Raman Identification Research Articles

Raman identification of edge alignment of bilayer graphene down to the nanometer scale.

The ideal edges of bilayer graphene (BLG) are that the edges of the top and bottom graphene layers (GLs) of BLG are well-aligned. Actually, the alignment distance between the edges of the top and bottom GLs of a real BLG can be as large as the submicrometer scale or as small as zero, which cannot be distinguished using an optical microscope. Here, we present a detailed Raman study on BLG at its edges. If the alignment distance of the top and bottom GLs of BLG is larger than the laser spot, the measured D mode at the edge of the top GL of BLG shows a similar spectral profile to that of disordered BLG. If the alignment distance is smaller than the laser spot, the D mode at a real BLG edge shows three typical spectral profiles similar to that at the edge of SLG, that of the well-aligned edge of BLG, or a combination of both. We show the sensitivity and ability of Raman spectroscopy to acquire the alignment distance between two edges of top and bottom GLs of BLG as small as several nanometers, which is far beyond the diffraction limit of a laser spot. This work opens the possibility to probe the edge alignment of multi-layer graphene.

Raman identification of calcite grains in the Chelyabinsk meteorite

Samples of the Chelyabinsk meteorite fallen in February 15, 2013, near Chelyabinsk, Russia, are analyzed by Raman spectroscopy. Olivines (forsterite), orthopyoxenes (enstatite), plagioclases (albite), iron oxides and sulfides, as well as calcite and, possibly, parisite were identified among mineral phases. Results were verified using scanning electron microscope with an energy-dispersive system (SEM-EDX). Data were compared with available materials on calcites from ordinary meteorites.

ラマン分光法を利用した黒色プラスチックを含む廃家電プラスチックの選別技術に関する基礎的研究

Plastics have been used in various applications. The amount of domestic production in 2009 was 1.1 Mt. These days, mechanical recycling for the plastic is required, but one of the biggest problems of this method is how to separate black plastics. Black plastics contain carbon black as a colorant, which make them difficult to be identified by infrared adsorption (IR) spectroscopy. Thus, in this study, we are putting forward Raman spectroscopy for separating plastics (including black plastics) from the discarded appliances. There are reports which indicate that PP, PS, and ABS represent 70–80% of the discarded plastics. Each of them has its own characteristic peaks in Raman spectrum. In case of PP black plastics, nearly 100% of the feed can be identified, however, PS is difficult to be identified when carbon black content is about 3%. ABS of the discarded appliances was not identified. Finally, other fillers such as bromine flame retardants and calcium volume expander did not have any effect on Raman spectrum. In addition, we run some experiments for separating the discarded plastics by means of combining Raman identification with triboelectric separation. In Raman identification, the longer we exposure, the more amount of recovery we got, but grade was the highest in 1.0 s exposure, and it was over 95%. In triboelectric separation, however, the grade of ABS and PS were about 70%.

29Si NMR and Raman Glimpses into the Molecular Structures of Acid and Base Set Silica Gels Obtained from TEOS and Na-Silicate

The molecular structures of various silica gels are compared using 29Si NMR and laser Raman spectroscopy. When gels are deposited onto a porous organic resin from tetra ethyl orthosilicate, TEOS, at acidic or basic conditions, their appearance and physical properties show dramatic differences. It is demonstrated that these differences are associated with distinct Q3/Q4 Si–O–Si connectivity ratios in the two materials although both are mainly constructed from 3 and 5 member siloxane rings (3R and 5R). Comparative NMR and Raman spectroscopic experiments on these gels and related model calculations indicate that Raman is disproportionally more sensitive for Q1 and Q2 connectivities than for Q3 and Q4. This is an important new aspect to consider in the Raman identification of Qn connectivities in amorphous silicates. It is also shown that the molecular structures of TEOS based gels differ when made in the presence or absence of the porous organic substrate. Hence the substrate seems to exert structure directing effect. Characteristic structural differences have been identified also between the TEOS based silica gels and gels prepared from a commercial 3.22 SiO2/Na2O ratio aqueous sodium silicate solution. Moreover the structure of an “as synthesized” base set Na-silicate hydrogel is also different from that of its acid set counterpart: the former gel contains mainly 4 and 5 member and larger siloxane rings while the latter one virtually does not show any ring-associated Raman vibration. This result provides direct experimental support for the decades-old theoretical predictions that physical differences of acid and base set gels might be related to their ring and branched linear chain structures, respectively. We also demonstrate that the acid set gel gradually develops siloxane rings during its washing and aging procedures.

