Raman Band Positions Research Articles

SEM/Raman spectroscopy of clathrites as analogs of authigenic carbonates in ocean worlds

AbstractThere is evidence from the near‐infrared observations of space missions of the presence of carbonates on the surface of several ocean worlds. However, their genesis remains unresolved. We investigate the hypothesis that these carbonates may be in the form of clathrites assuming that clathrate hydrates are stable phases in the crust and ocean of these ocean worlds. In order to support this, we studied a sample of a potential clathrite from the Hydrate Ridge cold seep (Cascadia Subduction Zone), the carbonate rock fossil of clathrate hydrates, as a terrestrial analogue. We characterised the mineralogy and texture of the sample by using a coupled confocal Raman microscope and scanning electron microscopy instrument with the aim of identifying possible geo‐ and biosignatures, which could be relevant for future missions of exploration to ocean worlds and Mars. Our results show that aragonite is the dominant mineral phase in the clathrite sample, but Mg‐calcite and dolomite were also identified. These three carbonates constitute a pattern related to clathrate hydrate formation and dissociation processes. Dolomite was defined as a biosignature of gas hydrate microbiomes because it was integrated within Mg‐calcite grains precipitated after clathrate hydrate dissociation. Nevertheless, no spectral changes were observed in Raman bands of carbonate minerals that would indicate the influence of clathrate hydrates in their genesis. We also observed that Raman band positions of the associated framboidal pyrites are a characteristic signature of the associated framboid‐like texture because its potential as biosignature may only be attributed by biochemical analysis.

Probing the mesophase formation in thermotropic liquid crystal HBDBA using temperature-dependent Raman spectroscopy and DFT method

Liquid crystalline properties of the synthesized liquid crystal (LC) N-(o-hydroxybenzylidene)-N′-(4-n-alkoxybenzylidene) azines (HBDBA) are probed thoroughly using the comprehensive array of techniques e.g. differential scanning calorimetry (DSC), differential thermal analysis (DTA), polarizing optical microscopy (POM), temperature-dependent Raman spectroscopy and density functional theory (DFT) method. In this study, intricate molecular interactions crucial for mesophase formation of liquid crystalline system HBDBA and molecular rearrangement that occurs during LC transitions are unravelled comprehensively. Remarkably, at the Cr → SmA phase transition, the peak position, linewidth, and intensity of signature Raman bands are prominently changed. A thorough analysis of Raman marker bands and DFT calculation confirm the disruption of intramolecular hydrogen bonds in HBDBA at the Cr → SmA transition. The conclusion of the present study enriches the understanding of the underlying mechanisms of mesophase formation and intricate molecular interactions and arrangement at the molecular level of the thermotropic LC.

Cluster structure of ultrahard fullerite revealed by Raman spectroscopy

We have discovered Raman peculiarities of sp3-bonded carbon nanoclusters forming ultrahard fullerite synthesized at pressure up to 85 GPa. The nanoclusters differ in the values of bulk modulus B0 ranging from 580 to 730 GPa. We found that the Raman frequency, corresponding to the C-C stretching mode of the nanoclusters, varies linearly from 1485 to 1640 cm−1, depending on the excitation wavelength used, which ranges from 785 nm to 257 nm. In particular, the nanoclusters with higher B0 have a higher Raman frequency. We also observed a resonant Raman spectrum when excited at a wavelength of 1064 nm. This showed a plateau from 1400 to 1720 cm−1, covering all Raman band positions of the nanoclusters from 1485 to 1640 cm−1. In addition, two Raman bands at 1285 and 1600 cm−1 appear at the resonance. The presence of several types of carbon sp3-bonded nanoclusters is confirmed by high-resolution transmission electron microscopy. Using moment tensor potentials, a class of machine learning interatomic potentials, we calculated the phonon density of states of the nanoclusters formed during the 3D polymerization of C60. The presence of high frequency modes in the resonant Raman spectra suggests the existence of bonds with force constants higher than those in a single crystal diamond. In addition, we observed a stiffening effect when analyzing the dependence of the mechanical stiffness on the cluster size, with smaller clusters exhibiting a more rigid structure.

