Nonresonant Raman Spectra Research Articles

The effect of Tri- and Tetra-vacancies defects on the electronic and vibrational properties of (14, 5) chiral carbon nanotube

In this theoretical work, using the spectral moment’s method and the bond polarisability model, the non-resonant Raman spectra of (14,5) chiral carbon nanotube with Tri- and Tetra-vacancies defects were calculated. The evolution of the Raman lines of defectives CNTs as a function of the defects concentration was discussed. It is observed that, the Raman spectra of defective carbon nanotubes present the D-band around 1350 cm-1. The Raman characteristics modes of TriV and TetraV defects are identified. The evolution of the electronic density of states as a function of the defects concentration was investigated. This study can provide benchmark to understand the experimental data of defective CNTs.

Raman spectroscopy analysis of single wall carbon nanotubes with penta- and hexa-vacancies defects

In this paper the effect of penta- and hexa-vacancies defects on a vibrational properties of single wall carbon nanotube (SWNT) was investigated. The bond-polarizability model combined with the spectral moments method are carried out to calculate the non-resonant Raman spectra. The changes of Raman spectra as a function of the nanotube chirality and the vacancies defects concentration on the wall of the nanotube are identified. The intensity ratio of D-band to G-band (ID /IG ratio) reflects the purity of SWNTs. Our study offers a means to distinguish between pristine and defective SWNTs even at low defect concentrations.

Probing temperature-dependent interlayer coupling in a MoS2/h-BN heterostructure

Stacking of atomically thin layers of two-dimensional materials has revealed extraordinary physical phenomena owing to van der Waals (vdW) interaction at the interface. However, most of the studies focused on the transition metal dichalcogenide (TMD)/TMD heterostructure, while the interlayer coupling of the TMD/hexagonal boron nitride (h-BN) heterostructure has not been extensively explored despite its importance. In this study, the temperature-dependent interlayer coupling is demonstrated in a heterostructure of molybdenum disulfide (MoS2) and h-BN. The interface between MoS2 and the insulating substrate exerts a significant spectroscopic impact on MoS2 through substrate-induced local strain, charged impurity, and vdW interactions. Under non-resonant conditions, temperature-dependent peak shifts in Raman and photoluminescence (PL) spectra of MoS2 reveal the evolution of interlayer coupling. Phonon frequencies and PL peak energies at different temperatures demonstrate how substrate-induced strain, impurity, and vdW interactions at the interface influence phonon vibration and excitonic transition of MoS2. Under resonant conditions at low temperature, anomalous Raman modes appear in the MoS2/h-BN heterostructure because of the enhanced electron-phonon coupling and vdW interactions. The anomalous Raman modes are quantitatively investigated by the deconvolution of the resonance Raman spectra and described by interlayer coupling at low temperature, in agreement with complementary indications from the temperature-dependent evolution of non-resonant Raman and PL spectra.

Multimodal detection and analysis of a new type of advanced Heinz body-like aggregate (AHBA) and cytoskeleton deformation in human RBCs.

A new type of aggregate, formed in human red blood cells (RBCs) in response to glutaraldehyde treatment, was discovered and analyzed with the classical and advanced biomolecular imaging techniques. Advanced Heinz body-like aggregates (AHBA) formed in a single human RBC are characterized by a higher level of hemoglobin (Hb) degradation compared to typical Heinz bodies, which consist of hemichromes. The complete destruction of the porphyrin structure of Hb and the aggregation of the degraded proteins in the presence of Fe3+ ions are observed. The presence of such aggregated, highly degraded proteins inside RBCs, without cell membrane destruction, has been never reported before. For the first time the spatial differentiation of two kinds of protein mixtures inside a single RBC, with different phenylalanine (Phe) conformations, is visualized. The non-resonant Raman spectra of altered RBCs with AHBA are characterized by the presence of a strong band located at 1037 cm-1, which confirms that glutaraldehyde interacts strongly with Phe. The shape-shifting of RBCs from a biconcave disk to a spherical structure and sinking of AHBA to the bottom of the cell are observed. Results reveal that the presence of AHBA should be considered when fixing RBCs and indicate the analytical potential of Raman spectroscopy, atomic force microscopy and scanning near-field optical microscopy in AHBA detection and analysis.

