Raman Scattering Study Research Articles

A Combined Theoretical and Experimental Raman Scattering Study of BaZrS3-BaHfS3 Solid Solutions.

Ba(Zr,Hf)S3 solid solutions are proposed for photovoltaic applications and a fast non-destructive measurement of the composition of these solutions and the identification of any possible secondary phases is a prerequisite for understanding their opto-electronic properties. Previously multi-wavelength Raman spectroscopy has been used for such purposes in other chalcogenide solution series. Here we calculate the non-resonant one-phonon Raman spectra of pure BaHfS3 and BaZrS3, which show only subtle differences between them, since the most prominent modes are dominated by the sulfur atoms and the change in mass of going from Hf to Zr is balanced by a near equal and opposite change in the bonding. To test this experimentally, a solution series of BaZr1-xHfxS3 (0≤x≤1) powders was synthesised and free of a secondary phase, HfS3 identified by 633 nm excitation Raman spectroscopy. The veracity of the synthesis method was confirmed by comparing X-ray diffractograms and optical absorption spectra of the BaZr0.5Hf0.5S3 alloy to a 50 : 50 mixture of the pure ternary compounds. Experimental non-resonant Raman measurements on the alloy powders confirm that only slight variations in the spectra are visible, making an alloy composition determination difficult. However, exciting the alloys resonantly, leads to the appearance of new two-phonon modes in the Raman spectrum, which change significantly across the alloy series. We consequently suggest that a rapid alloy composition measurement can be made unambiguously by measuring the ratio of the intensities of the 825 cm-1 and 625 cm-1 Raman features.

Resonant Raman Scattering Study of Strain and Defects in Chemical Vapor Deposition Grown MoS2 Monolayers.

The development of bottom-up synthesis routes for semiconducting transition metal dichalcogenides (TMDs) and the assessment of their defects are of paramount importance to achieve their applications. TMD monolayers grown by chemical vapor deposition (CVD) can be subjected to significant strain and, here, Raman and photoluminescence spectroscopies are combined to characterize strain in over one hundred MoS2 monolayer samples grown by CVD. The frequency changes of phonons as a function of strain are analyzed, and used to extract the Grüneisen parameter of both zone-center and edge phonons. Additionally, the intensity of the defect-induced longitudinal acoustic (LA) and transverse acoustic(TA) Raman bands are discussed in relation to strain and electronic doping. The experimental mode-Grüneisen parameters obtained are compared with those calculated by density functional theory (DFT), to better characterize the type of strain and its resulting effects on Grüneisen parameters. The findings indicate that the use of Raman spectra to determine defect densities in 2D MoS2 must be always conducted considering strain effects. To the best of the authors' knowledge, this work constitutes the first report on double resonance Raman processes studied as a function of strain in 2D-MoS2. The new approach to obtain the Grüneisen parameter from zone-edge phonons in MoS2 can also be extended to other 2D semiconducting TMDs.

Spin-Orbit Excitons in a Correlated Metal: Raman Scattering Study of Sr_{2}RhO_{4}.

Using Raman spectroscopy to study the correlated 4d-electron metal Sr_{2}RhO_{4}, we observe pronounced excitations at 220meV and 240meV with A_{1g} and B_{1g} symmetries, respectively. We identify them as transitions between the spin-orbit multiplets of the Rh ions, in close analogy to the spin-orbit excitons in the Mott insulators Sr_{2}IrO_{4} and α-RuCl_{3}. This observation provides direct evidence for the unquenched spin-orbit coupling in Sr_{2}RhO_{4}. A quantitative analysis of the data reveals that the tetragonal crystal field Δ in Sr_{2}RhO_{4} has a sign opposite to that in insulating Sr_{2}IrO_{4}, which enhances the planar xy orbital character of the effective J=1/2 wave function. This supports a metallic ground state, and suggests that c-axis compression of Sr_{2}RhO_{4} may transform it into a quasi-two-dimensional antiferromagnetic insulator.