Crystal chemistry of ferriallanite-(Ce) from Nya Bastnäs, Sweden: Chemical and spectroscopic study

A second study of ferriallanite-(Ce) from Nya Bastnäs, Sweden, extends current data by using electron probe micro-analysis (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis and brings new insights about its crystal chemistry obtained by Raman spectroscopy. The study presents the first Raman spectra for ferriallanite-(Ce) member of the allanite group (not considering the rather low-quality spectra published in preceding papers). The material does not show significant radiation damage, which is rare as allanite-group minerals often have undergone metamictisation due to significant amounts of incorporated radionuclides (U, Th). Some interior regions show pronounced zoning that correlates with variations in Raman-band positions. In spite of its significant REE content, the material is virtually non-luminescent. New additional data for allanite-(Ce) from Oßling, Germany and Domanínek, Czech Republic are also presented, which were used for comparison.

Helical Organic and Inorganic Polymers.

Despite being a staple of synthetic plastics and biomolecules, helical polymers are scarcely studied with Gaussian-basis-set ab initio electron-correlated methods on an equal footing with molecules. This article introduces an ab initio second-order many-body Green's function [MBGF(2)] method with nondiagonal, frequency-dependent Dyson self-energy for infinite helical polymers using screw-axis-symmetry-adapted Gaussian-spherical-harmonics basis functions. Together with the Gaussian-basis-set density-functional theory for energies, analytical atomic forces, translational-period force, and helical-angle force, it can compute correlated energy, quasiparticle energy bands, structures, and vibrational frequencies of an infinite helical polymer, which smoothly converge at the corresponding oligomer results. These methods can handle incommensurable structures, which have an infinite translational period and are hard to characterize by any other method, just as efficiently as commensurable structures. We apply them to polyethylene (2/1 helix), polyacetylene (Peierls' system) and polytetrafluoroethylene (13/6 helix) to establish the quantitative accuracy of MBGF(2)/cc-pVDZ in simulating their (angle-resolved) ultraviolet photoelectron spectra and of B3LYP/cc-pVDZ or 6-31G** in reproducing their structures, infrared and Raman band positions, phonon dispersions, and (coherent and incoherent) inelastic neutron scattering spectra. We then predict the same properties for infinitely catenated chains of nitrogen or oxygen and discuss their possible metastable existence under ambient conditions. They include planar zigzag polyazene (N2)x (Peierls' system), 11/3-helical isotactic polyazane (NH)x, 9/4-helical isotactic polyfluoroazane (NF)x, and 7/2-helical polyoxane (O)x as potential high-energy-density materials.

Non-destructive distinction between geogenic and anthropogenic calcite by Raman spectroscopy combined with machine learning workflow.

Here, we demonstrate, for the first time, the possibility of distinguishing between geogenic and anthropogenic calcite in a non-destructive and effective way. Geogenic calcite derives from natural sedimentary and metamorphic rocks whereas anthropogenic calcite is formed artificially due to the carbonation process in mortars and plaster lime binders. Currently, their distinction is a major unaddressed issue although it is crucial across several fields such as 14C dating of historical mortars to avoid contamination with carbonate aggregates, investigating the origins of pigments, and studying the origins of sediments, to name a few. In this paper, we address this unmet need combining high-resolution micro-Raman spectroscopy with data mining and machine learning methods. This approach provides an effective means of obtaining robust and representative Raman datasets from which samples' origins can be effectively deduced; moreover, a distinction between sedimentary and metamorphic calcite has been also highlighted. The samples, chemically identical, exhibit systematic and reliable differences in Raman band positions, band shape and intensity, which are likely related to the degree of structural order and polarization effects.

