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French researchers have improved Raman spectroscopy by using a mapping technique. Their approach allows prediction of some of the properties of nanomaterials; in particular those related to the mechanics or electric size dependent properties which modify the Raman signature, and the determination of topological and chemical maps of a wide range of materials. Raman spectroscopy can provide elegant sub-nanometre views of even heterogeneous materials down to the scale of chemical bonds and because it is sensitive to the lightweight elements found in covalent bonds it can provide detailed information that is inaccessible to X-ray techniques. However, Raman is yet to be widely adopted because it suffers from potentially debilitating resolution issues and takes too long for all but the most patient of laboratories. Philippe Colomban, head of the Laboratoire de Dynamique, Interaction et Réactivité, a shared facility of the CNRS and the Université Pierre et Marie Curie in Paris, Mickaël Havel, and colleagues recognise the power of Raman and the detailed information it, and Rayleigh scattering, might provide and so have investigated ways to circumvent the issues of time and resolution. The researchers have demonstrated that deconvolution of Raman images by the illuminating spot shape has allowed them to improve the X-Y resolution close to the diffraction limit of about half the wavelength and so carry out Rayleigh mapping as a competitive alternative to atomic force microscopy. 'AFM resolution remains much better,' Colomban told us, 'but in the case of very corrugated samples, Rayleigh mapping offer a good compromise.' The Rayleigh image thus helps them focus on a specific area of interest in their nanomaterial. Immediate Raman mapping then reveals the topological and chemical information they require. Indeed, a direct comparison between Rayleigh imaging and AFM showed that under specific conditions Rayleigh analysis could become a very competitive alternative to AFM close to the sub-micrometre range. Moreover, 'Smart' images revealing physical strain, strength, height, etc or chemical parameters, such as corrosion, can be obtained from models that link Raman parameters with physical-chemical parameters. Tests on silicon carbide fibres and a corroded composite - Hi-Nicalonf/(SiC/BN/C)m bore out the team's claims for their new approach. 'We could obtain information such as the distribution of the carbon grain size, the carbon or SiC structure, and the expected mechanical strength within the fibre section, information that was inaccessible by other methods except using a huge number of Transmission Electron Microscopy measurements,' Colomban told SpectroscopyNow. Related links:
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Colomban, smart Raman man |
