Micro‐Raman depth profiling on polished cross‐sections: the mapping of oxalates used in protective treatment of carbonatic substrate

We present the first depth profiling on a polished cross‐section carried out by micro‐Raman spectroscopy aimed at investigating the penetration depth of an inorganic protective material (ammonium oxalate) applied on carbonatic surfaces (ancient plaster) and to detect the distribution of mineralogical phases inside the material. The reason for such a Rapid Communication is the importance of our study for the field of conservation, in which at present the treatment with oxalates is a hot issue. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and Raman spectroscopic characterisation of the oxalate mineral wheatleyite Na2Cu2+(C2O4)2·2H2O

The mineral wheatleyite has been synthesised and characterised by Raman spectroscopy complimented with infrared spectroscopy. Two Raman bands at 1434 and 1470 cm⁻¹ are assigned to the ν_{(C O)} stretching mode and implies two independent oxalate anions. Two intense Raman bands observed at 904 and 860 cm⁻¹ are assigned to the ν(C C) stretching mode and support the concept of two non‐equivalent oxalate units in the wheatleyite structure. Two strong bands observed at 565 and 585 cm⁻¹ are assigned to the symmetric CCO in plane bending modes. The Raman band at 387 cm⁻¹ is attributed to the CuO stretching vibration and the bands at 127 and 173 cm⁻¹ to OCuO bending vibrations. A comparison is made with Raman spectra of selected natural oxalate bearing minerals. Oxalates are markers or indicators of environmental events. Oxalates are readily determined by Raman spectroscopy. Thus, deterioration of works of art, biogeochemical cycles, plant metal complexation, the presence of pigments and minerals formed in caves can be analysed. Copyright © 2008 John Wiley & Sons, Ltd.     

Studies on paint cross sections of a glass painting by using FT‐IR and Raman microspectroscopy supported by univariate and hierarchical cluster analyses

Fourier transform infrared (FT‐IR) and Raman spectroscopy is used for the non‐destructive analysis of painting materials and ageing compounds in micrometric cross sections of a glass painting. The combination of both techniques in conjunction with imaging/mapping function provides the spatial distribution of chemical components identified in vibrational spectra. The aim of our work is to show the applicability of the FT‐Raman mapping technique in the detection of painting materials. We also compare Raman information gained by using two laser excitations at 532 and 1064 nm implemented in microspectrometers with different confocality and spatial resolution. In turn among FT‐IR imaging techniques, we compare chemical images recorded in external reflection and attenuated total reflection modes that give chemical images of different size and spatial resolution. Our FT‐IR and Raman imaging characterize a number of painting materials such as pigments, binders, fillers as well as degradation products. Raman maps are constructed by using the univariate analysis. In turn, a profile of IR images requires the use of a more complex methodology. Here, we compare FT‐IR images of the painting cross sections obtained by using the univariate and hierarchical cluster analysis. We clearly show that the multivariate approach is a powerful tool for the credible construction of IR images, providing the relevant chemical information on the multicomponent stratigraphy of the samples. Moreover, the combination of all the methods allows us to demonstrate their degree of utility for the study on the paint cross sections of the works of art. Copyright © 2013 John Wiley & Sons, Ltd.     

The first spectroscopic analysis of Ethiopian prehistoric rock painting

An extensive micro‐Raman spectroscopic study of prehistoric rock paintings found in Hararghe region, Ethiopia, was carried out, with the aim to evaluate the production skill of the local artist and the period of production of the discovered paintings. Attenuated Total Reflection Fourier Transform Infrared (ATR‐FTIR) Spectroscopy and Laser Induced Breakdown Spectroscopy (LIBS) were used as auxiliary techniques. Micro sampling were carried out on parts of red, white, black painting figures representing domestic and wild animals. The pigments used by artists were hematite for red color, calcite or gypsum for white color, and carbonaceous material for black coloration. A green pigment was also investigated; it resulted made of green earth. A consistent amount of Ca‐oxalate was found particularly on red samples as well as on the white ones. Former studies attributed oxalates origin to a biological substrate attack, whereas in the present case Ca‐oxalate is ascribed to the use of an organic stuff to spread properly the pigments on the substrate.Principal Component Analysis was performed on the hematite spectra; it evinced that the spectral features could be indicative of different sites and of the relative age.1These novel evaluations put into new perspective the knowledge about rock art pictorial technology of the Horn of Africa. Copyright © 2011 John Wiley & Sons, Ltd.     