Surface-Enhanced Raman Scattering Studies of Au-Ag Bimetallic Nanoparticles with a Tunable Surface Plasmon Resonance Wavelength Synthesized by Picosecond Laser Irradiation

Here, we present a simple and green method of preparing Au-Ag bimetallic nanoparticles (NPs) with a tunable surface plasmon resonance (SPR) wavelength by using picosecond laser irradiation. Au-Ag alloy NPs have been produced by irradiating the solutions containing respective metallic salts in a polyvinyl alcohol (PVA) matrix using a picosecond laser in a single-step process. The SPR wavelength of the Au-Ag bimetallic NPs is observed to be shifted/changed with the Au-Ag concentration and the laser irradiation parameters. The Au-Ag NPs embedded in the PVA matrix are advantageous for Surface-Enhanced Raman scattering (SERS) applications. The estimated enhancement factors (EFs) were observed to vary as a function of conditions of the Au-Ag bimetallic alloy NPs synthesis and also on the concentration of Au at a fixed input fluence of irradiation. The SERS active platforms of Au-Ag bimetallic NPs showed EFs as high as of the order of 108 for Crystal Violet (CV) dye samples at nano molar concentrations. The present study demonstrates a simple, single-step, and green method that fabricates Au-Ag alloy-based nanocomposites suitable for SERS investigations with significantly higher orders of EFs.

Modeling of the Lattice Dynamics in Strontium Titanate Films of Various Thicknesses: Raman Scattering Studies.

While the bulk strontium titanate (STO) crystal characteristics are relatively well known, ultrathin perovskites' nanostructure, chemical composition, and crystallinity are quite complex and challenging to understand in detail. In our study, the DFT methods were used for modelling the Raman spectra of the STO bulk (space group I4/mcm) and 5-21-layer thin films (layer group p4/mbm) in tetragonal phase with different thicknesses ranging from ~0.8 to 3.9 nm. Our calculations revealed features in the Raman spectra of the films that were absent in the bulk spectra. Out of the seven Raman-active modes associated with bulk STO, the frequencies of five modes (2Eg, A1g, B2g, and B1g) decreased as the film thickness increased, while the low-frequency B2g and higher-frequency Eg modes frequencies increased. The modes in the films exhibited vibrations with different amplitudes in the central or surface parts of the films compared to the bulk, resulting in frequency shifts. Some peaks related to bulk vibrations were too weak (compared to the new modes related to films) to distinguish in the Raman spectra. However, as the film thickness increased, the Raman modes approached the frequencies of the bulk, and their intensities became higher, making them more noticeable in the Raman spectrum. Our results could help to explain inconsistencies in the experimental data for thin STO films, providing insights into the behavior of Raman modes and their relationship with film thickness.

A High-Pressure Brillouin and Raman Scattering Study on Na2FeSi3O8.5 Glass: Implications for Pressure-induced Shear Velocity Minima in Silicate Glasses

Sound velocities of Na2FeSi3O8.5 glass have been measured to 12 GPa by Brillouin spectroscopy. Poisson's ratio and bulk, shear, and Young's moduli are calculated as a function of pressure. The shear and Young's moduli and Poisson's ratio show a shift in the response to compression of the glass at ∼2.2 GPa, where the pressure dependence of the shear modulus reverses sign. This shift mirrors those of a wide suite of glasses, and further demonstrates that pressure-induced shear velocity minima are general phenomena in silicate glasses containing few network modifiers. Raman spectra have also been collected of the glass up to 6.5 GPa. A relation is proposed between the magnitude of shear velocity depression observed under pressure in silicate glasses and the ratio of the number of network-modifying cations and network-forming cations. This relation can prospectively be deployed to compositionally tailor the pressure dependence of the elastic velocities of silicate glasses.

