arXiv subjects

R. Barille

Publications and source records attributed to R. Barille.

13 recordsLinked to original sources

arXiv2026

Light-Sculpted Azopolymer Colloids: From Patchy Spheres to Porcupine and Pineapple Morphologies

A simple optical strategy to transform patchy PMMA azopolymer composite nanoparticles into complex, fully three-dimensional morphologies using controlled laser polarization is presented. The particles consist of a PMMA core decorated with nanoscale azopolymer patches that undergo localized photofluidization upon trans cis isomerization. Linear polarization drives directed mass transport within each patch, producing elongated super-cones that collectively yield porcupine like particles, whereas circular polarization generates isotropic bump deformations reminiscent of sea-pineapple structures. A nonlinear, volume-conserving geometric model quantitatively reproduces the patch-to-filament transition. Brownian and Jeffery-flow simulations reveal that these photoinduced morphologies dramatically alter hydrodynamic behavior, leading to enhanced anisotropic diffusion, reduced rotational randomization, and polarization-dependent transport amplification in shear flow. This light-driven, reversible sculpting method provides a versatile route to programmable colloidal shapes and highlights geometry as a powerful control parameter for microscale transport, active materials, and soft-matter physics.

physics.app-ph↗

arXiv2024

Laser Beam Shaping Using a Photoinduced Azopolymer Droplet-Based Mask

The dewetting of an azopolymer droplet, followed by the photostructuration of the evaporated droplet, is employed to create an amplitude mask. This straightforward process yields a large area featuring periodic micro- and nanostructures. The resulting pattern is utilized to generate a nondiffracting beam. Starting with a Gaussian beam illuminating the amplitude mask, the critical aspect is the production of a bright, ring-shaped beam with a high radius-to-width ratio and symmetric central laser spots, each with the same intensity. This alternative approach to shaping a laser beam is demonstrated as a rapid and cost-effective fabrication technique.

physics.optics↗

arXiv2020

Porosity properties of porous ceramic substrates added with zinc and magnesium material

Ceramic based materials covered with a mixture of mullite and zircon on the top, strengthened by the addition of zinc and magnesium compounds at different rates (37 % and 50 %) and made by a co-precipitation method are studied. The thermally treated and shaped materials prepared in the shape of cylindrical samples were modified to obtain different porosities. The addition of zinc to the ceramic based material leads to a significant increase and control of the density of porosity compared to the addition of magnesium. The porosity of all the materials was characterized. The permeability characteristics and the ability for all the pellets to absorb water until the saturation were also studied as a function of the porosity.

physics.app-ph↗

arXiv2017

Comparison the optical properties for Bi2O3 and NiO ultrathin films deposited on different substrates by DC sputtering technique for transparent electronics

Bismuth and Nickel transparent oxides thin films were grown on glass and flexible polythelene terephalate (PET) substrates by DC sputtering technique at room temperature 300 K. The structures of Bi2O3 and NiO films were analyzed by X-ray diffraction (XRD) analyses and scanning electron microscopy (SEM). A profilometry is used to measure the thicknesses of the ultrathin films. These values were established by a spectro-ellipsometry technique with a new amorphous dispersion model in the range of 200 nm to 2200 nm with one nm increment. In addition, the optical constants of these films were investigated using a double beam UV-Vis-NIR spectrometer and a spectro-ellipsometry and compared using the same wavelength range. They present an excellent agreement. According to the optical transmittance spectra of the films a high average transmittance in the visible region of each sample deposited onto different substrates is measured. Moreover, the absorption coefficients and the optical energy gaps for four types of optical transitions (allowed direct, forbidden direct, allowed indirect, forbidden indirect) of the films were determined and compared with the two different techniques. Finally, the nature of the structure and morphology of Bi2O3 and NiO ultrathin films has been analyzed and compared.

physics.app-ph↗

arXiv2017

Surface quasi periodic and random structures based on nanomotor lithography for light trapping

We compare the characteristics of two types of patterns obtained with two azopolymer materials: a Gaussian random pattern and a quasi-random grating pattern. The surface structurations have been obtained with a simple bottom-up technique by illuminating azopolymer thin films with a single laser beam. We demonstrate the interesting generated properties of these two surfaces. In particular, the surface with quasi-random gratings can address beam splittings for light coupling in different directions in an ultra-thin film. We use these two surfaces as a mold and replicate them on a transparent elastomeric material and we demonstrate a very good light entrapment. We also show that the efficiency of light trapping is 20% better with the quasi-random gratings than with the Gaussian random surface, and is close to 40%.

physics.optics↗

arXiv2017

A New Method for Patterning Azopolymer Thin Film Surfaces

We present a simple bottom-up approach via an incoherent unpolarized illumination and the choice of a solvent-droplet-induced-dewetting method to photoinducenano doughnuts on the surface of azopolymer thin films. We demonstrate that doughnut-shaped nanostructures can be formed and tailored with a wide range of typical sizes, thus providing a rich field of applications using surface photo-patterning. Furthermore, due to the presence of highly photoactive azobenzene derivative in the material, illumination of these nanostructures by a polarized laser light shows the possibility of a further growth and reshaping opening the way for fundamental studies of size-dependent scaling laws of optical properties and possible fabrication of nano-reactor or nano-trap patterns

physics.optics↗

arXiv2015

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.

physics.chem-ph↗

arXiv2014

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.

physics.optics↗

arXiv2014

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.

physics.optics↗

arXiv2009

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.

physics.optics↗

arXiv2006

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.

physics.optics↗

arXiv2006

Incoherent light induced self-organization of molecules

Although coherent light is usually required for the self-organization of regular spatial patterns from optical beams, we show that peculiar light matter interaction can break this evidence. In the traditional method to record laser-induced periodic surface structures, a light intensity distribution is produced at the surface of a polymer film by an interference between two coherent optical beams. We report on the self-organization followed by propagation of a surface relief pattern. It is induced in a polymer film by using a low-power and small-size coherent beam assisted by a high-power and large-size incoherent and unpolarized beam. We demonstrate that we can obtain large size and well organized patterns starting from a dissipative interaction. Our experiments open new directions to improve optical processing systems.

physics.optics↗

arXiv2005

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.

physics.optics↗