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Suspended nanochannel resonators (SNRs) are promising devices able to characterize mass down to the attogram scale, thus being able to detect nanoparticles or biomolecules. In this paper, we present a flexible fabrication process for SNRs based on a sacrificial layer approach that allows to easily tailor the dimensions of the nanochannel by changing the thickness of the sacrificial layer or its patterning during the lithographic step. The resonance properties of the fabricated SNR are investigated in terms of resonance frequency and frequency stability (Allan deviation). Liquids of different densities are injected in the device and, from the shift of the resonance peaks, the mass responsivity of the resonators is assessed to be up to 3.90 mHz/ag. To the best of our knowledge, the devices here presented are the first example of suspended nanochannel resonators with a channel height as low as 50 nm fabricated with a top-down approach.

In this work flexible composite nanogenerators were prepared aiming to identify and optimize the exploitation of the piezoelectric effect in mechanical energy harvesting. A novel shape-controlled synthesis of ZnO microstructures through hydrothermal route was achieved resulting in different morphologies and aspect-ratio particles, microwires, multipods, and desert-roses. The three different microparticles and round-shaped commercial nanoparticles were incorporated into a polydimethylsiloxane matrix and a comparative study on the piezoelectric output power dependence on the filler morphology was carried out. The highest performances, i.e. output voltage of 10 V and a maximum power of 55 µW, were obtained with the highest aspect-ratio ZnO filler, the microwires, dispersed in the PDMS matrix at a 40 wt% concentration. Considering the generated voltage dependence on the size and aspect-ratio of the fillers, a working mechanism was formulated. The nanogenerators were then exploited to charge a homemade carbon-based supercapacitor. The voltage charging curves confirm the voltage generation trend based on the high aspect-ratio particles, showing that the best performances are obtained by the microwires-based composite nanogenerator. This work thus contributes to clarify the piezoelectric mechanism in composite nanogenerators and to maximize the output power generation in view of self-powered nanodevices able to recover and store waste environmental energy.

Graphical abstractDisplay Omitted The optimised fabrication process for a PZT actuated microswitch was developed.A comparison between standard ad optimised process was carried out.The actuation properties of the device were evaluated.The optimised process improves the piezoelectric response.Actuating the device a resistance switch from 1k? to 2? was observed. In this work the fabrication of a piezoelectrically actuated microswitch for high current applications is proposed. The device was obtained by assembling two silicon substrates: one containing the signal lines and the other enclosing a silicon nitride (Si3N4) microcantilever. This latter operates as a switch by closing the circuit with a metal electrode on its tip. A layer of lead zirconate titanate (PZT), deposited by sol-gel method, constitutes the actuation element of the microcantilever. The bottom and top electrodes of the PZT were respectively made of thin Ta/Pt and Au layers while the signal lines and the contact electrode on the microcantilever tip were made of Ti/Al. A comparison between microcantilevers characterised by different bottom electrodes is presented: (i) Ta/Pt deposited at 300?C and patterned by wet etching, (ii) Ta/Pt deposited at 100?C and patterned by lift-off. The microcantilevers fabricated with the latter metallisation show a considerable symmetry of the piezoelectric response and a wide microcantilever displacement. Thus, in this device the cantilever microstructures are able to close the gap between the signal lines with a resulting contact resistance of about 2?.

We present a robust and flexible tactile sensor based on piezoresistive sensing material, constituted by a polymeric composite with nanostructured spiky particles as filler. The composite is able to exploit tunneling conduction mechanism when subjected to a compressive load. We have here integrated this quantum tunneling composite (QTC) with an ad-hoc electronic read-out circuit. In addition a software interface can monitor and visualize the applied mechanical pressure, thus leading to a complete tactile sensor device. Concerning the sensing material, the piezoresistive composite shows an enhanced tunneling conduction due to the presence of nickel particles with nanostructured sharp tips embedded in a silicone matrix. We registered an increase up to nine orders of magnitude of the composite electrical conduction in response to a mechanical strain. The sensor consisted in a continuous layer of functional composite sandwiched between a matrix of patterned top and bottom electrodes. The planar sensor can thus be modeled as a two-dimensional array of resistors whose value decreases by increasing the applied pressure. We also designed an ad-hoc electronic read-out circuit, able to read and process the resistance variations of the sensor upon a compressive load, thus providing not only the pressure intensity but also the pressure distribution data. A software interface was able to achieve the real-time tridimensional response and lead to the visualization of the compressed regions on the sensor. The present device is an efficient and low-cost prototype of tactile sensing skin, thus readily enabling its use for human robotic applications.

A high flexible and easy conformable piezoresistive composite material was used and tested to fit in complex-shaped structures and to be suitably integrated onto the robot surface for tactile sensing. In order to obtain the functional material in the form of self standing multilayer thin samples, two process flows based on microcasting and hot embossing techniques were optimized. The influence of different composition parameters on the functional performances was investigated and a huge variation of the electrical resistance, up to nine orders of magnitude, was registered when a mechanical pressure was applied to the prepared samples.