Photoinduced Doughnut-Shaped Nanostructures

We show that an incoherent unpolarized single-beam illumination is able to photoinduce nano-doughnuts on the surface of azopolymer thin films. We demonstrate that individual doughnut-shaped nano-objects as well as clusters of several adjacent nano-doughnuts can be formed and tailored with wide range of typical sizes, thus providing a rich field for applications in nanophotonics and photochemistry.Comment: 13 pages, 3 figures, first version to chem. phys. lett. 201

Light mediated emergence of surface patterns in azopolymers at low temperatures

Polymer thin films doped with azobenzene molecules do have the ability to organize themselves in spontaneous surface relief gratings (SRG) under irradiation with a single polarized beam. To shed some light in this still unexplained phenomenon, we use a new method that permits us to access experimentally the very first steps of the pattern formation process. Decreasing the temperature, we slow down the formation and organization of patterns, due to the large increase of the viscosity and relaxation time of the azopolymer. As a result decreasing the temperature allows us to access and study much shorter time scales,in the physical mechanisms underlying the pattern formation, than previously reported. We find that the patterns organize themselves in sub-structures which size increase with the temperature, following the diffusion coefficient evolution of the material. That result suggests that the pattern formation and organization is mainly governed by diffusive processes, in agreement with some theories of the SRG formation. Decreasing further the temperature we observe the emergence of small voids located at the junction of the sub-structures.Comment: 6 figures, 13 pages

Nonlocal communication with photoinduced structures at the surface of a polymer film

Nonlocal communication between two laser light beams is experimented in a photochromic polymer thin films. Information exchange between the beams is mediated by the self-induction of a surface relief pattern. The exchanged information is related to the pitch and orientation of the grating. Both are determined by the incident beam. The process can be applied to experiment on a new kind of logic gates.Comment: 7 pages, 4 figures, 2 table

Multistate polarization addressing using one single beam in an azo polymer film

Peculiar light-matter interactions can break the rule that a single beam polarization can address only two states in an optical memory device. Multistate storage of a single beam polarization is achieved using self-induced surface diffraction gratings in a photo-active polymer material. The grating orientation follows the incident light beam polarization direction. The permanent self-induced surface relief grating can be readout in real time using the same laser beam.Comment: 11 pages,3 figure

Near-Field Optical control of Doughnut-Shaped Nanostructures

The application of a local near-field optical excitation can be used to control step-by-step the reshape of individual doughnut-shaped azopolymer nano-objects by varying the time of illumination demonstrating its promising performance as a functional nano-object. The possibility to provide both photoinduced reshaping opens a way to the fundamental study of size-dependent scaling laws of optical properties, photoinduced reshaping efficiency and nanoreactor or nanoresonator behavior at nanometer scale. As an example the nano-object is used to self-assembly polystyrene nanospheres in a supraball.Comment: 15 pages, 6 figure

Mastering Nano-Objects with Photoswitchable Molecules for Nanotechnology Applications

Advance in the fabrication of nano-objects becomes more important for the development of new nanodevices with local properties leading to new functional devices. In this direction, the assembly of nanometer-scaled building objects into device configurations and functionalization is a promising investigated research field in nanotechnology. Optical recording and photofabrication techniques that exploit changes in material properties have gained importance, and there is a requirement for a decrease of the dimensions of the recording and processing surfaces. Photochromic materials leading to submicron structures responding to stimuli and in particular light are the best materials that exhibit multifunctional behaviors. Photomechanical properties of azopolymers show the perfect performance in photoinduced nanopatterning and reshaping by tailored light fields. Azopolymer nanostructures are then recognized as an excellent choice for a broad range of fundamental and applied research in modern nanotechnology. This chapter shows how polymer nanofilms, nanotubes, nanospheres, or nanowires containing azobenzene can be controlled by light for new photonics applications. Spatially confined excitation of unidirectional motions could make possible the local control of mechanical properties of the material and its structuration. The unprecedented flexibility of the reported photofluidization lithography with this material allows producing well-defined structures as lines, ellipsoids, rectangles, and circles at azopolymer surface with several tenth nanometers structural features

Spontaneous formation of optically induced surface relief gratings

A model based on Fick's law of diffusion as a phenomenological description of the molecular motion, and on the coupled mode theory, is developped to describe single-beam surface relief grating formation in azopolymers thin films. It allows to explain the mechanism of spontaneous patterning, and self-organization. It allows also to compute the surface relief profile and its evolution in time with good agreement with experiments

Cooperative interaction in azopolymers upon irradiation

We present two optical experiments which permits to evaluate individual and collective behaviours of molecules leading to a well-organized pattern in a randomly activated molecular assembly; in a first experiment a white light and a laser beam are sent together; in a second experiment a low-power coherent beam carr 3rd International Symposium on Molecular Materials (MOLMAT

Cognitive ability process at the molecular level

In the standard SRG formation in azo-dye containing photoactive polymers, the photoactive molecules are excited by a coherent illumination pattern. The highly reactive molecules move in a non-uniform way, inducing a mass transport from the bright regions to the neighbouring dark regions. The maximum heights of the light induced SRG correspond to light intensity minima. We show that a well-defined surface relief grating is induced in an azo-polymer film by the combination of one low power coherent laser beam with another high power incoherent and unpolarised beam. The information brought by the coherent signal beam has been transmitted to peripheral incoherent regions by the molecular self-assembling process: i.e., the organised molecules communicate non-local information about photo-induced structural organisation to the non organised neighbouring ones. They communicate by exchanging light through surface relief variations. In this way, we see that a totally incoherent beam can provide the movement which is necessary to induce a well-defined SRG. We find in this way one of the simplest systems allowing to figure out the minimal requirements to organise disordered materials into well organised structures. We verify experimentally that random motion plus information exchange lead to self-organisation. Our experiment shows that complex behaviour can be experimented using simple systems: weak coherent light can serve as a seed to create information into a polymer film in such a way that molecules powered by incoherent light will build and transmit well defined complex structures