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Photomechanical properties of azobenzene hybrids

by Rowe Alistair - published on

Grafting of azobenzene like molecules into polymer matrices results in a photo-deformable material that reacts mechanically to polarized light. It is therefore possible to optically mould thin films by projecting patterns of light onto the surface. This process is very efficient, only requiring small light doses (typically 1W/cm2 for a few minutes) to structure the material at the scale of a few tens of nanometres. This is achieved without requiring the usual time consuming and expensive lithographic techniques.

Contacts: Yves Lassailly and Jacques Peretti

We study photo-deformation phenomena induced by phot-isomerisation of azobenzene molecules. These studies use near field optical microscopy techniques that allow for the real-time, simultaneous mapping of both the optical excitation field and the photo-induced deformation with a spatial resolution better than 50 nm. The measurements revealed the mechanisms underlying matter displacement that result in small scale surface relief.

Image of a 3D grating fabricated by projecting an interference pattern onto an azo-polymer film. The topographic profile is that of a subsequently deposited Gold thin obtained by grazing angle evaporation.

Using a nano-indentation technique in collaboration with the University of Laval (Canada), we recently showed that the viscosity of films containing azobenzene molecules changes by more than an order of magnitude even at relatively weak light intensities and at temperatures far from the glass transition of these materials.

The control of the photomechanical properties of azobenzene based thin films also allows for the formation of hybrid structures like metallic gratings with adjustable geometries. An example of this is shown in the topographic image above, formed by projecting an interference pattern onto the film. The resulting Gold structure was subsequently formed by grazing angle evaporation onto this film and has a period of 820 nm and an amplitude of the order of 80 nm. These types of metallic structures have remarkable optical and plasmonic properties, in particular because of a diffraction driven coupling of the plasmon modes.

If you are interested in an internship or a potential Ph.D. in this subject, please contact Yves Lassailly or Jacques Peretti.