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Laboratoire de Physique de la Matière Condensée

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Optical Nanofabrication

People involved:

Jacques Peretti, Yves Lassailly, Khalid Lahlil, Jean-Pierre Boilot

External Collaborators

Céline Fiorini (CEA Saclay),
Margrit Hansbücken (CRMC-N Marseilles),
Fred Brouwer (Université d'Amsterdam, Pays Bas)

It is now fully established that incorporating photochromic molecules into organic or inorganic matrices produces large scale photo-induced matter migration effects due to repeated trans-cis isomerisation cycles. The most well-studied photochromic molecule is the azobenzene moiety, whose trans isomer is the most stable. Photoisomerisation of the molecule from the trans to cis conformation leads to a reorientation of the molecule into the matrix and to the subsequent mechanical deformation of the matrix.

Our reference material is made of an inorganic silica gel containing the azobenzene unit grafted to the Si backbone. Using shear-force distance control microscopy, the photo-induced deformation can be measured in-situ by scanning the optical fiber tip.

[Image: Silicon based metal semiconductor hybrid]
The CNRS logo inscribed in near-field on a 20 nm-thick Si-Azo film. The charactersitic lateral size of each dot is 55 nm and their mean height is 5 nm. Exposure time per dot: 2 s, l = 470 nm

Control of molecular motion can be optically achieved with a resolution of l/10 is brought about by inscribing artificial structures with a near field light source of nanometric size. This is achieved with the 50 nm apex of a tapered optical fibre. When combining near-field optical and interference techniques the dynamics of the photo-deformation can be monitored in real time and in situ. The figure below shows a 5x5 micron image of the surface deformation during continuous illumination by an interference pattern produced with two p-polarized laser beams. At t0, the optical signal detection is concomitant with the formation of a grating in-phase with the excitation, i.e. peaks and valleys corresponding respectively to bright and dark fringes. Then the inscribed pattern vanishes and another grating grows out-of-phase relative to the light intensity distribution. In this case, matter migrates from the bright fringes towards the dark fringes. Our combined microscope keeps track in real time of the kinetics of grating formation and shows for the first time that the photo-induced deformation of photochromic materials is a complex process which goes well beyond the prevailing migration matter phenomenon.

[Image: Silicon based metal semiconductor hybrid] Light intensity (left) and topography (right) images recorded during the first stages of the photo-induced deformation of a a sol-gel film containing azobenzene molecules upon exposure to an interference pattern produced by two 1 mW p-polarized laser beams. The full image acquisition time is 256 seconds. figure in a new window

Selected Publications:

*Copyright 2001 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.