Microanalysis of clay‐based pigments in painted artworks by the means of Raman spectroscopy

FT Raman spectroscopy and micro‐Raman spectroscopy with lasers of three different wavelengths (1064 nm, 785 nm and 532 nm) were used for analysis of reference samples of natural clay pigments including white clay minerals (kaolinite, illite, montmorillonite), green earths (glauconite and celadonite) and red earths (natural mixtures of white clay minerals with hematite). In addition, eight micro‐samples obtained from historical paintings containing clay pigments in ground and colour layers have been examined. Powder X‐ray diffraction and micro‐diffraction were used as supplementary methods. It was found that laser operating at 1064 nm provided the best quality Raman spectra for distinguishing different white clay minerals, but the spectra of green and red earths were affected by strong fluorescence caused by the presence of iron. Green earth minerals could be easily distinguished by 532 or 785 nm excitation lasers, even in small concentrations in the paint layers. On the other hand, when anatase (TiO₂) or iron oxides (such as hematite) were present as admixtures (both are quite common, particularly in red earths), the collection of characteristic spectra of clay minerals which form the main component of the layer was hindered or even prevented. Another complicating factor was the fluorescence produced by organic binders when analysing the micro‐samples of artworks. In those cases, it is always necessary to use powder X‐ray micro‐diffraction to avoid misleading interpretations of the pigment's composition. Copyright © 2013 John Wiley & Sons, Ltd.     

Raman spectra of selected mineral phases of the Morasko iron meteorite

Selected minerals from oval inclusions (nodules) in the Morasko IAB iron meteorite have been investigated by electron microprobe (EMP) and micro‐Raman spectroscopy. Collected spectra of quartz, forsterite‐rich olivine, chromite, kosmochlor (Na–Cr‐rich clinopyroxene) and Na‐feldspar (albite) were compared with corresponding measurements of earth minerals and used for fast identification of meteorite fragments not EMP characterized. Some structural conclusions concerning particular minerals, like solid‐state form or average crystallite size, were also drawn from the measured spectra. Copyright © 2013 John Wiley & Sons, Ltd.     

A Raman spectroscopic study of teeth affected with molar–incisor hypomineralisation

Raman spectroscopy was used to chemically map lesions associated with molar–incisor hypomineralisation in human teeth. Three teeth with hypomineralised lesions of differing severity, described as white, yellow or brown, were mapped using integral ratios of major component bands (hydroxyapatite, amide I and b‐type carbonate) and principal component analysis scores values. These lesions were found to contain depleted levels of mineral (hydroxyapatite) compared with those of healthy enamel. Principal component analysis also highlighted changes in the phosphate structure and variations in various organic constituents. These variations were consistent with increased disorder in the mineral component of the hypomineralised tooth lesions. Scanning electron microscopy–energy dispersive X‐ray spectroscopy supported the findings based on Raman spectroscopy. Copyright © 2015 John Wiley & Sons, Ltd.     

Modeling the physico‐chemistry of acid sulfate waters through Raman spectroscopy of the system FeSO4?H2SO4?H2O

Mine waters containing extremely high concentrations of sulfuric acid and dissolved iron are found in the Rio Tinto (Spain) area. In this study, Raman spectroscopy has been used to investigate the speciation of the system iron(II)–sulfuric acid–water as an approach to study Rio Tinto's stream water. Several solutions of aqueous sulfuric acid containing iron(II) sulfate in the range 0–1.65 mol/kg were prepared, and qualitative and quantitative analyses of the ions present in the solutions were carried out using Raman spectroscopy. The intrinsic features of Raman spectroscopy allowed the identification of the species present in solution and calculation of the species concentration through band‐fitting of the Raman spectra. The activity coefficient product of the system iron(II) sulfate–sulfuric acid–water as a function of salt concentration is reported. Previous findings on the formation of iron(II) hexahydrate complexes in the mentioned system have been corroborated by means of Raman spectroscopy. Copyright © 2007 John Wiley & Sons, Ltd.     

