Raman Bandwidth Research Articles

Calibration of Raman Bandwidths on the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) Deep Ultraviolet Raman and Fluorescence Instrument Aboard the Perseverance Rover.

In this work, we derive a simple method for calibrating Raman bandwidths for the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument onboard NASA's Perseverance rover. Raman bandwidths and shapes reported by an instrument contain contributions from both the intrinsic Raman band (IRB) and instrumental artifacts. To directly correlate bandwidth to sample properties and to compare bandwidths across instruments, the IRB width needs to be separated from instrumental effects. Here, we use the ubiquitous bandwidth calibration method of modeling the observed Raman bands as a convolution of a Lorentzian IRB and a Gaussian instrument slit function. Using calibration target data, we calculate that SHERLOC has a slit function width of 34.1 cm-1. With a measure of the instrument slit function, we can deconvolve the IRB from the observed band, providing the width of the Raman band unobscured by instrumental artifact. We present the correlation between observed Raman bandwidth and intrinsic Raman bandwidth in table form for the quick estimation of SHERLOC Raman intrinsic bandwidths. We discuss the limitations of using this model to calibrate Raman bandwidth and derive a quantitative method for calculating the errors associated with the calibration. We demonstrate the utility of this method of bandwidth calibration by examining the intrinsic bandwidths of SHERLOC sulfate spectra and by modeling the SHERLOC spectrum of olivine.

Revisiting the Raman Spectra of Carbonate Minerals

This work presents a new discussion about the vibrational properties of the carbonate ion displayed in several different environments. The microparameters introduced by cation substitution and different crystal lattices in addition to the crystal aggregation are present in the discussion. The work comments on how the Raman modes are affected by these changes by using data obtained with four different laser excitation sources. Raman spectra excited at 1064 nm are reported at 1 cm−1 resolution. New observations and approaches based on the Raman modes highlight the differences observed in the relative intensity and width of the bands. The new data contribute to the understanding of these materials and their spectra, bringing new observations based on the Raman modes. This work presents a new approach highlighting the differences observed in the relative intensity and width of the Raman bands. The results indicate some evidence of the influence of the crystal habit and/or the growth of the mineral itself on the Raman spectrum. In addition, the data show the influence of cation substitution upon Raman bandwidth and the interference of the size of the spot of the laser in the measurement.

The Impact of Extreme Low Temperatures on Raman Spectra of Amino Acids Relevant for the Search for Life on Europa.

Raman spectroscopy, an emerging technology for in situ space exploration, has been suggested for life detection for the Europa Lander Mission. However, obtaining spectra of samples from the europan icy shell requires measurements at temperatures down to -233°C, which will affect the Raman spectra of any potential biosignatures. In this study, we obtained Raman spectra of amino acids using a 785 nm Raman system at temperatures ranging down to -196°C, analogous to Europa's surface and near subsurface. Significant Raman band width narrowing and decreasing variance were observed at lower temperatures leading to higher-precision Raman measurements, which required higher spectral resolution that could be as high as 2 cm-1 for full identification of amino acids. Such spectral resolution is much higher than the resolution of contemporary Raman instruments for planetary exploration and may be particularly problematic for miniaturized instruments. Shifting of Raman bands to both higher and lower frequencies by as much as ∼25 cm-1 together with changes in the Raman band intensity were recorded. The emergence of new bands and diminishing of the original bands also occurred for some amino acids. A significantly increased fluorescence background was observed in spectra of fluorescent molecules (i.e., tryptophan). A link between the type of vibrational modes associated with Raman bands and the change in their Raman shift at extreme low temperatures was identified and described. This link offers an exciting new method of molecule identification solely based on the comparison of spectra collected at two different temperatures and could greatly improve the identification capabilities in Raman spectroscopy for a wide array of applications.

A new model for the calculation of homogeneously broadened Raman spectral bandwidths and bandshapes

