HT) and poly(3,4-ethylenedioxythiophene) (PEDOT) under the influence of mechanical strain and external electric fields. Theoretical calculations reveal the pronounced shifts in the main Raman peak if the conjugating length is changed by the mechanical strain, while in experiments, the peak position is unaffected under tensile and bending strain. Under an external electric field, the theoretical results predict a continuous red shift of the main Raman peak accompanied by the change in bond lengths, while in experiments, the same peak exhibits a red shift at an initial increase of the electric field strength and then becomes almost unchanged at a stronger electric field. The discrepancies between calculation and experimental results are attributed to the complex nature of the conjugated chains and noncrystalline domain present in the organic semiconductors, which limits the effectiveness of strain and electric field on the conjugated chains. The results of this study help to bridge the gap between the theoretical study and the actual response of conductive polymers for flexible and electronic device applications.

Halogen-bearing metasomatizing melt preserved in high-pressure (HP) eclogites of Pfaffenberg, Bohemian Massif

Abstract. Primary granitic melt inclusions are trapped in garnets of eclogites in the garnet peridotite body of Pfaffenberg, Granulitgebirge (Bohemian Massif, Germany). These polycrystalline inclusions, based on their nature and composition, can be called nanogranitoids and contain mainly phlogopite/biotite, kumdykolite, quartz/rare cristobalite, a phase with the main Raman peak at 412 cm−1, a phase with the main Raman peak at 430 cm−1, osumilite and plagioclase. The melt is hydrous, peraluminous and granitic and significantly enriched in large ion lithophile elements (LILE), Th, U, Li, B and Pb. The melt major element composition resembles that of melts produced by the partial melting of metasediments, as also supported by its trace element signature characterized by elements (LILE, Pb, Li and B) typical of the continental crust. These microstructural and geochemical features suggest that the investigated melt originated in the subducted continental crust and interacted with the mantle to produce the Pfaffenberg eclogite. Moreover, in situ analyses and calculations based on partition coefficients between apatite and melt show that the melt was also enriched in Cl and F, pointing toward the presence of a brine during melting. The melt preserved in inclusions can thus be regarded as an example of a metasomatizing agent present at depth and responsible for the interaction between the crust and the mantle. Chemical similarities between this melt and other metasomatizing melts measured in other eclogites from the Granulitgebirge and Erzgebirge, in addition to the overall similar enrichment in trace elements observed in other metasomatized mantle rocks from central Europe, suggest an extended crustal contamination of the mantle beneath the Bohemian Massif during the Variscan orogeny.

Investigation of gradient band gap in Cu2ZnSnS4 thin films with residual strain

This study investigates the change in the band gap of Cu2ZnSnS4 (CZTS) thin films under a gradual change in the residual strain of the thin films. Two CZTS thin film samples are fabricated at different initial substrate temperatures before annealing. X-ray diffraction results are obtained at various incidence angles, and the residual strains at the incidence angles are obtained from the Williamson–Hall plot. The larger the mean residual strain of the CZTS thin films, the greater are the redshift and full width at half maximum of the main Raman peak position. Results of Tauc plot analysis show that the CZTS thin film samples exhibit a gradient band gap. The sample with a wider distribution of the residual strain shows a greater band gap variation.

Effects of Cu+ ion implantation on band gap and Raman shift of Cu2ZnSnS4 thin films

In this study, shifts in the band gap and position of the main Raman peak of Cu2ZnSnS4 (CZTS) thin films were analyzed. These shifts were caused by residual tensile strain originating from artificially implanted Cu+ ions on the CZTS thin films. Cu+ ions were implanted at various doses in the CZTS thin films. The residual strain increased linearly as the logarithmic dose of Cu+ ions increased. According to the Raman spectrum analysis, the CZTS thin films had kesterite order structures. The band gap and the shift of the main Raman peak, P1, are linear functions of the residual strain and are linearly related to each other. A larger residual strain led to larger decreases of 1.50 eV and 337.5 cm−1 in the band gap and position of the main Raman peak (P1), respectively.

