Carbon nanotubes based ultrasonic transducer: realization process, morphological and mechanical properties

For instrumentation of microporosity in cementitous materials, carbon nanotubes based capacitive ultrasonic transducers (cMUT) are promising sensors. Their interest lies in the combination of high working frequencies (1 GHz) with small dimensions (1 µm²). In the proposed device, the cMUT membrane is made of aligned single-walled carbon nanotubes (SWNT) bridging a gap over a command electrode. We will describe the realization process of the vibrating membrane and its characterizations. First step of the device realization is the dispersion of SWNTs in N-methylpyrrolidone. Then, nanotubes are aligned by dielectrophoresis (DEP) between metallic electrodes onto a SiO2 substrate. A metallic layer is deposited over the electrodes edges to prevent nanotubes from slipping when suspended. The underlying SiO2 is then etched to release the membrane. Relevant features of the membrane are nanotubes alignment and density. Via SEM imaging, we have linked them with DEP operating parameters, in agreement with theoretical properties of DEP. To put a figure on membrane features, we are working on SEM image processing for nanotubes recognition. The method is based on advanced noise removal and contrast enhancement. First results of identification and measurement of intermeshed nanotubes on SEM pictures will be presented. We also mapped the Young's modulus of a suspended membrane using an AFM in contact mode, over surfaces of about 1 µm² surface. It opens the way for calculation of localized Young modulus, Poisson's ratio and thickness measurement of the membrane. We will check for correlations between mechanical data and quantitative properties of the deposition obtained from image processing. The optimization of membrane realization process and characterization techniques are presented, describing the present progress of our cMUT project. Next step will be actuation of the membrane to demonstrate vibrations at low frequency

Micro−transducteur ultrasonique capacitif à membrane de nanotubes de carbone : Perspectives pour le suivi immergé de la durabilité des matériaux cimentaires

Nous présentons des éléments de la conception, la réalisation et la caractérisation d'un micro−transducteur ultrasonique capacitif haute-fréquence dont la membrane vibrante est faite de nanotubes de carbone alignés. Le dispositif est conçu spécifiquement pour l'instrumentation immergée de la microporosité des matériaux cimentaires. La modélisation élasto−acoustique du dispositif valide préliminairement son intérêt applicatif pour la métrologie de la microporosité

Continuous wave operation of InAs-based quantum cascade lasers above 20 μm

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Cascade lasers epitaxially grown on Silicon substrates

International audienceThe direct epitaxy of III-V lasers on Silicon (Si) substrates has been considered for decades as an important objective for the realization of integrated photonics chips. However, the difference in crystal structure, lattice-constant, thermal expansion coefficient as well as issues related to the reactivity of the Si surface have made this topic extremely challenging. For that reason, the direct epitaxy of lasers having good performance and decent lifetime on Si was considered as an almost unattainable dream, and many labs and companies have thus developed ways to circumvent this issue using hybridization techniques. Very recently, major progress has been achieved however thanks to a better understanding of the defect generation mechanisms and systematic studies of their suppression or at least the drastic reduction of their density into the active region of the device. In this presentation, we will discuss the challenges related to the growth of III-V on Si as well as the progress made lately in that field. We will then discuss the current state-ofthe-art of III-V lasers grown on Si with a focus on IR Interband and Quantum Cascade lasers. We will show that the most recent devices have as good performance as their counterpart grown on their native substrates, which opens the way for integration into photonic chips

Selective growth of ordered hexagonal InN nanorods

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