AbstractRaman spectral bandwidths and bandshapes can provide detailed information on the physics and chemistry of a sample. The Raman band reported by a spectrometer (observed Raman band [ORB]) is a result of contributions from the true, intrinsic Raman band (IRB) and the spectrometer slit function. To obtain the IRB spectral width and shape, the effects of the spectrometer slit function must be removed from the ORB by measuring the spectrometer slit function and modeling the ORB as a convolution of the IRB and slit function. Though this model has proven to be useful, it is not based on physical parameters of the measurement and is limited. Thus, new ways to model Raman bandshape and bandwidth are needed. I previously developed a new method of modeling Raman bands using spectrometer geometric optics to examine the dependence of Raman band intensity on slit width. The model calculates the intensity of the ORB from the contributions of a continuum of dispersed slit functions. Here, I extend the use of this model for examining ORB spectral widths and shapes. I show that the model produces the same result as the convolution model when using Lorentzian Raman and Gaussian slit functions, confirming the validity of the model. However, in contrast to the convolution model, the new model is based on spectrometer geometric optics allowing one to account for various optical effects when modeling Raman spectra. This is demonstrated by modeling the effects of slit width on the Raman spectrum. I use the model to provide a detailed, physical understanding of the effects of slit width and IRB width on Raman bandshapes.

Effect of the spectrometer slit width and charge‐coupled device detector on Raman intensities

AbstractIt is well known that Raman intensities are affected by the spectrometer slit width. Wider slit widths provide increased Raman intensity at the cost of decreased spectral wavenumber resolution. However, the relationship between the spectrometer slit width and observed Raman intensities is poorly understood. In this work, we develop a model, based on spectrometer geometric optics, to quantify the effects of spectrometer slit width on observed Raman intensities. We find that the observed Raman intensities are strongly dependent on the ratio of the slit function width and intrinsic Raman band width. Thus, even for Raman spectra collected using the same slit width, the observed Raman intensities will be affected by the different intrinsic bandwidths of each Raman band. Thus, the effects of the slit function on Raman intensities must be considered for all Raman spectra when examining Raman intensities. In addition, we show that the spectrometer linear dispersion and charge‐coupled device (CCD) pixel size have a large dependence on the Raman intensities reported by the CCD. Thus, when comparing Raman intensities across instruments or for a single instrument with a nonlinear wavenumber calibration, Raman intensities must be calibrated for the effects of the CCD. Using our model, we develop a general method for correcting observed Raman intensities for the effects of the slit width, intrinsic Raman band width, and CCD.

Phase transition and trigger mechanism of initial reaction under pressure for benzofuroxan energetic materials: Raman spectroscopy and first‐principle calculations

AbstractLow‐pressure (below 2 GPa) Raman spectra of benzofuroxan are investigated using a gasketed Mao–Bell‐type sapphire anvil cell and Raman spectrometer to clarify the pressure‐induced structural change and molecular vibration behavior. The first‐principle calculations are performed to compare with the experimental data and to analyze the phase transition and trigger mechanism of initial reaction. Variations of pressure‐induced Raman band width, shift, and intensity are examined. The results show that the benzofuroxan molecule will become nonplanar with increasing pressure. A phase transition occurs because of an abrupt redshift in shift–pressure relationship and reduction of the cell volume, appearing of a new vibration band above 0.13 GPa. Several active vibration modes are found, and the effects of the active mode vibrations on the initial decomposition of benzofuroxan are analyzed using the relaxed scan method for the main change in bond length, bond angle, or dihedral angle to obtain the optimal reaction channel leading to initial decomposition. The results demonstrate that the initial decomposition is the open‐loop reaction in N(O)–O position, which is originated from the increase of dihedral angle O‐C‐N(O)‐O from the out‐of‐plane torsional vibration of furoxan ring (518 cm−1). The scanning energy barrier related to dihedral angle O‐C‐N(O)‐O is about 22.6 kcal/mol, which is consistent with the calculated activation barrier (18.1 kcal/mol) of open‐loop reaction. This proves the reliability of our conclusions.

Raman and theoretical studies on structural evolution of Li2BeF4 and binary LiF-BeF2 melts

The structural evolution of Li2BeF4 from crystalline to molten states has been investigated by Raman spectroscopic technique with the assist of density functional theory (DFT). The experimental results of temperature-dependent Raman spectra of Li2BeF4 showed that no solid-state phase transformation was taken place during heating process from 298 to 723 K. In the molten state, the structure of BeF42− anion was affected by Li+ cation and environment. For the binary LiF-BeF2 melts with varying LiF/BeF2 ratio, the stretching bands of beryllium‑fluorine bonds in molten Raman spectra were deconvolved identified by Gaussian function. When the concentration of BeF2 exceeding 33 mol%, the dimer Be2F73− was formed and dominated the spectrum. It was characterized to have a linear Be–F–Be geometry with two BeF4 moieties bridged by a single fluorine atom. A second anion Be3F104− processing a triple chain structure formed when the content of BeF2 increasing to 50 mol%. When the concentration of BeF2 went beyond 60 mol%, the Raman intensity and band width gradually decreased. While the intensity and band width of Raman spectra gradually decreased with the concentration of BeF2 exceeding to 60 mol%, which suggests that the band should be assigned to a hexatomic Be6F186− ring which was similar to the situation in the pure BeF2 network structure.