Optical forces and trapping potentials of a dual-waveguide trap based on multimode solid-core waveguides

We propose a novel design of the dual-waveguide trap for trapping and Raman identification of microscopic particles and biological objects in a fluid. The device is based on two embedded Si3N4waveguides launching counterpropagating beams into the fluidic channel of a lab-on-a-chip. For waveguides with a square cross-section of 1 µm2, a 5 µm gap in between and for a 785 nm operation wavelength, we perform finite-difference time-domain simulations of the beam profiles and the trapping forces acting on polystyrene beads (diameter 0.2-1.4 µm). The forces reach values up to 16 pN/W for a bead diameter of 1.4 µm, indicating that the trap is very suitable to trap particles in a fluid. This is confirmed by the trapping potentials deduced from the force curves. The design of waveguides and chip is completely compatible with glass-based microfluidic technology, thus enabling mass production and widespead application, contrary to previous approaches.

Charge transfer and optical phonon mixing in few-layer graphene chemically doped with sulfuric acid

Chemical doping is expected to substantially increase the density of free charge carriers by charge transfer and modify the Fermi level and screening effect of doped materials. Here, along with Raman identification of 3 and 4 graphene layers by a 633-nm laser excitation, we investigated charge transfer and optical phonon mixing in few layer graphenes in detail by utilizing sulfuric acid as an electron-acceptor dopant. Sulfuric acid molecules are found to be only physically adsorbed on the surface layers of graphenes without intercalations. The top and bottom layers of bilayer graphene can be intentionally doped differently by concentrated sulfuric acid. The difference of the hole doping between the top and bottom layers results in phonon mixing of symmetric and antisymmetric modes in bilayer graphene. The Raman frequency evolution with the doping level is in agreement with recent ab initio density-functional theory calculations [P. Gava, M. Lazzeri, A. M. Saitta, and F. Mauri, Phys. Rev. B 80, 155422 (2009)]. Chemical doping by adsorption-induced charge transfer offers a way to study the electronic and vibrational behaviors of few layer graphenes at high-carrier concentration.

Raman identification of H2CO in aqueous solutions

AbstractAqueous formaldehyde solutions of mole fraction from 0.05 to 0.20 were studied by Raman spectroscopy at temperatures up to 180 °C. The previously unreported Raman spectrum of formaldehyde under its non‐hydrated form H2CO has been identified, in addition to the already known bands from methanediol CH2(OH)2 and poly(oxymethylene)glycols HO(CH2O)nH formed by hydration and subsequent polymerization of the formaldehyde molecules. The experimental spectrum of formaldehyde in solutions agrees perfectly with the theoretical calculations. Copyright © 2010 John Wiley & Sons, Ltd.

Raman identification of strongly absorbing phases: the ceramic black pigments

AbstractTo get black decorations requires high ceramic technology and there are different ways of achieving this. Their identification can be very useful to discriminate between different manufactures or periods of production but this information is often very hard to achieve because of their strong absorption of the illuminating laser beam, whatever the wavelength used, causing a very low scattering intensity and, in case of power increase, a transformation of phase which may lead to the misinterpretation of the spectra obtained. We test the use of five instruments with different characteristics (wavelength and power of excitation, spectral resolution, filters and microscope) applied to a group of heterogeneous samples which have in common the presence of a black glaze. The results obtained (manganese oxides, cobalt oxides or a mixture of the two even with the addition of haematite) are compared considering the different methodologies used and leading to a preference towards high‐sensitivity rather than high‐resolution spectrometers, notch‐filtered rather than edge‐filtered instruments and microscopic configuration used on freshly created cross‐sections. The importance of the objective choice is demonstrated. Small grains may be preferred. Copyright © 2010 John Wiley & Sons, Ltd.

ChemInform Abstract: XRD and Raman Identification of the Zirconia Modifications in Copper/ Zirconia and Palladium/Zirconia Catalysts Prepared from Amorphous Precursors.

ChemInform Abstract: XRD and Raman Identification of the Zirconia Modifications in Copper/ Zirconia and Palladium/Zirconia Catalysts Prepared from Amorphous Precursors.

The characterization of non-planar graphene nanowires with an Ω shape cross-section

We report on SEM, AFM, and Raman identification of non-planar several monolayer-thick graphene nanostructures with curved shapes. During mechanical exfoliation we obtained graphene flakes with nanowire/nanotube-like objects (diameters between 8 and 35 nm) with cross-sectional profile reminiscent of the Greek capital letter omega (Ω). The curved shapes of these objects were confirmed by AFM and SEM imaging. Non-planar Ω – nanostructures open up new possibilities for graphene electron energy band engineering.