A comprehensive study on the ionomer properties of PFSA membranes with confocal Raman microscopy

The proton exchange membrane is the heart of many electrochemical energy systems, and their performance and longevity depend on a careful selection and processing of membrane materials. In this work, we use confocal Raman microscopy to investigate application-relevant properties of perfluorinated sulfonic acid (PFSA) membranes. Raman spectra of Nafion, Aquivion, and 3M Ionomer at different equivalent weights show differences in the spectral area and position of various Raman bands but reveal a clear trend of band intensities versus equivalent weight. Characteristics of these ionomers such as swelling and water uptake were determined with through-plane imaging. The technique offers advantages over conventional measurements, such as contact-free and non-destructive data acquisition. Calibration curves for the equivalent weight were derived for the different PFSAs with excellent linear fits that allow a quantification of the ionizable group content. The high spatial resolution of confocal Raman microscopy of less than 2 μm enables the local evaluation of all these ionomer properties. Furthermore, Raman imaging was employed to characterize composite membranes, which shows that it can resolve individual phases and features in multi-layered membranes. This study provides a comprehensive summary of confocal Raman microscopy as a powerful tool for the analysis of ionomer and membrane properties.

Determination of skarn garnet compositions using Raman spectroscopy

AbstractGarnet is a key and defining mineral of skarns and associated metalliferous deposits. Variation in garnet composition, commonly expressed by the proportions of different end‐members, is widely used to determine the physical–chemical features of hydrothermal fluids. Skarn garnets from the Fujiashan W‐Cu‐Mo deposit, eastern China, were investigated by Raman spectroscopy and electron probe microanalysis to assess the quantitative correlation between Raman band positions and proportions of garnet end‐members. Compositions and Raman band positions of so‐called “grandite” garnet (Adr18–98Grs0–79), where Adr and Gr are the end‐members andradite and grossular, respectively, display a spatial zonation at Fujiashan that correlates with the distance from the contact between skarn and causative intrusion. Raman band positions determined in the ranges 234–246, 351–368, 369–375, 515–544, 814–826, and 873–882 cm−1 demonstrate moderate to very strong (R2 up to 0.99) linear correlations with mol% andradite and grossular components. This is attributed to homovalent substitution between Fe3+ and Al3+ in the octahedral site, which has an indirect effect on bond lengths and angles of Si‐O vibration, resulting in linear variation of Raman band positions. The band between 515 and 544 cm−1 is the most sensitive to compositional variation, and its position enables robust estimation of end‐member proportions within 10% of results calculated from electron probe microanalysis. This research highlights the potential of Raman spectroscopy as a rapid, powerful method to assess the composition of skarn garnet, enabling accelerated construction of spatial zonation models for skarns during skarn deposit exploration.

A comprehensive multiparametric Raman analysis of graphene evolution under prolonged near-IR femtosecond laser irradiation

Laser processing is a promising technique for graphene modification and patterning, with applications in the development of several electronic devices. In-situ Raman spectroscopy allows monitoring laser processing, providing information on numerous perturbations of the graphene lattice, such as disorder, strain, and doping, among others. This work focuses on the study of a graphene layer under prolonged irradiation with a femtosecond near-infrared laser at different average powers below the ablation threshold. The temporal evolution of the spectral parameters is analyzed, including the central position, width, and area of the main Raman bands attributed to graphene and silicon substrate, as well as the background signal. In addition, we present the correlation curves between most of these parameters. Our results show an initial instantaneous effect, linear with irradiation power, in which mainly p-type doping occurs. With prolonged fs-laser irradiation, the evolution of the spectral parameters can be divided into several intervals associated with different doping and strain stages. At each stage, the parameters present multiple time dependencies, nevertheless, several correlations between them are revealed. This work highlights the complexity of the evolution of the complete Raman spectrum of graphene and the relevance of a comprehensive multiparametric analysis.

Impact of in/ex situ annealing and reaction temperature on structural, optical and electrical properties of SnS thin films

