38 research outputs found

    Nanofabrication with Pulsed Lasers

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    An overview of pulsed laser-assisted methods for nanofabrication, which are currently developed in our Institute (LP3), is presented. The methods compass a variety of possibilities for material nanostructuring offered by laser–matter interactions and imply either the nanostructuring of the laser-illuminated surface itself, as in cases of direct laser ablation or laser plasma-assisted treatment of semiconductors to form light-absorbing and light-emitting nano-architectures, as well as periodic nanoarrays, or laser-assisted production of nanoclusters and their controlled growth in gaseous or liquid medium to form nanostructured films or colloidal nanoparticles. Nanomaterials synthesized by laser-assisted methods have a variety of unique properties, not reproducible by any other route, and are of importance for photovoltaics, optoelectronics, biological sensing, imaging and therapeutics

    Structure optimization of electro-optic polymer waveguides for low half-wave voltage modulators

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    conference 7728 " Nonlinear Optics and its Applications ", session " Posters--Tuesday " [7728-52]International audienceIn this article, we discuss the waveguide dimensions optimization aiming to reduce the Vπ. For that purpose, various cover materials are investigated leading to a minimum effective core area " Aeff". The index contrast (core-cladding) at λ= 1550 nm, is varying from 0.07 to 0.21. As a result, the Aeff decreases from 12 μm2 down to 2.3 μm2, the total thickness of the waveguide is thus reduced and consequently the Vπ. Optimal parameters were calculated at λ= 1550 nm for single mode inverted-rib waveguides structure. The PAS1 a new polymer is used as electro-optic material for the core. An analytical model taking account the losses by tunnelling, allowed us to estimate the optimum distance between electrodes to reduce the Vπ which could be about 1.6V ( 0.8 V in a push-pull configuration). Related with the bandwidth of the modulator, permittivity measurements were carried out on core and cladding polymers as well. The process of waveguides fabrication is described in details and several waveguides are performed. Finally, a new experimental technique for precision measurements of the propagation losses in waveguides is presented. The principle is simple, and the propagation losses measured is found to be independent of coupling conditions

    Electro-optic and converse-piezoelectric properties of epitaxial GaN grown on silicon by metal-organic chemical vapor deposition

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    We report the measurement of the (r13, r33) Pockels electro-optic coefficients in a GaN thin film grown on a Si(111) substrate. The converse piezoelectric (d33) and electro-absorptive coefficients are simultaneously determined. Single crystalline GaN epitaxial layers were grown with a AlGaN buffer layer by metal organic chemical vapor deposition, and their structural and optical properties were systematically investigated. The electro-optic, converse piezoelectric, and electro-absorptive coefficients of the GaN layer are determined using an original method. A semi-transparent gold electrode is deposited on the top of the GaN layer, and an alternating voltage is applied between top and bottom electrodes. The coefficients are simultaneously and analytically determined from the measurement of the electric-field-induced variation ΔR(θ) in the reflectivity of the Au/GaN/buffer/Si stack, versus incident angle and light polarization. The method also enables to determine the GaN layer polarity. The results obtained for a Ga-face [0001] GaN layer when using a modulation frequency of 230 Hz are for the electro-optic coefficients r13 = +1.00 ± 0.02 pm/V, r33 = +1.60 ± 0.05 pm/V at 633 nm, and for the converse piezoelectric coefficient d33 = +4.59 ± 0.03 pm/V. The value measured for the electro-absorptive variation at 633 nm is Δko/ΔE = +0.77 ± 0.05 pm/V

    Electrooptic and converse-piezoelectric properties of epitaxial GaN/Si structures for optoelectronic applications

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    International audienceIn order to take advantage in all-optic optoelectronic devices, we have investigated the optical and piezoelectric properties of GaN films deposited on (111) silicon. Films are epitaxially grown by MOCVD, thanks to a buffer made of (Al, Ga) N intermediate layers [1]. Structural properties of GaN are analyzed using TEM and the influence of threading dislocations density is discussed. Optical properties are investigated using a prism coupling [2]. Electrooptic measurements are performed using an original technique [3]. A semi-transparent gold electrode is deposited on top of GaN layer and an alternating voltage is applied between top and bottom electrodes. The electro-optic, converse piezoelectric, and electro-absorptive coefficients are simultaneously determined from the measurement of the electric field induced variation ΔR(θ) in the reflectivity of the Au/GaN/buffer/Si stack versus incident angle. The method also enables to determine the GaN layer polarity. The results obtained for a Ga-face [0001] GaN layer when using a modulation frequency of 230 Hz are for the electro-optic coefficients r13 = +1 pm/V, r33 = +1.60 pm/V at 633 nm, and for the transverse piezoelectric coefficient d33 = +4.59 pm/V. The value measured for the electro-absorptive variation is Δko/ΔE = +0.77 pm/V. The electro-optic coefficients for GaN /Si and the electro-absorptive coefficient are measured for the first time. The converse piezoelectric value agrees with values previously reported

    Study On Laser-Induced Periodic Structures And Photovoltaic Application

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    International audienceWe have irradiated silicon with a series of femtosecond laser pulses to improve light absorption at the silicon surface. The laser treated surface namely black silicon shows excellent optical properties on mono and multicrystalline silicon wafers with a reflectivity reduction down to 3%, without crystal orientation dependence. After the laser process, the front side of samples has been boron-implanted by Plasma Immersion Ion Implantation to create the 3D p+ junction. Improved electrical performances have also been demonstrated with a 57% increase in the photocurrent, compared to non-texturized surfac

    Bonobos fall within the genomic variation of chimpanzees.

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    To gain insight into the patterns of genetic variation and evolutionary relationships within and between bonobos and chimpanzees, we sequenced 150,000 base pairs of nuclear DNA divided among 15 autosomal regions as well as the complete mitochondrial genomes from 20 bonobos and 58 chimpanzees. Except for western chimpanzees, we found poor genetic separation of chimpanzees based on sample locality. In contrast, bonobos consistently cluster together but fall as a group within the variation of chimpanzees for many of the regions. Thus, while chimpanzees retain genomic variation that predates bonobo-chimpanzee speciation, extensive lineage sorting has occurred within bonobos such that much of their genome traces its ancestry back to a single common ancestor that postdates their origin as a group separate from chimpanzees
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