Complete Raman Spectrum Research Articles

Biochemical component analysis of human myopic corneal stroma using the Raman spectrum.

This study aimed to measure the Raman spectrum of the human corneal stroma lens obtained from small incision lenticule extraction surgery (SMILE) in Asian myopic eyes using a confocal Raman micro-spectrometer built in the laboratory. Forty-three myopic patients who underwent SMILE with equivalent diopters between - 4.00 and - 6.00 D were selected, and the right eye data were collected. Corneal stroma lenses were obtained during surgery, and the Raman spectra were measured after air drying. The complete Raman spectrum of human myopic corneal stroma lens tissue was obtained within the range of 700-4000cm-1. Thirteen characteristic peaks were found, with the stronger peaks appearing at 937cm-1, corresponding to proline, valine, and the protein skeleton of the human myopic corneal stroma lens; 1243cm-1, corresponding to collagen protein; 1448cm-1, corresponding to the collagen protein and phospholipids; and 2940cm-1, corresponding to the amino acid and lipids, which was the strongest Raman peak. These results demonstrated that Raman spectroscopy has much potential as a fast, cost-effective, and reliable diagnostic tool in the diagnosis and treatment of eye diseases, including myopia, keratoconus, and corneal infection.

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.

Raman spectroscopy and lattice dynamics calculations of tetragonally-structured single crystal zinc phosphide (Zn3P2) nanowires

Earth-abundant and low-cost semiconductors, such as zinc phosphide (Zn3P2), are promising candidates for the next generation photovoltaic applications. However, synthesis on commercially available substrates, which favors the formation of defects, and controllable doping are challenging drawbacks that restrain device performance. Better assessment of relevant properties such as structure, crystal quality and defects will allow faster advancement of Zn3P2, and in this sense, Raman spectroscopy can play an invaluable role. In order to provide a complete Raman spectrum reference of Zn3P2, this work presents a comprehensive analysis of vibrational properties of tetragonally-structured Zn3P2 (space group P42/nmc) nanowires, from both experimental and theoretical perspectives. Low-temperature, high-resolution Raman polarization measurements have been performed on single-crystalline nanowires. Different polarization configurations have allowed selective enhancement of A1g, B1g and Eg Raman modes, while B2g modes were identified from complementary unpolarized Raman measurements. Simultaneous deconvolution of all Raman spectra with Lorentzian curves has allowed identification of 33 peaks which have been assigned to 34 (8 A1g + 9 B1g + 3 B2g + 14 Eg) out of the 39 theoretically predicted eigenmodes. The experimental results are in good agreement with the vibrational frequencies that have been computed by first-principles calculations based on density functional theory. Three separate regions were observed in the phonon dispersion diagram: (i) low-frequency region (<210 cm−1) which is dominated by Zn-related vibrations, (ii) intermediate region (210–225 cm−1) which represents a true phonon gap with no observed vibrations, and (iii) high-frequency region (>225 cm−1) which is attributed to primarily P-related vibrations. The analysis of vibrational patterns has shown that non-degenerate modes involve mostly atomic motion along the long crystal axis (c-axis), while degenerate modes correspond primarily to in-plane vibrations, perpendicular to the long c-axis. These results provide a detailed reference for identification of the tetragonal Zn3P2 phase and can be used for building Raman based methodologies for effective defect screening of bulk materials and films, which might contain structural inhomogeneities.

