Quantitative absorption spectroscopy of nano-objects

International audienceWe report on an optical microscopy technique aimed at measuring the absolute absorption cross section of individual nanoparticles. It relies on the thermally induced variation of the refractive index of the surrounding medium subsequent to light absorption by the nanoparticle. The technique is illustrated on gold nanoparticles featuring a well-defined plasmonic resonance. Different plasmonic modes were evidenced and quantified. The simplicity and rapidity of the measurements make it possible to investigate absorption resonances of absorbing nanostructures and microstructures in a reasonable time frame. Furthermore, the experimental approach is simply based on the use of a wavefront analyzer, which is straightforward to implement on any conventional microscope

Photo-induced heating of nanoparticle arrays

International audienceThe temperature distribution throughout arrays of illuminated metal nanoparticles is investigated numerically and experimentally. The two cases of continuous and fs-pulsed illumination are addressed. In the case of continuous illumination, two distinct regimes are evidenced: a temperature confinement regime - where the temperature increase remains confined at the vicinity of each nanosource of heat - and a temperature delocalization regime - where the temperature is uniform throughout the whole nanoparticle assembly despite of their nanometric size. We show that the occurrence of one regime or another simply depends on the geometry of the nanoparticle distribution. In particular, we derived simple expressions of i) dimensionless parameters aimed at predicting the degree of temperature confinement and ii) analytical expressions aimed at estimating the actual temperature increase at the centre of an assembly of nanoparticles under illumination, preventing heavy numerical simulations. All these theoretical results are supported by experimental measurements of the temperature distribution on regular arrays of gold nanoparticles under illumination. In the case of fs-pulsed illumination, we explain what are the two conditions that must be fulfilled to observe a further enhanced temperature spatial confinement

Light-Assisted Solvothermal Chemistry Using Plasmonic Nanoparticles

Solvothermal synthesis, denoting chemical reactions occurring in metastable liquids above their boiling point, normally requires the use of a sealed autoclave under pressure to prevent the solvent from boiling. This work introduces an experimental approach that enables solvothermal synthesis at ambient pressure in an open reaction medium. The approach is based on the use of gold nanoparticles deposited on a glass substrate and acting as photothermal sources. To illustrate the approach, the selected hydrothermal reaction involves the formation of indium hydroxide microcrystals favored at 200 °C in liquid water. In addition to demonstrating the principle, the benefits and the specific characteristics of such an approach are investigated, in particular, the much faster reaction rate, the achievable spatial and time scales, the effect of microscale temperature gradients, the effect of the size of the heated area, and the effect of thermal-induced microscale fluid convection. This technique is general and could be used to spatially control the deposition of virtually any material for which a solvothermal synthesis exists. © 2016 American Chemical Society

Polarized nonlinear nanoscopy in metal and ferroelectric nanostructures

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Nano-scale characterization of gold nanostructures using polarized nonlinear microscopy

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