Calibration of Raman bandwidth in large Raman images using a mercury–argon lamp

AbstractRaman imaging has proven to be an important tool in the analysis of astromaterials. Raman imaging can describe the composition and mineralogy of astromaterials in a nondestructive manner preserving precious samples for additional study. Raman bandwidth is a common spectroscopic marker used to elucidate information such as composition, latent strain, and thermal processing history. The observed Raman bandwidth of a sample is a result of a convolution of the true Raman lineshape and the spectrometer's slit function. Thus, to compare Raman bandwidths across spectra and instruments, one needs to calibrate the Raman spectrum to account for effects of the slit function. Astromaterials are heterogeneous requiring the collection of large Raman images for adequate sampling. It is well known that the wavenumber calibration of an instrument drifts with time throughout Raman image collection. Here, we find that the spectrometer slit function also varies with time and laboratory temperature throughout Raman image collection. We utilize a mercury–argon (Hg–Ar) lamp integrated into our Raman microscope in a novel manner to calibrate the bandwidth in each Raman spectrum within our Raman image. We can do this because the narrow Hg–Ar lamp emission lines approximate the spectrometer slit function for each Raman spectrum allowing for the calculation of the true Raman bandwidth from each Raman spectrum within the Raman image. Our technique allows for the comparison of Raman bandwidth throughout a Raman image and between Raman images/spectra collected using different instruments, facilitating scientific analyses that are reproducible across multiple laboratories.

Raman spectroscopy of biochar from the pyrolysis of three typical Chinese biomasses: A novel method for rapidly evaluating the biochar property

Biochar from the pyrolysis of rice husk, pine wood and rice straw under the temperature from 250 °C to 800 °C were obtained and characterized by Raman spectroscopy. The biochar properties and chemical structure evolution were investigated, and correlations between biochar properties and Raman spectral parameters were set up. The results indicate that pyrolysis temperature has a more significant influence on biochar yield than feedstock. The volatile content in raw biomass linearly decreases with the decrease of biochar yield, and the atom H/C ratio of biochar linearly decreases with the decrease of Vdaf (volatile content in dry ash free basis). The change characteristics of Raman bands position and bandwidth indicate that carbon order degree of biochar progressively increases with the increase of pyrolysis temperature, and detailed chemical structure of biochar from different raw biomass can significantly differ from each other. Reasonable correlations between biochar properties including yield, Vdaf, the atom H/C ratio and the fluorescence interference degree in Raman spectrum (defined as α) of biochar have been found. A series of functions were proposed for rapid evaluation of biochar properties. Specially, the correlation that H/C = 0.3652 + 2.2887∗α-2.4035∗α^2 + 0.8221∗α^3 can be universal for carbon-based fuels including biochar, coals, coal chars and bio-oil chars.

Insights into the CaSO4–H2O System: A Raman-Spectroscopic Study

Even though being the subject of natural scientific research for many decades, the system CaSO4–H2O, consisting of the five crystalline phases gypsum, bassanite, and the anhydrites III, II, and I, has left many open questions for research. Raman spectroscopy was used because of its structural sensitivity and in situ measurement capability to obtain further insight by studying phase transitions in both ex situ and in situ experiments. The findings include significant contributions to the completeness and understanding of Raman spectroscopic data of the system. The dehydration path gypsum–bassanite–anhydrite III was shown to have strong parallels to a physical drying process, which depends on many parameters beyond the burning temperature. Raman band width determination was demonstrated to enable the quantitative discrimination of α-bassanite and β-bassanite as well as the postulated three sub-forms of anhydrite II (AII), which are all based on differences in crystallinity. In the latter case, the observed continuous structural variations over increasing burning temperatures were elucidated as a combination of decreasing surface areas and healing of crystal lattice defects. We propose an only two-fold sub-division of AII into reactive “disordered AII” and much less reactive “crystalline AII” with a transition temperature of 650 °C ± 50 K.