Fluorine doping as a feasible method to enhancing functional properties of Ce0.8Sm0.2O1.9 electrolyte

In this work, materials with a fluorite structure of the Ce0.8Sm0.2O1.9-(3х)/2F3х series are obtained and studied for the first time. The synthesis method has been developed based on the solid-phase interaction of SmF3 with a highly dispersed precursor obtained in reactions of solution combustion synthesis (SCS) of cerium and samarium nitrates with a mixture of glycine and citric acid. The materials in the range of 0.01 = x ≤ 0.1 possess a cubic structure (Fm-3m space group), the unit cell parameter decreases according to the size factor. The Raman spectra study shows that for Ce0.8Sm0.2O1.9 the main Raman peak is described by the sum of two components with maxima at 460.5 cm−1, FWHM = 28.1 cm−1 and at 484.5 cm−1, FWHM = 18.3 cm−1. After the introduction of fluorine, the third component appears at ∼461.2 cm−1 with a much smaller FWHM equal to12.1 cm−1. Thus, the Raman spectra analysis allows the presence of fluorine in the fluorite-like materials including sintered ceramics to be identified. The conductivity maximum (3.7 mS cm−1 at 600 °C, Ea = 0.95 eV) and the maximal electrolyte domain boundary value (1.58 × 10−22 atm) is reached at x = 0.10 of fluorine content, which generally determines the prospects for the fluorine-doped material application in the SOFC technology.

Effect of ion interactions on the Raman spectrum of NO3−: Toward monitoring of low-activity nuclear waste at Hanford

Raman spectroscopy is a valuable in-situ technique for many applications. The concentrations of species in complex ionic mixtures of nuclear waste can be estimated using Raman measurements. However, it has been experimentally observed that ion interactions can cause a modification of Raman peak intensities and positions. The present work explores the nonlinear behavior associated with the nitrate anion, NO3−, which is present in abundance in low activity nuclear waste. We examine changes in the main Raman peak of the nitrate anion in the presence of other ions. A wide range of concentrations are covered, including those expected during direct-feed low-activity waste (DFLAW) processing at the Hanford site in the State of Washington. The experiments showed that the ions interact and associate to form ion pairs, which results in a blue shift (i.e., a shift towards higher wavenumbers) in the main Raman peak of nitrate. The results indicate that cation concentration is a better predictor of the peak shift, compared to ionic strength, both for binary and multicomponent mixtures. These findings have direct implications on the development of spectra-to-composition models for the DFLAW system, since they show deviations from the linearity assumptions used in common chemometric models.

Determination of lead in food by surface-enhanced Raman spectroscopy with aptamer regulating gold nanoparticles reduction

Lead ion (Pb2+) is a main heavy metal in food that causes heavy teratogenicity and carcinogenicity. In this study, a rapid and sensitive SERS method for detecting Pb2+ in food was established by aptamer regulating gold nanoparticles reduction. The reduction of HAuCl4 catalyzed by H2O2 is a slow process, and graphene oxide (GO) has excellent catalytic performance for the reaction, which enabled the system to generate gold nanoparticles (AuNPs) with high Raman activity. When the aptamer was introduced into the system, its binding with GO reduced the reaction speed. Upon adding Pb2+ to the system, the aptamer preferentially combined with Pb2+ and GO was released to accelerate the AuNPs production. The concentration of the AuNPs was proportional to the intensity of the added Raman signal molecule 4-MBA and the main Raman peak of Pb2+ appeared at 1595.80 cm−1. The ability of a novel aptamer (M4-16) and traditional aptamers (T30695, TBA) for Pb2+ determination was compared, and the concentration of the aptamer, HAuCl4 and heating time were optimized to build optimal detection system. After several pretreatment of the original SERS spectroscopy, combined with the comparison of various models, the first-order derivative preprocessing combined with competitive adaptive reweighted sampling model achieved the best performance (Rc = 0.9966, Rp = 0.9972), the detection limit for Pb2+ was 0.1 μg L−1. The combination of SERS technology and chemometrics is a promising method that could be used to achieve rapid and highly sensitive detection of Pb2+ in food.

Effects of Bond Disorder and Surface Amorphization on Optical Phonon Lifetimes and Raman Peak Shape in Crystalline Nanoparticles

Optical phonons in nanoparticles with the randomness of interatomic bonds are considered both analytically and numerically. For weak dilute disorder two qualitatively different regimes of separated and overlapped levels are observed, resembling the case of random atomic masses investigated previously. At stronger and/or more dense disorder, the particles become essentially inhomogeneous, thus constituting the minimal model to describe an amorphous phase, where the picture of vibrational modes becomes more subtle. We concentrate here on the experimentally relevant case of strong disorder located near the particle surface and formulate the core-shell model aimed to describe the ubiquitous phenomenon of particle surface amorphization. We observe a peculiar effect of volume optical phonons "repelling" from the disordered shell. It results in the Raman spectrum in the form of a combination of narrow well-resolved peaks stemming from the quantized modes of a pure particle core (red-shifted due to its effective smaller size), and the noisy background signal from the disordered shell placed primarily to the right from the main Raman peak.