Identification of minerals and organic materials in Middle Eocene ironstones from the Bahariya Depression in the Western Desert of Egypt by means of micro‐Raman spectroscopy

The Middle Eocene ironstones of the Bahariya Depression consist of four iron ore types: manganiferous mud‐ironstone, fossiliferous ironstone, stromatolitic ironstone and nummulitic–ooidal–oncoidal ironstone. The upper surfaces of these sequences were subjected to subaerial weathering and a lateritic iron ore type was formed. The chemical composition of these ironstone types was investigated by means of micro‐Raman spectroscopy. Various closely related iron‐containing and manganese‐containing minerals were detected by means of the above‐mentioned approach. The high spatial resolution and sensitivity of this method allowed us to identify minerals that could not be detected by other techniques. Well‐preserved organic materials were observed in one type of ironstones. Therefore, using Raman spectroscopy, we were able to provide evidence that the formation of some of the investigated rocks was biologically mediated. The application of Raman spectroscopy is considered a powerful technique for the identification of both organic and inorganic substances in the studied iron ore deposits. Copyright © 2011 John Wiley & Sons, Ltd.     

拉曼光谱在天然纤维素结构研究中的应用进展

纤维素是木质纤维生物质细胞壁的骨架物质,也是生物燃料制备过程中重要的前驱体。作为重要的天然有机高分子,纤维素分子结构的研究备受关注。拉曼光谱仪因其较高的分辨率及无损检测的特点可在多尺度研究天然纤维素复杂分子链及聚集态结构。本文在比较了色散型拉曼光谱仪和傅里叶变换拉曼光谱仪的构造及相关参数的基础上,详细综述了拉曼光谱技术在植物细胞壁纤维素微区分布、天然纤维素酶解发酵、分子链空间取向、分子形变、结晶度与多晶态转变等方面的研究进展。并对拉曼光谱技术在天然纤维素分子结构研究中存在的问题进行了总结,提出了可能的解决方案,以促进拉曼光谱技术在天然有机高分子研究领域的应用。     

Phosphate and amide III mapping in sialoliths with Raman microspectroscopy

Sialoliths, a cause of the salivary gland infection, are reported to be composed of inorganic and organic substances. However, the precise mechanism of sialolith formation remains unclear. The purpose of this report is to elucidate this mechanism by analyzing the precise distribution of phosphate (an inorganic substance) and amide III (an organic substance) in sialoliths by using Raman microspectroscopy. Sialoliths from the submandibular gland duct were analyzed by this form of observation and by a scanning electron microscope (SEM) equipped with an energy‐dispersive X‐ray spectroscope (EDX). In Raman microspectroscopy we analyzed the spectral peak of the phosphate (PO₄³⁻) symmetric stretching vibrational mode (υ₁) at 960 cm⁻¹ and that of amide III at 1265 cm⁻¹ to demonstrate the mapping of an image of these elements showing a semiquantitative distribution of phosphate and amide III in the sialoliths. It was found that phosphate and amide III were concentrated at the center of the sialoliths, and the phosphate distribution in the sialoliths showed concentric laminations. These results indicated the possibility that the sialoliths originated from a nidus of organic materials and progressively grew by the deposition of layers of organic and inorganic materials. Copyright © 2008 John Wiley & Sons, Ltd.     

