Déformation photoinduite dans les films minces contenant des ...

Chapter 4. Photomechanical response of hybrid metal/azo-polymer layered structures1314.2.2 Apertureless near-field photomechanical response of hybridmetal/azo-polymer layered structurespastel-00527388, version 1 - 19 Oct 2010We study the near-field photoinduced deformation of a hybrid metallic/photochromiclayerd structure consisting in a gold layer 20 nm thick evaporated on an azobenzenecontainingsol-gel film 200 nm thick, which had been spin-coated over a glass plate(Figure 4.13(a)). The study of the far-field photomechanical response of this systemhas been presented in 4.1.Performing the single-line scan experiment as described in 4.2.1.2 (scan width = 5 µm,tip-sample shear-force interaction = 4V ), produces the deformation reported in Figure4.13(b). The structure A is obtained after scanning along the same line during200 s at a frequency of 1.15 Hz in the dark. The structure B is obtained in the samescanning conditions but under exposure to a single p-polarized light beam of power density1 mW/mm 2 . We see the remarkable mass depletion of the zone scanned by the tip,which is almost three times deeper when exposing the sample to illumination (B, 15 nm)than with no irradiation (A, 5 nm), the width of the groove also being larger in B (280nm) then in A (130 nm). Moreover, we observe a weak matter accumulation aroundthe grooves, which is more evident in B (4 nm) while it is difficult to evaluate in A.In (c) we report the same experiment, but using different scanning durations. With 80 swe obtain the deformations C (light on) and D (light off) while with 200 s we observe thedeformations shown in E (light on) and F (light off). The deformation effect is indeedmore efficient under illumination in C ([depth, width] = [6, 78] nm) and E ([15, 130] nm)than with no irradiation in D ([3, 60] nm) and F ([5, 118] nm). Moreover, we observealso in this case the weak matter accumulation on the edges of the deformation in E(4 nm) and F (2 nm), while it is difficult to estimate for C and D.These results are visualized in Figure 4.14, where the values of the deformation depthand width obtained under illumination (□) and without illumination () are plotted.Our observations indicate that also in the case of a hybrid system constituted by a metalliclayer on a photochromic thin film, the tip-sample interaction induces a mechanicaldeformation. Unlike the uncoated sol-gel Si-DR1 film, we observe a depletion of the zoneunderneath the tip. The deformation amplitude depends on the scan duration and isenhanced under illumination. It seems that matter is mechanically dragged by the tip,while under irradiation the photomechanical effect in the photochromic thin film leadsthe tip to dig deeper into the gold film.