We present the first European network of tree ring δ13C and δ18O, containing 23 sites from Finland to Morocco. Common climate signals are found over broad climatic‐ecological ranges. In temperate ...regions we find positive correlations with summer maximum temperatures and negative correlations with summer precipitation and Palmer Drought Severity Indices (PDSI) with no obvious species‐specific differences. Regional δ13C and δ18O chronologies share high common variance in year‐to‐year variations. Long‐term variations, however, exhibit differences that may reflect spatial variability in environmental forcings, age trends and/or plant physiological responses to increasing atmospheric CO2 concentration. Rotated principal component analysis (RPCA) and climate field correlations enable the identification of four sub‐regions in the δ18O network ‐ northern and eastern Central Europe, Scandinavia and the western Mediterranean. Regional patterns in the δ13C network are less clear and are timescale dependent. Our results indicate that future reconstruction efforts should concentrate on δ18O data in the identified European regions.
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.
We have analyzed theoretically and experimentally the linewidth of the first harmonic of the photocurrent (radio-frequency (RF) linewidth) in monolithic passively mode-locked semiconductor lasers. ...Due to the absence of restoring force, the timing jitter is directly related to the RF linewidth, avoiding possible underestimations made with conventional methods of phase noise measurement. The RF linewidth is also analytically related to the pulse characteristics using Haus's model. The timing stability performance of a promising two-section quantum-dot laser is presented using RF linewidth measurements. Experimental evolution of the RF linewidth with power and pulsewidth is finally compared to the analytical expression.
The huge mechanical energy available in the environment, mostly in form of kinetic energy of fluids such as wind, ocean and river currents or waves, is currently harvested by cumbersome, low ...efficiency and high environmental impact technologies. New approaches are needed for producing more compact and distributed mechanical energy converters. Nanogenerators and related micro and nanotechnologies can help in developing new environmentally friendly and biocompatible technologies. To face this challenge, new conversion physical principle, device structures and system architectures are currently being studied and developed. This work reviews the most recent advances on nanogenerators for harvesting energy transported by liquids in the environment such as water motion in rivers and marine environments and kinetic energy in rain. It discusses the most common physical transduction mechanisms, with a focus on piezoelectric and triboelectric nanogenerators (PENG/TENG), the requirements for producing flexible devices for effective conversion and the system architectures for optimizing the fluid-device interaction for producing large and fast oscillations, such as flapping, fluttering or galloping, from quasi-static or quasi-laminar fluid motion. Additionally, the work encompasses challenges such as waterproofing and antibiofouling, important issues in sub-marine and underwater environment.
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•Recent advances on nanogenerators for harvesting energy by liquids are reviewed.•Fluid energy nanogenerators are a promising class of devices for renewable energy.•FENGs networks are used for large-scale electrical energy production (blue energy).
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► In this work we fabricate flexible piezoelectric cantilevers. ► We provide the optimized process for AlN smart integration on Kapton. ► The resonance frequency is characterized by ...piezoresponse AFM. ► The predicted frequency of flexible cantilever is obtained by Comsol Multiphysics.
In this work we present for the first time the fabrication and the characterization of flexible micro cantilevers based on Aluminum Nitride (AlN) as piezoelectric active layer and polyimide as elastic substrate. The AlN thin film, embedded into two layers of Molybdenum (Mo), is grown by sputtering deposition and presents highly c-axis oriented hexagonal crystal structure. The flexible structures are successfully realized by a two masks process, exploiting a silicon support to perform device key fabrication steps together with optimized processes for peeling off and patterning of the flexible layer. The realized flexible cantilevers present a bending downwards because of the residual compressive stress of the Mo/AlN/Mo multilayer on polyimide. The mechanical response of the realized flexible cantilevers has been investigated by piezoresponse measurements and the experimentally obtained first resonance frequency resulted to be around 15kHz. This value has been compared with simulations of the structures performed by finite element method.
In this work we propose a new technological approach to fabricate a fully integrated three-axis Hall magnetic sensor. The three axial device fabrication process exploits microfabrication technologies ...applied to a GaAs-based heterostructure to obtain at the same time three mutually orthogonal sensors: an in-plane Hall sensor and two out-of-plane Hall sensors. A two dimensional electron gas (2DEG) AlGaAs/InGaAs/GaAs multilayered structure constitutes the sensing medium of the micromachined devices, whereas an underlying strained InGaAs/GaAs bilayer allows the self-positioning of the out-of-plane devices by virtue of sacrificial layer removal and strain release. The in-plane and out-of-plane Hall sensors, show an excellent linearity versus the magnetic field with an absolute sensitivity as high as 0.03
V/T at 0.6
V bias voltage.
In this paper it is reported a novel approach for the fabrication of polymeric microtubes based on the combination of semiconductor strain released thin films and Layer-by-Layer (LbL) deposition ...technique. The structure consisting of a LbL self-assembled polylectrolytes (PEs) film deposited onto a strained GaAs/InGaAs bilayer, was properly patterned and structured to enable the self rolling of an array of channels of different lengths. Then, the semiconductor film, acting as a sacrificial template, was selectively etched to obtain polymer microtubes. The so-realized polymeric channels were characterized in detail using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Additionally, such microtubes were analyzed by confocal microscopy to prove the successful incorporation of a dye molecule within the polymeric nanowalls.
In this work we report on the high temperature characterization of two different interdigitated metal–semiconductor–metal (MSM) GaN-based photodetectors. The active material of the two MSM devices ...consists of bulk GaN grown by metal organic chemical vapor deposition (MOCVD), and of an AlGaN/GaN heterostructure grown by molecular beam epitaxy/magnetron sputtering epitaxy (MBE/MSE) system. Some of the trapping mechanisms which are at the origin of the persistent photocurrent (PPC) effects in GaN-based devices have been studied. The analysis of the decay time as a function of the temperature shows that in both devices the GaN excitonic resonances provide the most important contribution to the PPC on the millisecond time scale at low temperature. The densities of the trap centers involved in the PPC were obtained in both samples by measuring the photocurrent as a function of optical power sweeped in the upward and downward direction.
A semiconductor laser containing seven InAs-InGaAs stacked quantum-dot (QD) layers was grown by molecular beam epitaxy. Shallow mesa ridge-waveguide lasers with stripe width of 120 mum were ...fabricated and tested. A high modal gain of 41 cm -1 was obtained at room temperature corresponding to a modal gain of ~6 cm -1 per QD layer, which is very promising to enable the realization of 1.3-mum ultrashort cavity devices such as vertical-cavity surface-emitting lasers. Ground state laser action was achieved for a 360-mum-cavity length with as-cleaved facets. The transparency current density per QD layer and internal quantum efficiency were 13 A/cm 2 and 67%, respectively
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