Adsorption behaviour on silver nanocolloids at various concentrations of a bioactive therapeutic derivative of methylhydrazine: Experimental, DFT and molecular docking investigations

A detailed theoretical and experimental study was implemented on a novel bioactive molecule 2-(3-bromobenzoyl)-N-methylhydrazine-1-carboxamide (BMC). Density Functional Theory (DFT), Time Dependent (TD)-DFT and Surface Enhanced Raman Scattering (SERS) studies were reported for the adsorption of BMC on silver hydrosols. SERS at various concentrations are discussed and there are orientation changes for BMC with concentration and BMC assumes a tilted orientation with the metal. The adsorption energy of BMC is −64.41 kcal/mol when adsorbed with Ag6, pointing to a chemisorption process. TD-DFT predicts a Ultraviolet (UV)-vis absorption of 595.11 when BMC adsorbed on Ag6, while that of BMC is 276.12 nm and the redshift, lowered intensity in UV spectra, caused by the aggregation of colloidal silver nano particles, was used to establish the adsorption of BMC on Ag6. Molecular docking is performed on BMC and BMC-Ag6 to find their ability to bind to target proteins, IP0I (human butyrylcholinesterase) and 4PQE (human acetylcholinesterase) and drug likeness properties are also assessed. The binding scores are high for BMC-Ag6 and hence the Ag6 will perform as a drug delivery vehicle.

Insights into Plasmon-Induced Dimerization of Rhodanine–A Surface-Enhanced Raman Scattering Study

Plasmon-mediated chemical reactions (PMCRs) have attracted considerable interest in recent times. The PMCR initiated by hot carriers is known to be influenced by the type of metals and the excitation wavelength. Herein, we have carried out the surface-enhanced Raman scattering (SERS) investigation of rhodanine (Rd), an important pharmacologically active heterocyclic compound, adsorbed on silver and gold nanoparticles (AgNP and AuNP) using 514.5 and 632.8 nm lasers. The prominent Raman band at 1566 cm-1 observed in the SERS spectra is attributed to the characteristic ν(C═C) stretching vibration of the Rd dimer and not of Rd tautomers. The chemical transformation of Rd to Rd dimer on metal surfaces is plausibly triggered by the indirect transfer of energetic hot electrons generated during the non-radiative decay of plasmon. The mechanism involved in the dimerization of Rd via the indirect transfer of hot electrons is also presented. The effect of wavelength on the dimerization of Rd is also observed on the AgNP surface, which indicates that the dimerization occurs more efficiently on the AgNP surface with excitation at 514.5 nm wavelength.

The concentration dependent SERS studies of a bioactive 4-chlorobenzylidene derivative: Experimental and DFT investigations

In this work, the vibrational spectroscopy of the compound (E)-4-(tert-butyl)-Nˈ-(4-chlorobenzylidene)benzyhydrazide (TCB), which was studied in conjunction with theoretical calculations, is applied for Surface Enhanced Raman Scattering (SERS) studies. The assignments of the vibrational modes were completed with Density Functional Theory (DFT)/B3LYP/6-311++G*. The information gathered is utilized to determine the chemical and electrical characteristics in addition to wavenumber measurements. The TCB molecule’s chemisorbed status on colloidal nanoparticles is confirmed by acquired red shift and decreased intensity behavior in the UV–VIS spectrum analysis. Additionally, the SERS spectra at varied concentrations and the chemisorption of the molecule with metal cluster were recorded and examined. Additionally, a silver cluster-based theoretical SERS model is put forth. The findings presented here will help in the construction of more dependable SERS sensors by thoroughly describing the concentration-dependent profile of analyte orientation.

Raman Scattering Study of Amino Acids Adsorbed on a Silver Nanoisland Film.

We studied the surface-enhanced Raman spectra of amino acids D-alanine and DL-serine and their mixture on silver nanoisland films (SNF) immersed in phosphate-buffered saline (PBS) solution at millimolar amino acid concentrations. It is shown that the spectra from the amino acid solutions differ from the reference spectra for microcrystallites due to the electrostatic orientation of amino acid zwitterions by the metal nanoisland film. Moreover, non-additive peaks are observed in the spectrum of the mixture of amino acids adsorbed on SNF, which means that intermolecular interactions between adsorbed amino acids are very significant. The results indicate the need for a thorough analysis of the Raman spectra from amino acid solutions, particularly, in PBS, in the presence of a nanostructured silver surface, and may also be of interest for studying molecular properties and intermolecular interactions.