Ab Initio Wavelength-Dependent Raman Spectra: Placzek Approximation and Beyond.

We analyze how to obtain non-resonant and resonant Raman spectra within the Placzek as well as the Albrecht approximation. Both approximations are derived from the matrix element for light scattering by application of the Kramers, Heisenberg, and Dirac formula. It is shown that the Placzek expression results from a semi-classical approximation of the combined electronic and vibrational transition energies. Molecular hydrogen, water, and butadiene are studied as test cases. It turns out that the Placzek approximation agrees qualitatively with the more accurate Albrecht formulation even in the resonant regime for the excitations of single vibrational quanta. However, multiple vibrational excitations are absent in Placzek but can be of similar intensities to single excitations under resonance conditions. The Albrecht approximation takes multiple vibrational excitations into account, and the resulting simulated spectra also exhibit good agreement with experimental Raman spectra in the resonance region.

Nonresonant Raman spectra of the methyl radical 12CH3 simulated in variational calculations

We report first-principles variational simulation of the non-resonant Raman spectrum for the methyl radical (12CH3) in the electronic ground state. Calculations are based on a high level ab initio potential energy and dipole moment surfaces of CH3 and employ the accurate variational treatment of the ro-vibrational dynamics implemented in the general code TROVE [S. N. Yurchenko, W. Thiel, and P. Jensen, J. Mol. Spectrosc. 245, 126–140 (2007); A. Yachmenev and S. N. Yurchenko, J. Chem. Phys. 143, 014105 (2015)]. TROVE can be applied to arbitrary molecules of moderate size and we extend here its capabilities towards simulations of Raman spectra. The simulations for CH3 are found to be in a good agreement with the available experimental data.

β-As Monolayer: Vibrational Properties and Raman Spectra.

Recently, semiconducting and other extraordinary properties of the monolayer of the V-group element have attracted a broad interest and attention. The success of experimentally growing antimonene and black phosphorus makes the arsenic monolayer a reasonable candidate for two-dimensional semiconductors. By using DFT calculation, we investigate the vibrational properties and Raman spectra of the buckled honeycomb monolayer of arsenic (β-As) for four commonly used laser lines. By calculating Raman tensor of each active modes of the β-As monolayer, we obtained polarization angle-dependent Raman intensities when the wave vector of incident light is parallel and perpendicular with the plane of the β-As monolayer. We found that the nonresonant Raman spectra have two peaks at 235 and 305 cm–1 that correspond to the in-plane vibrating mode Eg and out-of-plane vibrating mode A1g, which is similar to germanene, blue phosphorene, and β-Sb monolayer Raman spectra. There are two (four) minima and two (four) maxima when the polarization direction of scattered light is parallel (perpendicular) to that of the incident light and the wave vector of the incident light is parallel to the β-As monolayer. The Raman intensities of neither parallel polarization configuration nor perpendicular polarization configuration depend on the polarization direction when the wave vector of incident light is perpendicular to the β-As monolayer. The relation between shapes of the polar plots and relative values of Raman tensor elements is found. The Raman intensities decrease with increasing wavelength of incident laser lines in most cases. Our results will help experimentalists to identify the existence and the orientation of the β-As monolayer while they are growing the β-As monolayer.

Nonresonant and Resonant Surface-Enhanced Raman Scattering of N-Ethyl-N-(2-hydroxyethyl)-4-(4-nitrophenylazo) Aniline in Poly(methyl methacrylate) on Ag Films with Surface Roughness

