Focal Point: Imaging Optical Near‐field in Plasmonic Nanostructures

International audienceOver the past five years, new developments in the field of plasmonics have emerged with the desire to finely tune a variety of metallic nanostructures to enable a desired function. The use of plasmonics in spectroscopy is of course of great interest due to large local enhancements in the optical near-field confined in the vicinity of a metal nanostructure. For a given metal, such enhancements are dependent on the shape of the structure as well as the optical parameters (wavelength, phase, polarization) of the impinging light, offering a large degree of control over the optical and spatial localization of the plasmon resonance. In this focal point, we highlight recent work that aims at revealing the spatial position of the localized plasmon resonances using a variety of optical and non-optical methods

A near field optical image of a gold surface: a luminescence study

International audienceThis paper addresses recent experimental findings about luminescence of a gold tip in near-field interaction with a gold surface. Our electrochemically etched gold tips show a typical, intrinsic luminescence that we exploit to track the plasmon resonance modeled by a Lorentzian oscillator. Our experimental device is based on a spectrometer optically coupled to an atomic force microscope used in tuning fork mode. Our measurements provide evidence of a strong optical coupling between the tip and the surface. We demonstrate that this coupling strongly affects the luminescence (Intensity, wavelength and FHWM) as a function of the tip position in 2D maps. The fluctuation of these parameters is directly related to the plasmonic properties of the gold surface and is used to qualify the optical near field enhancement (which subsequently plays the predominant role in surface enhanced spectroscopies) with a very high spatial resolution (typically around 20 nm). We compare these findings to the independently recorded near-field scattered elastic Rayleigh signal

A Surface Enhanced Raman Spectroscopy study of aminothiophenol and aminothiophenol-C60 self-assembled monolayers: evolution of Raman modes with experimental parameters

International audienceP-aminothiophenol (PATP) is a well known molecule for the preparation of self-assembled monolayers on gold via its thiol functional group. After adsorption, it has been demonstrated that this molecule is anchored to gold through its thiol group, and standing nearly upright at the surface with the amino functional group on top. This molecule has been extensively studied by Surface Enhanced Raman Spectroscopy but its exact SERS spectrum remains unclear. Here we demonstrate that it can be strongly affected by at least two experimental parameters: laser power and layer density. Those features are discussed in terms of a dimerization of the PATP molecules. The free amino group affords the adsorption of other molecules, like C60. In this case, a complex multilayer system is formed and the question of its precise characterisation remains a key point. In this article, we demonstrate that surface enhanced Raman spectroscopy combined with X-Ray photoelectron spectroscopy can bring very important information about the organisation of such a self-assembled multilayer on gold. In our study, the strong evolution of Raman modes after C60 adsorption suggests a change in the organisation of aminothiophenol molecules during C60 adsorption. These changes, also observed when the aminothiophenol layer is annealed in toluene, do not prevent the adsorption of C60 molecules

High-pressure behavior of polyiodides confined into single-walled carbon nanotubes: A Raman study

International audienceThe high-pressure behavior of polyiodides confined into the hollow core of single-walled carbon nanotubes organized into bundles has been studied by means of Raman spectroscopy. Several regimes of the structural properties are observed for the nanotubes and the polyiodides under pressure. Raman responses of both compounds exhibit correlations over the whole pressure range (0–17 GPa). Modifications, in particular, take place, respectively, between 1 and 2.3 GPa for polyiodides and between 7 and 9 GPa for nanotubes, depending on the experiment. Differences between one experiment to another are discussed in terms of nanotube filling homogeneity. These transitions can be presumably assigned to the tube ovalization pressure and to the tube collapse pressure. A nonreversibility of several polyiodide mode modifications is evidenced and interpreted in terms of a progressive linearization of the iodine polyanions and a reduction in the charged species on pressure release. Furthermore, the significant change in the mode intensities could be associated to an enhancement of lattice modes, suggesting the formation of a new structure inside the nanotube. Changes in the nanotube mode positions after pressure release point out a decrease in the charge transfer in the hybrid system consistent with the observed evolution of the charged species

High-pressure behavior of polyiodides confined into single-walled carbon nanotubes: A Raman study

International audienceThe high-pressure behavior of polyiodides confined into the hollow core of single-walled carbon nanotubes organized into bundles has been studied by means of Raman spectroscopy. Several regimes of the structural properties are observed for the nanotubes and the polyiodides under pressure. Raman responses of both compounds exhibit correlations over the whole pressure range (0–17 GPa). Modifications, in particular, take place, respectively, between 1 and 2.3 GPa for polyiodides and between 7 and 9 GPa for nanotubes, depending on the experiment. Differences between one experiment to another are discussed in terms of nanotube filling homogeneity. These transitions can be presumably assigned to the tube ovalization pressure and to the tube collapse pressure. A nonreversibility of several polyiodide mode modifications is evidenced and interpreted in terms of a progressive linearization of the iodine polyanions and a reduction in the charged species on pressure release. Furthermore, the significant change in the mode intensities could be associated to an enhancement of lattice modes, suggesting the formation of a new structure inside the nanotube. Changes in the nanotube mode positions after pressure release point out a decrease in the charge transfer in the hybrid system consistent with the observed evolution of the charged species

Nanotubes de carbone monoparois dans des conditions extrêmes de pression et de température