In this work, SnS thin films were prepared by in situ and ex situ annealing process of precursor films deposited by RF (Radio Frequency) magnetron sputtering employing binary SnS target. In situ annealing treatment was performed in sputtering chamber and ex situ annealing treatment was performed using RTP (Rapid Thermal Processing) system under Ar+H2 mix gas employing 225, 300 and 375 °C as reaction temperatures in order to find out the best fabrication parameters of SnS thin film since it has been used as an absorber layer in the cell structure. The EDX (Energy Dispersive X-ray Spectroscopy) measurements showed that precursor and reacted films have almost stoichiometric composition except for in situ annealed sample at 375 °C. XRD (X-ray Diffraction) patterns of all samples revealed orthorhombic SnS phase regardless of annealing route and temperature. In addition to SnS phase, formation of SnS2 phase was observed in in situ annealed SnS samples at 225 and 300 °C. Moreover, in situ annealed samples displayed larger crystallite size and lower micro strain compared to ex situ annealed samples. Raman spectra of the samples confirmed formation of orthorhombic SnS phase and it was also seen that crystalline quality gave rise to shift in position of Raman bands for some samples. Only a SEM (Scanning Electron Microscopy) image of in situ annealed sample at 375 °C displayed distinct surface morphology. Optical band gap values of the samples showed variation between 1.35 and 1.66 eV. Electrical characterization of the films showed that resistivity values changed from 3.34×103 to 2.28×104 Ω-cm and carrier concentration values changed from 1.34×1014 to 1.05×1015 cm−3. It was seen that in situ annealing at 375 °C exhibited more promising results for potential SnS based photovoltaic applications.

Raman spectroscopy and high pressure study of synthetic Ga,Ge-rich tourmaline

We present Raman spectroscopic analysis of the synthetic Ga,Ge-rich tourmalines at pressures up to 30 GPa for the first time. Based on the experimental data, we obtained correlation between the Raman band positions and the cation substitutions in the tetrahedral and octahedral sites at ambient conditions. A new band of Ge–O stretching vibrations, which is not common in natural tourmalines, occurs at ~ 870 cm−1. The main Raman bands shift to the higher frequencies with increasing pressure due to decrease in the bond lengths, associated with structural deformations. The lattice dynamic calculated spectra of tourmalines with various compositions resemble those measured experimentally. Analysis of experimental and theoretical data reveals a possible phase transition at ~ 18.4 GPa in the tourmalines with up to 10 wt% Ga2O3 and 9 wt% GeO2.

Phase Stability of Chloroform and Dichloromethane at High Pressure

Chloroform (CHCl3) and dichloromethane (CH2Cl2) are model systems for the study of intermolecular interactions, such as hydrogen bonds and halogen–halogen interactions. Here we report a joint computational (density-functional perturbation theory (DFPT) modelling) and experimental (Raman scattering) study on the behaviour of the crystals of these compounds up to a pressure of 32 GPa. Comparing the experimental information on the Raman band positions and intensities with the results of calculations enabled us to characterize the pressure-induced evolution of the crystal structure of both compounds. We find that the previously proposed P63 phase of CHCl3 is in fact a metastable structure, and that up to 32 GPa the ambient-pressure Pnma structure is the ground state polymorph of this compound. For CH2Cl2 we confirm the stability of the ambient-pressure Pbcn structure up to 32 GPa. We show that the high-pressure evolution of the crystal geometry of CHCl3 in the Pnma structure is a result of the subtle balance between dipole–dipole interactions, hydrogen bonds and Cl···Cl contacts. For CH2Cl2 (Pbcn structure) the dipole–dipole interactions and hydrogen bonds are the main factors influencing the pressure-induced changes in the geometry.

Raman spectroscopic studies of O–H stretching vibration in Mn-rich apatites: A structural approach

