In this work, we demonstrate a fully integrated three-axis Hall magnetic sensor by exploiting microfabrication technologies applied to a GaAs-based heterostructure. This allows us to obtain, by the same process, three mutually orthogonal sensors: an in-plane Hall sensor and two out-of-plane Hall sensors. The micromachined devices consist of a two-dimensional electron gas AlGaAs/InGaAs/GaAs multilayer which represents the sensing structure, grown on the top of an InGaAs/GaAs strained bilayer. After the release from the substrate, the strained bilayer acts as a hinge for the multilayered structure allowing the out-of-plane self-positioning of devices. Both the in-plane and out-of-plane Hall sensors show a linear response versus the magnetic field with a sensitivity for current-biased devices higher than 1000 V A−1 T−1, corresponding to an absolute sensitivitymore than 0.05 V T−1 at 50 μA. Moreover, Hall voltage measurements, as a function of the mechanical angle for both in-plane and out-of-plane sensors, demonstrate the potential of such a device for measurements of the three vector components of a magnetic field.

This paper presents a novel biotelemetry system based on a fully-passive architecture; High Electron Mobility Transistors are used as sensing elements. The main advantages and drawbacks related to the approach here proposed are deeply analyzed and some possible solutions identified. Furthermore, some preliminary experimental results are given and discussed.

Arrays of liquid crystal defects-linear smectic dislocations-are used to trap semiconductor CdSe/CdS dot-in-rods which behave as single-photon emitters. Measurements of the emission diagram are combined together with measurements of the emitted polarization of the single emitters. It is shown that the dot-in-rods are confined parallel to the linear defects to allow for a minimization of the disorder energy associated with the dislocation cores. It is demonstrated that the electric dipoles associated with the dot-in-rods, tilted with respect to the rods, remain oriented in the plane including the smectic linear defects and perpendicular to the substrate, most likely due to dipole/dipole interactions between the dipoles of the liquid crystal molecules and those of the dot-in-rods. Using smectic dislocations, nanorods can consequently be oriented along a unique direction for a given substrate, independently of the ligands' nature, without any induced aggregation, leading as well to a fixed azimuthal orientation for the dot-in-rods' dipoles. These results open the way for the fine control of nanoparticle anisotropic optical properties, in particular, fine control of single-photon emission polarization.

Wind and fluid flow represent some of the most attractive renewable energy sources for addressing climate change, pollution and energy insecurity issues. Wind harvesting technologies, in particular, are the fastestgrowing electric technologies in the world because of their efficiency and lower environmental impact with respect to traditional energy sources, despite exhibiting major drawbacks such as big infrastructure investment and environment invasiveness, producing high levels of noise and requiring the need of large areas for their installation. A single wind turbine can produce megawatts of power and they have the potential to cover the entire world's energy demand in the next few years, but they have a technological limit in a cut-in wind speed of about 4 m s(-1), below which the turbines do not operate, excluding them as an energy source for slow air flows. At the same time most of the wind available in the environment is below the turbines' threshold speed. In this paper we show that small flags, made by piezoelectric thin film on flexible polymers and whose shape resembles the dry leaves of trees, can efficiently act as harvesters of energy from wind at extremely low speed, such as from a gentle blow or breath. We demonstrate that piezoelectricity on flexible polymers is achievable by depositing a thin film of piezoelectric aluminium nitride (AlN), sandwiched between metal electrodes with columnar grains coherent through the polycrystalline layers, on Kapton substrates. The prototype flags have a natural curling due to the release of the residual stress of the layers. While the curling is essential for the activation of the maximum flag oscillation, this system is so elastic and light that oscillations start at a cut-in flow speed of 0.4 m s(-1), the lowest reported so far, with an open circuit peak to peak voltage of 40 mV. The voltage increases to 1.2 V when the flag is flattened and parallel to the fluid flow lines, with a generated power of 0.257 mW cm(-3)

This paper presents a new AlN-based MEMS devices suitable for vibrational energy harvesting applications. Due to their particular shape and unlike traditional cantilever which efficiently harvest energy only if subjected to stimulus in the proper direction, the proposed devices have 3D generation capabilities solving the problem of device orientation and placement in real applications. Thanks to their particular shape, the realized devices present more than one fundamental resonance frequencies in a range comprised between 500 Hz and 1.5 kHz, with a voltage generation higher than 300μV and an output power up to 0.4 pW for single MEMS device.

In this work the micro-fabrication of flexible MicroElectroMechanical transducers based on the piezoelectric effect is reported. We developed the technological protocol to realize a piezoelectric transducer composed by a Molybdenum (Mo) top electrode, the Aluminum Nitride active layer and a Mo bottom electrode on a polymeric tape. The process starts from the DC sputtering deposition of the Molybdenum layer at room temperature on Kapton HN. The Molybdenum is chosen not only for its electrical properties but also because it enhances the crystal orientation of AlN. The next step is the deposition of AlN that occurs at high temperature, around 250°C. Temperature and physical sputtering enhanced by applying a DC bias on the substrates are two important parameters to improve the crystal orientation of the film. These extreme growth conditions guarantee a very good crystal structure without damaging the Kapton substrate. Then a final Mo layer is sputtered at room temperature. SU8-25 thick photo resist is used to define the top electrode and the AlN layer, and in a second mask step the Mo bottom electrode. The developer, the PG remover and SU8 negative resist itself have shown a chemical compatibility with Kapton HN. We measured the piezoelectric response on a capacitor test structure: through the Dynamic Mechanical Analyzer we applied controlled forces, and at the same time, by an LCR meter we performed measurements of the capacitance.