Multivariate analysis of combined Raman and fibre‐optic reflectance spectra for the identification of binder materials in simulated medieval paints

The non‐invasive identification of paint materials used in works of art is essential, both for preserving and restoring them, and also for understanding and verifying the history surrounding their creation. As such, the development of suitable non‐invasive techniques has received much interest in recent years. We have investigated the use of Fourier transform (FT)‐Raman spectroscopy and fibre‐optic reflectance spectroscopy (FORS), together with multivariate principal‐component analysis (PCA) techniques, in order to identify the pigment and binding materials used in made‐up samples representative of real artwork. We demonstrate that both types of spectroscopy provide complementary information which can be used to identify the pigments and binders in paint samples. We show that PCA with FT‐Raman spectra can be used to assist in the identification of oil‐based binders, and that the additional data provided by FORS spectra enables PCA on combined spectra to identify more complex proteinaceious and polysaccharide‐based binding media. The results presented here demonstrate that multivariate analyses of lead‐based paints, using data measured by FT‐Raman and FORS in conjunction, have much potential for identifying individual pigments and binders in paint samples. This provides a path towards computer‐assisted characterisation of paint materials on artwork. Copyright © 2013 John Wiley & Sons, Ltd.     

Aperture based Raman spectroscopy on SiGe film structures with high spatial resolution

We have investigated silicon–germanium (SiGe) line structures employing metallic apertures in combination with Raman spectroscopy to obtain high‐spatial strain resolution below the diffraction limit. The apertures were cut into specifically shaped electrochemically etched tungsten tips, which were adjusted within the Raman laser beam on the sample surface by a tuning fork atomic force microscope. With this setup, line structures on patterned SiGe films with a center‐to‐center distance down to 200 nm were resolved in the Raman scans, evidently indicating a resolution clearly below the far‐field Raman resolution of about 600 nm for the used instrument. This setup allows improved local strain analysis by Raman spectroscopy and shows potential for further near‐field Raman applications. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman imaging and photodegradation study of phthalocyanine containing microcapsules and coated particles

We present the results of using Raman molecular imaging and atomic force microscopy (AFM) investigation of the composition, stability, and photodegradation of polyelectrolyte multilayer microcapsules and coated microparticles containing copper–phthalocyanine and iron–phthalocyanine. The influence of laser light on degradation of these phthalocyanine dyes embedded in the walls of polyelectrolyte multilayer capsules and shells of microparticles was studied by both AFM and Raman molecular imaging, but only the latter technique gave information on dynamics of photodegradation. Raman peak assignment was performed according to theoretical calculations. The degradation rate of phthalocyanine dyes is estimated from Raman signal measurements and a model is proposed to account for the degradation rate. Practical applications of our approach are outlined. Copyright © 2011 John Wiley & Sons, Ltd.     

Characterization of pottery from Republic of Macedonia. III. A study of comparative mineralogical detection efficiency using micro‐Raman mapping and X‐ray diffraction

Point‐to‐point micro‐Raman and X‐ray diffraction (XRD) techniques were employed for characterization of minerals present in the pottery body of 27 glazed Byzantine and Ottoman pottery shreds, excavated at two different archaeological sites in the Republic of Macedonia: in Skopje (Skopsko Kale) and in Prilep (Markovi Kuli and Sv. Atanas Church). The Raman spectra of 18 Byzantine samples (dating from 12th−14th century) and nine Ottoman samples (dating from 17th−19th century) revealed 26 different minerals. XRD measurements were further performed on the same powder samples to validate the mineralogical assessment obtained by point‐to‐point micro‐Raman spectroscopy. Although only 13 different mineral phases were obtained by the XRD, the results obtained from the Raman and XRD spectra for the most abundant minerals in the investigated pottery bodies match quite well. However, the identification of the less abundant minerals in the clay matrixes from the XRD data was very difficult, if at all possible. The results emphasize the specifics of the applied techniques and their limits. Additionally, wavelength dispersive X‐ray fluorescence spectroscopy was used for the elemental analysis. Copyright © 2011 John Wiley & Sons, Ltd.     

