Light depolarization effects in tip enhanced Raman spectroscopy of silicon (001) and gallium arsenide (001)

We report on the effects of light depolarization induced by sharp metallic tips in Tip-Enhanced Raman Spectroscopy (TERS). Experiments on Si(001) and GaAs(001) crystals show that the excitation field depolarization induces a selective enhancement of specific Raman modes, depending on their Raman tensor symmetry. A complete polarization analysis of the light backscattered from the tip confirms the TERS findings. The spatial confinement of the depolarization field is studied and its dependence on the excitation wavelength and power are explored

A graphical method for performance mapping of machines and milling tools

Optimal design of the machining setup in terms of installed machines, cutting tools and process parameters is of paramount importance for every manufacturing company. In most of the metal cutting companies, all choices related to machine eligibility and cutting parameters selection typically come from heuristic approaches and follow supplier indications or base on the skill of experienced machine operators. More advanced solutions, such as model-based and virtual approaches, are adopted less frequently mainly due to the lack of these techniques in grasping the underlying knowledge successfully. Aim of this work is to introduce a synthetic graphical representation of machining centers and cutting tools capabilities, to provide an accessible way to evaluate the feasibility and close-to-limit conditions of the cutting process. Taking inspiration from previous scientific works from the measurement engineering field, a set of 2D and 3D graphs are presented to map machine, tools and process capabilities, as well as their obtainable manufacturing performances and expectable tool life. This approach synthesizes the nominal data coming from different sources (catalogues, database, tool model geometries etc.) and the real cutting tools parameters used during the production phase. Some examples are provided to show the potential of this graphical evaluation in supporting process planning and decision-making and in formalizing the machining setup knowledge. Further developments are devoted to extend the method to other manufacturing processes, including hybrid processes. At the same time, an in-process data gathering software will be integrated for building a solid database that can be used by an autonomous multi-technological process selector, as well as by a pre-process condition advisor in an Industry 4.0 oriented way

Raman characterization of singlewalled carbon nanotubes and PMMA-nanotubes composites

The Raman spectroscopy have allowed us to perform studies on singlewalled nanotubes (SWNT's) produced by following methods: electric arc, laser ablation and solar energy. As this characterization method provides a great deal of informations, we will present a comparison between the nanotubes produced by all these processes and the influence of some synthesis parameters. By using spin casting, we have produced thin films of PMMA-SWNT's for different concentrations. Then, we have characterized these new materials by Raman spectroscopy. The aim of these investigations is to get information on the possible interactions between these two materials. In particular, we have studied the evolution of the composites films spectra as a function of the nanotubes concentration in the polymer.This work has been fully supported by the European Community through its Training and Mobility of Researcher program under network contract : NAMITECH, ERBFMRX- CT96-0067 @GlZ-MIHT) and by the tiench CNRS program : ULTIMATECH.Peer reviewe

Optical Nanoantennas for Multiband Surface-Enhanced Infrared and Raman Spectroscopy

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Optical properties of gold nanostructures: Application to the surface enhanced Raman scattering and to the development of a nanobiosensor

The application of Surface Enhanced Raman Spectroscopy (SERS) for detection of biomolecules is a subject of intense current research worldwide. In this article the observation of the dependence of the Raman enhancement versus the nanoparticle size is clearly demonstrated on nanocylinders and nanowires. Remarkably the enhancement is observed to be maximum for a specific diameter or length. We finally show that the SERS signal depends on the molecule used and that the SERS active substrates should be actually optimized for each targeted protein

Interest of Raman spectroscopy for the study of dental material: The zirconia material example

2 - RevueThe mechanical properties, the biocompatibility and the aesthetic aspect make of zirconia a material of interest for orthopaedics and dental prosthetics. This ceramic presents a transformation of phase ability, which is responsible for its high mechanical resistance and fracture toughness. In biomedical applications, tetragonal metastable zirconia is used. Under mechanical stresses, zirconia grains experience a transformation towards a monoclinic structure. This phenomenon exists also under hydrothermal stresses and is known as low temperature degradation, it is well described for yttria partially stabilised zirconia, 3Y-TZP. Kinetics of transformation is usually studied using X-ray diffraction or AFM. The aim of this article is to present Raman spectroscopy as an alternative and non-destructive method to study the transformation of zirconia. After a presentation of Raman scattering, examples of tetragonal, cubic and monoclinic zirconia Raman spectra are presented. The calibration procedure to assess the penetration of the laser probe in the material is detailed and found to reach 70 [mu]m. The quantitative measurement of monoclinic zirconia volume is explained. An example illustrates the decrease of the transformation from 12 at the material subsurface to 2% in a 70 [mu]m depth

Light depolarization induced by sharp metallic tips and effects on Tip-Enhanced Raman Spectroscopy

1 - ArticleTip-Enhanced Raman Spectroscopy is based on the field enhancement and confinement provided by sharp metallic lips, used to locally excite the Raman emission from molecules, crystals and nanostructures. This technique has recently demonstrated capabilities for nanometer scale optical resolution in Raman analysis and has enormous potential applications in nano- and bio-technologies. In this paper we describe the state-of-the-art experimental techniques, focusing the attention oil the strategies to reduce the far-field background, on new processes to fabricate sharp metallic tips and on the effect of the depolarization produced by metallic tips on Tip-Enhanced Raman spectra of bulk crystals

A Raman Study of MMP2 and MnSOD, Two Pathology Biomarkers

International audienceMatrix Metalloproteinases (MMPs) are cell-secreted soluble and membranetethered enzymes that degrade extracellular matrix (ECM) proteins. These proteases play a key role in diverse physiological and pathological processes, including embryonic development, wound repair, inflammatory diseases and cancer [1]. On the other hand, Superoxide Dismutases (SODs) are metalloenzymes that defend biological systems against oxidative damage mediated by the superoxide anion [2]. The vibrational spectra of MMPs and SODs can provide crucial information about conformational changes induced by external factors, e.g. the interaction with metal ions, drugs, others proteins or peptides. On the other side, Raman spectroscopy can be used as a tool for non-invasive and non-ambiguous spectral detection of these proteins at very low concentration (10-8-10-12 M), with potential applications in early diseases diagnosis [3]. At present, there is still insufficient knowledge on the Raman spectral fingerprints of these proteins. Here we present a complete Raman analysis of MMP2 and MnSOD using multiwavelength-excitation at 514, 633, and 785 nm