In this paper, we analyze the birefringence effect in circular photonic crystals (CphCs). The studied CphCs are dielectric rings (DRs) and photonic crystals with cylindrical air holes arranged in circular patterns. The dielectric concentric circular patterns admit two preferred propagation directions defined by an extraordinary and an ordinary refractive index, representing two electric field polarizations. These electric fields are diffracted inside the crystal or are localized in a central microcavity region. We prove the induced artificial anisotropy in DRs through the geometrical equivalence with the corresponding thin-film multilayer structure. The equivalence is obtained through the geometrical synthesis of the wavefront propagation inside the artificial anisotropic structure. As applications, we analyze a Si/SiO2 DR Bragg reflector and a GaAs CphC microcavity resonator. The Bragg theory is validated by numerical time-domain approaches that are well suited to solve scattering problems. The microcavity resonance analysis and the Q-factor evaluation are performed by the finite-element method modeling.

The fabrication of three-dimensional platinum nanoprotrusions by ion beam induced deposition (IBID) is here proposed to study their interaction with cultured rat primary neurons. The broad versatility of IBID allows to test the effects on cells network morphology of different protrusions shapes, from straight pillars to nail-headed or sphere-headed vertical structures. A preferential adhesion of cells on fabricated Pt nanostructures is clearly shown by fluorescence and scanning electron microscopy, with dense and suspended neuritic networks observed on arrays of large-headed pillars. This technique could be exploited to improve cells/electrodes adhesion and to increase the detected extracellular electric signal.

Hair cells are ubiquitous in nature. These natural and efficient mechanoreceptors are exploited as efficient transducers for flow sensing and chemical sensing in many living systems, ranging from cells to aquatic animals. In aquatic environment hair cells are probably the most effective mechanism of sensing and environment perception. Mimicking these mechanoreceptors and their structure and behavior for developing MEMS artificial hair cells (AHC) could be a powerful approach for producing efficient underwater sensors and technologies. In this paper we review the most recent approaches and designs to realize waterproof hair cell-like mechanotransducers for applications in underwater flow and acoustic sensing, mimicking the so-called “lateral line” in fishes. Recent developments for the achievement of artificial lateral lines to be applied in underwater autonomous vehicles will be highlighted. Finally research strategies to obtain artificial hair cells biosensing in liquid environment will be introduced.

In this work, form birefringence physics and the mechanisms of Si/SiO2 dielectric concentric optical rings are investigated. The optical rings are modeled by means of a Bragg reflector. Similarly to a negative uniaxial crystal, the dielectric concentric pattern admits two preferred propagation directions defined by an extraordinary and an ordinary refractive index representing two field polarizations. The circular grating profile splits the electromagnetic field into a radial (extraordinary field) and a tangential (ordinary field) component which represent two modes of the periodic structure. These two modes are characterized by the refractive index ellipse obtained by the Huygens principle. The model is developed through the wave front propagation inside the anisotropic structure. The Bragg theory and conservation of momentum vectors provide the Bragg angles of the ordinary and extraordinary rays for different optical wavelengths. The Bragg theoretical model is validated by the finite difference time domain (FDTD) approach for a wavelength of λ = 0.98 μ m.

We report on the development of efficient and low cost single photon sources for quantum communications. The work discusses the suitability of colloidal nanocrystals as sources of quantum light as well as it draws out possible solutions to overtake the drawbacks of these emitters, such as blinking and polarization.

In this work, we studied the effect of some growth parameters on the polarization behavior of InAs/GaAs closely stacked quantum dot (CSQDs). In particular, we focused on the surface reconstruction time of GaAs spacer, its thickness and the number of QD layers. We found that the most effective parameter to enhance the TM/TE intensity ratio is the surface reconstruction time of the GaAs spacer before the subsequent QD deposition. By varying this parameter between 20 s and 120 s, a TM/TE ratio as high as 0.86 has been achieved. A further fine tuning of GaAs spacer thickness and QD layer number increased this ratio up to a value of 0.92 in structures containing only 3 QD layers.

In this work we analyze the birefringence effect in circular photonic crystals such as dielectric rings (DR) and photonic crystals with air holes arranged in circular patterns. The dielectric concentric circular patterns admit two preferred electric fields orthogonal components defined by an extraordinary and an ordinary refractive index. These electric fields, localized in the central region of the circular photonic crystal (CPC) will be radiated at different wavelengths. This behaviour allows to characterize the analysed structures as wavelength division multiplexers. We first analyze the induced anisotropy of the multiplexers, and, then, we study the wavelength selectivity. Similar emitted wavelengths related to a air-hole CPC and to a corresponding DR structure are observed. The multiplexing behaviour is numerically modelled by the finite element method approach which provides the emitted resonant wavelengths and the quality Q-factors for a membrane-type optical wavelength division multiplexer obtained by the CPC design.

In this work we present the design of a three-dimensional wavelength converter consisting of GaAs/AlGaAs nonlinear ridge waveguide with a quasi-phase-matched grating. A fundamental mode at λFU = 1.55 μ m, and a copropagating second harmonic mode at λSH = 0.775 μ m are considered. The second harmonic generation process in the χ(2) nonlinear waveguides is analysed by analytical and numerical approaches. The numerical approach is performed by the Hertzian potential formulation typically used for the modelling of χ(2) nonlinear processes. A good agreement between analytical and numerical results is observed.

We report the evidence of a polarized single photon flux from a colloidal nanoparticle. We analyze, by time and polarization resolved spectroscopy measurements, the polarization behavior of a single CdSe/CdS core/shell dot in rod, achieving a polarization ratio at room temperature of ∼75% and a lifetime of the excited state of ∼11 ns.