Microscopic mapping of dopant content and its link to the structural and thermal stability of yttria-stabilized zirconia polycrystals

The effect of yttria content on structural and thermal stability of zirconia in yttria-stabilized zirconia (YSZ) polycrystalline ceramics was systematically investigated by Raman spectroscopy and X-ray photoelectron spectroscopy. Taking advantage of an experimentally retrieved linear dependence of Raman bandwidth on yttria content, Raman imaging was applied as an effective tool in examining the local yttrium distribution in YSZ ceramics and its relationship with environmentally driven polymorphic transformation. A significant variation of monoclinic fraction with yttria content and temperature was found and interpreted according to a newly proposed model, which takes into account the change in lattice hydroxyl and oxygen vacancies and the possible formation of stable defect complexes.

Optimizing of Raman gain and bandwidth for dual pump fiber optical parametric amplifiers based on four-wave mixing

Abstract This article has been retracted by IOP Publishing Limited as it contains substantial overlap with the following article published in Journal of Telecommunications System & Management: El-khashab et al 2018 J. Telecommun. Syst. Manage. 7 1. As a member of the Committee for Publication Ethics (COPE), IOP Publishing Limited has investigated this in accordance with COPE guidelines and it was agreed the article should be retracted. IOP Publishing Limited have been unable to contact the authors regarding this retraction, despite numerous attempts. The authors are encouraged to contact IOP Publishing Limited if they wish to contest this retraction.

Characterisation of titanium oxide layers using Raman spectroscopy and optical profilometry: Influence of oxide properties

Abstract This study evaluates the use of a combination of Raman spectroscopy and optical profilometry as a surface characterisation technique for the examination of oxide layers grown on titanium metal substrates. The titanium oxide layers with thickness of up to 8 µm, were obtained using a low-pressure oxygen microwave plasma treatment of the titanium metal substrate. The effect of the microwave plasma processing conditions (input power, pressure and treatment time) on the Raman bandwidth, intensity and peak position was evaluated. Also, the effect of these processing conditions on the surface roughness parameters (Sa, Sdq, Ssk and Sku) of the oxide layers was investigated. Analysis of the peak positions of Eg and A1g modes indicated that the effects of input power and chamber pressure was to induce a shift towards the lower frequency with increasing input power and pressure (1–2 kPa). The intensity of the Raman bands was found to be dependent on the morphology and surface chemistry of the oxide layer. The intensity of Raman band (A1g), was found to be particularly influenced by the average surface roughness (Sa) and the crystallite size. Exponential and polynomial relations were found to correlate with these properties. A two-latent variable Partial Least Squares Regression model developed on Raman spectral data could predict surface roughness with a coefficient of determination (R2) of approx. 0.87 when applied to the testing of an independent set of titanium oxide test coatings.

Pressure induced anomalous magnetic behaviour in nanocrystalline YCrO3 at room temperature

High pressure behaviour of nanocrystalline YCrO3 is investigated up to 10 GPa using electrical, magnetic, synchrotron x-ray diffraction and Raman spectroscopy measurements. High pressure dielectric constant measurements show a sharp peak at 4.5 GPa, though the sample is found to be in ferroelectric phase up to the highest pressure of our study from piezoelectric current measurements. X-ray diffraction measurements show absence of any structural phase transition, however anomalies are observed in the unit cell structural parameters at about 4.3 GPa and the Y-atom position shows a maximum shift at the same pressure. In the absence of any structural transition, anomalous behaviour of relevant Raman modes with minimum in the Raman band width at about same pressure indicate towards a spin-phonon interaction. AC magnetic measurements in the toroid anvil cell show an anomalous enhancement of magnetic moment above 4 GPa indicating a collective magnetic response of nanoparticles.

Optimizing of Raman Gain and Bandwidth for Dual Pump Fiber Optical Parametric Amplifiers Based on Four-Wave Mixing

This article has been retracted by IOP Publishing Limited as it contains substantial overlap with the following article published in Journal of Telecommunications System & Management: El-khashab et al 2018 J. Telecommun. Syst. Manage. 7 1. As a member of the Committee for Publication Ethics (COPE), IOP Publishing Limited has investigated this in accordance with COPE guidelines and it was agreed the article should be retracted. IOP Publishing Limited have been unable to contact the authors regarding this retraction, despite numerous attempts. The authors are encouraged to contact IOP Publishing Limited if they wish to contest this retraction.

CdSxSe1-x quantum dots as colouring agents of Art Nouveau and contemporary stained glass: a combined transmission electron microscopy and Raman study.