Colloidal Cu2ZnSnS4-based and Ag-doped Nanocrystals: Synthesis and Raman Spectroscopy Study

Cu2ZnSnS4 (CZTS) is one of the promising materials for absorber layers of new-generation thin film solar cells. Various synthetic routes of materials preparation and structural characterization have been explored so far. Further tuning of the CZTS properties is realized via partial substitution of the cations. Here we have used an affordable and scalable method of synthesizing colloidal CZTS nanocrystals (NC) in an aqueous solution. Variation of the synthesis parameters, in particular pH of the solution, was employed to improve the crystallinity of the NCs. Furthermore, CZTS NCs with partial substitution of Cu for Ag were also successfully synthesized. Raman spectroscopy was employed as a prime tool of structural characterization of the NCs obtained, along with optical absorption spectroscopy and ab initio DFT lattice dynamics calculations. An experimentally observed slight upward shift of the main phonon Raman peak upon increase of the Ag content in (AgxCu1-x)2ZnSnS4 NCs is in agreement with the trend predicted by DFT calculation. No pure Ag2ZnSnS4 NCs could be formed, indicating a critical role of Cu in forming the kesterite structure NCs under given synthesis conditions in an aqueous medium.

Real or fake yellow in the vibrant colour craze: Rapid detection of lead chromate in turmeric

For centuries, the colour of foods has played a significant role in the way products are perceived and valued. Generally, the more vibrant the product, the higher its quality and price. For modern-day consumers, various brightly coloured foods are known as superfoods and often consumed at higher concentrations than before. There is emerging attention for adulteration of turmeric with the vibrant yellow, toxic and carcinogenic compound lead chromate. Rapid detection of this hazardous lead chromate is important to protect consumers, therefore this study aimed to develop a spectroscopy-based method to detect lead chromate in turmeric powder. The potential of Fourier transform-Raman (FT-Raman) spectroscopy was investigated experimentally by measuring multiple turmeric powder samples adulterated with different concentrations of lead chromate (0.1%–10.0%, w/w). The acquired FT-Raman spectra were analysed by both univariate and multivariate statistics. Linear correlation of the intensity of the main lead chromate Raman peak at 840 cm−1 against the lead chromate concentration gave a limit of detection (LOD) of 0.6%. For the partial least squares regression (PLSR) model, based on the 1750-200 cm−1 range, a LOD of 0.5% was obtained. Lead chromate was successfully detected for samples adulterated from 0.5% or higher. Raman spectroscopy is a promising screening technique for the rapid detection of lead chromate in turmeric powder at concentrations over 0.5%. However, the LOD for this study is still above the maximum levels that have been found in practice and future studies should focus on increasing the sensitivity of the technique.

Crystalline and amorphous calcium carbonate as structural components of the Calappa granulata exoskeleton

The exoskeleton of crustaceans consists of chitin biopolymers where the embedded inorganic biominerals, mainly CaCO3, affect strongly its mechanical properties. Raman and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopies and Transmission Electron Microscopy (TEM) are applied to investigate the CaCO3 structure in various parts of the Calappa granulata crab exoskeleton. The shape of the main Raman peak of CaCO3 reveals the presence of two phases which are identified as calcite and amorphous calcium carbonate (ACC). The relative concentration of the two phases in various parts of the exoskeleton is determined from the area ratio under the corresponding peaks. The results of the Ca L3,2-edge NEXAFS analysis are in line with the Raman findings, since the energy separation of peaks that appear in the lower frequency region of the main L2 and L3 peaks due to crystal field splitting, is directly related to the percentage of the ACC phase in the total CaCO3 mineral content. The C K-edge spectra are used for the determination of the extent of calcification of the exoskeleton. Furthermore, dark and bright field TEM images reveal the presence of nanocrystallites with an average size of 20 nm. The structure of the nanocrystallites, as derived from the Selected Area Electron Diffraction patterns, is calcite. The results suggest that ACC plays a structural role in the exoskeleton of Calappa granulata.

