Search results for "RAMAN"
showing 10 items of 1328 documents
Number of observable features in the acoustic-Raman spectra of nanocrystals
2012
Low-frequency Raman scattering spectra are presented for gold nanocrystals with diameters 3.5 and 13 nm. The frequencies of the Raman peaks but also their number are shown to vary with the nanocrystal size. These results are analyzed using both the continuous elastic medium approximation and an atomistic approach. We show that the number of atoms in the nanocrystal determines an upper limit of the number of observable Raman features. The frequency range in which the continuous elastic medium approximation is valid is defined by comparison with the calculations based on the atomistic approach.
Making Graphene Luminescent by Direct Laser Writing
2020
Graphene is not intrinsically luminescent, due to a lack of bandgap, and methods for its creation are tricky for device fabrication. In this study, we create luminescent graphene patterns by a simple direct laser writing method. We analyze the graphene using Raman spectroscopy and find that the laser writing leads to generation of line defects after initial formation of point defects. This Raman data enables us to create a model that explains the luminescence by a formation of small domains due to confinement of graphene by line defects, which is conceptually similar to the mechanism of luminescence in graphene quantum dots. peerReviewed
Ultrastable, Uniform, Reproducible, and Highly Sensitive Bimetallic Nanoparticles as Reliable Large Scale SERS Substrates
2015
International audience; A strong interest exists in developing surface-enhanced Raman spectroscopy (SERS) substrates that uniformly enhance Raman signals of chemical and biological molecules over large scales while reaching the detection limit of trace concentrations. Even though the resonant excitation of localized surface plasmons of single or assembled metallic nanoparticles used in SERS substrates can induce large electromagnetic fields, these substrates display a SERS activity which suffers from poor reproducibility, uniformity, and stability, preventing them from being reliable for applications. In this work, we have developed self-supported large scale Ag/Au bimetallic SERS-active su…
Optical Diagnostics with Ultrafast and Strong Field Raman Techniques
2014
In this chapter, we will discuss some coherent techniques, namely Raman Induced Polarization Spectroscopy (RIPS) and femtosecond Coherent Raman Anti-Stokes Spectroscopy (fs-CARS). We will demonstrate their ability to be used as non-invasive optical diagnostic tools for temperature, density, or concentration measurements, as well as a means of testing collision induced energy transfer models (in a low field regime), and studying the so-called inhomogeneous lineshape effects that are particularly enhanced in the case of hydrogen. We will also show how molecular alignment achieved in a strong field regime can provide additional information about collisional relaxation processes. In all cases, …
Fluoreno[2,1-a]fluorene: an ortho-naphthoquinodimethane-based system with partial diradical character.
2019
Fluoreno[2,1-a]fluorene, a molecule comprising fused ortho-quinodimethane units in a 1,5-napthoquinodimethane core, has been prepared and investigated with spectroscopy (UV-Vis-NIR, 1H-NMR and Raman), SQUID magnetometry, spectroelectrochemistry and quantum chemistry. While para-quinodimethanes with a 2,6-substitution pattern exist as closed-shell species and meta-quinodimethanes with 2,7-substitution favour a ground electronic state with very large diradical character, our 1,5-substituted ortho-naphthoquinodimethane-based system exhibits an intermediate degree of diradical character.
Simultaneous detection of tissue autofluorescence decay distribution and time-gated photo-bleaching rates
2015
ABSTRACT Experimental methodology for parallel measurements of in-vivo skin autofluorescence (AF) lifetimes and photo-bleaching dynamic has been developed and tested. The AF lifetime decay distributio ns were periodically collected from fixed tissue area with subsequent detection of the fluorescence intensity decrease dynamic at different time gates after the pulse excitation. Temporal distributions of human in-vivo skin AF lifetimes and bleaching kinetics were collected and analyzed by means of commercial time-corr elated single photon counting system. Keywords: TCSPC, skin autofluoresc ence, and photo-bleaching. 1. INTRODUCTION Laser induced time-resolved autofluorescence (AF) spectroscop…
MICRO-SCALE STUDY OF RESIDUAL STRESSES IN CR2O3 COATINGS SPRAYED BY APS
2020
International audience; Whichever the application field, every material forming process generates residual stresses on the surface. While they are likely to enhance the aimed properties of the final mechanical part, these stresses may also drastically reduce them and result in early failures. Therefore, understanding the residual stress state remains a major challenge when coating complex parts, especially as most characterization methods at the microscopic scale involve specific sample preparation procedures which may affect the residual stresses field. This work investigates the residual stress state that exists in chromium oxide coatings deposited via Atmospheric Plasma Spray (APS), usin…
Mechanical Coupling in Gold Nanoparticles Supermolecules Revealed by Plasmon-Enhanced Ultralow Frequency Raman Spectroscopy
2016
International audience; Acoustic vibrations of assemblies of gold nanoparticles were investigated using ultralow frequency micro-Raman scattering and finite element simulations. When exciting the assemblies resonantly with the surface plasmon resonance of electromagnetically coupled nano-particles, Raman spectra present an ultralow frequency band whose frequency lies below the lowest Raman active Lamb mode of single nanoparticles that was observed. This feature was ascribed to a Raman vibration mode of gold nanoparticle " supermolecules " , that is, nanoparticles mechanically coupled by surrounding polymer molecules. Its measured frequency is inversely proportional to the nanoparticle diame…
Hexakis-adducts of [60]fullerene as molecular scaffolds of polynuclear spin-crossover molecules
2021
A family of hexakis-substituted [60]fullerene adducts endowed with the well-known tridentate 2,6-bis(pyrazol-1-yl)pyridine (bpp) ligand for spin-crossover (SCO) systems has been designed and synthesized. It has been experimentally and theoretically demonstrated that these molecular scaffolds are able to form polynuclear SCO complexes in solution. UV-vis and fluorescence spectroscopy studies have allowed monitoring of the formation of up to six Fe(ii)–bpp SCO complexes. In addition, DFT calculations have been performed to model the different complexation environments and simulate their electronic properties. The complexes retain SCO properties in the solid state exhibiting both thermal- and …
ZnO/ZnS heterostructures for hydrogen production by photoelectrochemical water splitting
2016
This work studies the photoelectrochemical behavior of novel ZnO/ZnS heterostructures obtained by means of anodization in water and glycerol/water/NH4F electrolytes with different Na2S additions under controlled hydrodynamic conditions. For this purpose different techniques such as Field Emission Scanning Electronic Microscopy (FE-SEM) with EDX, Raman spectroscopy and photoelectrochemical water splitting tests under standard AM 1.5 conditions have been carried out. The obtained results showed that the hydrodynamic conditions promoted an ordered nanotubular morphology which facilitates electron-hole separation and consequently, the photoelectrochemical activity for water splitting is enhance…