Abstract Nonresonant and resonant surface-enhanced Raman scatterings (SERS and SERRS) were studied for N-ethyl-N-(2-hydroxyethyl)-4-(4-nitrophenylazo) aniline (Disperse Red 1, or DR1) in poly (methyl methacrylate) on Ag films with surface roughness. DR1 is a chromophore that consists of azobenzene bridged between electron-donating amine and electron-accepting nitro groups, and it has attracted great attention because of its large molecular hyperpolarizability. DR1 hybridized with metal nanoparticles or nanostructures is promising as a building block for nonlinear plasmonics. Our experimental results demonstrated that the Raman cross sections were highly enhanced both at the molecular nonresonant and resonant excitation wavelengths. The spectroscopic properties of SERRS were taken from resonant Raman (RR), and the enhanced RR cross sections were attributed to electromagnetic enhancements due to surface plasmons (SP). The SERS spectrum was also similar to the RR spectrum, rather than the non-resonant Raman (NR) spectrum, even at the molecular non-resonant excitations. A diagram of energy levels was drawn for the DR1/Ag interfaces by using ultraviolet-visible linear absorption and ultraviolet photoelectron spectroscopic data. The enhanced NR cross sections were explained in terms of the electromagnetic enhancements, as well as the metal-to-molecular charge-transfer, by using the energy diagram.

Vibrational Signatures of Carboxylated Graphene: A First-Principles Study

Raman and infrared (IR) spectroscopies are fast, efficient, and nondestructive techniques commonly used for structural characterization of nanoscale materials. The complimentary characters of the Raman and IR spectroscopies make them ideally suited for experimental studies of carbon nanostructures. Using first-principles computational methods based on density functional perturbation theory, we computed nonresonant Raman and IR absorption spectra of carboxylated graphene containing no surface defects, containing Stone–Wales defects, and containing divacancies. Our calculations demonstrated that the presence of point defects near the functionalization sites significantly altered the Raman and IR spectra of carboxylated graphene. In all cases, we observed the emergence of new Raman and IR absorption bands in the range of low and high vibration frequencies. The calculated Raman and IR spectra showed clearly distinguishable spectroscopic signatures associated to different types of structural defects present in...

Giant Electron-Phonon Coupling and Deep Conduction Band Resonance in Metal Halide Double Perovskite.

The room-temperature charge carrier mobility and excitation-emission properties of metal halide perovskites are governed by their electronic band structures and intrinsic lattice phonon scattering mechanisms. Establishing how charge carriers interact within this scenario will have far-reaching consequences for developing high-efficiency materials for optoelectronic applications. Herein we evaluate the charge carrier scattering properties and conduction band environment of the double perovskite Cs2AgBiBr6 via a combinatorial approach; single crystal X-ray diffraction, optical excitation and temperature-dependent emission spectroscopy, resonant and nonresonant Raman scattering, further supported by first-principles calculations. We identify deep conduction band energy levels and that scattering from longitudinal optical phonons- via the Fröhlich interaction-dominates electron scattering at room temperature, manifesting within the nominally nonresonant Raman spectrum as multiphonon processes up to the fourth order. A Fröhlich coupling constant nearing 230 meV is inferred from a temperature-dependent emission line width analysis and is found to be extremely large compared to popular lead halide perovskites (between 40 and 60 meV), highlighting the fundamentally different nature of the two "single" and "double" perovskite materials branches.

Do Mono-oxo Sites Exist in Silica-Supported Cr(VI) Materials? Reassessment of the Resonance Raman Spectra

The monomeric, single-atom oxochromium species present on the surface of silica-supported Cr(VI) catalysts was characterized in detail using resonance Raman (RR) spectroscopy over a range of excitation wavelengths corresponding to the primary electronic transitions of Cr(VI)/SiO2. The findings resolve a long-standing controversy regarding the possible contribution of mono-oxoCr(VI) sites, (SiO)4Cr═O, postulated to coexist with the well-established dioxoCr(VI) sites, (SiO)2Cr(═O)2. Density functional theory (DFT) calculations and a normal coordinate analysis conducted using a chromasiloxane model cluster confirm prior assignments of bands in the nonresonant Raman spectrum at 986 and 1001 cm–1 to the symmetric and antisymmetric stretching modes, respectively, of the dioxoCr(VI) sites. For all excitation energies, the symmetric stretch shows apparent resonant enhancement. Since all of the electronic transitions are strongly allowed, this finding is consistent with A-term enhancement. UV excitation at 257 nm ...