Laser ablation technique is employed in order to generate polydimethylsiloxane (PDMS)/Ag NPs in situ, starting from a silver target in a solution of PDMS prepolymer and toluene. The produced surfactant-free nanoparticles are characterized by high resolution transmission electron microscopy (HRTEM) and scanning TEM-high angle annular dark field (STEM-HAADF) imaging modes, showing the majority of them to be of the order of 4 nm in diameter with a small percentage of larger Ag-AgCl multidomain NPs, embedded into a PDMS matrix. Low concentrations of carbon onion-like nanoparticles or larger fibers are also formed in the toluene-PDMS prepolymer solution. In accordance with this, UV-vis spectra shows no peak from silver NPs; their small size and their coverage by the PDMS matrix suppresses the signal of surface plasmon absorption. Inductively coupled plasma measurements reveal that the concentration of silver in the polymer is characteristically low, ∼0.001% by weight. The electrical properties of the PDMS nanocomposite films are modified, with current versus voltage (I-V) measurements showing a low current of up to a few tenths of a pA at 5 V. The surface resistivity of the films is found to be up to ∼1010 Ω/sq. Under pressure (e.g. stress) applied by a dynamic mechanical analyzer (DMA), the I-V measurements demonstrate the current decreasing during the elastic deformation, and increasing during the plastic deformation.

Ion Beam Induced Deposition (IBID) is employed to fabricate three-dimensional nanoprotrusions on top of the recording pads of an active pixel sensor array (APS-MEA) featuring 4096 microelectrodes. Modified APS-MEAs are envisioned as enhanced tools to achieve real-time “in-cell” recordings from thousands of sensing elements, thus aiming to large-scale in-vitro registrations with unprecedented signal quality. A generalized electric model is proposed to address the revealed complexity of the neuron/electrode interface, and simulations have been conducted revealing the most advantageous cell/electrode coupling conditions. Preliminary results on the recording of spontaneous activity in cultured neuronal networks by means of nanostructured microelectrodes demonstrate the compatibility of IBID technology and APS-MEA infrastructure. The interface between cultured mammalian neurons and modified microelectrodes is revealed by FIB/SEM analysis, fostering the employment of the proposed electrical model for interpretation of electrical recordings from nanostructured microelectrodes.

In this work we report on our recent studies on Silicon-Nitride PhC single-defect nanocavity membranes embedding colloidal nanocrystals. A novel structure consisting of a layer of nanocrystals sandwiched between two layers of Silicon-Nitride has been used. Photoluminescence measurements prove the efficient coupling among the nanoemitters and the optical modes localized in the Si3N4 photonic crystal nanocavities, showing enhancement of the spontaneous emission in resonant conditions. This technology enables the realization of NC-based ultra-small lasers and non-classical light sources operating at visible wavelengths on silicon substrates.

The paper presents a novel multilayer micro-ring structure suitable to be used as THz emitter or detector. The realization process exploits the self-rolling properties of a suspended InGaAs/GaAs bi-layer obtained by controlled strain release of a thin film from a substrate. Numerical and preliminary experimental results will be presented and discussed. It is demonstrated that the proposed approach is an optimum candidate for the design of very high-frequency resonators.

The oscillator strength in CdSe/CdS colloidal dot-in-rods is evaluated and assessed to be of ~1.5. On the basis of this finding, the possibility to reach the strong coupling regime with photonic crystals nanocavities is discussed. In spite that carefully choosing the cavity parameters the strong coupling regime could be analytically achieved at room temperature, theoretical considerations show that the typical Rabi doublet cannot be resolved. The work draws also a viable strategy toward the observation of the strong coupling at cryogenic temperatures.

We present a method that allows determining the band-edge exciton fine structure of CdSe/CdS dot-in-rods samples based on single particle polarization measurements at room temperature. We model the measured emission polarization of such single particles considering the fine structure properties, the dielectric effect induced by the anisotropic shell, and the measurement configuration. We use this method to characterize the band-edge exciton fine structure splitting of various samples of dot-in-rods. We show that, when the diameter of the CdSe core increases, a transition from a spherical like band-edge exciton symmetry to a rod-like band edge exciton symmetry occurs. This explains the often reported large emission polarization of such particles compared to spherical CdSe/CdS emitters.

In this work, we analyze the pressure sensing of a thin film molybdenum/aluminumnitride/molybdenum (Mo/AlN/Mo) microwave/RF MEMS filter fabricated by a simple technology. After an experimental characterization in a frequency range between 1 and 36 GHz, we focused on the piezoelectric effect due to the stress properties of the piezoelectric AlN layer by applying forces by means of weights. Variations in the bandpass region of the microwave/RF filter are observed by proving high sensitivity also for low applied weights. We check by a properly designed three-dimensional (3D) finite-element method (FEM) tool the pressure-sensing property of the proposed device. Finally, we analyze the bad gap property of a chip with central defect around 40 GHz.

We report theoretical and experimental investigations of the optical response of two-dimensional periodic arrays of rectangular gold nanopatches grown on a monolayer graphene placed on a glass substrate. We discuss the numerical analysis and optical characterization by means of reflection spectra and show that rectangular nanopatches display a polarization-dependent response, at normal incidence, which leads to double plasmonic resonances due to the Wood anomaly. We detail the fabrication process highlighting how the resist primer and the adhesion layer can reduce and impede the graphene doping due to the environment and to the nanopatches, respectively, by means of Raman spectroscopy.