Abstract The O–H stretching vibration mode in crystals of (Mn,Cl)-rich and F-poor minerals of the apatite-supergroup has been studied by micro-Raman spectroscopy. The main purpose was to check if such an analysis can provide a quick and simple method to assess the distribution of Ca and Mn together with traces of Fe + Mg (= Mn*) on nonequivalent cationic sites in the apatite structure, especially in small and strongly heterogeneous crystals directly in thin sections. The O–H stretching vibration mode can then be treated as a useful structural probe giving information on the M2 occupants bonded to XOH. Pieczkaite, with the empirical formula (Mn4.49Fe0.47Ca0.05Mg0.01)Σ5.01P2.99O12[Cl0.83(OH)0.17], displays the O–H stretching mode centered at ~3380 cm–1, which shows that the complete replacement of Ca by Mn* at the M2 site is connected with a shift of the O–H stretching band ~192 cm–1 toward lower wavenumbers in relation to the O–H Raman band position reported for hydroxylapatite. The value is high enough to be an indicator of the M2Mn*···OH content in any sample of Mn-enriched apatite. Studies of the fine structure of the band disclosed its dependence on (1) the local combinations of Ca and Mn* forming triplets of M2 cations bonded to the X anion, (2) the presence of OH+Cl at the two half-occupied X sites that form chemical bonds with the M2 cations varying in strength and length, and (3) the spatial geometry of the X–M2 bonds and polarizability of the monovalent X anion by varying cations in the M2M2M2 triplets. The deconvolution of the band into maximum eight component bands with constant Raman shifts opens the possibility of evaluating the averaged M2M2M2 triplet bonded to oxygen of the XOH group. If the OH/(OH+Cl) fraction is known, the amounts of Ca and Mn* bonded to XOH can also be estimated. Application of the method to the holotype parafiniukite showed a slightly different distribution of Ca in M2M2M2 triplets than had been assumed from single-crystal X-ray diffraction. However, it corroborates suggestions that in the apatite structure there may be a preference for M2Ca to be bonded to XOH and M2Mn* to XCl. Our results show that the proposed method can be used as an independent tool in structural studies of Mn-rich minerals of the apatite-supergroup, providing results complementary to single-crystal X-ray diffraction. This method can easily be adjusted to modern apatite-type nanomaterials synthesized for biomedical and various industrial applications.

Determination of the plutonium content and O/M ratio of (U,Pu)O2-x using Raman spectroscopy

Oxygen stoichiometry in (U,Pu)O2-x nuclear fuels, while of prime interest, is still difficult to be determined at the micrometric scale. It has been recently evidenced that Raman microscopy is a promising tool to characterize (U,Pu)O2-x samples at a microscopic scale by probing the oxygen sublattice. Its use for determining the local O/M ratio was studied in this work on mixed oxide samples mostly containing 239Pu and natural uranium, in addition to minor traces of other isotopes, including decay products and 241Am. The first step was to dissociate the influence of the Pu/(U+Pu+Am) content, self-irradiation and O/M ratio on Raman spectra and especially on the main Raman band position in fluorite structure, the T2g. In this aim, freshly annealed and aged U1-yPuyO2-x samples, with 0.19 < y < 0.46 and different O/M ratios, were analyzed by XRD and Raman spectroscopy. After figuring out that self-irradiation alone had no significant impact on the T2g position, two mathematical relations were determined, linking the T2g position to the Pu/(U+Pu+Am) content and to the lattice parameter. Finally, the oxygen hypostoichiometry direct impact on (U,Pu)O2-x Raman spectra was determined for the first time. In agreement with past results observed in CeO2-x, a O/M ratio decrease induces a T2g shift towards lower frequencies in (U,Pu)O2-x. Combining the whole results, an equation allowing to determine the T2g position according to the O/M ratio and Pu/(U+Pu+Am) content was established. Raman spectrometer associated to a confocal optical microscope can then be used to determine locally (≈1 µm) either the Pu/(U+Pu+Am) content or the O/M ratio. This study proves the relevance of such method to characterize the fuel pellets in an industrial way.

Quantification of stress transfer in a model cellulose nanocrystal/graphene bilayer using Raman spectroscopy

Graphene and cellulose possess a multitude of unique and useful properties for applications in electronics, sensors and composites which has led to significant scientific interest over the past 5–10 years. Despite this interest, there has been no experimental work investigating the interface or stress transfer efficiency between these materials, which limits future developments in this field. With the aim of investigating this interface, we have created a model bilayer composite, consisting of a tunicate derived cellulose nanocrystal (T-CNC) film and a monolayer of graphene produced by chemical vapour deposition. Raman spectroscopy has been used to monitor the four-point bending of this model bilayer composite. Shifts in the position of Raman bands, unique for both the cellulose and graphene components of this model composite, are recorded. Using a novel analysis of these Raman band shifts, we have formed an expression which deconvolutes the total stress transfer efficiency of the model system. Using this deconvolution, a stress transfer efficiency of 66% has been derived at the cellulose/graphene interface. In addition, splitting of the graphene Raman G band has allowed calculation of the shear strain in the graphene, which is assumed to be equal to that at the cellulose-graphene interface. The individual T-CNCs in the reference samples showed location dependent preferential orientations. The film was found to be stiffer when the T-CNCs were oriented parallel to the loading axis. It was intended that the varying stiffness of the cellulose film could be used to analyse the effects of underlying film stiffness on stress transfer efficiency, but conclusions from this test were limited. The detailed interface analysis presented here will help to inform design in future cellulose/graphene devices.