Study of carrier concentration profiles in Al‐implanted Ge by micro‐Raman spectroscopy under different excitation wavelengths

The distribution profile of Al implanted in crystalline Ge has been investigated by micro‐Raman spectroscopy. Using different excitation laser lines, corresponding to different optical penetration depths, the Al concentration at different depths beneath the sample surface has been studied. We have found a strong correlation between the intensity of the Al–Ge Raman peak at ~370 cm⁻¹, which is due to the local vibrational mode of substitutional Al atoms, and the carrier concentration profile, obtained by the spreading resistance profiling analysis. A similar connection has been also observed for both shape and position of the Ge–Ge Raman peak at ~300 cm⁻¹. According to these experimental findings, we propose here a fast and nondestructive method, based on micro‐Raman spectroscopy under different excitation wavelengths, to estimate the carrier concentration profiles in Al‐implanted Ge. Copyright © 2013 John Wiley & Sons, Ltd.     

Experimental study of the Raman strain rosette based on the carbon nanotube strain sensor

This work presents a new technique named Raman strain rosette for the micro‐strain measurement of both Raman active and Raman inactive materials. The technique is based on the theoretical model of the carbon nanotube (CNT) strain sensor that applies the resonance and polarization Raman properties of CNTs and calculates the synthetic contributions of uniformly dispersed CNTs to the entire Raman spectrum. In our work, the proposed technique is applied in different experiments on the Raman inactive materials, such as step‐by‐step uniaxial tensile and Raman mapping around a circular hole. The experimental results reached by the Raman strain rosette are consistent with the actual values as a whole. This study verifies that the Raman strain rosette is applicable to quantitative measurement of all the in‐plane components of the strain tensor (including both normal and shear strains) by three polarized Raman detections for each sampling spot on a microscale. The technique is further applicable to achieving the strain fields through Raman mapping. Copyright © 2010 John Wiley & Sons, Ltd.     

Investigation of stress and structural damage in H and He implanted Ge using micro‐Raman mapping technique on bevelled samples

The results on structural damage in germanium wafers caused by hydrogen and helium implants of typical doses used in Smart Cut™ Technology (1–6 × 10¹⁶ atoms/cm²) are investigated using Raman mapping and spreading resistance profiling techniques. Raman line‐mapping measurements were performed up to the depth of ~400 nm into a Ge substrate (well beyond the limit of visible light penetration depth) using a bevelling technique. From analysis of the Ge–Ge Raman peak it was found that implantation of H and He introduced a different type of stress, tensile and compressive, respectively and significant structural damage with maximum at the projected range. The obtained data shows that hydrogen incorporation in Ge can act as an acceptor. This is undesirable when the hydrogen ion‐cut technology is applied to high resistivity Ge. The crystalline structure after implantation is completely recovered when annealed at 600 °C for both types of implants. Spreading resistance profiling results reveal that 4−8x10¹⁵ acceptors/cm³ remain after 600 °C, and these are thought to be because of vacancy related defect clusters. Copyright © 2011 John Wiley & Sons, Ltd.     

SERS detection of red organic dyes in Ag‐agar gel

Micro‐Raman spectroscopy has been widely employed in the last few years for the study of artworks, allowing for the characterization of a high class of pictorial materials. However, the detection of organic dyes by conventional Raman spectroscopy is quite difficult, due to the high fluorescence provided by these compounds. Recently, remarkable improvements have been achieved by the introduction of the surface enhanced Raman spectroscopy (SERS) technique for the analysis of organic dyes. In the present work, a new method is presented, based on the use of a SERS probe made of agar‐agar coupled with silver nanoparticles, for a non‐destructive and minimally invasive micro‐extraction of dyes from textiles. Ag‐agar gel has been tested first on textile mock‐ups dyed with alizarin, purpurin and carminic acid. SERS measurements have been performed adopting laser light excitations at 514.5 and 785 nm of a micro‐Raman setup. Highly structured SERS band intensities have been obtained. After having verified the safety of the method by colorimetric, X‐ray fluorescence and attenuated total reflectance Fourier transform infrared techniques, a real case, a pre‐Columbian piece of textile, have been investigated by Ag‐agar gel. This cutting‐edge method offers new possibilities for a sensitive and non‐destructive analysis of fluorescent materials. Copyright © 2012 John Wiley & Sons, Ltd.     