Raman spectra of nitrogen‐containing organic compounds obtained using a portable instrument at −15 °C at 2860 m above sea level

Well‐resolved Raman spectra of samples of nitrogen‐containing compounds were detected using a portable Raman instrument (Ahura First Defender XL) outdoors at a low ambient temperature of −15 °C and at an altitude of 2860 m (Pitztall, Austria). The portable Raman spectrometer tested here is equipped with a 785‐nm diode laser and a fixed frontal probe. Solid form of formamide, urea, 3‐methylpyridine, aniline, indene, 1‐(2‐aminoethyl)piperazine, indoline and benzofuran were detected unambiguously under high‐mountain field conditions. The main Raman features (strong, medium and partially weak bands) were observed at the correct wavenumber positions (with a spectral resolution 7–10 cm⁻¹) in the wavenumber range 200–1600 cm⁻¹. The results obtained demonstrate the possibility of employing a miniaturised Raman spectrometer as a key instrument for investigating the presence of nitrogen‐containing organic compounds and biomolecules outdoors under low temperature conditions. Within the payload designed by European Space Agency (ESA) and National Aeronautics and Space Administration (NASA) for future missions, focussing not only on Mars, Raman spectroscopy represents an important instrumentation for the detection of organic nitrogen‐containing compounds relevant to life detection on planetary surfaces or near sub‐surfaces. Copyright © 2009 John Wiley & Sons, Ltd.     

An analysis of bivalve larval shell pigments using micro‐Raman spectroscopy

Micro‐Raman spectroscopy has been used on adult bivalve shells to investigate organic and inorganic shell components but has not yet been applied to bivalve larvae. It is known that the organic matrix of larval shells contains pigments, but less is known about the presence or source of these molecules in larvae. We investigated Raman spectra of seven species of bivalve larvae to assess the types of pigments present in shells of each species and how the ratio of inorganic : organic material changes in a dorso‐ventral direction. In laboratory experiments, we reared larvae of three clam species in waters containing different organic signatures to determine if larvae incorporated compounds from source waters into their shells. We found differences in spectra and pigments between most species but found less intraspecific differences. A neural network classifier for Raman spectra classified five out of seven species with greater than 85% accuracy. There were slight differences between the amount and type of pigment present along the shell, with the prodissoconch I and shell margin areas being the most variable. Raman spectra of 1‐day‐old larvae were found to be differentiable when larvae were reared in waters with different organic signatures. With micro‐Raman spectroscopy, it may be possible to identify some unknown species in the wild and trace their natal origins, which could enhance identification accuracy of bivalve larvae and ultimately aid management and restoration efforts. Copyright © 2014 John Wiley & Sons, Ltd.     

Darling–Dennison resonance of thiourea adsorbed on the silver electrode revealed by surface enhanced Raman spectroscopy

We report surface enhanced Raman spectroscopy (SERS) of Darling–Dennison resonance of thiourea on Ag electrode excited at 514.5 nm laser excitation. Darling–Dennison resonance indicates that two degenerate Raman modes interact with each other and their degenerate first‐order overtone modes obtain energy and appear in Raman spectra. Our study showed that the ratio of intensity of the Darling–Dennison resonance is up to 0.24 of its fundamental Raman intensity, when the applied electrode voltage is at –0.4 V versus the saturated calomel electrode. This phenomenon was also observed on the Ag island film surface at ambient condition. These observations demonstrated strong evidence for Darling–Dennison resonance band in SERS. The implications of these observations are also discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

Raman scattering study of molecules adsorbed on ZnS nanocrystals

The adsorption of 4‐mercaptopyridine (4‐Mpy) molecules on ZnS nanocrystals was investigated by means of Raman spectroscopy. We compared the Raman signals of 4‐Mpy molecules adsorbed on ZnS nanocrystals and Ag substrate. The differences in the adsorption of 4‐Mpy molecules on the semiconductor and the metal substrate were noted. The results demonstrated that adsorbed species on the semiconductor ZnS nanocrystals can be detected by Raman spectroscopy. Copyright © 2006 John Wiley & Sons, Ltd.     