In this paper we present a reliable process to fabricate GaN/AlGaN one dimensional photonic crystal (1D-PhC) microcavities with nonlinear optical properties. We used a heterostructure with a GaN layer embedded between two AlGaN/GaN Distributed Bragg Reflectors on sapphire substrate, designed to generate a λ= 800 nm frequency downconverted signal (χ(2) effect) from an incident pump signal at λ= 400 nm. The heterostructure was epitaxially grown by metal organic chemical vapour deposition (MOCVD) and integrates a properly designed 1D-PhC grating, which amplifies the signal by exploiting the double effect of cavity resonance and non linear GaN enhancement. The integrated 1D-PhC microcavity was fabricate combing a high resolution e-beam writing with a deep etching technique. For the pattern transfer we used ~ 170 nm layer Cr metal etch mask obtained by means of high quality lift-off technique based on the use of bi-layer resist (PMMA/MMA). At the same time, plasma conditions have been optimized in order to achieve deeply etched structures (depth over 1 micron) with a good verticality of the sidewalls (very close to 90°). Gratings with well controlled sizes (periods of 150 nm, 230 nm and 400 nm respectively) were achieved after the pattern is transferred to the GaN/AlGaN heterostructure. javascript:;

Multipoint Light Emitting Optical Fibers (MPF) has been recently demonstrated as a versatile tool for spatially addressable optogenetics experiments. Their fabrication has been possible thanks to a number of key microfabrication technologies, in particular the unique nanofabrication capabilities of a Focused Ion Beam. This work provides the complete description of MPF fabrication, detailing the optimization process for each fabrication step.

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 15 kHz. This value has been compared with simulations of the structures performed by finite element method.

Energy harvesting at low frequency is a challenge for microelectromechanical systems. In this work we present a piezoelectric vibration energy harvester based on freestanding molybdenum (Mo) and aluminum nitride (AlN) ring-microelectromechanical-system (RMEMS) resonators. The freestanding ring layout has high energy efficiency due to the additional torsional modes which are absent in planar cantilevers systems. The realized RMEMS prototypes show very low resonance frequencies without adding proof masses, providing the record high power density of 30.20 μW mm−3 at 64 Hz with an acceleration of 2g. The power density refers to the volume of the vibrating RMEMS layout.

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.

We report on effective prevention of GaAs corrosion in a cell culture liquid environment by means of polymerized (3-mercaptopropyl)-trimethoxysilane thin film coatings. Aging in physiological solution kept at 37 °C revealed no significant oxidation after 2 weeks, which is the typical period of incubation of a neuron cells culture. The method was also applied to High Electron Mobility Transistors (HEMT) arrays with unmetallized gate regions, in view of their application as neural signal transducers. Significant reduction of the degradation of the HEMT behavior was obtained, as compared to uncoated HEMTs, with good channel modulation efficiency still after 30 days aging.

The absorption of electromagnetic waves has always attracted a large interest because of its cross-the-board nature that spans from microwave to optical frequencies in both linear and nonlinear regimes. At the same time, the experimental isolation of bi-dimensional (2D) materials has recently unveiled how single layers might also be very attractive because of their unprecedented optical and absorption properties. In particular, graphene, a 2D version of graphite, exhibits a remarkably high absorption value (∼2.3%) in the visible range [1] when compared to metals or dielectric materials. In this paper, we will review and illustrate the quest for the enhanced absorption in photonic nanostructures that incorporate monolayer and multilayer graphene sheets emphasizing the difference in terms of configurations and strategies proposed in literature. Then, we will detail the optical performance of graphene-based one-dimensional (1D) gratings that support guided mode resonances showing how it is possible to tune theoretically and experimentally their total absorption ranging from 2.3% to perfect absorption by means of metallic and dielectric reflectors or engineered super cells.

We investigate graphene-based optical absorbers that exploit guided mode resonances (GMRs) attaining theoretically perfect absorption over a bandwidth of few nanometers (over the visible and near-infrared ranges) with a 40-fold increase of the monolayer graphene absorption. We analyze the influence of the geometrical parameters on the absorption rate and the angular response for oblique incidence. Finally, we experimentally verify the theoretical predictions in a one-dimensional, dielectric grating by placing it near either a metallic or a dielectric mirror, thus achieving very good agreement between numerical predictions and experimental results.

The optimization of H1 photonic crystal cavities for applications in the visible spectral range is reported, with the goal to obtain a versatile photonic platform to explore strongly and weakly coupled systems. The resonators have been realized in silicon nitride and weakly coupled to both organic (fluorophores) and inorganic (colloidal nanocrystals) nanoparticles emitting in the visible spectral range. The theoretical Purcell factor of the two dipolelike modes in the defect has been increased up to ∼90, and the experimental quality factor was measured to be ∼750.

Tapered and micro-structured optical fibers (TFs) recently emerged as a versatile tool to obtain dynamically addressable light delivery for optogenetic control of neural activity in the mammalian brain. Small apertures along a metal-coated and low-angle taper allow for controlling light delivery sites in the neural tissue by acting on the coupling angle of the light launched into the fiber. However, their realization is typically based on focused ion beam (FIB) milling, a high-resolution but time-consuming technique. In this work we describe a laser micromachining approach to pattern TFs edge in a faster, more versatile and cost-effective fashion. A four-axis piezoelectric stage is implemented to move and rotate the fiber during processing to realize micropatterns all-around the taper, enabling for complex light emission geometries with TFs.