The use of Raman microscopy and laser desorption ionization mass spectrometry in the examination of synthetic organic pigments in modern works of art

Synthetic organic pigments are widely used in modern and contemporary works of art. They have been examined by a variety of techniques including spectroscopic methods such as Fourier transform infrared spectroscopy, Raman, and X‐ray powder diffraction as well as chromatographic or mass spectrometric techniques such as pyrolysis‐gas chromatography/mass spectrometry and laser desorption ionization mass spectrometry (LDI–MS). Often, a combination of techniques has been used to examine these pigments. This paper describes use of Raman spectroscopy to create a database of colorants including two pigments not previously reported, PO1 and PO2. Then, using Raman spectroscopy in combination with LDI–MS, samples from modern works of art by artists including Mark Rothko, Barnett Newman, and José de Rivera were examined in order to identify the pigments present. One finding was that Rothko used a variety of red pigments over the course of his career including PR11 which has not been previously reported in artwork, and PO2 found with its positional isomer PR1. Knowledge of the colorants serves to inform conservators about display and treatment decisions. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.     

Detailed spectroscopic analysis of complex multi‐component materials using a combination of Raman mapping with BTEM

The combined application of Raman microscopy and self‐modeling curve resolution techniques can address a wide range of material characterization problems. In particular, the combination of Raman microscopy and the Band‐Target Entropy Minimization (BTEM) algorithm has been applied to various organic, inorganic, pharmaceutical and bio‐material related problems. In the present contribution, the principles behind this type of analysis are reviewed, followed by a number of case‐by‐case studies. For each of these examples, a Raman microscopic mapping measurement (consisting of 100 s up to 1000 s of spectra) is performed, followed by BTEM analysis which provides the underlying pure component spectra of the constituents present in the system without the use of any a priori information. In most cases, outstanding signal‐to‐noise ratios for components at the 0.1‐1.0 % level can be obtained, and sometimes trace constituents can also be detected. Subsequently, the identity of the components can be determined by comparison to spectral libraries. Finally, the reconstructed pure component spectra can be further used to obtain the spatial distribution of the constituents present in the sample. Copyright © 2012 John Wiley & Sons, Ltd.     

Investigation on porosity changes of Lecce stone due to conservation treatments by means of x‐ray nano‐ and improved micro‐computed tomography: preliminary results

Cultural heritage materials are subject to continuous chemical and physical changes depending on the establishment of a dynamic equilibrium with the environment in which they are placed. In particular, different phenomena can take place, such as formation of black crusts, corrosion of the material, internal cracks. Lecce stone, a biocalcarenite mainly used for historical buildings in South Italy, has a high total porosity. In order to prevent its deterioration, different kinds of hydrophobic organic products are applied on the surface of the restored artefacts. Since the efficacy of the treatments depends mostly on the penetration depth and the distribution of the products in the pores, porosity and internal structure of the stone material were mainly investigated in this research. Micro x‐ray computed tomography (µ‐CT) has been used to study and characterize the internal structure of different samples, untreated and treated with protective products. The porosity and other parameters of the rock were then calculated and compared, before and after the conservation treatment, in order to highlight the changes due to the application of the product. On the other hand, small pieces of the untreated and treated samples were analysed by sub‐micron resolution x‐ray tomography where it was possible to see the distribution of the products inside the pores. 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.     

红外光谱法在草酸钙结石研究中的应用

泌尿系结石是一种世界范围的常见病。草酸钙是泌尿系结石中最常见的组分 ,尿石中的草酸钙主要是以一水草酸钙 (COM)、二水草酸钙 (COD)的形式存在。区分草酸钙结石中的COM和COD及其比例 ,对于准确诊断结石的成因和提出正确的预防其复发的方法非常重要。红外光谱法是研究泌尿系结石的一种较理想的常用方法 ,具有快速、简便、鉴定成分准确、使用样品少、可以回收等优点。文中重点综述了傅里叶变换红外光谱 (FTIR)在泌尿系结石研究中对COM和COD的定性和定量分析方法 ,并介绍了零交叉点一次导数光谱法、FTIR与四极质谱仪、FTIR与傅里叶变换拉曼光谱仪 (FTRS)联合分析尿石的方法。     