Raman characterization of the structural evolution in amorphous and partially nanocrystalline hydrogenated silicon thin films prepared by PECVD

Hydrogenated silicon (Si:H) thin films were obtained by plasma‐enhanced chemical vapor deposition (PECVD). Raman spectroscopy was used to investigate the structural evolution in phosphor‐doped n‐type amorphous hydrogenated silicon thin films, which were prepared under different substrate temperatures and gas pressures. Meanwhile, the effect of nitrogen doping on the structure of P‐doped thin films was also investigated by Raman spectroscopy. Moreover, the transition from the amorphous state to the nanocrystalline state of undoped Si:H films deposited through low argon dilution was studied by Raman spectroscopy, X‐ray diffraction, and transmission electron microscopy. The results show that Raman spectroscopy can sensitively detect the structural evolution in hydrogenated silicon thin films deposited under different conditions in a PECVD system. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectroscopy of sol–gel derived titanium oxide thin films

Raman spectra of TiO₂ films prepared via the sol–gel process were studied by UV and visible Raman spectroscopy. The evolution of the phases of TiO₂ films during annealing was investigated, and the relative intensities of the Raman bands excited with 325 nm were found to be distinct from those of the bands excited with 514 nm. The transmittance and FTIR spectra of the films annealed at different temperatures were characterized. The crystallization process of the powders and thin films treated by different annealing methods were also studied with Raman spectroscopy. The results show that the change in the relative intensities is caused by the resonance Raman effect. The anatase to rutile transition of the powder occurs at 700 °C, while that of the thin film occurs at 800 °C. The analysis of Raman band shape (peak position and full width at half‐maximum) after conventional furnace annealing and rapid thermal annealing indicates the influence of the non‐stoichiometry and phonon confinement effect. Copyright © 2011 John Wiley & Sons, Ltd.     

Confocal Raman microscopy for simultaneous monitoring of partitioning and disordering of tricyclic antidepressants in phospholipid vesicle membranes

Characterization of drug–membrane interactions is important in order to understand the mechanisms of action of drugs and to design more effective drugs and delivery vehicles. Raman spectra provide compositional and conformational information of drugs and lipid membranes, respectively, allowing membrane disordering effects and drug partitioning to be assessed. Traditional Raman spectroscopy and other widely used bioanalytical techniques such as differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) typically require high sample concentrations. Here, we describe how temperature‐controlled, optical‐trapping confocal Raman microscopy facilitates the analysis of drug–membrane interactions using micromolar concentrations of drug, while avoiding drug depletion from solution by working at even lower lipid concentrations. The potential for confocal Raman microscopy as an effective bioanalytical tool is illustrated using tricyclic antidepressants (TCAs), which are cationic amphiphilic molecules that bind to phospholipid membranes and influence lipid phase transitions. The interaction of these drugs with vesicle membranes of differing head‐group charge is investigated while varying the ring and side‐chain structure of the drug. Changes in membrane structure are observed in Raman bands that report intra‐ and intermolecular order versus temperature. The partitioning of drugs into the membrane can also be determined from the Raman scattering intensities. These results demonstrate the usefulness of confocal Raman microscopy for the analysis of drug–membrane systems at biologically relevant drug concentrations. Effective tools for monitoring drug–membrane interactions are crucial for rational design of new drugs. Copyright © 2009 John Wiley & Sons, Ltd.     

Controlled SnO2 nanocrystal growth in SiO2–SnO2 glass‐ceramic monoliths

Crack‐free (100–x) SiO₂–x SnO₂ glass‐ceramic monoliths have been prepared by the sol–gel method obtaining for the first time SnO₂ concentrations of 20% with annealing at 1100 °C. Heat‐treatment resulted in the formation and growth of SnO₂ nanocrystals within the silica matrices. Combined use of Fourier transform–Raman spectroscopy and in situ high‐temperature X‐Ray diffraction shows that SnO₂ particles begin to crystallize in the cassiterite‐type phase at 80 °C and that their average apparent size remains around 7 nm, even after annealing at 1100 °C. Nanocrystal sizes and size distributions determined by low‐wavenumber Raman are in good agreement with those obtained from transmission electron microscopy measurements. Results indicate that the formation and the growth of SnO₂ nanocrystals impose a residual porosity in the silica matrix. Copyright © 2011 John Wiley & Sons, Ltd.     