H2S‐Induced Structural Changes of Insulin Protein in Early Lag Phase: Key to Detaining Amyloid Formation

Amyloid fibrils are formed by soluble proteins that assemble into insoluble fibers associated to many types of diseases such as Diabetes Type 2, and Alzheimer's Disease. Amyloid formation can be divided into three phases: the lag phase, where native protein unfolds and begins to self‐aggregate; the elongation phase, in which these aggregates grow into fibrils, and the steady phase, where saturation of mature fibrils occurs. Hen egg white lysozyme (HEWL) amyloid fibrils are inhibited in the presence of hydrogen sulfide (H2S) (Rosario, 2014). To further explain the means by which H2S inhibits amyloid fibrillation, insulin from bovine pancreas (IBP), was tested upon experimentation with increasing concentrations of H2S. ThT Fluorescence analysis revealed a decrease in peak intensity as the concentration of H2S increased in each sample, proving H2S to be an inhibitor of insulin amyloids. Atomic Force Microscopy (AFM) of the control sample showed an array of fibrillary structures. However, as the concentration of H2S increased, samples went from having a combination of fibrillary structures and small conglomerated spherules to the sole appearance of small spherules. Far UV‐Circular Dichroism spectra of the native protein and the protein interacting with H2S were very similar. However, non‐resonance Raman spectra revealed the presence of newly formed trisulfide bridges in the interaction between insulin and the H2S species as opposed to the disulfide bridges found in native and fibrillated insulin protein. The data suggest H2S‐protein interactions favor a structural change in the process of protein denaturing. The H2S species intervenes with amyloid formation early on during the lag phase inhibiting the formation of protofibrils and potential mature fibrils.Support or Funding InformationResearch reported in this publication was supported by an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under grant number P20GM103475. It was also supported by the National Institute of General Medical Sciences of the National Institutes of Health under Award Number T34GM008419. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Raman active modes in defective peapods

The vibrational properties of defective single-walled carbon nanotube filled with C60 fullerene is the subject of the current study. For this aim we use the spectral moments method in the framework of the bond-polarization theory to calculate the non-resonant Raman spectra of hexa-vacancy defective C60 peapods. Essentially, the vibrational properties are closely coupled with the atomic structure of the system. The evolution of the Raman spectrum as a function of the spatial arrangement of defects in carbon nanotubes is discussed. This work provides benchmark theoretical results to understand the experimental data of defective C60 peapods. #single_wall_carbon_nanotube #C60_peapods #hexa-vacancy_defect #Raman_spectroscopy #pectral_moment_method

Raman and 2D electronic spectroscopies: A fruitful alliance for the investigation of ground and excited state vibrations in chlorophyll a

Vibrational coherences and their time evolution are crucial for the correct description of the dynamical behavior of materials, also influencing the dynamics of electronic coherences and transport processes. For this reason, vibrational coherences are now becoming the subject of wider investigation, especially in the framework of 2D electronic spectroscopies. A correct interpretation of vibrational coherences in 2DES responses requires the comparison with Raman spectra.Here we propose a methodology that goes beyond the typical practice of merely looking for frequencies present in both signals. In particular, we discuss suitable experimental conditions and correction procedures that allows a direct comparison of Fourier spectra obtained from the analysis of the signal beating at specific coordinates in 2D maps with resonant and non-resonant Raman spectra, to clearly identify the vibrational modes more strongly coupled with the electronic transition.The advantages of this approach have been illustrated using Chla chromophore as a case study.

Structure and Raman Spectra of C60 and C70 Fullerenes Encased into Single-Walled Boron Nitride Nanotubes: A Theoretical Study

We report the structures and the nonresonant Raman spectra of hybrid systems composed of carbon fullerenes ( C 60 and C 70 ) encased within single walled boron nitride nanotube. The optimal structure of these systems are derived from total energy minimization using a convenient Lennard-Jones expression of the van der Waals intermolecular potential. The Raman spectra have been calculated as a function of nanotube diameter and fullerene concentration using the bond polarizability model combined with the spectral moment method. These results should be useful for the interpretation of the experimental Raman spectra of boron nitride nanotubes encasing C 60 and C 70 fullerenes.

