Déformation photoinduite dans les films minces contenant des ...

Chapter 5. Nanostructured hybrid systems 139dark curve) we confirm that the gold domains do not change the mass migration SRGgrowth, compared to the uncoated case (gray curve).5.1.2 Particle dispersion and surface functionalizationpastel-00527388, version 1 - 19 Oct 2010In order to avoid particle coalescence into bigger structures, it is possible to force themto bind to specific sites on the surface. This can be achieved functionalizing the surfaceusing an amminic layer, which creates NH − NH sites, where gold nanoparticles aretrapped.In Figure 5.3 we show the results obtained using a 23-(2- aminoethylamino)- propyltrimethoxysilane(AEAPTMS) layer on a sol-gel Si-DR1 thin film (200 nm) depositedon a glass plate (a). The deposition of the AEAPTMS layer is done by evaporation incontrolled atmosphere, after strong heating (150 ◦ , 8 hrs) of the sol-gel Si-DR1 fillm, sincewe observed the dissolution of the photochromic film without strong thermal treatment.As shown in (b), after a 3 min dip-coating into a gold nanoparticle solution, we obtaina good dispersion of the nanoparticles on the surface.In the aim to detect whether, under illumination, a lateral movement of the nanoparticlesis associated to the SRG growth, we use a Kretshmann configuration to fabricatethe interference pattern, with an inter-fringe of ≃ 230 nm, which allows to induce adeformation approximately one order of magnitude wider than the nanoparticle size.Unfortunately, as shown in (c-d), we observe a very weak deformation (≃ 2 nm) underexposure to p-polarized light interference, with an intensity of 1mW/mm 2 per beam.Probably, this is due to the strong thermal treatment of the sample prior to the functionalization,which has radically diminished the matrix mobility 1 .Using a good compromise between the AEAPTMS concentration and the thermal treatment,it should be possible to obtain well dispersed nanoparticles and to preserve mattermobility, hence to determine with more precision whether a lateral movement of smallgold structures can be induced by the matter migration processes.In conclusion, in a sol-gel Si-DR1 sample coated with gold nanoparticles, we do notobserve any lateral movement of the gold structures present on the surface associatedto the photoinduced mass migration. Indeed, they follow the same deformation ofthe underlying photochromic film, so that only their vertical displacement is induced.This result seems to confirm that the mass migration phenomena are rather bulk thansurface processes.1 The small difference of the nanoparticle distribution observed between (c) and (d) could be due toa combined effect of tip-dragging and imaging artefacts.