Densification of sol–gel silica thin films induced by hard X‐rays generated by synchrotron radiation

In this article the effects induced by exposure of sol–gel thin films to hard X‐rays have been studied. Thin films of silica and hybrid organic–inorganic silica have been prepared via dip‐coating and the materials were exposed immediately after preparation to an intense source of light of several keV generated by a synchrotron source. The samples were exposed to increasing doses and the effects of the radiation have been evaluated by Fourier transform infrared spectroscopy, spectroscopic ellipsometry and atomic force microscopy. The X‐ray beam induces a significant densification on the silica films without producing any degradation such as cracks, flaws or delamination at the interface. The densification is accompanied by a decrease in thickness and an increase in refractive index both in the pure silica and in the hybrid films. The effect on the hybrid material is to induce densification through reaction of silanol groups but also removal of the organic groups, which are covalently bonded to silicon via Si—C bonds. At the highest exposure dose the removal of the organic groups is complete and the film becomes pure silica. Hard X‐rays can be used as an efficient and direct writing tool to pattern coating layers of different types of compositions.     

SERS detection of polychlorinated biphenyls using β‐cyclodextrin functionalized gold nanoparticles on agriculture land soil

A highly sensitive surface‐enhanced Raman scattering (SERS) platform for the selective trace analysis of persistent organic pollutant (POP) such as polychlorinated biphenyl (PCBs) was reported based on β‐CD modified gold nanoparticles (AuNPs) with the real environmental sample of polluted soil. The synthesized gold nanoparticles were characterized using UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD) and transmission electron microscopy (TEM). In polluted soil the presentation of PCB is confirmed by using GC‐MS. It is further verified and confirmed by using SERS. When the contaminated soil was added to the system, the binding of soil with β‐CD resulted in the aggregation of AuNPs, and excellent Raman signal was obtained which can reflect the isomers of polychlorinated biphenyls. Copyright © 2015 John Wiley & Sons, Ltd.     

Metal‐assisted regioselectivity in nucleophilic substitutions: a study by Raman spectroscopy and density functional theory calculations

A series of complexes (Fe^II, Cu^II and Ni^II) of the N,O bidentate ligand 6,7‐dichloroquinoline‐5,8‐dione in water was investigated by using Raman spectroscopy, and the experimental peaks were assigned with the help of computed spectra by density functional theory (DFT) calculations. A strong shift to lower wavenumbers was observed for the vibration of the CO group involved in chelation, depending on the type of metal ion. When each complex was used in the substitution reaction by the nucleophilic reagent piperidine, two products having the same molecular composition but showing the substituent in different regions of the molecule were obtained, and moreover their regioselective formation was in agreement with the size of the Raman shifts previously observed for the complexes. This example confirms the potential of the approach involving Raman spectroscopy combined with DFT calculations in the characterization of metal complexes as key intermediates in organic reactions, with the possibility of predicting the metal system capable to achieve the highest selectivity. Copyright © 2010 John Wiley & Sons, Ltd.     

Vibrational properties of ibuprofen–cyclodextrin inclusion complexes investigated by Raman scattering and numerical simulation

The modifications to the vibrational spectra produced by inclusion into cyclodextrins on the vibrational spectra of of the non‐steroidal anti–inflammatory drug ibuprofen, by inclusion into cyclodextrins have been investigated by means of Raman scattering and numerical simulation. These changes are discussed and explained by comparison with the theoretical vibrational wavenumbersfrequencies and Raman intensities obtained by quantum and classical numerical simulations, disentangling the effects directly related to the complexation process, from those to be ascribed to non‐covalent dimerization of ibuprofen due to hydrogen bonding. Copyright © 2008 John Wiley & Sons, Ltd.