In this paper, we propose a flexible piezoelectric MEMS transducer based on aluminum nitride thin film grown on polyimide soft substrate and developed for tactile sensing purposes. The proposed device consists of circular micro-cells, with a radius of 350 μm, made of polycrystalline c-axis textured AlN. The release of compressive stress by crystalline layers over polymer substrate allows an enhanced transduction response when the cell is patterned in circular dome-shaped geometries. The fabricated cells show an electromechanical response within the full scale range of 80 mN (200 kPa) both for dynamic and static load. The device is able to detect dynamic forces by exploiting both piezoelectric and flexoelectric capabilities of the aluminum nitride cells in a combined and synergistic sensing that occurs as voltage generation. No additional power supply is required to provide the electrical readout signals, making this technology suitable candidate when low power consumption is demanding. Moreover a capacitance variation under constant stress is observed, allowing the detection of static forces. The sensing ability of the AlN-based cells has been tested using an ad hoc setup, measuring both the applied load and the generated voltage and capacitance variation.

We report a new approach to fabricate suspended composite membranes consisting of carbon-coated iron nanopowder uniformly dispersed in a polydimethylsiloxane matrix. The approach is based on the use of selectively photopolymerized thick SU-8 layer wherein the unexposed to ultraviolet light area represents the sacrificial layer. Circular composite membranes of different sizes are designed, fabricated, and characterized. The membranes’ deflections upon the application of an external magnetic field, measured by optical microscopy, show a quadratic dependence on the diameter, in agreement with the theory. Tensile tests proved that the fillers do not affect the elastic properties of the matrix, since the Young’s modulus of the composite material is similar with the one of the pure polymer. The versatile approach presented in this work allows to easily and rapidly fabricate suspended composite membranes that provide diaphragm materials with excellent performances, which can find broad applicability in microfluidic applications (valves, micro-pumps) and in MEMS technology (tactile displays, mobile devices).

Optogenetic approaches to manipulate neural activity have revolutionized the ability of neuroscientists to uncover the functional connectivity underlying brain function. At the same time, the increasing complexity of in vivo optogenetic experiments has increased the demand for new techniques to precisely deliver light into the brain, in particular to illuminate selected portions of the neural tissue. Tapered and nanopatterned gold-coated optical fibers were recently proposed as minimally invasive multipoint light delivery devices, allowing for site-selective optogenetic stimulation in the mammalian brain [Pisanello , Neuron82, 1245 (2014)]. Here we demonstrate that the working principle behind these devices is based on the mode-selective photonic properties of the fiber taper. Using analytical and ray tracing models we model the finite conductance of the metal coating, and show that single or multiple optical windows located at specific taper sections can outcouple only specific subsets of guided modes injected into the fiber.

We present a way to selectively tune the properties of the degenerated modes confined in a single point defect two-dimensional photonic crystal cavity based on a triangular lattice of air holes. We investigate the dependence of the modal properties of the resonator on the position of the first neighbor holes, showing that it is possible to finely tune the resonant frequency of only one of these two modes and to increase the quality factor of the mode that has no frequency shift. This is achieved by controlling the wavevector components inside the cavity. This approach is a viable strategy for the development and the optimization of several innovative devices based on bi-modal cavity arrays, such as arrays of integrated optical filters and optical read-out sections for biosensing applications.

This work presents modeling, fabrication and characterization of planar microcoils for wireless power transfer in medical implanted devices, proposing integrated technology as a way to reduce the dimensions and achieve higher efficiency. The wireless power transfer (WPT) architecture is composed by: a primary coil carrying the alternating current signal to generate a magnetic field and the receiving coil to convert magnetic field in current, that is located parallel to the primary one with a gap between the two inductors. In the proposed design the two microcoils are circular with short-circuited turns to minimize electrical resistance. The electrical measurements on the fabricated test structures with different pitch sizes show a dramatic reduction of coil resistance to few ohms with respect to classic coil design. The experimental values of the resistance and inductance (from 24 to 45 nH) are in good agreement with the analytical model. The efficiency of fabricated microcoils for wireless power transfer is predicted by Finite element method (FEM) at 10 kHz modeling in terms of coupling factor ranging the distance of the inductors from 0 to 1 mm. FEM results show that the transfer efficiency can be further enhanced by the introduction of a ferromagnetic material on the back side of each coil in order to confine the magnetic field. High coupling factor above 65% can be achieved with this shielding layer, even with lowest pitch value and high coil distances.

Optical stimulation and silencing of neural activity is a powerful technique for elucidating the structure and function of neural circuitry. In most invivo optogenetic experiments, light is delivered into the brain through a single optical fiber. However, this approach limits illumination to a fixed volume of the brain. Here a focused ion beam is used to pattern multiple light windows on a tapered optical fiber. We show that such fibers allow selective and dynamic illumination of different brain regions along the taper. Site selection is achieved by a simple coupling strategy at the fiber input, and the use of asingle tapered waveguide minimizes the implant invasiveness. We demonstrate the effectiveness of this approach for multipoint optical stimulation in the mammalian brain invivo by coupling the fiber to a microelectrode array and performing simultaneous extracellular recording and stimulation at multiple sites in the mouse striatum and cerebral cortex.

Herein we describe the realization of nanowalled polymeric microtubes through a novel and versatile approach combining the layer-by-layer (LbL) deposition technique, the self-rolling of hybrid polymer/semiconductor microtubes and the subsequent removal of the semiconductor template. The realized channels were characterized in detail using scanning electron and atomic force microscopes. Additionally, we report on the incorporation of a dye molecule within the nanowalls of such microtubes, demonstrating a distribution of the fluorescence signal throughout the whole channel volume. This approach offers the possibility to tailor the properties of micro/nanotubes in terms of size, wall thickness and composition, thus enabling their employment for several applications.

