Flux flow properties for clean and dirty superconducting limits in strong pinning niobium films are studied. Measurements of electric field vs current density characteristics at high J values ͑J Ӎ 10 6 A/cm 2 ͒ are successfully compared to theoretical models of flux flow and of flux flow instability in a large range of temperatures and magnetic fields. The nonlinear regime at high dissipation is analysed in the frame of a modified Larkin Ovchinnikov model that takes into account a quasiparticles heating effect. This model elaborated by Bezuglyj and Shklovskij ͑BS͒ defines a transition magnetic field B t above which the quasiparticles distribution became nonuniform due to a finite heat removal from the substrate. From the BS model, we can deduce values of the nonequilibrium lifetime of quasiparticles qp , which are 10 to 100 times shorter in the dirty sample compared to the clean one and whose temperature dependance is specific to the electronic nature of the Nb film. The study of the nonlinear regime provides also a quantitative determination of the thermal transparency of the film-substrate interface.
Metasurfaces have facilitated the replacement of conventional optical elements with ultrathin and planar photonic structures. Previous designs of metasurfaces were limited to small deflection angles and small ranges of the angle of incidence. Here, we have created two types of Si-based metasurfaces to steer visible light to a large deflection angle. These structures exhibit high diffraction efficiencies over a broad range of angles of incidence. We have demonstrated metasurfaces working both in transmission and reflection modes based on conventional thin film silicon processes that are suitable for the large-scale fabrication of high-performance devices.
An original and low cost method for the fabrication of patterned surfaces bioinspired from butterfly wings and lotus leaves is presented. Silica-based sol-gel films are thermally imprinted from elastomeric molds to produce stable structures with superhydrophobicity values as high as 160 degrees water contact angle. The biomimetic surfaces are demonstrated to be tuned from superhydrophobic to superhydrophilic by annealing between 200 degrees C and 500 degrees C.
Computer-generated planar holograms are a powerful approach for designing planar lightwave circuits with unique properties. Digital planar holograms in particular can encode any optical transfer function with high customizability and is compatible with semiconductor lithography techniques and nanoimprint lithography. Here, we demonstrate that the integration of multiple holograms on a single device increases the overall spectral range of the spectrometer and offsets any performance decrement resulting from miniaturization. The validation of a high-resolution spectrometer-on-chip based on digital planar holograms shows performance comparable with that of a macrospectrometer. While maintaining the total device footprint below 2 cm 2 , the newly developed spectrometer achieved a spectral resolution of 0.15 nm in the red and near infrared range, over a 148 nm spectral range and 926 channels. This approach lays the groundwork for future on-chip spectroscopy and lab-on-chip sensing.
A novel strategy for fabricating nanoimprint templates with sub-10 nm patterns is demonstrated by combining electron beam lithography and atomic layer deposition. Nanostructures are replicated by step-and-repeat nanoimprint lithography and successfully transferred into functional material with high fidelity. The process extends the capacity of step-and-repeat nanoimprint lithography as a single digit nanofabrication method. Using the ALD process for feature shrinkage, we identify a size dependent deposition rate.
A step and repeat UV nanoimprint lithography process on pre-spin coated resist film is demonstrated for patterning a large area with features sizes down to sub-15 nm. The high fidelity between the template and imprinted structures is verified with a difference in their line edge roughness of less than 0.5 nm (3σ deviation value). The imprinted pattern's residual layer is well controlled to allow direct pattern transfer from the resist into functional materials with very high resolution. The process is suitable for fabricating numerous nanodevices.
A one-step, fast, and potential low cost process has been developed to fabricate silicalike glass nanostructures by combining sol-gel chemistry and thermal nanoimprint. An inorganic-organic sol-gel thin film is patterned at low pressure and temperature with flexible stamps. Various geometries are achieved with a patterning resolution of about 150nm and pattern aspect ratio higher than 4. To obtain pure silica structures a thermal annealing at high temperatures is required. During this step most of the structures collapse due to fluidization of the sol-gel material. It is shown that if a suitable condensation level is obtained during imprinting, the nanostructures are thermally stable.
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