Rigid composite materials for anechoic chamber application

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Structure and morphological study of nanometer W and W3O thin films

International audienceIn this paper, the structure of nanometer tungsten thin films has been correlated to their surface morphology. Films have been deposited by RF-sputtering at a working pressure of 0.5 Pa and with a power density of 1.18 W/cm 2. Two phases with different morphology has been observed : W 3 O with a nanograins structure is present in the first step of the tungsten growth; and, when the thickness is increased, a pure tungsten Wolfram phase (W) with a lamellar structure appears. We demonstrate that W 3 O is related to a pollution of the target surface between two growth runs. We succeed to suppress this phase and to obtain pure tungsten Wolfram nanolayer, in order to realize [W/WO 3 ] n multilayer

Electromagnetic absorber composite made of carbon fibers loaded epoxy foam for anechoic chamber application

International audienceThis paper presents a new electromagnetic absorbing material developed from carbon fibers loaded epoxy foam for an application in anechoic chamber. The composite was developed in order to replace the currently used pyramidal absorbers made of carbon particles loaded polyurethane foam. Epoxy-composites filled with different weight percentages (from 0 wt.% to 4 wt.%) and length (1 and 3 mm) of carbon fibers were achieved. After an optimization of the dispersion of carbon fibers in composite materials, the dielectric properties of the composites were measured using a coaxial-probe in the frequency range 4–18 GHz. Results have shown that the complex permittivity of the composites increases with the amount of charge and also with the length of the carbon fibers. Absorption performance of a prototype prepared with a low concentration (0.5 wt.%) of carbon fibers was measured in an anechoic chamber: it shows a mean gain of 10 dB compared to a commercial absorber. © 2017 Elsevier B.V

Mechanical properties of Al/Al2O3 nanolaminated films: correlation to microstructure

peer reviewedaudience: researcher, professional, studentWear resistance and the hardness of Al/Al2O3 nanolaminated films were investigated in this study. Monolithic films and multilayers were deposited on a silicon substrate with two different substrate temperatures: T-s= 25 degrees C and T-s= -90 degrees C. The period thickness of multilayers was lowering from 40 to 2 nm. From nanoindentation measurements, it appears that the hardness of multilayers has an intermediate value between those of metal (Al) and ceramic (Al2O3). The tribological test was conducted by the pin-on-disc method. The T-s=25 degrees C deposited multilayers, as well as single films, demonstrated poor wear resistance. The best wear resistance was obtained for multilayers deposited at the lowest substrate temperature (T-s= -90 degrees C). The results are ill good agreement with structural characterization. X-ray reflectometry demonstrated that the multilayer character of Al/Al2O3 is more pronounced for T-s= -90 degrees C. (C) 2000 Elsevier Science S.A. All rights reserved

Lanthanum titanate ceramics : electrical characterizations in large temperature and frequency ranges

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Ion beam sputtered aluminum based multilayer mirrors for extreme ultraviolet solar imaging

International audienc

Lanthanum titanium perovskite compound: Thin film deposition and high frequency dielectric characterization

International audiencePerovskite lanthanum titanium oxide thin films were deposited on (001) MgO, (001) LaAlO3 and Pt(111)/TiO2/SiO2/(001) Si substrates by RF magnetron sputtering, using a La2Ti2O7 homemade target sputtered under oxygen reactive plasma. The films deposited at 800 degrees C display a crystalline growth different than those reported on monoclinic ferroelectric La2Ti2O7 films. X-ray photoelectron spectroscopy analysis shows the presence of titanium as Ti4+ ions, with no trace of Ti3+, and provides a La/Ti ratio of 1.02. The depositions being performed from a La2Ti2O7 target under oxygen rich plasma, the same composition (La2Ti2O7) is proposed for the deposited films, with an unusual orthorhombic cell and Cmc2(1) space group. The films have a textured growth on MgO and Pt/Si substrates, and are epitaxially grown on LaAlO3 substrate. The dielectric characterization displays stable values of the dielectric constant and of the losses in the frequency range [0.1-20] GHz. No variation of the dielectric constant has been observed when a DC electric field up to 250 kV/cm was applied, which does not match a classical ferroelectric behavior at high frequencies and room temperature for the proposed La2Ti2O7 orthorhombic phase. At 10 GHz and room temperature, the dielectric constant of the obtained La2Ti2O7 films is epsilon similar to 60 and the losses are low (tan delta < 0.02