Blinking and single-photon emission can be tailored in CdSe/CdS core/shell colloidal dot-in-rods. By increasing the shell thickness it is possible to obtain almost non-blinking nanocrystals, while the shell length can be used to control single-photon emission probability.

In optogenetics, light-sensitive proteins are genetically targeted into specific classes of neurons in living animal models (typically mice), making possible to control their neural activity by means of visible light delivered into the brain tissue. In this paper, recent advances on techniques for in-vivo optical stimulation and inhibition of neuronal activity in optogenetic experiments are reported, with particular emphasis on new a new generation of fiber-optic technologies.

We demonstrate an ultracompact optical filter based on two coupled high-index contrast GaAs photonic crystal (PhC) membranes. The PhC membranes consist of a square lattice of air holes and behave as a FabryPerot cavity whose reflectivity and transmissivity depend on the air gap between the two membranes. The normal-incidence reflectance measurements and the numerical simulation of reflection spectra show a high sensitivity to the geometrical parameters, such as the distance between the slabs, whose control would make the device suitable for a new class of tunable optical filters.

The force (F) and the power consumption (P) of a magnetic actuator are modeled, measured and optimized in the context of developing micro-actuators for large arrays, such as in portable tactile displays for the visually impaired. We present a novel analytical approach complemented with finite element simulation (FEM) and experiment validation, showing that the optimization process can be performed considering a single figure of merit F/√P. The magnetic actuator is a disc-shaped permanent magnet displaced by planar microcoil. Numerous design parameters are evaluated, including the width and separation of the coil traces, the trace thickness, number of turns and the maximum and minimum radius of the coil. We obtained experimental values of F/√P ranging from 2 to 12 mN/√W using up to 2-layer coils of both microfabricated and commercial printed circuit board (PCB) technologies. This performance can be further improved by a factor of two by adopting a 6-layer technology. The method can be applied to a wide range of electromagnetic actuators.

In this work we propose a new technological approach aimed at improving the performances of DNA-chips in terms of detection sensitivity, signal-to-noise ratio and parallel analyses (spatial and spectral). It is based on the efficient enhancement of markers fluorescence through the insertion of photonic crystal nanocavities (PhC) in DNA-chips, thus giving higher sensitivity and allowing detection of small amounts of target biomolecules in the investigated solution. Moreover, this strategy univocally associates a specific emission wavelength to a specific nanocavity (and to the bio-probe immobilized on it), therefore allowing to infer the presence of a determined element in the solution by a simple spectral analysis of the optical response of the read-out region. This guarantees parallel detection of multiple elements and faster analysis time. The proposed 2D-PhC cavity assisted bio-chip read-out can be easily extended from DNA to a wide range of biomolecules, such as proteins, antibodies, aptamers, receptors.

A soft Parylene conformal coating encapsulation is demonstrated to be an efficient method to control the mechanical and sensory properties of a bioinspired artificial hair cell, tuning the mechanoreceptive responsivity from a sub-linear to a super-linear behaviour such as hair cells adapt to a natural environment.

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.

In this work, we investigate the effects produced on the light absorption and scattering by silver nanoparticles, arranged in a periodic pattern, placed on the top of amorphous thin silicon (α-Si) layer. Solar conversion efficiency in thin film solar cells can be enhanced exploiting surface plasmon (SP) waves and resonances. The deposition of metal nanoparticles layers on the top of a thin film silicon solar cell can increase light absorption and consequently the energy conversion in the frequency range where the silicon intrinsic absorptance is low. Our analysis reveals that the performance of each structure depends on shape, size and thickness of the substrate, which seems to hugely affect light scattering, and in particular the back one.

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.

We propose colloidal CdSe/CdS dots in rods as nonclassical sources for quantum information technology. Such nanoemitters show specific properties such as strongly polarized emission of on-demand single photons at room temperature, dipolelike behavior and mono-exponential recombination rates, making us envision their suitability as sources of single photons with well defined quantum states in quantum cryptography based devices.

In this work we propose rod-shaped core/shell CdSe/CdS colloidal nanocrystals as efficient non-classical light sources. These nanoemitters show peculiar features such as pronounced photoluminescence stability and high single-photon emission efficiency at room-temperature, making us envision their possible employment as single-photon sources for quantum communications protocols.

We show that Silicon Nitride (Si3N4) photonic crystal (PhC) resonators are powerful building blocks to realize biocompatible photonic devices based on spontaneous emission engineering of nanoemitters in the visible spectral range. The versatility of this technological platform is demonstrated also in biological applications, where nanocavity modes are coupled to DNA strains marked with Cyanine 3 (Cy3) organic dyes and antibodies bounded to fluorescent proteins (TRITC).

We propose silicon nitride two-dimensional photonic crystal resonators as flexible platform to realize photonic devices based on spontaneous emission engineering of nanoemitters in the visible spectral range. The versatility of our approach is demonstrated by coupling the two dipole-like modes of a closed band gap H1 nanocavity with: (i) DNA strands marked with Cyanine 3 organic dyes, (ii) antibodies bounded to fluorescent proteins and (iii) colloidal semiconductor nanocrystals localized in the maximum of the resonant electric field. The experimental results are in good agreement with the numerical simulations, highlighting the good coupling of the nanocavities with both organic and inorganic light emitters.

Colloidal nanocrystals, i.e. quantum dots synthesized trough wet-chemistry approaches, are promising nanoparticles for photonic applications and, remarkably, their quantum nature makes them very promising for single photon emission at room temperature. In this work we describe two approaches to engineer the emission properties of these nanoemitters in terms of radiative lifetime and photon polarization, drawing a viable strategy for their exploitation as room-temperature single photon sources for quantum information and quantum telecommunications.

