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2018-04-11 - Colloque/Présentation - poster - Anglais - 1 page(s)

Guyot Corentin , Vandestrick Philippe, Marenne Ingrid, Deparis Olivier, Voué Michel , "Reflectivity, imaging ellipsometry and scattering analysis of gold nanoparticles growing in a polymer matrix" in Meeting of the Belgian Physical Society, Anvers, Belgique, 2018

  • Codes CREF : Matériaux optiques (DI1256)
  • Unités de recherche UMONS : Physique des matériaux et Optique (S878)
  • Instituts UMONS : Institut de Recherche en Science et Ingénierie des Matériaux (Matériaux)
  • Centres UMONS : Physique des matériaux (CRPM)
Texte intégral :

Abstract(s) :

(Anglais) Nano-objects and more particularly metal nanoparticles (NPs) play a central role in the development of nanotechnology-based optical devices. The collective oscillations of their conduction electrons are at the origin of their optical properties : localized surface plasmon resonance (LSPR). Numerous studies were carried out to investigate the optical properties of plasmonic nanocomposite materials from the experimental, theoretical as well as numerical points of view [1]. One can use Au NPs in spectral selective coatings to block solar infrared radiation, in random lasers, in non-linear optical applications and more recently as saturable absorbers in passive Q-switch systems [2]. In this study, we consider the back-scattering issue for fiber optics integration because nobody has so far paid attention to the modifications of the optical properties of the nanocomposites induced by the in situ growth of the nanoparticles. A wide range of experimental methods is available for the synthesis of such materials. This methods can be divided in two groups : the synthesis of NPs in a liquid medium which provides more control during their growth or their in situ synthesis following the irradiation or the thermal annealing of the solid phase (e.g. HAuCl4 or AgNO3-doped polymer film). By this second approach, we have less control on the shape and the size of the NPs and their growth mechanisms are not yet completely understood. In particular, we considered the annealing of Au3+-doped PVA films and we quantified the optical scattering which is induced by the gold nanoparticles growth. We also monitored the evolution of the locally resolved optical properties of the film using imaging ellipsometry (IE), controlled the evolution of the reflectivity and determined the roughness of the films using atomic force microscopy (AFM). The optical scattering of the nanocomposite films was analyzed by the bi-directional reflection distribution function (BRDF). The BRDF was measured in collimated mode (l = 570-10 nm) with an angle of incidence of qi = 20. Annealing of the samples at 135 C during 90 min increases the roughness of the film and the light scattering at the surface. The BRDF shows that annealing samples induces an important back-reflection of the incident light (Fig.[1(a)] and Fig.[1(b)]). In parallel with the increase of the scattering, the locally resolved Y and D ellipsometric angles are also strongly modified by the annealing process and a diffraction pattern corresponding to local modifications of the optical properties gradually appears : spots can be observed in the Y and D images (D images : Fig.[2(a)] and Fig.[2(b)]). They are suspected to be the manifestation of light intensity diffraction patterns. Moreover, remembering that the D angle is related to the relative phase change undergone by the p and s components on the incident light wave, the D images clearly bring evidence for a local change of the relative phase upon reflection. This change is due to the growth of the Au NPs which locally change the optical response of the film. The reflectivity of the samples were measured before, during and after the annealing process. It shows the progressive thinning of the polymer film as well as the decreasing reflectivity around 550 nm due to the energy absorption by the growing of the Au NPs.