Resonance Raman Spectro-Electrochemistry to Illuminate Photo-Induced Molecular Reaction Pathways.

Electron transfer reactions play a key role for artificial solar energy conversion, however, the underlying reaction mechanisms and the interplay with the molecular structure are still poorly understood due to the complexity of the reaction pathways and ultrafast timescales. In order to investigate such light-induced reaction pathways, a new spectroscopic tool has been applied, which combines UV-vis and resonance Raman spectroscopy at multiple excitation wavelengths with electrochemistry in a thin-layer electrochemical cell to study [RuII(tbtpy)2]2+ (tbtpy = tri-tert-butyl-2,2′:6′,2′′-terpyridine) as a model compound for the photo-activated electron donor in structurally related molecular and supramolecular assemblies. The new spectroscopic method substantiates previous suggestions regarding the reduction mechanism of this complex by localizing photo-electrons and identifying structural changes of metastable intermediates along the reaction cascade. This has been realized by monitoring selective enhancement of Raman-active vibrations associated with structural changes upon electronic absorption when tuning the excitation wavelength into new UV-vis absorption bands of intermediate structures. Additional interpretation of shifts in Raman band positions upon reduction with the help of quantum chemical calculations provides a consistent picture of the sequential reduction of the individual terpyridine ligands, i.e., the first reduction results in the monocation [(tbtpy)Ru(tbtpy•)]+, while the second reduction generates [(tbtpy•)Ru(tbtpy•)]0 of triplet multiplicity. Therefore, the combination of this versatile spectro-electrochemical tool allows us to deepen the fundamental understanding of light-induced charge transfer processes in more relevant and complex systems.

Crystal structure change in grossular–Si–free katoite solid solution: Oxygen position splitting in katoite

Single crystals of katoite hydrothermally synthesized were examined by single–crystal X–ray diffraction, EPMA, and Raman spectroscopic techniques. The chemical formulas of the katoite fell inside the miscibility gap proposed by Kyritsis et al. (2009). The systematic absences observed through single–crystal X–ray diffraction were completely consistent with the cubic space group Ia3d. In two kinds of katoite with chemical formulas Ca3Al2(SiO4)0.57(H4O4)2.43 and Ca3Al2(SiO4)0.69(H4O4)2.31, the O atom position was split into two independent crystallographic sites, O1 and O2; the O1 is coordinated with Si, whereas the O2 forms a tetrahedral interstice. The a lattice parameter monotonically decreased as increasing Si content. The variation lay along a straight line between grossular and Si–free katoite solid solution. The coordination volume of the T site decreased with Si incorporation into the T site. The coordination volume of CaO8 dodecahedra also decreased with the Si incorporation into the T site because the edges of the CaO8 dodecahedron are shared with the adjacent TO4 tetrahedra. These contractions lead to a monotonous decrease of the a lattice parameter. The volume of the AlO6 octahedra, on the other hand, increased with the Si incorporation. There were no clear structural constraints resulting in a miscibility gap in the solid solution. A Raman band corresponding to the OH stretching vibration was observed at 3650 cm−1, but with the substitution of Si for H, a new Raman peak appeared at 3580 cm−1. The two Raman band positions remained unchanged with increasing Si content. These results strongly suggest that there are two types of OH stretching vibration in siliceous katoite. We therefore conclude that with Si substitution for H the O position is split into two inequivalent sites that correspond to the SiO4 and H4O4 tetrahedra. The oxygen position splitting in katoite results in the emergence of two Raman bands at 3580 and 3650 cm−1.

Topic Review: Application of Raman Spectroscopy Characterization in Micro/Nano-Machining.

