Zinc oxide (ZnO) nanowires (NWs) are excellent candidates for the fabrication of energy harvesters, mechanical sensors, piezotronic and piezo-phototronic devices thanks to the interplay between piezoelectric and semiconducting properties. The growth of ZnO NWs on flexible substrates would further broaden their possible applications. However, such a growth requires low temperature synthesis to prevent any damage to the flexible polymer. Another difficulty lies in the fact that the deposition of patterned ceramic thin films on flexible substrates is challenging, especially under vacuum free conditions. In this framework, printing technologies like inkjet and gravure printing have a noteworthy potential since they allow to deposit thin films onto flexible substrates and offer several other advantages like cost efficiency, use of low temperatures, vacuum-free processing, high throughput and the possibility of patterning during the deposition process. In this work, we report the chemical bath deposition (CBD) growth of high quality ZnO NWs on polyethylene terephthalate (PET) starting from inkjet printed seed layer constituted of ZnO nanoparticles and a comparison with that obtained with seed layer deposited by gravure technology. Using Piezoresponse Force Microscopy (PFM), we observed that the Zn-polar domains are homogeneously distributed at the top surface of the grown ZnO NWs. This work demonstrates the key benefit of the printing techniques over conventional methods (e.g. Atomic Layer Deposition, ALD) to deposit seed layers at low temperature on flexible substrates. This opens the possibility of manufacturing completely vacuum-free solution-based flexible piezoelectric devices.
Piezoelectric thin films are widely used in MEMS and NEMS actuators and resonators, but also in mechanical sensors and energy harvesters for IoT applications and Wireless Sensors Networks. Nanotechnology involving piezoelectric materials is a key research direction, with benefits expected from nanostructuring and the replacement of toxic materials. Piezoelectric nanocomposites based on semiconducting nanowires (NWs) are an alternative to thin films with nanostructuration benefits, such as low temperature fabrication and higher flexibility than thin films. In addition, they exhibit larger piezoelectric coefficient than their thin films counterparts. In this work we study the piezoelectric performance of vertically grown ZnO NWs based on Finite Element simulations in the PFM (Piezoresponse Force Microscopy) configuration. In this AFM (Atomic Force Microscope) mode, the AFM tip is placed in contact with the top surface of the NW while applying a voltage, thus inducing a deformation of the structure by the reverse piezoelectric effect. Different parameters are assessed: the effect of the surrounding air, the NW size and geometry and the effect of the semiconducting properties, in particular the doping level and surface traps density. The results are compared to previous theoretical approaches and experimental findings.
Due to small refractive change, it is difficult to obtain high confined glass integrated waveguide. A proposed solution is to make firstly a planar waveguide by ion exchanged and then to use an optical grade dicing to realize two separated grooves. The cutting and the polishing of the glass are made at the same time. Monomode ridge waveguide with a smallest width of 4 μm and a height of tens micrometers are characterized, either in the near-infrared domain or in the visible domain. The propagation losses can be smaller than 1 dB/cm with fiber coupling losses around 2 dB depending on the fiber used to excite the waveguide.
KEYWORDS: Aircraft structures, Thermoelectric materials, Smart structures, Current controlled current source, Microsystems, Signal processing, Electronics, Instrument modeling, Chemical elements, Structural health monitoring
Vibration harvesting has been intensively developed recently and systems have been simulated and realized, but real-life situations (including aircraft Structure Health Monitoring (SHM)involve uneven, low amplitude, low frequency vibrations. In such an unfavorable case, it is very likely that no power can be harvested for a long time. To overcome this, multi-source harvesting is a relevant solution, and in our application both solar and thermal gradient sources are available. We propose in this paper a complete Microsystem including a piezoelectric vibration harvesting module, thermoelectric conversion module, signal processing electronics and supercapacitor. A model is proposed for these elements and a VHDL-AMS simulation of the whole system is presented, showing that the vibration harvesting device alone cannot supply properly a SHM wireless node. Its role is nevertheless important since it is a more reliable source than thermoelectric (which depends on climatic conditions). Moreover, synergies between vibration harvesting and thermoelectric scavenging circuits are presented.
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