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Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions? Contact the NRC Publications Archive team atPublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. For the publisher's version, please access the DOI link below./ Pour consulter la version de l'éditeur, utilisez le lien DOI ci-dessous.Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Photomechanical effects in azo-polymers studied by neutron reflectometry Yager, Kevin G.; Tanchak, Oleh M.; Godbout, Chris; Fritzsche, Helmut; Barrett, Christopher J. NRC Publications Record / Notice d'Archives des publications de CNRC:http://nparc.cisti-icist.nrc-cnrc.gc.ca/eng/view/object/?id=eecae0d0-f627-4c85-a847-dfacdf4964b5 http://nparc.cisti-icist.nrc-cnrc.gc.ca/fra/voir/objet/?id=eecae0d0-f627-4c85-a847-dfacdf4964b5 Chemistry, McGill UniVersity, Montreal, QC, Canada, H3A 2K6, and Canadian Neutron Beam Centre, National Research Council, Chalk RiVer, ON, Canada K0J 1J0 ReceiVed July 31, 2006; ReVised Manuscript ReceiVed October 5, 2006 ABSTRACT: Neutron reflectometry is used to study photomechanical effects in thin films of azobenzene polymer cast onto silicon substrates. A significant photoexpansion effect, up to 17%, is observed at 25°C, due to the free volume requirement of the azobenzene chromophore photoisomerization. Above a distinct crossover temperature of ∼50°C, the material response is inverted and instead photocontraction effects, of more than -15%, are observed. In this case the combined photomotion and thermal mobility enables aggregation and crystallization of the azobenzene dipoles. The photomechanical effects, which can be reversed, occur readily using a variety of irradiation powers, incident polarizations, and film thickness values. This photomechanical behavior, which appears to be general to all azo materials, is likely the origin for a wide variety of curious photomotions observed in these systems, including macroscopic bending of samples and micron-scale surface mass transport.

The temporal evolution of the charge density distribution in femtosecond laser produced electron pulses was studied using electron-laser pulse cross correlation techniques and compared to analytical predictions and simulations. The influence of propagation time and weak magnetic focusing were both investigated. Our results show that ultrashort electron pulses develop a relatively uniform internal charge density as they propagate, which is in good agreement with analytical predictions, and that weakly focusing an ultrashort electron pulse results in an increased internal charge density towards the leading edge of the pulse.

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