Revealing the Origin of Luminescence Center in 0D Cs4PbBr6 Perovskite

Zero dimensional perovskite Cs4PbBr6 has attracted considerable attention recently not only because of its highly efficient green photoluminescence (PL), but also its two highly debated opposing mechanisms of the luminescence: embedded CsPbBr3 nanocrystals versus intrinsic Br vacancy states. After a brief discussion on the root cause of the controversy, we provide sensitive but non-invasive methods that can not only directly correlate luminescence with the underlying structure, but also distinguish point defects from embedded nanostructures. We first synthesized both emissive and non-emissive Cs4PbBr6 crystals, obtained the complete Raman spectrum of Cs4PbBr6 and assigned all Raman bands based on density functional theory simulations. We then used correlated Raman-PL as a passive structure-property method to identify the difference between emissive and non-emissive Cs4PbBr6 crystals and revealed the existence of CsPbBr3 nanocrystals in emissive Cs4PbBr6. We finally employed a diamond anvil cell to probe the response of luminescence centers to hydrostatic pressure. The observations of fast red-shifting, diminishing and eventual disappearance of both green emission and Raman below Cs4PbBr6 phase transition pressure of ~3 GPa is compatible with CsPbBr3 nanocrystal inclusions as green PL emitters and cannot be explained by Br vacancies. The resolution of this long-lasting controversy paves the way for further device applications of low dimensional perovskites, and our comprehensive optical technique integrating structure-property with dynamic pressure response is generic and can be applied to other emerging optical materials to understand the nature of their luminescent centers.

Multiplex coherent anti-Stokes Raman scattering spectroscopy for trace chemical detection.

Trace chemical detection is a particularly challenging problem of significant Army interest. Optical diagnostic techniques offer rapid, accurate, sensitive, and highly selective detection of hazardous materials in a variety of systems. Multiplex coherent anti-stokes Raman scattering (MCARS) spectroscopy generates a complete Raman spectrum from the material of interest using a combination of a supercontinuum pulse, which drives multiple molecular vibrations simultaneously, and a narrowband probe pulse. In this study, we demonstrated the ability of MCARS to detect trace amounts of both explosive materials and chemical warfare agent simulants with limits of detection below 0.2 ng and 0.1 nl, respectively. Integration times were on the order of 10 ms, using a compact USB spectrometer. Characteristics of supercontinuum generation were studied and compared to results in the literature. Finally, an algorithm that utilizes a combination of the maximum entropy method and advanced Fourier filtering to analytically remove the non-resonant background from the MCARS spectra without any a priori knowledge of the vibrational spectrum of the material of interest.

Nuclear Tracks Morphology Study Using Raman Methodology

In this work, a new methodology for rendering profiles of etched nuclear tracks is presented, using confocal micro-Raman spectrometry instrumentation. The precise profile of etched nuclear tracks with normal and/or angular incidence of the particle can be determined in few minutes, with a great visual and numerical resolution, that means a quantitative and qualitative simultaneous chemical and morphology characterization with the Raman technique. The Raman image routine is designed to acquire at each image pixel a complete Raman spectrum. This is a mapping of the functional groups that form the polymeric structure, which may be broken by the damage caused by the incident radiation and/or the etching process.

Investigation of lipid bodies in a colon carcinoma cell line by confocal Raman microscopy

Summary Objective The investigation of living cells under physiological conditions requires sensitive, sophisticated and in particular, non-invasive methods. Raman spectroscopy provides vibrational information about the sample. Combined with high-resolution confocal microscopy, it allows a complete Raman spectrum to be recorded at every confocal image point. This technique was applied here for the investigation of lipid bodies in a colon carcinoma cell line. Materials and methods The colorectal adenocarcinoma cell line Caco-2 and the rat intestine epithelial cell line IEC-6 were analysed with the confocal Raman microscope alpha300 R (WITec GmbH, Germany), using a frequency-doubled Nd:YAG laser at 532 nm and 10 mW for excitation. The use of a water immersion lens (63×, NA 1.0) allowed a lateral resolution in the sub-micrometer range. Raman images of cells were generated from the data sets by integrating over specific Raman bands. Mapping of the C–H stretching band (2800–3030 cm−1) allowed for the visualisation of the whole cell, whereas the automated statistical evaluation of all spectra by k-means cluster analysis resulted in spectral unmixed images which provided an insight into the chemical composition of the sample. Results With the described method, it was possible to visualise the distribution of different cellular biomarkers. Lipid bodies, in particular, which are reported to be present in increased numbers in colorectal cancer cells as compared to normal tissue, could be characterised and localised. A quantitative approach was developed to assess the fraction of lipid bodies in the total cell area. This method was applied for comparison between malignant and non-malignant cell lines. The fraction of lipid bodies turned out to be significantly higher in malignant (13.8%, n = 21) than in non-malignant cells (1.8%, n = 16). Conclusion Confocal Raman microscopy is shown to be a powerful method for the investigation of lipid bodies.

