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2019-05-27 - Colloque/Présentation - poster - Anglais - page(s)

Guyot Corentin , Deparis Olivier, Voué Michel , "Gold nanoparticles growing in a polymer matrix : what can we learn from imaging ellipsometry ?" in The 8th International Conference on Spectroscopic Ellipsometry, Barcelone, Espagne, 2019

  • 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) With respect to the conventional synthesis of gold colloids by the Frens-Turkevitch method [1] and their dispersion of a host matrix, ”one-pot” synthesis [2] provides the opportunity of preparing at once thin films with a high concentration of gold nanoparticles (GNPs). Typically, the UV-visible absorbance of a 400nm-thick polymer film prepared by the latter method is similar to the one measured on a colloidal suspension in a 1cm optical path cuvette. These synthesis methods open the doors to application fields as various as selective coatings to block solar infrared radiation, electronic and opto-electronic applications, non-linear optical devices and, more recently, saturable absorbers for passive Q-switched lasers with ps recovery time. [3,4] In our study, we considered the annealing of Au3+-doped poly(vinyl alcohol) (PVA) films with submicron thickness. We monitored the time evolution of the locally resolved optical properties of the films using imaging ellipsometry (IE), real-time UV-visible reflectometry and AFM. The growth of the GNPs in the film is accompanied by a slight increase of its roughness. The latter results in light back-scattering that could have a negative impact of the optical properties of such film optical devices. The locally-resolved (Y;D) ellipsometric angles are strongly modified during the annealing process and a diffraction pattern corresponding to local modifications of the optical properties gradually appears : spots can be observed in the ellipsometric maps (D images : Fig. 1a and b, before and after film annealing, respectively). They are evidences 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 modification of the relative phase upon reflection. This change is probably due to the growth of the GNPs which locally changes the optical response of the film. The kinetics of the process allowed us to identify two regimes in the changes of the local optical properties that can be discussed with respect to depolarization of the impinging light upon reflection and to multiple scattering.