908 research outputs found
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
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
The scenario of two-dimensional instabilities of the cylinder wake under EHD forcing: A linear stability analysis
We propose to study the stability properties of an air flow wake forced by a dielectric barrier discharge (DBD) actuator, which is a type of electrohydrodynamic (EHD) actuator. These actuators add momentum to the flow around a cylinder in regions close to the wall and, in our case, are symmetrically disposed near the boundary layer separation point.
Since the forcing frequencies, typical of DBD, are much higher than the natural shedding frequency of the flow, we will be considering the forcing actuation as stationary.
In the first part, the flow around a circular cylinder modified by EHD actuators will be experimentally studied by means of particle image velocimetry (PIV). In the second part, the EHD actuators have been numerically implemented as a boundary condition on the cylinder surface. Using this boundary condition, the computationally obtained base flow is then compared with the experimental one in order to relate the control parameters from both methodologies.
After validating the obtained agreement, we study the Hopf bifurcation that appears once the flow starts the vortex shedding through experimental and computational approaches. For the base flow derived from experimentally obtained snapshots, we monitor the evolution of the velocity amplitude oscillations. As to the computationally obtained base flow, its stability is analyzed by solving a global eigenvalue problem obtained from the linearized NavierâStokes equations. Finally, the critical parameters obtained from both approaches are compared
Surface relief grating formation on nano-objects
We exploit the photoinduced migration effect in azopolymer thin films to induce surface relief patterning of nano-objects. Manipulation and precise control of the molecular order is achieved at the nanoscale. Interaction between a laser beam from an argon laser and the azopolymer nano-objects induces structures on the surface. The self-patterning process is observed to depend on the laser beam polarization
Polylactide-based films with the addition of poly(ethylene glycol) and extract of propolisâphysico-chemical and storage properties
Polymeric films based on polylactide (PLA) with the addition of poly(ethylene glycol) (PEG) and a chloroformic extract of propolis were obtained. In the case of the studied films, polylactide (PLA) played the role of polymeric matrix and poly(ethylene glycol) was used as a plasticizer, while the extract of propolis was incorporated as a compound that could significantly affect the properties of the obtained materials, especially the water vapour permeation rate and the stability of the food products. Moreover, changes in structure, morphology, mechanical and storage properties as well as differences in colour, thickness and transparency after introducing propolis into the PLAâPEG system were determined. Based on the obtained results, it was established that the addition of the chloroformic extract of propolis significantly influences the most important properties taken into account during food packaging. It was also noticed that films with incorporated propolis were characterised by a significant improvement in the water vapour barrier property. Moreover, the obtained results prove that packaging containing a chloroformic propolis extract allow for the maintenance of the quality of the fruit stored for an extended period of time. To summarise, the application of a chloroformic propolis extract enables the formation of packaging materials that extend the shelf life of stored food products
Chemical vapor deposition of iron, iron carbides, and iron nitride films from amidinate precursors
Iron bis(N,N-diisopropylacetamidinate) [Fe2(”-iPr-MeAMD)2(2-iPr-MeAMD)2] and iron bis(N,N-di-tert-butylacetamidinate) [Fe(tBu-MeAMD)2] were used as precursors for the metallorganic chemical vapor deposition (MOCVD) of iron-containing compounds including pure iron, iron carbides, Fe3C and Fe4C, and iron nitrides Fe4C. Their decomposition mechanism involves hydrogen migration followed by dissociation of the FeâN bond and the release of free hydrogenated ligand (HL) and radicals. Surface intermediates are either released or decomposed on the surface providing FeâN or FeâC bonds. MOCVD experiments were run at 10 Torr, in the temperature ranges of 350â450°C with Fe2(”âiPr-MeAMD)2(2-iPr-MeAMD)2 and 280â350°C with Fe(tBu-MeAMD)2. Films prepared from Fe2(”âiPr-MeAMD)2(2-iPr-MeAMD)2 contain Fe, Fe3C, and Fe4C. Those prepared from Fe(tBu-MeAMD)2 contain Fe, Fe3C, and also Fe4C or Fe4N, depending on the temperature and hydrogen to precursor ratio (H/P) in the input gas. The room-temperature coercive field of films processed from Fe(tBu-MeAMD)2 is 3 times higher than that of the high temperature processed Fe4N films
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