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International audience; (Figure Presented) In a twist: A design strategy for molecule-based electronic materials using aromatic compounds with a nonplanar core is presented. A new class of hexabenzocoronene is put forth that has its core severely distorted out of planarity into a corrugated structure. When substituted with four alkoxy side chains, this material self-assembles into infinitely long columns through stacking (see picture) and acts as an active layer in field-effect transistors. © 2005 Wiley-VCH Verlag GmbH & Co. KGaA.

International audience; Broad-band monolithic integrated active frequency doublers operating in dc-100-GHz frequency range are presented. Circuits are fabricated in a self-aligned InP double heterojunction bipolar transistor process. Three integrated doubler versions have been designed. Inductive peaking and active splitting effects are quantified and compared. Circuit measurements give sinusoidal output waveform at 100 GHz with an rms timing jitter of 400 fs. Circuits have a maximum conversion gain of +1 dB at 60 GHz. the fundamental suppression is better than 24 dB in the whole frequency range.

In this paper we present a prototype of a Strip Resistive Thick GEM photosensitive gaseous detector filled with Ne and ethylferrocene vapours at a total pressure of 1 atm for an early forest fire detection system. Tests show that it is one hundred times more sensitive than the best commercial ultraviolet flame detectors and therefore, it is able to reliably detect a flame of 1.5x1.5x1.5 m3 at a distance of about 1km. An additional and unique feature of this detector is its imaging capability, which in combination with other techniques, may significantly reduce false fire alarms when operating in an automatic mode. Preliminary results conducted with air filled photosensitive gaseous detectors are also presented. The approach main advantages include both the simplicity of manufacturing and affordability of construction materials such as plastics and glues specifically reducing detector production cost. The sensitivity of these air filled detectors at certain conditions may be as high as those filled with Ne and EF. Long term test results of such sealed detectors indicate a significant progress in this direction. We believe that our detectors utilized in addition to other flame and smoke sensors will exceptionally increase the sensitivity of forest fire detection systems. Our future efforts will be focused on attempts to commercialize such detectors utilizing our aforementioned findings., Presented at the International Conference on Micropattern gaseous detectors, Crete, Greece, June 2009

International audience; Ionization chambers working in ambient air in current detection mode are attractive due to their simplicity and low cost and are widely used in several applications such as smoke detection, dosimetry, therapeutic beam monitoring and so on. The aim of this work was to investigate if gaseous detectors can operate in ambient air in pulse counting mode as well as with gas amplification which potentially offers the highest possible sensitivity in applications like alpha particle detection or high energy X-ray photon or electron detection. To investigate the feasibility of this method two types of open-end gaseous detectors were build and successfully tested. The first one was a single wire or multiwire cylindrical geometry detector operating in pulse mode at a gas gain of one (pulse ionization chamber). This detector was readout by a custom made wide -band charge sensitive amplifier able to deal with slow induced signals generated by slow motion of negative and positive ions. The multiwire detector was able to detect alpha particles with an efficiency close to 22%. The second type of an alpha detector was an innovative GEM-like detector with resistive electrodes operating in air in avalanche mode at high gas gains (up to 104). This detector can also operate in a cascaded mode or being combined with other detectors, for example with MICROMEGAS. This detector was readout by a conventional charge -sensitive amplifier and was able to detect alpha particles with 100% efficiency. This detector could also detect X-ray photons or fast electrons. A detailed comparison between these two detectors is given as well as a comparison with commercially available alpha detectors. The main advantages of gaseous detectors operating in air in a pulse detection mode are their simplicity, low cost and high sensitivity. One of the possible applications of these new detectors is alpha particle background monitors which, due to their low cost can find wide application not only in houses, but in public areas: airports, railway station and so on.

International audience; In the past decades, introduction of nanostructured materials created a breakthrough allowing the improvement of thermoelectric materials figure of merit. Nanostructuration of silicon through sintering of nanoparticles has been widely reported as an efficient thermoelectric material. Fabrication of flexible thermoelectric devices that could be incorporated in system-in-package as energy generator is a stimulating challenge. In this objective, inkjet printing of silicon nanoparticles was performed on various substrates through jetting parameters optimization and chemical treatments for surface energy tailoring. An annealing step was applied for recovering of electrical conduction and modification of thermal conductivity. Two types of sintering methods under nitrogen were evaluated: Rapid Thermal Annealing and microwave annealing. Morphological evolution was monitored by scanning electron microscopy and Raman microspectroscopy. The latter was also used for evaluation of the thermal conductivity. First steps of sintering have been observed at temperature as low as 600 °C. Thermal conductivity can be tailored from values ~1W/mK up to ~100W/mK by varying the temperature and the length of the annealing step. Electrical conductivity is improved up to 800 °C where oxidation takes place and limits carriers transport. Doping of the nanoparticles will now be performed in order to improve the electrical conductivity and realize a printed thermoelectric device.

Silicon nanoparticles-based inks were investigated in respect of their suitability for photovoltaic and thermoelectric applications. Nanoparticles with a diameter ranging between 20 to 150 nm were functionalized in order to avoid oxidation as well as having a good stability in suspension. After inkjet-printing and drying, they were annealed up to 1000 °C under nitrogen atmosphere by both rapid thermal and microwave annealing. The influence of the annealing treatment on the structural, electrical, optical and thermal properties was investigated by Raman, SEM, electrical and optical measurements. SEM and Raman demonstrate evolution of the microstructure at temperature as low as 600 °C. Optical, electrical and thermal properties depend strongly on the annealing temperature and tend to exhibit a modification of physical properties above 800 °C when the smallest nanoparticles begin to melt. The annealing method has been identified to be of primary importance on the layer microstructure and its thermal behavior.

International audience; A broad-band monolithic integrated active frequency doubler operating in DC-100 GHz frequency range is presented. The circuit is fabricated in a self-aligned InP DHBT process. Circuit measurements show sinusoidal output waveform at 100 GHz with a rms time jitter of 400 fs. The doubler has a maximum conversion gain of +1 dB at 60 GHz. The fundamental suppression is better than 24 dB in the whole frequency range.