Влияние малых доз гамма-излучения на оптические свойства наноструктурированного кремния, полученного методом металл-стимулированного химического травления in situ

Влияние малых доз гамма-излучения на оптические свойства наноструктурированного кремния, полученного методом металл-стимулированного химического травления in situ

Beyond the surface: Raman micro-SORS for in depth non-destructive analysis of fresco layers

We applied micro-scale Spatially Offset Raman Spectroscopy (micro-SORS) to perform the analysis of the layer composition in a fresco of the San Giuseppe church in Cagliari (XVIII century – under restoration). Standard Raman analysis of the surface evidenced the presence of expected pigments in the final plaster layer, such as hematite and calcium sulphate, beside the contribution of calcite. The second one is observed in its anhydrous form on the substrate layers (main Raman peak at 1024 cm−1) and in its hydrate form (1006 cm−1) from the surface. With micro-SORS analysis we evaluated the stratigraphy of the different layers of the plaster by monitoring the intensity ratio of the calcite and the anhydrous calcium sulphate. Four different layers with separation boundaries at about 80 μm, 600 μm and 2400 μm of defocusing distance were evidenced, corresponding to the painting layer “velo”(down to 80 μm), the plaster “rasatura” (down to 600 μm), the “arriccio” layer (down to 2400 μm) and the “rinzaffo” layer (below 2400 μm). The cross-sectional analysis by SEM imaging of a fragment from the fresco confirmed the micro-SORS findings, promoting the technique as a new non-invasive stratigraphy tool for cultural heritage.

The Raman spectra of the Na2SO4‐K2SO4 system: Applicability to soluble salts studies in built heritage

AbstractThe Raman spectra of the Na2SO4‐K2SO4‐H2O system are not well‐defined in the literature. Specifically, the proper identification of sodium and potassium sulphate (aphthitalite or glaserite, K3Na(SO4)2) and anhydrous sodium sulphate (thenardite, Na2SO4) is particularly problematic because their vibrational profiles present the same main Raman peak at 993 cm−1 and very similar low frequency bands. As proved in bibliography, the similarity of their spectra can often lead to uncertain or erroneous identifications. Considering that aphthitalite and thenardite can be found as degradation products on built heritage materials and the degree of danger associated to them is not the same, being the second one the most harmful, the resolution of this problem has a critical importance. For this reason, in the present work, the Raman spectra of aphthitalite and thenardite are deeply studied to identify the vibrational fingerprints enabling their correct identification. The results here summarized and provided by two different Raman instruments highlight that the spectrum of aphthitalite displays characteristic bands at 1,084 and 1,202 cm−1. In contrast, the bands at 1,100, 1,129, and 1,152 cm−1 seem to be characteristic of thenardite. Furthermore, when those secondary bands are not observed or mixtures of both compounds are present, the ratio between their most intense bands at 452 and 993 cm−1 is the key for their correct characterization. On the whole, this study fills the gaps observed in literature and gives the solution for the correct identification of aphthitalite and thenardite even when secondary bands are not observed.

Hydrothermally synthesized porous Mn3O4 nanoparticles with enhanced electrochemical performance for supercapacitors

Porous like nanostructures are significant electrodes for electrochemical capacitors owing to their high surface area and variable pore sizes. In this study, an attempt was made to synthesize porous like Mn3O4 structure using H2O2 at different concentrations via solvent assisted hydrothermal method. The concentration of H2O2 during synthesis played critical role in controlling microstructure, morphology and hence supercapacitive performance. The XRD pattern shows, there is no much change in the diffraction peaks but peak broadening with addition of H2O2 was notified, which indicates decrease in crystallite size. The Raman studies also support the XRD result and the main Raman peak at 658 cm−1 shifted with increase in solvent concentration which is due to grain size effect. The SEM micrographs confirmed that the samples synthesized at 3 M H2O2 concentration are of porous like structure with variable pore sizes which is positive sign for supercapacitor applications. The electrical conductivity of the sample increased with temperature. The electrochemical properties of porous Mn3O4 were studied using CV, CP and EIS. The Mn3O4 exhibited a specific capacitance of 435 F g−1 at a scan rate of 1 mV s−1 with good rate capability and excellent capacitive retention.