The defects and subsurface damages induced by crystal growth and micro/nano-machining have a significant impact on the functional performance of machined products. Raman spectroscopy is an efficient, powerful, and non-destructive testing method to characterize these defects and subsurface damages. This paper aims to review the fundamentals and applications of Raman spectroscopy on the characterization of defects and subsurface damages in micro/nano-machining. Firstly, the principle and several critical parameters (such as penetration depth, laser spot size, and so on) involved in the Raman characterization are introduced. Then, the mechanism of Raman spectroscopy for detection of defects and subsurface damages is discussed. The Raman spectroscopy characterization of semiconductor materials’ stacking faults, phase transformation, and residual stress in micro/nano-machining is discussed in detail. Identification and characterization of phase transformation and stacking faults for Si and SiC is feasible using the information of new Raman bands. Based on the Raman band position shift and Raman intensity ratio, Raman spectroscopy can be used to quantitatively calculate the residual stress and the thickness of the subsurface damage layer of semiconductor materials. The Tip-Enhanced Raman Spectroscopy (TERS) technique is helpful to dramatically enhance the Raman scattering signal at weak damages and it is considered as a promising research field.

Charge transfer dynamical processes at graphene-transition metal oxides/electrolyte interface for energy storage: Insights from in-situ Raman spectroelectrochemistry

Hybrids consisting of supercapacitive functionalized graphene (graphene oxide; GO reduced graphene oxide; rGO multilayer graphene; MLG, electrochemically reduced GO; ErGO) and three-dimensional graphene scaffold (rGOHT; hydrothermally prepared) decorated with cobalt nanoparticles (CoNP), nanostructured cobalt (CoO and Co3O4) and manganese (MnO2) oxide polymorphs, assembled electrochemically facilitate chemically bridged interfaces with tunable properties. Since Raman spectroscopy can capture variations in structural and chemical bonding, Raman spectro-electrochemistry in operando i.e. under electrochemical environment with applied bias is employed to 1) probe graphene/metal bonding and dynamic processes, 2) monitor the spectral changes with successive redox interfacial reactions, and 3) quantify the associated parameters including type and fraction of charge transfer. The transverse optical (TO) and longitudinal optical (LO) phonons above 500 cm−1 belonging to Co3O4, CoO, MnO2 and carbon-carbon bonding occurring at 1340 cm-1, 1590 cm−1 and 2670 cm-1 belonging to D, G, and 2D bands, respectively, are analyzed with applied potential. Consistent variation in Raman band position and intensity ratio reveal structural modification, combined charge transfer due to localized orbital re-hybridization and mechanical strain, all resulting in finely tuned electronic properties. Moreover, the heterogeneous basal and edge plane sites of graphene nanosheets in conjunction with transition metal oxide ‘hybrids’ reinforce efficient surface/interfacial electron transfer and available electronic density of states near Fermi level for enhanced performance. We estimated the extent and nature (n− or p−) of charge transfer complemented with Density Functional Theory calculations affected by hydration and demonstrate the synergistic coupling between graphene nanosheets and nanoscale cobalt (and manganese) oxides for applied electrochemical applications.

Structural, optical and photoelectrical properties of thermally annealed amorphous In15Sb15Se70 chalcogenide films

In this work, the effect of annealing on the structure and photoelectrical properties of In15Sb15Se70 films has been investigated. The annealed films (333–453 K) were characterized by XRD, SEM, TEM, optical absorption, Raman spectroscopy and photoconductivity measurements. The amorphous/crystalline structure of as-prepared and annealed samples was confirmed by XRD and SEM/TEM studies. The crystallization of Se, Sb2Se3 and In4Se3 phases has been observed upon annealing of the film samples. The position and shape of Raman bands have been significantly altered with annealing temperature. The indirect optical gap varies from 1.53 to 1.08 eV which is very useful for solar cell applications. DC activation energy and photosensitivity were found to decrease with annealing temperature. The decay of photocurrents was well fitted to stretched exponential function and the minimum value for fit parameters for the sample annealed at 373 K has revealed least defect states in mobility gap for In15Sb15Se70 films.