Conformational Selectivity of Merocyanine on Nanostructured Silver Films: Surface Enhanced Resonance Raman Scattering (SERRS) and Density Functional Theoretical (DFT) Study.

In this study, detailed structural and vibrational analysis of merocyanine has been investigated using Raman, surface enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS). The Raman, SERS and SERRS studies aided by density functional theoretical (DFT) calculations clearly established the prevalence of the trans- and cis-conformers of the protonated form of merocyanine (MCH+) in solid and acetonitrile solution. The binding characteristics of merocyanine adsorbed on nanostructured silver-coated films (SCFs) were investigated using excitation-dependent SERS, concentration-dependent SERRS and DFT studies. The conformers of merocyanine involved in the surface adsorption processes were recognized. The prominent marker bands observed at 1538 (ethylenic C=C stretch) and 1133 cm−1 (pyridinium C-N stretch) in the Raman spectrum of merocyanine in acetonitrile shifted to 1540 and 1126 cm−1, respectively on the nanostructured SCFs. The shift in the marker bands is associated with either the preferential binding of selective conformer or change in resonance equilibrium between the benzenoid and quinoid forms. The excitation wavelength dependent SERS spectrum infers that in addition to the major contribution from the electromagnetic enhancement, chemical (resonance) effect leads to the amplification of the 1540 cm−1 band. The concentration-dependent SERRS study showed maximum enhancement for the nanostructured SCFs functionalized with 1 μM concentration of merocyanine, indicative of monolayer coverage. For lower concentrations of merocyanine, the SERRS signal intensity reduced without any alteration in the peak positions. The SERRS study thus, revealed sub-nanomolar (0.1 nM) sensing of merocyanine using nanostructured SCFs with the analytical enhancement factor (AEF) of ∼ 1010 for the 1126 cm−1 and 1540 cm−1 Raman bands for MC concentration of 0.1 nM. In this study, combination of SERRS and DFT have clearly established the predominance of trans-MCH+ on the nanostructured silver surface with minor contribution from cis-MCH+, which remain exclusively bound to the surface via the phenoxyl ring O atom. This conformational surface selectivity of geometrical isomers of merocyanine using nanostructured surfaces can be further explored for energy efficient and economical separation of geometrical isomers.

Raman Scattering Study of Natural and Synthetic Compounds Containing Polyene Chains

Raman Scattering Study of Natural and Synthetic Compounds Containing Polyene Chains

Raman Scattering Study on the Influence of E-Beam Bombardment on Si Electron Lens.

Microcolumns have a stacked structure composed of an electron emitter, electron lens (source lens), einzel lens, and a deflector manufactured using a micro electro-mechanical system process. The electrons emitted from the tungsten field emitter mostly pass through the aperture holes. However, other electrons fail to pass through because of collisions around the aperture hole. We used Raman scattering measurements and X-ray photoelectron spectroscopy analyses to investigate the influence of electron beam bombardment on a Si electron lens irradiated by acceleration voltages of 0, 20, and 30 keV. We confirmed that the crystallinity was degraded, and carbon-related contamination was detected at the surface and edge of the aperture hole of the Si electron lens after electron bombardment for 24 h. Carbon-related contamination on the surface of the Si electron lens was verified by analyzing the Raman spectra of the carbon-deposited Si substrate using DC sputtering and a carbon rod sample. We report the crystallinity and the origin of the carbon-related contamination of electron Si lenses after electron beam bombardment by non-destructive Raman scattering and XPS analysis methods.