Mapping the intracellular distribution of carbon nanotubes after targeted delivery to carcinoma cells using confocal Raman imaging as a label-free technique

The uptake of carbon nanotubes (CNTs) by mammalian cells and their distribution within cells is being widely studied in recent years due to their increasing use for biomedical purposes. The two main imaging techniques used are confocal fluorescence microscopy and transmission electron microscopy (TEM). The former, however, requires labeling of the CNTs with fluorescent dyes, while the latter is a work-intensive technique that is unsuitable for in situ bio-imaging. Raman spectroscopy, on the other hand, presents a direct, straightforward and label-free alternative. Confocal Raman microscopy can be used to image the CNTs inside cells, exploiting the strong Raman signal connected to different vibrational modes of the nanotubes. In addition, cellular components, such as the endoplasmic reticulum and the nucleus, can be mapped. We first validate our method by showing that only when using the CNTs' G band for intracellular mapping accurate results can be obtained, as mapping of the radial breathing mode (RBM) only shows a small fraction of CNTs. We then take a closer look at the exact localization of the nanotubes inside cells after folate receptor-mediated endocytosis and show that, after 8-10 h incubation, the majority of CNTs are localized around the nucleus. In summary, Raman imaging has enormous potential for imaging CNTs inside cells, which is yet to be fully realized.     

Subsurface analysis of painted sculptures and plasters using micrometre‐scale spatially offset Raman spectroscopy (micro‐SORS)

A recently developed variant of spatially offset Raman spectroscopy (SORS) for the non‐invasive analysis of thin painted layers, micro‐SORS, has been applied, for the first time, to real objects of Cultural Heritage – namely painted sculptures and plasters. Thin layers of paint originating from multiple restoration processes often applied over many centuries have been analysed non‐destructively using micro‐SORS to depths inaccessible to, or unresolvable into separate layers, by conventional confocal Raman microscopy. The concept has been demonstrated on several artistic artefacts of historical significance originating from Italy and dating from the medieval to the 18th century. The technique extends the depth applicability of Raman spectroscopy and with its inherently high chemical specificity that expands the portfolio of existing non‐destructive analytical tools in Cultural Heritage permitting to avoid cross‐sectional analysis often necessitated with this type of samples with conventional Raman microscopy. Currently, the method is non‐invasive only for artworks that can be placed under Raman microscope although there is a prospect for its use in a mobile system with largely removed restrictions on sample dimensions. © 2015 The Authors Journal of Raman Spectroscopy Published by John Wiley & Sons Ltd.     

Raman microscopy of prehistoric paintings in French megalithic monuments

Remains of pictorial decorations in a series of six representative megalithic monuments of Brittany (France) and two French stelae have been studied by micro‐Raman spectroscopy for the first time. Fungal colonies on the painted orthostats made it difficult to obtain in situ Raman spectra of the paint components. Nevertheless, paint micro‐specimens studied in the laboratory by micro‐Raman spectroscopy, X‐ray photoelectron spectroscopy and scanning electronic microscopy combined with energy dispersive X‐ray spectroscopy have made possible to characterise the materials present. The minerals α‐quartz, albite, microcline, muscovite, phlogopite, celadonite, beryl and anatase have been identified in the granitic rocks supporting the paintings, while dolomite and calcite are dominant in the calcareous rocky substrata. Haematite is the main component of the red pictographs, whereas amorphous carbon and manganese oxides/oxihydroxides have been used in the black ones. Calcite, gypsum and amorphous carbon have been detected as additional components of the paint in some cases. Contamination with modern tracing materials (polystyrene and ε‐copper‐phthalocyanine blue) has been detected in several cases. The presence of pigments as decorative elements in megalithic monuments of Western France and its possible relation with those of the Iberian Peninsula create interesting expectations for the knowledge of the European megalithic culture. Copyright © 2015 John Wiley & Sons, Ltd.