Sperm cells progressive motility is the most important parameter involved in the fertilization process. Sperm middle piece contains mitochondria, which play a critical role in energy production and whose proper operation ensures the reproductive success. Notably, sperm progressive motility is strictly related to mitochondrial membrane potential (MMP) and consequently to mitochondrial functionality. Although previous studies presented an evaluation of mitochondrial function through MMP assessment in entire sperm cells samples, a quantitative approach at single-cell level could provide more insights in the analysis of semen quality. Here we combine laser scanning confocal microscopy and functional fluorescent staining of mitochondrial membrane to assess MMP distribution among isolated spermatozoa. We found that the sperm fluorescence value increases as a function of growing progressive motility and that such fluorescence is influenced by MMP disruptors, potentially allowing for the discrimination of different quality classes of sperm cells in heterogeneous populations.

We propose a technological approach aimed at improving biochips performances, based on an efficient spectral modeling and enhancement of markers fluorescence through the insertion of photonic crystal nanocavities (PhC-NCs) in the readout area of biochips. This strategy univocally associates a specific emission wavelength to a specific bioprobe immobilized on a nanocavity, therefore guaranteeing parallel detection of multiple elements and faster analysis time. Moreover, PhC-NCs significantly enhance the markers fluorescence, thus improving the detection sensitivity.

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.

The integration of a polycrystalline material such as aluminum nitride (AlN) on a flexible substrate allows the realization of elastic tactile sensors showing both piezoelectricity and significant capacitive variation under normal stress. The application of a normal stress on AlN generates deformation of the flexible substrate on which AlN is grown, which results in strain gradient of the polycrystalline layer. The strain gradient is responsible for an additional polarization described in the literature as the flexoelectric effect, leading to an enhancement of the transduction properties of the material. The flexible AlN is synthesized by sputtering deposition on kapton HN (poly 4,4′- oxydiphenyl pyromellitimide) in a highly oriented crystal structure. High orientation is demonstrated by X-ray diffraction spectra (FWHM = 0.55° of AlN (0002)) and HRTEM. The piezoelectric coefficient d 33 and stress sensitive capacitance are 4.7 ± 0.5 pm V -1 and 4 × 10 -3 pF kPa -1, respectively. The parallel plate capacitors realized for tactile sensing present a typical dome shape, very elastic under applied stress and sensitive in the pressure range of interest for robotic applications (10 kPa to 1 MPa). The flexibility of the device finalized for tactile applications is assessed by measuring the sensor capacitance before and after shaping the sensing foil on curved surfaces for 1 hour. Bending does not affect sensor's operation, which exhibits an electrical Q factor as high as 210, regardless of the bending, and a maximum capacitance shift of 0.02%.

Two-dimensional electron gas (2DEG) transport in Al0.3Ga0.7N/AlN/GaN heterostructures has been studied using magnetic-field dependent Hall-effect measurements and advanced mobility spectrum analysis techniques over the temperature range from 95 K to 300 K. It is shown that electronic transport is due to a single well-defined 2DEG species, with room-temperature sheet concentration and average mobility of 9.3×1012 cm-2 and 1,880 cm2/Vs, respectively. No parasitic conduction through the bulk GaN layer was detected. Importantly, it is shown that the 2DEG exhibits an approximately Gaussian mobility distribution, the linewidth of which broadens with increasing temperature. This is the first reported observation of thermal broadening effects in the 2DEG mobility distribution.

Cancer cell motility is one of the major events involved in metastatic process. Tumor cells that disseminate from a primary tumor can migrate into the vascular system and, being carried by the bloodstream, transmigrate across the endothelium, giving rise to a new tumor site. However, during the invasive process, tumor cells must pass through the extracellular matrix, whose structural and mechanical properties define the parameters of the migration process. Here, we propose 3D-complex cage-like microstructures, realized by two-photon (TP) direct laser writing (DLW), to analyze cell migration through pores significantly smaller than the cell nucleus. We found that the ability to traverse differently sized pores depends on the metastatic potential and on the invasiveness of the cell lines, allowing to establish a pore-area threshold value able to discriminate between non-tumorigenic and tumorigenic human breast cells.

Physical and mechanical properties of extracellularmatrix (ECM) have been proved to be crucial in the metastatic process. However, currently available studies on the interplay between ECM stiffness and cancer cell invasive behaviour are performed on planar assays, while the in vivo interaction takes place in three-dimensions. To take into consideration the ECM structural and mechanical complexity in the cell/structure interactions, we fabricated 3D microscaffolds through two-photon lithography (2PL) and tested how they are invaded by human colorectal adenocarcinoma (LS-174T) tumor cells, showing that it is possible to detect significant differences in cells/structure interactionwhen structural parameters are modified. In particular, both scaffold geometry and 2PL fabrication parameters were optimized to obtain 3D polymeric cylindrical structures with controlled Young's modulus and with linear stiffness gradients. The ability of LS-174T to migrate in the scaffolds was tested in different experimental conditions, including scaffolds functionalization and under β-catenin downregulation. It was observed that high Young's modulus scaffolds are always less invaded than softer ones, confirming the role of the 3D micro-environmental stiffness in mediating cells migration, including when specific functionalization or pharmacological treatments are performed.

