Stress-driven AlN cantilever-based flow sensor for fish lateral line system

In this work, we report on the fabrication and characterization of stress-driven aluminum nitride (AlN) cantilevers to be applied as flow sensor for fish lateral line system. The fabricated structures exploit a multilayered cantilever AlN/molybdenum (Mo) and a Nichrome 80/20 alloy as piezoresistor. Cantilever arrays are realized by using conventional micromachining techniques involving optical lithography and etching processes. The fabrication of the piezoresistive cantilevers is reported and the operation of the cantilever as flow sensor has been investigated by electrical measurement under nitrogen flowing condition showing a sensitivity to directionality and to low value applied forces

Conformable Nanowire-in-Nanofiber Hybrids for Low-Threshold Optical Gain in the Ultraviolet

The miniaturization of diagnostic devices that exploit optical detection schemes requires the design of light sources combining small size, high performance for effective excitation of chromophores, and mechanical flexibility for easy coupling to components with complex and nonplanar shapes. Here, ZnO nanowire-in-fiber hybrids with internal architectural order are introduced, exhibiting a combination of polarized stimulated emission, low propagation losses of light modes, and structural flexibility. Ultrafast transient absorption experiments on the electrospun material show optical gain which gives rise to amplified spontaneous emission with a threshold lower than the value found in films. These systems are highly flexible and can conveniently conform to curved surfaces, which makes them appealing active elements for various device platforms, such as bendable lasers, optical networks, and sensors, as well as for application in bioimaging, photo-cross-linking, and optogenetics

Design, fabrication and characterization of piezoelectric cantilever MEMS for underwater application

This work shows a preliminary microfabrication route for a novel directional hydrophone based on a cross-shaped design of piezoelectric cantilevers. A thin layer of aluminum nitride (AlN) using Molybdenum (Mo) thin film as electrodes will be exploited as piezoelectric functional layer for the microfabrication of a cantilever-based ultrasonic micro electro mechanical system (MEMS) hydrophone. A parameterized simulation based on length of these cantilevers between 100 and 1000 μm allowed to set the first resonant mode between 20 kHz and 200 kHz, the desired underwater ultrasonic acoustic range. The microsystem was designed with cantilevers facing each other in a cross configuration in order to have novel MEMS hydrophone with an omnidirectional response. In order to investigate the first resonance frequency mode and displacement measurements, a Laser Doppler Vibrometer was used and good agreement between simulations and experimental results was achieved. Responsivity and directionality measurements of the piezoelectric MEMS cantilevers were performed in water. Maximum sensitivity up to −153 dB with omnidirectional directivity pattern was achieved by fabricated MEMS sensor

Wearable piezoelectric mass sensor based on pH sensitive hydrogels for sweat pH monitoring

Colorimetric and electrochemical (bio)sensors are commonly employed in wearable platforms for sweat monitoring; nevertheless, they suffer from low stability of the sensitive element. In contrast, mass-(bio)sensors are commonly used for analyte detection at laboratory level only, due to their rigidity. To overcome these limitations, a flexible mass-(bio)sensor for sweat pH sensing is proposed. The device exploits the flexibility of piezoelectric AlN membranes fabricated on a polyimide substrate combined to the sensitive properties of a pH responsive hydrogel based on PEG-DA/CEA molecules. A resonant frequency shift is recorded due to the hydrogel swelling/shrinking at several pH. Our device shows a responsivity of about 12 kHz/pH unit when measured in artificial sweat formulation in the pH range 3-8. To the best of our knowledge, this is the first time that hydrogel mass variations are sensed by a flexible resonator, fostering the development of a new class of compliant and wearable devices

Colloidal nanocrystals air bridge fabricated by direct lithography

We report on the direct lithographic fabrication of a polymeric air bridge embedding semiconductor colloidal nanocrystals (NCs). Two ensembles of NCs emitting at 637 nm and 550 nm, respectively, were dispersed into different matrices of SU-8 negative photoresist. The first matrix was deposited on a Si substrate and localized by photolithography thus obtaining an array of red-emitting stripes with micrometer resolution. The second matrix was then deposited on the first layer of stripes and analogously localized in order to obtain a second array perpendicular to the lower one. Suspended emitting structures in the micrometer range were therefore obtained, as confirmed by scanning electron microscopy (SEM) and spatially resolved photoluminescence (PL) measurements on the fabricated sample. The developed and applied method allows the fabrication of three-dimensional active structures by means of several realigned lithographic steps. This opens the way to the fabrication of extremely efficient photonic devices whose optical properties, such as spectral filtering, directionality and emission efficiency, can be finely tuned through a 3D photonic crystal (PC) technology