Synthesis, theoretical and experimental characterisation of thin film Cu2Sn1-xGexS3 ternary alloys (x = 0 to 1): Homogeneous intermixing of Sn and Ge

Cu2Sn1-xGexS3 is a p-type semiconductor alloy currently investigated for use as an absorber layer in thin film solar cells. The aim of this study is to investigate the properties of this alloy in thin film form in order to establish relationships between group IV composition and structural, vibrational and opto-electronic properties. Seven single phase Cu2Sn1-xGexS3 films are prepared from x = 0 to 1, showing a uniform distribution of Ge and Sn laterally and in depth. The films all show a monoclinic crystal structure. The lattice parameters are extracted using Le Bail refinement and show a linear decrease with increasing Ge content. Using density-functional theory with hybrid functionals, we calculate the Raman active phonon frequencies of Cu2SnS3 and Cu2GeS3. For the alloyed compounds, we use a virtual atom approximation. The shift of the main Raman peak from x = 0 to x = 1 can be explained as being half due to the change in atomic masses and half being due to the different bond strength. The bandgaps of the alloys are extracted from photoluminescence measurements and increase linearly from about 0.90 to 1.56 eV with increasing Ge. The net acceptor density of all films is around 1018 cm−3. These analyses have established that the alloy forms a solid solution over the entire composition range meaning that intentional band gap grading should be possible for future absorber layers. The linear variation of the unit cell parameters and the band gap with group IV content allows composition determination by scattering or optical measurements. Further research is required to reduce the doping density by two orders of magnitude in order to improve the current collection within a solar cell device structure.

Resonant Raman scattering based approaches for the quantitative assessment of nanometric ZnMgO layers in high efficiency chalcogenide solar cells

This work reports a detailed resonant Raman scattering analysis of ZnMgO solid solution nanometric layers that are being developed for high efficiency chalcogenide solar cells. This includes layers with thicknesses below 100 nm and compositions corresponding to Zn/(Zn + Mg) content rations in the range between 0% and 30%. The vibrational characterization of the layers grown with different compositions and thicknesses has allowed deepening in the knowledge of the sensitivity of the different Raman spectral features on the characteristics of the layers, corroborating the viability of resonant Raman scattering based techniques for their non-destructive quantitative assessment. This has included a deeper analysis of different experimental approaches for the quantitative assessment of the layer thickness, based on (a) the analysis of the intensity of the ZnMgO main Raman peak; (b) the evaluation of the changes of the intensity of the main Raman peak from the subjacent layer located below the ZnMgO one; and (c) the study of the changes in the relative intensity of the first to second/third order ZnMgO peaks. In all these cases, the implications related to the presence of quantum confinement effects in the nanocrystalline layers grown with different thicknesses have been discussed and evaluated.

Paramagnetic anatase titania/carbon nanocomposites

The nanocomposites comprising of anatase titania nanoparticles uniformly distributed inside the porous carbon matrix were synthesized using furfuryl alcohol, tetrabutyltitanate, and nonionic surfactant. The characterization of the nanocomposite by scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray analysis, x-ray diffractometry, and Raman spectroscopy revealed the formation of anatase titania nanoparticles of average sizes 10 to 20 nm. The observed broadening and blueshift of the main Raman peak of titanium dioxide nanoparticles were explained using the phonon confinement effect. The nanocomposite exhibited strong paramagnetism at low temperatures and was diamagnetic at higher temperatures, as well as a small contamination by magnetic impurities was detected. The paramagnetism originated from the amorphous defect-rich carbon and oxygen vacancies in titania.

Thermoanalytical study and structure of stoichiometric As–Sb–S glasses

The glass-forming system (As2S3)100−x(Sb2S3)x was studied by thermal analysis (conventional and StepScan differential scanning calorimetry) and Raman spectroscopy. It was found that the bulk glasses are homogeneous up to x = 60, while supercooled melts are unstable and when x ≥ 40, Sb2S3 (stibnite) crystallizes during heating. Depending on the chemical composition, the glass transition temperature initially increases as the Sb2S3 concentration is increased from 0 to 5 %, decreases to a minimum at ~20 %, and then gradually increases as the concentration is further increased and the main Raman peak also shifts non-monotonically. Combining these results with chemometric analysis of the Raman spectra showed that the image of the structure of the studied glasses can be described by the linear combination of three chemically different stable clusters, rather than by the chains crossing model, CCM, and that the properties of the glasses are controlled by medium-range order.

The three A symmetry Raman modes of kesterite in Cu_2ZnSnSe_4

We investigate CZTSe films by polarization dependent Raman spectroscopy. The main peaks at 170 cm(-1), and 195 cm(-1) are found to have A symmetry. The Raman signal at 170 cm(-1) is found to be composed of two modes at 168 cm(-1) and 172 cm(-1). We attribute these three Raman peaks to the three A symmetry modes predicted for kesterite ordered Cu(2)ZnSnSe(4). The main Raman peak is asymmetrically broadened towards lower energies. Possible sources of the broadening are tested through temperature and depth dependent measurements. The broadening is attributed to phonon confinement effects related to the presence of lattice defects.