Fast identification of substance by measuring two Raman peaks with dual strip silicon photomultipliers and gated photon counting technique

In this report, we use carbon tetrachloride as an example to demonstrate that substance can be quickly identified through the measurement of the two Raman peaks simply by an integrated module of dual strip silicon photomultipliers operating at room temperature in conjunction with a gated photon counting technique. Both the peak positions and the relative intensity ratio of the two Raman peaks are used to identify the substance with a reduced false acceptance rate. A complete Raman spectrum of the substance can also be measured by using this method combined with a scanning monochromator.

Confocal Raman microscopy as a diagnostic tool for investigation of living neuroblastoma tumour cells

Abstract The investigation of living cells at physiological conditions requires very sensitive, sophisticated and non-invasive methods. In this study, Raman spectroscopy, a chemically and structurally sensitive measuring technique is combined with high-resolution confocal microscopy to investigate different biomolecules inside of cells. In Raman spectral imaging mode, a complete Raman spectrum is recorded at every confocal image point, giving insight into the chemical composition of each sample compartment. Neuroblastoma is the most common solid extra-cranial tumour in children. One of the unique features of neuroblastoma cells is their ability to differentiate spontaneously, eventually leading to complete remission. Since differentiation agents are currently used in the clinic for neuroblastoma therapy, there is a special need to develop non-invasive and sensitive new methods to monitor the level of differentiation in neuroblastoma cells. Differentiation of neuroblastoma cells was induced by treatment with retinoic acid and cells at different degrees of differentiation were analysed with the confocal Raman microscope alpha300 R (WITec GmbH, Germany), using a frequency doubled Nd:YAG laser at 532 nm and 10 mW for excitation. Integration time per spectrum was 80–100 ms. A lateral resolution in submicrometer range was achieved by using a 60× water immersion lens with a numerical aperture of 1.0. Raman images of cells were generated from these sets of data by either integrating over specific Raman bands or by cluster analysis. The automated evaluation of all spectra results in spectral unmixed images, which provide insight into the chemical composition of the sample. With these procedures, different cell organelles, cytosol, membranes could be distinguished. Since neuroblastoma cells at high degree of differentiation overproduce noradrenaline, an attempt was made to trace the presence of this neurotransmitter as a marker for the differentiation process. The results of this work may have applications in the monitoring of molecular changes and distribution of biomolecules as they occur during the differentiation of neuroblastoma cells.

Femtosecond stimulated Raman microscopy

A novel type of non-linear Raman microscopy, femtosecond stimulated Raman microscopy (FSRM), is introduced. It employs femtosecond white light pulses and intense picosecond pulses which are derived from a femtosecond laser/amplifier system. The pulses are coupled into a microscope set-up and induce a stimulated Raman process at the focus. The Raman interaction spectrally modulates the white light. These modulations are read-out in multi-channel fashion and allow recording of a complete Raman spectrum of the focal region. By raster-scanning the sample, complete Raman images can be obtained. Raman images of polystyrene beads in water demonstrate the feasibility of the approach.

