DÃ©formation photoinduite dans les films minces contenant des ...

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Chapter 1. The azobenzene molecules: photochromic materials and photodeformationeffects 14pastel-00527388, version 1 - 19 Oct 2010approaches have been proposed. A class of models considers the statistical redistributionof the molecules due to the elementary displacement of each azobenzene, following an isomerizationcycle [25, 41]. In this sense, the mass migration is related to the distributionof the absorption probability of each photoactive unit, hence to the spatial distributionof the light intensity and to the light polarization. Another class of models considersthe photochromic material as a viscoelastic system whose photofluidification dependson the photoisomerization of the azobenzene molecules [10, 11, 42]. The Navier-Stokesformalism is used to describe the matter transport phenomena, which are supposed tobe produced by the electromagnetic forces due to the interactions between the light fieldand the material. In the case of the statistical models, the matter transport is mainlyrelated to the anisotropic photoresponse of the molecules, while in the other type ofmodels the movement is mainly due to the interaction between the electromagnetic fieldand the material, while the azobenzene photoisomerization has a ’softening’ effect.Another photodeformation mechanism has been recently identified, the matrix photoexpansion,which has been observed, by different techniques [16, 43], in the illuminatedzones, independently from the polarization. It has been attributed to the augmentationof the matrix volume in the enlightened zones, as a consequence of the molecular stericre-arrangement in order to gain the free volume necessary to accomodate molecules afterthe photoisomerization. Although the obtained deformation has been observed to bepermanent in several experiments, the existence of an elastic regime has been reported[43, 44].
Chapter 1. The azobenzene molecules: photochromic materials and photodeformationeffects 15(a)(b)pastel-00527388, version 1 - 19 Oct 2010Figure 1.6: Far-field (a) and near-field (b) photoinduced deformation on a sol-gelDR1 film [7].1.3.1.3 Far-field and near-field experimentsThe observation of the photoinduced deformation obtained by illumination in the far andin the near field reveals a contradictory behavior (Figure 1.6). Irradiating the sampleusing a metal-coated tip in the far field (tip-to-sample distance > λ/2π) a groove isobserved in correspondence of the enlightened zone, while two lobes appear on the sides,whose orientation is parallel to the light field polarization (a).On the other hand,when the experiment is performed illuminating in the near field, a relief is observed inthe illuminated zone, underneath the tip (b), with a diameter corresponding to the tipaperture.The behavior observed in the far-field experiment has the same characteristic as thematter transport observed under p-polarized interference, where matter migrates fromthe bright fringes towards the dark fringes along the light electric field direction. Onthe other hand, the phenomenon observed in the near-field experiments [7, 29, 45, 46]is similar to the results obtained using the superposition of an s-polarized intensitygradient and a p-polarized assisting beam [40], where matter migration towards theirradiated zones is obtained.
Page 1 and 2: Thèse de doctorat de l’Ecole Pol
Page 3 and 4: AcknowledgementsAt the beginning it
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Page 7: ContentsAbstractiAcknowledgementsii
Page 10 and 11: List of Figures1.1 The trans/cis ph
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Page 18 and 19: Introduction 2In this work, we stud
Page 20 and 21: Bibliography[1] A. Natansohn, P. Ro
Page 22 and 23: Introduction 6azobenzene-containing
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Page 26 and 27: Chapter 1. The azobenzene molecules
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Page 66 and 67: pmma-dr1Chapter 2. Experimental set
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Page 72 and 73: Chapter 3. Microscopic mechanisms a
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Chapter 3. Microscopic mechanisms a
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TOPOGRAPHYgratamplxxphotoexpansion
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pmmaChapter 3. Microscopic mechanis
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Chapter 4. Photomechanical response
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sg+goldChapter 4. Photomechanical r
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P-250s-4VChapter 4. Photomechanical
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P-250s-4VChapter 4. Photomechanical
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Chapter 5Nanostructured hybrid syst
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Chapter 5. Nanostructured hybrid sy
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Bibliography[1] A. Natansohn, P. Ro
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Conclusionspastel-00527388, version
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Bibliography[1] Chi-Ming Che et Al.
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Appendix A 156⎛ ⎞ ⎛n g sinθ
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Appendix A 158hence for each compon
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Appendix BPhotoisomerization dynami
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Appendix B 162( 1Since λ 2 = −(
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Appendix C 164L = 5000 nmu = 1 nmL!
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Appendix D 166n. light power densit
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Bibliography[1] A. Natansohn, P. Ro
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Bibliography 170azobenzene-containi
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Bibliography 172as estimated from a
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Bibliography 174[53] C. Barrett, A.
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