Combined X-ray Diffraction and Raman Identification of Synthetic Organic Pigments in Works of Art: From Powder Samples to Artists’ Paints

X-ray diffraction (XRD) complemented by Raman spectroscopy analyses of synthetic organic pigments in powder samples, layered paint systems, and commercial artists’ paints bound in acrylic, alkyd, and oil media are presented. The potential and limitations of the techniques to identify and characterize mixtures of these pigments, along with inorganic extenders, in works of art are exemplified and discussed. Stratified model paint systems that mimic the layering structure typically found in modern paintings are used to evaluate the effect of the μXRD experimental parameters, as well as extenders or fillers commonly found in modern artists’ paint formulations, on the quality of the patterns recorded in microsamples of paint. XRD is demonstrated for the first time to be an effective tool for the specific identification of synthetic organic pigment mixtures and fillers in acrylic and alkyd bound artists’ paints, while the identification of these pigments by XRD in oil bound paints appears problematic. Detailed ...

On-site Raman identification and dating of ancient glasses: A review of procedures and tools

The potential of on-site Raman microspectroscopy for the analysis of colorless and colored amorphous silicates is reviewed. We present the experimental procedures and models used to characterize the glassy silicate network from the structural and compositional point of view. Examples illustrate the potential of the technique, among which the identification of fakes/copies and the quantification of the corrosion degree, results in a dating capability.

Identification of iron‐gall inks with near‐infrared Raman microspectroscopy

AbstractThe identification of iron‐gall inks on a number of 18th, 19th, and 20th century documents and a 12th century manuscript has been conducted using near‐infrared Raman microspectroscopy. These historic iron‐gall inks were found to display characteristic Raman bands generally occurring around 1475 cm−1, between 1310 and 1350 cm−1 (variable), 490–640 cm−1 (combined broad band), and 400 cm−1. These bands have promise as analytical spectroscopic markers for in situ non‐destructive Raman identification of iron‐gall ink on historic collections and were in good agreement with Raman data collected for laboratory‐prepared iron‐gall ink complexes and inks prepared following traditional iron‐gall ink recipes. All historic ink spectra contained a fluorescent background, the degree of which varied between samples. Copyright © 2008 John Wiley & Sons, Ltd.

Raman identification of natural red to yellow pigments: ochre and iron‐containing ores

AbstractRed and yellow natural (roasted) pigments have been used for millennia. This paper reports on the Raman characterization of about 50 pigments of the Ôkhra ‘Mathériauthèque’ collection from different origins: violet, red, orange, apricot, yellow ochre, Umbrian and Siena earths from France (Puisaye, Ardennes, Vaucluse), Italy (Siena, Sardinia, Venice, etc.), Germany, Sweden, Cyprus and India (Madras). Comparison is made with ‘Bengara’ Japanese pigments. Goethite is the chromophore of yellow pigments, and haematite (sometimes with magnetite) that of red ochre and earths. Umbrian pigment (‘Terre d'Ombre’) contains additional manganese oxides. Color shades are related to the content of secondary phases: iron oxides (haematite, goethite, magnetite), quartz, gypsum and anhydrite, calcite, dolomite, alums (jarosites), and to the Fe/M substitution in the haematite structure. The set of secondary phases can be used to confirm a provenance signature (Supplementary Material available). Copyright © 2008 John Wiley & Sons, Ltd.

Raman identification of corrosion products on automotive galvanized steel sheets

AbstractIron oxides (haematite, maghemite, magnetite), (oxy)hydroxides (lepidocrocite), carbonates, as well as zinc carbonate and oxide, have been identified on corroded galvanized steel samples after corrosion accelerating tests in the laboratory and compared with those observed on samples taken from vehicles that have been in circulation for five years in severe weather conditions. Spectra recorded on the corroded parts are compared with synthesized compounds. (Hydroxy)carbonates are clearly evidenced on galvanized and phosphated steel sheets. Corrosion layers beneath the paint could be detected. White regions always correspond to a ZnO‐rich phase but maghemite (γ‐Fe2O3) and sometimes akaganite (β‐FeOOHCl) are observed at the centre (maroon) of very corroded spots. Maghemite is observed in strongly corroded regions. Goethite (α‐) and lepidocrocite (γ‐FeOOH) (and akaganite) are observed at the surface of less corroded regions of phosphate‐free galvanized steel and are absent for phosphate‐coated steel. Green rust is observed only on galvanized samples corroded in the laboratory. Copyright © 2008 John Wiley & Sons, Ltd.

