Structured transparent low emissivity coatings with high microwave transmission

Abstract In order to reduce the energy consumption of buildings, modern windows include metal-containing coatings. These coatings strongly attenuate the microwaves used for mobile communications. Here, we present a novel approach to improve radio signal transmission by structuring a low emissivity coating. Laser ablation is used to scribe a line pattern on the coating. The microwave attenuation of the initial coating ranges between -25 and -30 dB between 850 MHz and 3 GHz. The optimized patterning reduces it down to -1.2 ± 0.6 dB. The fraction of the ablated area is relatively low. Our experiment al results show that it is possible to reach a level of attenuation close to that of a glass substrate by removing less than 4% of the coating area. The ablated lines are thin enough to not be noticed in most common lighting situations. Therefore, we achieve a dual spectral selectivity: the coated glass is transparent in the visible range, reflective in the infrared and nearly as transparent as its glass substrate to microwaves. Additionally, numerical simul ations were performed and show that the attenuation at grazing incidences is dominated by the behaviour of the glass substrate

Effects of Odd–Even Side Chain Length of Alkyl-Substituted Diphenylbithiophenes on First Monolayer Thin Film Packing Structure

Because of their preferential two-dimensional layer-by-layer growth in thin films, 5,5′bis(4-alkylphenyl)-2,2′-bithiophenes (P2TPs) are model compounds for studying the effects of systematic chemical structure variations on thin-film structure and morphology, which in turn, impact the charge transport in organic field-effect transistors. For the first time, we observed, by grazing incidence X-ray diffraction (GIXD), a strong change in molecular tilt angle in a monolayer of P2TP, depending on whether the alkyl chain on the P2TP molecules was of odd or even length. The monolayers were deposited on densely packed ultrasmooth self-assembled alkane silane modified $SiO_2$ surfaces. Our work shows that a subtle change in molecular structure can have a significant impact on the molecular packing structure in thin film, which in turn, will have a strong impact on charge transport of organic semiconductors. This was verified by quantum-chemical calculations that predict a corresponding odd–even effect in the strength of the intermolecular electronic coupling.Chemistry and Chemical BiologyEngineering and Applied Science

La vidéo, outil multiple

Burnier Michel, Lory Jen-Luc. La vidéo, outil multiple. In: Bulletin de l'Association française des anthropologues, n°16-17, Mai 1984. Audio Visuel, sous la direction de Colette Piault, Marc H. Piault et Christiane Bougerol . pp. 58-63

Optical properties of in vacuo lithiated nanoporous WO3:Mo thin films as determined by spectroscopic ellipsometry

Incorporation of Mo into pure WO3 thin films is of interest for electrochromic devices, as it improves colour neutrality in the dark state. Existing literature still lacks reliable quantitative data on the complex dielectric function of such coatings. In this study, we deposited WO3 and MoxW1−xO3 thin films by magnetron sputtering and subsequently characterised them by X-ray photoelectron spectrometry (XPS), grazing incidence X-ray diffraction (GIXRD) and scanning electron microscopy (SEM). In vacuo-lithiation was performed to incorporate lithium inside the thin films. The lithiated films were evaluated with variable-angle spectroscopic ellipsometry (VASE) from 340 to 990 nm and with transmission measurements from 330 to 2100 nm. The ellipsometric data were analysed with a straightforward model composed of the sum of Tauc-Lorentz and Lorentz oscillators dispersion laws. One Lorentz oscillator positioned around 1.3 eV is associated with the reduction of W6+ to W5+ by lithium incorporation. One Lorentz oscillator positioned around 2.3 eV is associated with additional states in the band-gap due to the presence of Mo in the lithiated film. The proposed model allows a better comprehension of the involved electronic transitions and allows to determine the refractive index and extinction coefficient of the materials precisely

Solar cooking potential in Switzerland: Nodal modelling and optimization

Solar cooking is one possible solution to reduce the domination of fossil fuel in the domestic sector and to benefit from renewable energy. This study assesses the solar cooking potential in Switzerland. A nodal model, based on energy balance equations of a box-type solar cooker is implemented in Matlab. Model parameters that cannot be determined experimentally or analytically are evaluated through an optimization procedure based on a Genetic Algorithm (GA). The model is able to predict the temperature of the cooking vessel with an average relative error around 5%. Based on its reliability, the model is simulated over a year for different locations in Switzerland in order to determine the solar cooking potential. It is characterized by a metric that represents the number of days in a year the oven could be used to cook potatoes for two persons. It is found that the cooking times of potatoes can be well predicted by an Arrhenius law with an activation energy of 74.14 [kJ/mol]. The potato cooking criterion is based on the Arrhenius equation and determines if the pot simulated temperature profile of a particular day allows to cook potatoes. The North-East of Switzerland is the least favourable area for solar cooking with theoretically around 155 cooking days per year. Around 240 days are estimated to be suitable for cooking in the cantons of Valais and Grisons, which represents a significant potential for solar cooking in Switzerland

Co-Sputtered Monocrystalline GeSn for Infrared Photodetection

We demonstrate monocrystalline growth of GeSn on Ge and Si substrates by co-sputtering. We discuss the evolution of film growth with thickness, elucidating the effects of substrate temperature, sputtering source, and the importance of hydrogen dilution in the plasma

Mobile communication through insulating windows: a new type of low emissivity coating

Building materials attenuate the microwaves used for telecommunication depending on their composition and thickness. Modern windows contain glass with a metallic coating. This might cause a low quality of cell phone reception inside some buildings. In order to improve the transmission of microwaves used for telecommunication through modern glazing, a novel patterned coating was developed. In this work, the morphology and chemical composition of the pattern was characterized. The attenuation to microwaves of coated, uncoated and patterned glass was measured and simulated. The effect of the size of the air gap of a double glazing was studied by numerical simulation. Typical attenuation to the microwaves of building materials used for telecommunications is presented and compared to our newly developed patterned coating. In this paper, we demonstrate that a specific laser treatment on a conductive coating can strongly improve its performances regarding the transmission of microwaves