Coupling of organic cation and inorganic lattice in methylammonium lead halide perovskites: Insights into a pressure-induced isostructural phase transition

Organic-inorganic hybrid metal-halide perovskite (OIHP) materials provide a tunable platform for engineering their optoelectronic properties. Although several high-pressure studies have been conducted from the OIHP family of single crystals and films, the exact nature of the dynamic coupling of the $\mathrm{C}{\mathrm{H}}_{3}\mathrm{N}{\mathrm{H}}_{3}$ (MA) cation with the octahedral lattice framework and the mechanisms responsible for the structural phase transformation under pressure are not well captured. By combined photoluminescence (PL), synchrotron-based x-ray diffraction, and Raman-scattering studies as a function of pressure from methylammonium lead bromide ($\mathrm{M}\mathrm{A}\mathrm{Pb}{\mathrm{Br}}_{3}$), we shed light on an isostructural phase transition due to the coupling of the MA cation and the $\mathrm{Pb}{\mathrm{Br}}_{6}$ lattice through hydrogen bonding. The sharp discontinuities at $\ensuremath{\sim}$ 1 GPa and $\ensuremath{\sim}$ 3 GPa in the PL peak positions correlate with the structural changes observed in high-pressure XRD and Raman-scattering studies. The electronic band edge as a function of pressure is calculated within density-functional theory. The PL peak position, intensity and width of the excitonic peak show significant changes at 2 GPa, which corroborate the changes observed in high-pressure Raman-scattering studies. The frequencies of the lattice modes and the C--H/N--H bending and stretching modes of the MA cation show anomalous changes and other nuances at 2 GPa. The suppression of rotational and orientational disorder of the organic moiety is initiated at 2 GPa and the ordering is completed by 3.0 GPa, leading to an order-disorder type cubic II ($Im\overline{3}$) to orthorhombic ($Pnma$) phase transition. Along with the revelation of an isostructural transformation at 2 GPa, this paper highlights the impact of molecular vibrations on the electronic properties of $\mathrm{M}\mathrm{A}\mathrm{Pb}{\mathrm{Br}}_{3}$ under pressure.

Pressure dependence of the interlayer and intralayer E2g Raman-active modes of hexagonal BN up to the wurtzite phase transition

We present a Raman-scattering study of the interlayer and intralayer ${E}_{2g}$ Raman-active modes of hexagonal boron nitride $(h\ensuremath{-}\mathrm{BN})$ under hydrostatic pressure for pressures up to the transition to the wurtzite phase (10.5 GPa). Pressure coefficients and Gr\uneisen parameters are determined for both modes, and are compared to ab initio calculations based on density functional perturbation theory. The pressure coefficient of the low-energy interlayer mode is higher than that of the high-energy intralayer mode owing to the large compressibility of the $h\ensuremath{-}\mathrm{BN}$ crystal along the $c$ direction. Both modes exhibit a sublinear phonon frequency increase with pressure, which is more marked in the case of the low-energy mode. The intensity of the low-energy mode increases with pressure, suggesting an enhancement of the mode polarizability as the honeycomb layers become closer. The Raman spectrum of the metastable wurtzite phase is observed at ambient pressure in the transited sample after decompression.

Self-assembling of metallic Rh over DNA as nano-chains: An effective organosol for catalysis and SERS studies

Rarely explored materials in organic medium for catalytic applications are one of the promising methods for high rate conversion and selectivity to achieve monodispersity. In this present work, for the first time, we have prepared Rh NPs in organic medium (as organosol) using microwave heating condition. The process results a colloidal solution that is stable for more than five months while keeping at low temperature in refrigerator. The self-assembled Rh-DNA as organosol was formed in two different morphologies such as nano-chains and nano-beads simply by varying the metal ions to DNA molar concentration as Rh-DNA (0.0035 M) and Rh-DNA (0.007 M), respectively. Interestingly, here, DNA was used as a scaffold which has manifold advantages over other commonly used scaffolds by providing its aromatic base pairs, negative phosphate groups and hydroxyl groups to stabilize Rh3+ metal ions. This colloidal solution can readily be dispersed in many organic solvents (protic and aprotic) which is an added advantage compared to aquasol where dispersion to other organic solvents is a problem for catalytic applications. The as prepared two set of Rh-DNA (0.0035 and 0.007 M) were applied for catalytic nitro compound reduction and Surface Enhanced Raman Scattering (SERS) studies. The synthesized two sets of Rh-DNA organosol was highly capable of reducing four different nitro compounds and comparatively, Rh-DNA (0.0035 M) showed better catalytic activity than other one. The enhancement factor (EF) values was calculated at different concentrations ranging from 10−3 M to 10−6 M and the obtained highest EF value is 2.89 × 106 for Rh-DNA (0.0035 M) while using methylene blue (MB) as a Raman probe molecule. This method of synthesis is too simple and gives highly stable solution of Rh-DNA that can be successfully utilized in multidisciplinary applications particularly in medicinal and energy related fields in near future.