The use of cadmium chalchogenide nanoprecipitates to obtain brightly coloured glasses enormously expanded by the beginning of the twentieth century, when the production of cadmium-based pigments was already well established. Six historical stained glass pieces produced between the late 1920s and modern days have been investigated in order to delineate the average size and the elemental composition of the nanocrystals. As non-invasive conditions are now mandatory when considering objects belonging to cultural heritage, Raman spectroscopy is used to measure the (average) elemental composition of the nanoparticles. Zinc substitution is also detected by the shifting of the Raman peak position. Moreover, a tentative evaluation of size distribution and crystallinity of the nanoparticles has been performed considering those parameters that are mainly influenced by the disorder of the system, such as Raman band width, surface phonons and the ratio between second and first order band intensities. A confirmation of the above-mentioned conclusion is searched by means of transmission electron microscopy (TEM) and local elemental analysis. Raman investigations allowed identifying a different and more pronounced disorder characterizing the oldest glasses, also verified by TEM observations, suggesting a different manufacture.This article is part of the themed issue 'Raman spectroscopy in art and archaeology'.

Enhanced Raman amplification by conventional and hybrid photonic crystal based ring structure

In this paper, we present new structures based on ring, conventional photonic crystal and hybrid PhC for enhanced Raman amplification. The structures consist of two separate entrances for the pump and signal. In this way, only pump is coupled into the ring and signal passes through the amplified pump without creating coupling noise. Using engineered nano holes filled with optofluidic materials in the signal and pump paths, we reduce pump and signal group velocity to improve the structure and achieve larger Raman gain and less dispersion. The time evolution and propagation of picosecond signal pulses and dispersion inside the device are analyzed and Raman gain, Raman bandwidth and bit rate are studied in one-ring and two-ring structures. To model Raman amplification in these structures, Maxwell equations are solved using finite difference time domain method considering optical nonlinear parameters like two photon absorption, free carrier absorption and Kerr effect.

Toward a Raman/FORS discrimination between Art Nouveau and contemporary stained glasses from CdSxSe1 − x nanoparticles signatures

CdSxSe1 − x quantum dots received considerable attention in academic studies and as cut‐off filters and indirect‐gap semiconductors. These later compounds have also been used for artistic purposes to produce colored glass since the 1920s thanks to their bright colors. Because non‐invasive conditions are now mandatory when considering objects belonging to the cultural heritage, the use of Raman and fiber optics reflectance spectroscopy has been identified as potential ones to obtain information about the nanostructure of six samples of historical glass produced between the late 1920s and modern days. The average elemental composition of the nanocrystals has been deduced processing both optical and vibrational data, and the result arising has been compared taking into account the several factors affecting the experimental results. The diffusion of zinc inside the nanocrystals has also been questioned by the shift caused on the CdS‐ and CdSe‐like phonon band wavenumber and on the absorption edge wavelength. An investigation of the size distribution and crystallinity of CdSxSe1 − x nanoparticles has been also performed considering those parameters that are mainly influenced by the disorder of the system, such as the extent of the Urbach tail and the Raman bandwidth. Thanks to the results obtained, discrimination between the more recent glass and the older Art Nouveau ones has been verified, leading to the identification of a useful analytical protocol for conservation purposes. Copyright © 2015 John Wiley & Sons, Ltd.

Vibrational Relaxation Study of Polar Aprotic Molecule: Experimental and Theoretical Approach

Present study deals with the interacting nature of C-H stretching mode of dimethyl sulfoxide in binary liquid mixtures using methyl benzene and deuterated methyl benzene solvents. Peak frequency of C-H stretching mode shows blue shift with the increase in solvent concentration. Variation of Raman bandwidth with the solvent concentration has been studied. Hartree Fock theoretical calculation for geometry optimization and vibrational wavenumber calculation have been carried out to explain the experimental findings. Calculated values are found in good agreement with the experimental results. Vibrational relaxation time has been studied corresponding to solvent concentrations to elucidate the interacting mechanisms of the binary mixtures.

Micro Structural Analysis of In2S3 Thin Films by Raman Spectroscopy

In2S3 thin films with different thicknesses were deposited on glass substrates using the thermal evaporation method. The as-deposited films were annealed in vacuum at 330 and 400°C for 30 and 60 min. We used Raman spectroscopy and X-ray diffraction to evaluate the effect of thermal treatment on the film structures. Raman active modes that can be classified as 9A1 and 14E modes have been observed in the Raman spectra of the In2S3 thin films. Variations in the Raman shift and bandwidth of different In2S3 thin films reveal the influence of the annealing effect. Results of Raman spectroscopy and XRD show that the annealing effect changes the crystallization phase from tetragonal to cubic at high temperatures.