Raman spectral imaging—A nondestructive, high resolution analysis technique for local stress measurements in silicon

In this study, Raman spectral imaging is used to investigate the stress fields around Vickers indents produced with various load forces on a silicon sample. Raman spectroscopy, a chemically and structurally sensitive measuring technique, is combined with high resolution confocal microscopy, thus enabling the identification of different chemical compounds or polymorphs within a sample or in this case, the stress field around the indents. In Raman spectral imaging mode, a complete Raman spectrum is recorded at every confocal imaging point with integration times below 100 ms. The automated evaluation of spectral features (sum, peak position, width, etc.) from the large number of recorded spectra (typically 10,000–100,000 spectra) produces chemical images of the analyzed heterogeneous material, providing insight into the chemical composition of the samples studied. To demonstrate the capabilities of the Raman spectral imaging technique for semiconductor applications, Vickers indents in a crystalline silicon Si(1 1 1) wafer have been characterized by combining Raman spectral imaging with atomic force microscopy (AFM). AFM images provide the topographic structure of the indents, whereas Raman spectral images are used to generate the stress images around the Vickers indent by analyzing the shift of the first order Raman line of silicon at 520 cm −1. At load forces of 1–5 mN, only a very small deformation of the surface topography (Δ z < 30 nm) is observed. At higher load forces (10–100 mN), the depth of the indent increases to a maximum of 240 nm, leading to deformation of the silicon in the vicinity of the indent. This deformation forms a stress field around the indent. At a load force of 5 mN the compressive strain along the long edge of the indent extends over 1.5 μm from the center. With increasing load, this strain expands over several micrometers. The stress fields around the indents are composed of tensile stress at the corners of the indent and compressive strain along the edges.

Raman spectroscopy of arsenolite: crystalline cubic As 4O 6

The complete Raman spectrum of arsenolite, cubic crystalline As 4O 6, is reported for the first time. The previously unseen E g mode has been found at 443 cm −1. Further, there is additional support for the assignment of the 415 cm −1 mode as T 2 g .

The complete Raman spectrum of nanometric SnO2 particles

The complete Raman spectrum of SnO2 nanoparticles in presented and analyzed. In addition to the “classical” modes observed in the rutile structure, two other regions shown Raman activity for nanoparticles. The Raman bands in the low-frequency region are attributed to acoustic modes associated with the vibration of the individual nanoparticle as a whole. The high-frequency region is activated by surface disorder. A detailed analysis of these regions and the changes in the normal modes of SnO2 are presented as a function nanoparticle size.

Rapid Micro-Raman Imaging Using Fiber-Bundle Image Compression

A new technique for rapid Raman imaging and chemical analysis of micro-composites and biomaterials, with potential applications in real-time robotic vision, automated manufacturing, and medical imaging, is described and demonstrated. The key feature of this new instrument is a fiber-optic bundle used to compress two-dimensional images onto a one-dimensional fiber stack, which serves as the entrance slit of an imaging optical spectrograph. Thus a complete Raman spectrum is simultaneously collected from every point within a sample in a single scan of a charge-coupled-device (CCD) detector. The method is demonstrated by using Raman imaging of a microscopic mixed-salt sample. Its efficiency relative to alternative Raman imaging methods is quantitatively evaluated, and potential applications in other spectral imaging measurements are discussed. Index Headings: Raman spectroscopy; Spectral imaging; Chemical imaging; Fiber optics; Chemical sensor.

Raman spectrum of the [SnI3]− ion and other halogenostannate(II) complexes including mixed halides

AbstractThe complete Raman spectrum of the pyramidal triiodostannate(II) ion [SnI3]− (ν1 = 162 cm−, strong, polarized; ν2 = 61 cm−, medium, polarized; ν3 = 148 cm−, strong, depolarized; ν4 = 48 cm−, strong, depolarized) is observed in a diethyl ether extract from a solution of tin(II) iodide containing hydriodic acid. Previous reports of the frequencies of [SnCl3]− are confirmed but for [SnBr3]− ν1 is revised from 211 to 205 cm−1. The complex acids H[SnX2Y] and H[SnXYZ] (X, Y or Z = Cl, Br or I) are observed in solvent extracts of tin(II) mixed halide solutions and a set of ν(Sn—halogen) frequencies is compiled. Appreciable co‐extraction of [SnX2(H2O)] occurs at halogen acid concentrations below 3 mol l−1.