Elucidating the effect of the lead iodide complexation degree behind the morphology and performance of perovskite solar cells

The inclusion of iodide additives in hybrid perovskite precursor solutions has been successfully exploited to improve the solar cell efficiency but their impact on perovskite formation, morphology and photovoltaic performance is still not clear. Here an extensive analysis of the effect of iodide additives in the solution-phase and during the perovskite film formation, as well as their effect on device performance is provided. The results demonstrate that in the solution-phase the additives promote the formation of lead poly-iodide species resulting in the disaggregation of the inorganic lead iodide framework and in the formation of smaller nuclei inducing the growth of uniform and smooth perovskite films. Most importantly, the complexation capability of different iodide additives does not only directly affect film morphology but also influences the density of defect states by varying the stoichiometry of precursors. These findings demonstrate that the fine control of the interactions of the chemical species in the solution-phase is essential for the precise control of the morphology at the nanoscale and the growth of the perovskite films with a reduced density of defect states. Therefore, the in-depth understanding of all the processes involved in the solution-phase is the first step for the development of a facile and reproducible approach for the fabrication of hybrid perovskite solar cells with enhanced photovoltaic performance

Parylene-coated bioinspired artificial hair cell for liquid flow sensing

In this work we report the design and development of a biomimetic waterproof Si/SiN multilayered cantilever whose internal stress gradient bends the beam out of the plane enabling flow velocity detection in water. A water resistant parylene conformal coating has been deposited on the artificial hair cell for waterproof operation. The sensing mechanism is represented by a piezoresistive strain-gauge along the cantilever beam. A set-up for analysing sensor responsivity in air and water has been used and its electrical behavior is reported. Responsivity of 0.7 mV/(cm/s) is recorded and a linear response of sensor read-out signal amplitude with respect to flow pulses up to 30 Hz. Parylene conformal coating is demonstrated to be an efficient method for water sealing and can be effective in the post-fabrication for tuning the micromechanical cantilever properties

Design and fabrication of photonic devices based on colloidal nanocrystals

Thanks to their low fabrication costs and the well established surface-functionalization techniques which allow their merging into a wide range of materials, wet-chemical synthesized colloidal nanocrystals are finding broad application in several fields, from pharmacology to cosmetics, food industry, textiles, optics and so on. In particular, semiconductor nanocrystals are widely exploited as quantum optical emitters, showing very high quantum yield (close to unity), stability, low tendency to photobleaching and possibility to be tuned from ultraviolet to infrared range. The realization of high performing photonic devices based on this class of emitters is therefore an extremely intriguing challenge; on the other hand, the best way to manipulate these emitters and integrate them in solid matrices, without dramatically decreasing their optical properties, is still under debate. Here we present a method for the fabrication of the main building blocks of photonic circuits by exploiting the localization of colloidal nanocrystals dispersed in polymeric matrices through lithographic techniques. The realization of waveguide structures, suspended stripes and photonic crystal nanocavities is shown as a demonstration of this approach

Design and fabrication by thermal imprint lithography and mechanical characterization of a ring-based PDMS soft probe for sensing and actuating forces in biological systems

In this paper, the design, fabrication and mechanical characterization of a novel polydimethylsiloxane (PDMS) soft probe for delivering and sensing forces in biological systems is proposed. On the basis of preliminary finite element (FEM) analysis, the design takes advantage of a suitable core geometry, characterized by a variable spring-like ring. The compliance of probes can be finely set in a wide range to measure forces in the micronewton to nanonewton range. In particular, this is accomplished by properly resizing the ring geometry and/or exploiting the mixing ratio-based elastic properties of PDMS. Fabrication by the thermal imprint lithography method allows fast and accurate tuning of ring sizes and tailoring of the contact section to their targets. By only varying geometrical parameters, the stiffness ranges from 1080 mNm-1 to 50 mNm-1, but by changing the base-curing agent proportion of the elastomer from 10:1 to 30:1, the stiffness drops to 37 mNm-1. With these compliances, the proposed device will provide a new experimental tool for investigating force-dependent biological functions in sensory systems. © 2019 by the authors