To study the evolution of single wall carbon nanotubes (SWNT) under high pressure and high temperature, Raman spectroscopy and X-ray absorption spectroscopy measurements have been performed. Some experiments have also been done to explore the possibility to synthesise new carbon phases using doped nanotubes as precursor material. This PhD thesis is divided in two parts. The first one is about Raman spectroscopy of SWNT under pressure up to 40 GPa in diamond anvil cell. We have followed the evolution of the resonant character of the tubes under pressure using two excitating wavelengths (632.8 nm and 514.5 nm). Our results clearly demonstrate that a progressive loss of resonance occurs under pressure. The resonant character is totally lost for pressure higher than 20 GPa. The effects of the batch of the SWNT and the choice of the pressure transmitting media have also been studied. In the second part iodine doped SWNT were studied. Raman spectroscopy experiments in diamond anvil cell and X-ray absorption spectroscopy in Paris Edinburgh press measurements have been performed. We have also done high pressure high temperature syntheses (14.5 GPa, 1500_C) on iodine doped SWNT in a multi-anvils press. The analysis of the resulting products has confirmed that doped SWNT can be promising precursors for the synthesis of new carbon phases.Au cours de cette thèse des études principalement de spectroscopie Raman et de spectroscopie d'absorption des rayons X produits par rayonnement synchrotron ont été réalisées dans le but de mieux comprendre l'évolution des propriétés des nanotubes de carbone sous pression et leur intérêt comme matériau précurseur pour la synthèse de nouvelles phases carbonées sous hautes pressions. Cette thèse est constituée de deux parties. La première porte sur l'étude par spectroscopie Raman des nanotubes de carbone monoparois en cellule à enclumes de diamant pour des pressions jusque 40 GPa. Pour suivre l'évolution des propriétés de résonance sous pression, deux longueurs d'onde d'excitation (632.8 et 514.5 nm) ont été employées. Nos résultats montrent qu'une perte des propriétés de résonance se produit de manière progressive sous pression. A 20 GPa les nanotubes de carbone ont totalement perdu leurs propriétés de résonance. L'effet du milieu transmetteur de pression utilisé et l'influence de la provenance des nanotubes de carbone sont également discutés, notamment au niveau du profil des modes hautes fréquences. La seconde partie est consacrée aux nanotubes de carbone monoparois dopés à l'iode. Des expériences de spectroscopie Raman en cellule à enclumes de diamant et d'absorption des rayons X en presse Paris-Edinburgh ont été réalisées sur ce type d'échantillon. Une série de synthèses à haute pression et haute température en presse multi-enclumes (conditions de synthèse: 14.5 GPa, 1500C) ont confirmé la possibilité d'utiliser les nanotubes de carbone dopés comme précurseur pour l'obtention de nouvelles phases carbonées

Nanotubes de carbone monoparois dans des conditions extrêmes de pression et de température

Des études de spectroscopie Raman et de spectroscopie d'absorption des rayons X ont été réalisées pour mieux comprendre l'évolution des propriétés des nanotubes de carbone sous pression et leur intérêt comme matériau précurseur pour la synthèse de nouvelles phases carbonées. La première partie porte sur l'étude par spectroscopie Raman des nanotubes de carbone monoparois en cellule à enclumes de diamant (Pmax : 40 GPa). Pour suivre l'évolution des propriétés de résonance sous pression, deux longueurs d'onde d'excitation (632.8 et 514.5 nm) ont été employées. Nous observons une perte de résonance progressive sous pression. L'effet du milieu transmetteur et de l'origine des tubes sont également discutés. La seconde partie est consacrée aux nanotubes de carbone dopés à l'iode (spectroscopie Raman et EXAFS). Des synthèses à haute presion et haute température confirment la possibilité d'utiliser les nanotubes de carbone doppés comme précurseur pour l'obtention de nouvelles phases carbonéesLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Vibrational modes of aminothiophenol : a TERS and DFT study

International audienceWe report Tip Enhanced Raman Spectroscopy (TERS) mapping and Density Functional (DFT) calculations of aminothiophenol (ATP) grafted on a gold surface. The TERS mapping has demonstrated Raman modes of (ATP) and its dimerised derivative Dimercaptoazobenzene (DMAB). This feature confirms that the plasmon activated chemical reaction of ATP has occurred during TERS measurements. In some specific part of the samples some unidentified Raman modes are observed. We suggest that they could come from intermediate species formed during the conversion of ATP into DMAB. These modes are compared with calculated Raman spectra of some possible intermediate species. These results confirm the high potentiality of TERS measurements for nanochemistry

Water Adsorption on MgO Surfaces: A Vibrational Analysis

Using DFT calculations, we have considered different adsorption configurations of water molecules on MgO surfaces. In some cases, we have observed a chemical reaction between water and the surface, with the formation of hydroxyl groups. We have systematically compared the calculated Raman spectra of the final optimized structures with the measured spectra from MgO nanoparticles. Our results confirm the high reactivity of MgO surfaces with water. Some obtained structures can be considered precursors for the transformation of MgO into Mg(OH)2. We suggest that some of them could be identified using Raman spectroscopy. Our study confirms the high potentiality of Raman spectroscopy, associated with numerical calculations, for the study of chemical reactivity of nanoparticles