Time-Resolved Resonance Raman Identification and Structural Characterization of a Light Absorbing Transient Intermediate in the Photoinduced Reaction of Benzophenone in 2-Propanol

A nanosecond time-resolved resonance Raman (ns-TR3) spectroscopic study of the triplet state benzophenone reaction with the 2-propanol hydrogen-donor solvent and subsequent reactions is presented. The TR3 spectra show that the benzophenone triplet state (npi*) hydrogen-abstraction reaction with 2-propanol is very fast (about 10 to 20 ns) and forms a diphenylketyl radical and an associated 2-propanol radical partner. The temporal evolution of the TR3 spectra also indicates that recombination of these two radical species occurs with a time constant of about 1170 ns to produce a LAT (light absorbing transient) intermediate that is identified as the 2-[4-(hydroxylphenylmethylene)cyclohexa-2,5-dienyl]propan-2-ol (p-LAT) species. Comparison of the TR3 spectra with results obtained from density functional theory calculations for the species of interest was used to elucidate the identity, structure, properties, and major spectral features of the intermediates observed in the TR3 spectra. The structures and properties of the reaction intermediates observed (triplet benzophenone, diphenyl ketyl radical, and p-LAT) are briefly discussed.

Quality classification via Raman identification and SEM analysis of carbon nanotubebundles using artificial neural networks

One of the major obstacles for successful mass production of carbon nanotubes (CNTs) isperforming quick and precise characterization of the properties of a given batch ofnanotubes. In this paper, we have identified a set of intermediate steps that will lead to acomprehensive, scalable set of procedures for analyzing nanotubes. The proposedmethodology was originated with data processing of Raman spectra of multi-wall carbonnanotubes (MWCNT) turfs and image enhancement of SEM micrographs. Image analysistechniques of SEM images were employed and stereological relations were determinedfor SEM images of CNT structures; these results were utilized to estimate themorphology of the turf (i.e. CNTs alignment and curvature) using an artificialneural networks (ANN) classifier. This model was also used to investigate the linkbetween Raman spectra of CNTs and the quality of the turf morphology. Thisnovel methodology will improve our capability to control the quality of the grownnanotubes through the use of this system in a supervised growth environment.

On-site Raman identification and dating of ancient/modern stained glasses at the Sainte-Chapelle, Paris

Abstract The experimental procedures and most important conclusions of the first on-site Raman study of the stained glass windows in the upper chapel of the Sainte-Chapelle, Paris are discussed. Some of the windows suffered damage during/after the French Revolution and were partly restored in the 19th century. Measurements were performed with a new portable Raman instrument on colourless, blue and green stained glasses. We illustrate how the Raman signature of the glass makes it possible to distinguish between medieval K/Ca or 19th century restored Na/Ca-based silicates and to determine their weathering degree. This is achieved by means of the extraction of vibrational parameters and then processing them, using chemometric approaches, principal components and cluster variation analyses with varying degrees of complexity. The Raman scattering intensity of weathered glasses is used to determine their relative age. The results differ from those presented in the Corpus Vitrearum Medii Aevi (obtained by visual inspection) and therefore demonstrate the need for updating these reports with modern methods such as in situ Raman spectroscopy.

Raman identification of yellow synthetic organic pigments in modern and contemporary paintings: Reference spectra and case studies

The characterization of the binding media and pigments in modern and contemporary paintings is important for designing safe conservation treatments, as well as for determining suitable environmental conditions for display, storage and transport. Raman spectroscopy is a suitable technique for the in situ non-destructive identification of synthetic organic pigments in the presence of the complex binding media characteristic of synthetic resin paints or colour lithographic inks. The precise identification of a pigment by comparing its spectrum to that of a reference is necessary when conservation treatments with aqueous solutions or organic solvents are being considered for a work of art, since solubility properties can sometimes vary within the same pigment group. The Raman spectra of 21 yellow synthetic organic pigments, belonging to the monoazo, monoazo lakes, diarylide, disazo condensation, benzimidazolone, bisacetoacetarylide, azo-methine metal complex, isoindolinone and isoindoline groups are presented. Since modern artists frequently mixed paint developed for other applications, in addition to colorants developed as artists’ paints, other synthetic organic pigments were included in the spectral database. Two monoazo pigments, Pigment Yellow 1 and Pigment Yellow 3, a benzimidazolone, Pigment Yellow 154 and a phthalocynanine, Pigment Green 7, were identified in sample cross-sections from four modern and contemporary paintings in the collection of The Museum of Modern Art in Ljubljana, Slovenia.

The investigation of single bacteria by means of fluorescence staining and Raman spectroscopy

AbstractThe successful combination of Raman spectroscopy and fluorescence labelling of single bacterial cells is presented. The results show that the selected dyes (DAPI, SYTO 9, CFDA, SYTOX blue and PI) in most cases do not influence the Raman spectrum of a labelled bacterium significantly compared to an unstained bacterium spectrum. The labelling of bacteria offers the possibility of live/dead or biotic/abiotic differentiation prior to a Raman identification step. Copyright © 2007 John Wiley & Sons, Ltd.