Déformation photoinduite dans les films minces contenant des ...

Introductionpastel-00527388, version 1 - 19 Oct 2010The present work is dedicated to the study of the photodeformation effects inducedat micro-nanoscale in photoactivable systems. In particular, we investigate the photomechanicalresponse of photochromic thin films containing an azobenzene derivate,the Disperse Red 1 (DR1) grafted to a mineral sol-gel matrix or to an organic polymer(PMMA) backbone. Since their first discovery in 1995 [1, 2], these phenomena havebeen widely investigated under various illumination configurations [3–9]. Experimentsperformed with far field photo-excitation by focused gaussian beams [10, 11], Besselbeams [12] and interfering beams [1, 2, 8, 13, 14] have demonstrated that the efficiencyof the deformation process and the shape of the photoinduced pattern are very muchdependent on the light polarization distribution. Experiments performed with nearfieldexcitation by a local light source [6, 15] have shown a specific photomechanicalresponse which exhibits apparent contradictory behaviors when compared to far fieldconfigurations, but which confirms the important role of the polarization.The understanding of the mechanisms at the origin of the photodeformation phenomenais still debated [16–18]. First, it requires to establish the relationship between the photodeformationand the properties of the light excitation, namely power density, dose,polarization and spatial distribution. Several studies have shown the influence of theseparameters on the deformation efficiency [3], but direct measurements of the correlationbetween the local light field structure and the photoinduced deformation are lacking.Second, the characterization of the reversibility and the repeatability of the photodeformationis still an open question. It has been demonstrated that under particularpolarization configurations it is possible to optically erase the photoinscribed structures[19, 20], but very little is known on the possibility to obtain successive reversible deformationcycles. Finally, the directionality of the deformation phenomena has notbeen clearly addressed. Several observations demonstrate the fundamental role of thepolarization on the orientation of the photoinduced relief pattern [3], but very littleinformation is available on the direction of the matter migration.1