Quantum-mechanical calculation of the intensity distribution in Raman and resonance Raman spectra of a phenylalanine aqueous solution

Quantum-mechanical calculations of the intensity distribution in the resonance Raman spectrum of an aqueous solution of phenylalanine, excited by light with wavelengths of 193, 204, 218, and 235 nm, and in the nonresonant Raman spectrum excited at a wavelength of 488 nm have been performed. The calculation results are in satisfactory agreement with the experimental data in the literature. Spectral lines characteristic of phenylalanine are observed, which can be used as markers when analyzing the peptide structure. It is noted that the contribution of highly excited electronic states (spaced by less than 10 eV from the resonant lines) to the scattering tensor components must be taken into account. The important role of the Herzberg–Teller effect in the description of spectral intensity distribution is demonstrated.

Vibrational spectroscopic characterization of arylisoquinolines by means of Raman spectroscopy and density functional theory calculations.

Promising new antimalarial agents were investigated using FT-NIR and deep-UV resonance Raman spectroscopy. The Raman spectra of the seven arylisoquinolines (AIQ) were calculated with the help of density functional theory (DFT). Very good agreement with the experimental data was achieved and a convincing mode assignment was performed with the help of the calculated potential energy distribution (PED). For the non-resonant Raman spectra the most prominent bands were assigned to ν(C[double bond, length as m-dash]C) stretching modes of the isoquinoline system. To differentiate between substances with similar structures, deep-UV resonance Raman spectra were recorded. Raman bands in the range between 1250 and 1210 cm-1 were assigned to ν(C[double bond, length as m-dash]C) stretching vibrations in combination with δ(HCC) deformation vibrations of the aryl rests. These vibrations of the aryl part of the molecules were selectively enhanced, which, thus, enabled the differentiation of similar active agents from each other. For λexc = 257 nm excitation, strong ν(C[double bond, length as m-dash]C) vibrations of the isoquinoline (benzo-) part dominate the Raman spectrum in the range between 1685 and 1585 cm-1 and for λexc = 244 nm the Raman signals between 1430 and 1350 cm-1 were enhanced and assigned to ν(C[double bond, length as m-dash]C) of the isoquinoline (pyridino-) system.

C60 Filling Rate in Carbon Peapods: A Nonresonant Raman Spectra Analysis

We calculated the nonresonant Raman spectra of C60 peapods to determine the concentration of C60 fullerenes inside single-walled carbon nanotubes. We focus on peapods with large diameters for which C60 molecules can adopt a double helix configuration or a two-molecule layer configuration. Our calculations are performed within the framework of the bond-polarizability model combined with the spectral moment’s method. The changes in the Raman spectra as a function of C60 filling rate and the configuration of C60 molecules inside the nanotubes are identified and discussed. Our calculations support the experimental method proposed by Kuzmany to evaluate the concentration of C60 molecules inside nanotubes.

Filling rate dependence on theoretical Raman spectra of carbon C60 peapods

We use the spectral moments method in the framework of the bond-polarization theory to calculate nonresonant Raman spectra of C60 peapods as a function of the concentration of fullerenes inside the single wall carbon nanotubes. The evolution of the average Raman intensity ratios between Raman mode of C60 molecules and nanotube as a function of the concentration of fullerenes has been analyzed and a general good agreement is found between calculations and measurements. #CARBON_NANOTUBES #PEAPODS #RAMAN_SPECTROSCOPY #SIMULATION #SPECTRAL_MOMENT_METHOD

Theoretical study of electronic and vibrational properties of dimer of single-wall carbon nanotubes

This work focuses on a bundle of two van der Waals-coupled single wall carbon nanotubes. The non-resonant Raman spectra of inhomogeneous dimers of single walled of carbon nanotubes are calculated in the framework of spectral moments method, together with a bond-polarizability model. The evolution of the low frequency Raman-active modes as a function of the nanotube diameters is discussed. Effects of van der Waals coupling on charge transfer processes are also investigated. The obtained results are compared to experimental Raman data measured on dimer sample.