Déformation photoinduite dans les films minces contenant des ...

Chapter 4. Photomechanical response of hybrid metal/azo-polymer layered structures128(a)(b)10 x 10 !m 2 5 x 5 !m 2 5 x 5 !m 2(c)!""#"$!#%&$'PABCDEFABCDEFQ2010101010101010pastel-00527388, version 1 - 19 Oct 2010A (nm)0-10-200 2 4 6 8P6 nm!mQA (nm)500 1 2!mA500 1 2!mB500 1 2!mC500 1 2!mD500 1 2Figure 4.10: Photomechanical effects of the tip-sample interactions in a sol-gel Si-DR1 film: superstructure on top of the surface gratings. Interaction amplitude =2V , scanning frequency = 1 Hz, τ exp = 600 s, laser = p-polarized interfering beams,1 mW/mm 2 per beam, λ = 473 nm. Sample = sol-gel Si-DR1, 200 nm thick.!mEPP-10min-2V500 1 25 µm (indicated by the two arrows). The structure width of 400 nm is similar to thosepreviously obtained. This structure corresponds to a matter accumulation superimposedonto the 20 nm high SRG. Matter accumulation is clearly more important in the SRGgrooves than on top of the SRG reliefs.!mIn Figure 4.11 we have plotted the tipinduceddeformation a tip (x) extracted from the measured profiles a line (x) and a far (x)()(see eq. 4.4). The deformation amplitude A 0 line − A0 farreaches 6 nm while the averagedeformation ā tip due to the near-field interaction is 3.7 nm for 600 s of exposure. Theseare much smaller values than those obtained with a tip-to-sample shear-force set-pointof 4 V for even shorter exposure time. This is very surprising, since when changing theset-point from 4 V to 2 V one only changes the tip-to-sample distance by about 1 nm.This is not likely to induce a significant change in the optical near field, which hardlyexplains the different photo-deformation amplitude observed. On the other hand, thestrong effect of the distance on the near-field photodeformation efficiency could ratherbe related to the mechanical interaction between the tip and the sample surface.F