Low‐frequency dynamics of solid poly(L‐alanine) from Raman spectroscopy

AbstractRaman modes from amorphous α‐helical poly(L‐alanine) in the low‐frequency region &lt; 150 cm−1 have been observed and assignments and values compared with mode‐analysis calculations. The temperature dependence of the complete Raman spectrum of α‐poly(L‐Ala) is also reported.

Vtbrational spectra of monomeric and dimeric 2-Hydroxycyclohexanone (adipoin)

Raman spectra of aqueous solutions of 2-hydroxycyclohexanone (adipoin) in the concentration range 0.34–0.034 M have been recorded between 1500 and 1800 cm−1. The variation in intensity of the carbonyl stretching band at 1714 cm−1 with concentration has been studied using the 1640 cm−1 band of water as an internal intensity standard. From the results of this study it is concluded that dissociation into the monomer is essentially complete in aqueous solution. IR and Raman spectra of solid (dimeric) adipoin have also been recorded. The absence of a carbonyl stretching band in the Raman spectrum indicates that the solid compound contains no monomer. A weak carbonyl stretching band is observed in the IR spectrum of a KBr pellet of adipoin and this is attributed to hydrolysis by the trace of water present in the KBr. A complete Raman spectrum of the aqueous solution together with an IR spectrum between 1500 and 1000 cm−1 have been obtained. Assignments of observed bands in both monomer and dimer spectra are suggested. An absence of frequency coincidences between IR and Raman spectra of the solid compound indicates that the dimer has a centre of symmetry and probably belongs to the point group C2h.

Optical and Raman spectra of single crystals of perylene-TCNQ charge transfer complexes

Optical transmission and reflection measurements are reported for the quasi one dimensional solids perylene-TCNQ (P1T1) and (perylene)3-TCNQ (P3T1) in the region from 300 to 1200 nm. Raman spectra of single crystals of both compounds were obtained from 20 to 3000 cm−1. With 457.9 nm excitation, combinations and overtones of perylene are observed for the first time. A complete Raman spectrum of perylene and its deuterated homologue including librations is thus obtained via selective resonance enhancement of that molecule.

The complete Raman spectrum of paraelectric and ferroelectric lead germanate

New measurements have been made of the complete Raman spectrum of Pb5Ge3O11 at temperatures above and below the ferroelectric transition at Tc approximately=450K. The data set is of much higher quality than that previously reported. Numerous first-order Raman bands are observed at low temperature consistent with group theoretical predictions. TO-LO splittings of polar modes were investigated and, contrary to other work, were found to be small for most cases. A molecular crystal approximation gives a reasonable description of the spectrum, where modes at higher frequencies can be classified as internal vibrations of GeO44- tetrahedra. Several A-symmetry modes, including the soft mode, exhibit a strong temperature dependence in their intensities in the ferroelectric phase. Their behaviour is consistent with expectations, but there are some E-symmetry modes whose intensities change unusually between 110 and 293K.

Two-phonon difference scattering in solid xenon

We have measured the complete second-order Raman spectrum of solid xenon at two temperatures: 125 and 156 K. In addition to the familiar two-phonon sum processes, we have carefully measured the spectrum of two-phonon difference processes, which produce a central peak, whose linewidth is temperature dependent. At 156 K the width is 6.8 ${\mathrm{cm}}^{\ensuremath{-}1}$, while at 125 K it is 4.3 ${\mathrm{cm}}^{\ensuremath{-}1}$, half-width at half maximum (HWHM). Comparison with recent calculations suggests that the observed anharmonic effects are significantly larger than expected and that such experimental results may provide a sensitive test for the interatomic potential of solid rare gases.