Synthesis and Single-Particle Surface-Enhanced Raman Scattering Study of Plasmonic Tripod Nanoframes with Y-Shaped Hot-Zones.

Herein, plasmonic metal tripod nanoframes with three-fold symmetry were synthesized in a high yield (∼83%), and their electric field distribution and single-particle surface-enhanced Raman scattering (SERS) were studied. We realized such complex frame morphology by synthesizing analogous tripod nanoframes through multiple transformations. The precise control of the Au growth pattern led to uniform tripod nanoframes embedded with circle or line-shaped hot spots. The linear-shaped nanogaps ("Y"-shaped hot-zone) of the frame structures can strongly and efficiently confine the electric field, allowing for strong SERS signals. Coupled with a high synthetic yield of the targeted frame structure, strong and uniform SERS signals were obtained inside the nanoframe gaps. Remarkably, quite reproducible SERS signals were obtained with these structures-the SERS enhancement factors with an average value of 7.9 × 107 with a distribution of enhancement factors from 2.2 × 107 to 2.2 × 108 for 45 measured individual particles.

Plasmonic Nanoslit Arrays Fabricated by Serial Bideposition: Optical and Surface-Enhanced Raman Scattering Study.

Recently, studies have been carried out to combine surface-enhanced Raman spectroscopy substrates that are based on either localized surface plasmon or surface plasmon polariton structures. By combining these two systems, the individual drawbacks of each can be overcome. However, the manufacturing methods involved so far are sophisticated, labor-intensive, expensive, and technically demanding. We propose a facile method for the fabrication of a flexible plasmonic nanoslit surface-enhanced Raman scattering (SERS) sensor. We utilized the pattern on periodic optical disks as an inexpensive substitute for printing the periodic pattern on polydimethylsiloxane with soft imprint lithography. The Ag nanoslits were fabricated by serial bideposition using the dynamic oblique angle deposition technique. The nanoslit structures were physically and optically characterized, and the experimental results were compared to the results of the numerical simulation: Monte Carlo and finite-difference time-domain simulation. The AgNS samples showed excellent SERS performance with an enhancement factor of ∼105 and a limit of detection of 5 × 10-7 g/mL for a Rhodamine 6G solution. Their biosensing capability was demonstrated by the sensing of bilirubin.

Direct Detection of Bacteria Using Positively Charged Ag/Au Bimetallic Nanoparticles: A Label-free Surface-Enhanced Raman Scattering Study Coupled with Multivariate Analysis

Rapid detection and discrimination of pathogenic bacteria for food safety, environmental pollution, medical diagnoses, and chemical and biological threats remains a considerable challenge. In the p...

Raman spectroscopy and microstructural characterization of anti-diabetic drug metformin hydrochloride

Results of our high-resolution and high-sensitivity Raman-scattering study of metformin hydrochloride, one of the most frequently used and popular oral anti-diabetic drug which also possesses anti-aging, anti-tumor and anti-inflammatory properties is presented. It is demonstrated that rather narrow (4–10 cm−1) spectral lines of molecular vibrations are observed in the metformin hydrochloride pressed powder sample in the important spectral range of 70–1600 cm–1. Thus these “fingerprints” can be used to reveal which chemical bonds produce measurable spectral components corresponding to the vibrations of known particular functional groups and the presence of crystalline state of the metformin hydrochloride without evidence of an amorphous phase. These formulations exhibit considerable advantages and makes the metformin hydrochloride as promising model for novel developments and applications as molecular biosensor in medicine and environmental systems.