We propose the realization of a compact fully-passive biotelemetry tag composed of a high-electron mobility transistor (HEMT) connected to a wireless link. The Gallium Arsenide based gateless HEMT serves both as the environmental sensing element and as the amplitude modulator of the carrier signal received by the antenna. A prototype demonstrator operating in the MHz range has been developed: it consists of an array of transistors with different gate geometries and two spiral loop resonators implementing the wireless link. More specifically, one resonator (Tag-resonator) is connected to the array of transistors, while the other one (Reader-resonator) is connected to a power generator/reader device; the wireless link uses the magnetic coupling between the two resonators. Experimental results demonstrate that the reader-resonator exhibits an intensity modulation of the resonance dip depending on the voltage applied to the HEMT gate. These results will be used as a guideline for the realization of biocompatible sub-millimeter tags operating in the Gigahertz frequency range.

In this paper we discuss the possibility of implementing a novel bio-sensing platform based on the observation of the shift of the leaky surface plasmon mode that occurs at the edge of the plasmonic band gap of metal gratings, when an analyte is deposited on top of the metallic structure. We report numerical calculations, fabrication and experimental measurements to prove the sensing capability of a two-dimensional array of gold nano-patches in the detection of a small quantity of Isopropyl Alcohol (IPA) deposited on top of sensor surface. The calculated sensitivity of our device approaches a value of 1000 nm/RIU with a corresponding Figure of Merit (FOM) of 222 RIU−1. The presence of IPA can also be visually estimated by observing a color variation in the diffracted field. We show that color brightness and intensity variations can be ascribed to a change in the aperture size, keeping the periodicity constant, and to different types of analyte deposited on the sample, respectively. Moreover, we demonstrate that unavoidable fabrication imperfections revealed by the presence of rounded corners and surface roughness do not significantly affect device performance.

We experimentally investigate the nonlinear response of two-dimensional periodic arrays composed of gold nanopatches on silicon substrate, functionalized by means of a conjugated rigid thiol. The surface-enhanced Raman scattering (SERS) response is empirically evaluated using a laser source operating in the visible spectral range at k¼633 nm. Nonlinear results are then correlated to optical and structural properties of the samples under investigation. SERS mapping and estimation of the SERS enhancement factor are examined to determine stability and reproducibility of the results, highlighting also the contribution of the plasmonic resonance excited in the two-dimensional periodic array, and the dependence on the numerical aperture of the microscope objective used in the micro-Raman system.

We experimentally demonstrate the color tuning abilities of two-dimensional periodic arrays of gold nano-patches on silicon substrate. We observe that changes in the geometrical parameters of the array can shift significantly the plasmonic resonance that occurs at the edge of the plasmonic band gap. Experimental proof of this shift is provided by the observation of an important change in the color of the diffracted field. Calculations of the diffracted spectra match the observed color changes very well and provide an efficient means for the design of sensing platforms based on color observation.

A transmission belt is described which comprises a body made of a first elastomeric material, a plurality of teeth and a plurality of longitudinal cords buried in the body of the belt and a back. The belt has a working surface on said teeth and the working surface is at least partially covered by a covering made of a plastic and/or metal material. Defining the area comprised between the plane defined by the neutral axis of the cords, the working surface and the median transverse planes of two adjacent teeth as the unitary longitudinal section, the covering preferably occupies at least 25% of the unitary longitudinal section.

A multi-point light-delivering device, comprising a waveguide carrying light along a longitudinal axis and including multiple optical windows, through which the carried light is out-coupled from the waveguide. The waveguide comprises a tapered region along which the optical windows are distributed, wherein each optical window out-couples a specific subset of propagating modes of the carried light to which the optical window is matched.

Electroactive microelectromechanical device of the Artificial Hair Cell type, comprising a moving cilium structure including a substrate (11, 12; 42) and a cantilever (18; 48), partly or entirely in.piezoelectric material, subject to bending or deformation following the action of a force and/or an applied voltage (Vapp1), said cantilever (18; 48) comprising a multilayer (13, 14a, 14b, 16) inducing a stress-driven geometry in which a portion (19) of said cantilever (18; 48) lies outside of a plane defined by the substrate (11, 12; 42). According to the invention said cantilever (18; 48) is associated to a piezoresistive element, in particular of piezoresistive material (15) configured to measure the bending or deformation of said cantilever (18; 48).

The present invention concerns an integrated triaxial magnetic sensor device 100 apt to detect a magnetic field comprising: a substrate 120 having a surface defining a reference plane (x,y); a first sensor unit 101 arranged on a first main surface 121 of the substrate in a first plane substantially parallel to the reference plane; a second sensor unit 102 arranged on a second plane, and a third sensor unit 103 arranged on a third plane, the second and third planes being not parallel to the reference plane. The device further comprises: a first cantilever structure 115 raised with respect to the reference plane by a first elevation angle and having a second main surface 125 arranged along the second plane, the first cantilever structure including the second sensor unit 102, and a second cantilever structure 116 raised with respect to the reference plane by a second elevation angle and having a third main surface 126 arranged along the third plane, the second cantilever structure including the third sensor unit 103, in which the first and the second cantilever structure are structurally connected to the substrate 120 through a respective first and second hinge structure 113, 114 curved with respect to the reference plane and bearing the respective cantilever structure while maintaining it raised with respect to the reference plane.

A method of identifying target analytes in a sample, particularly a biological sample, comprising the steps of putting a plurality of target analytes, bound to a common luminescent marker, in contact with a plurality of molecular probes immobilized on a support, each of said molecular probes being capable of complementary binding to a respective target analyte, if said target analyte is present in the sample, providing to said support an excitation radiation and detecting an emission radiation coming from said support as a result of at least one complementary binding event, characterized by the fact that: said support comprises a plurality of photonic crystal resonators, at least two of said resonators being characterized by different resonance wavelengths; each of said molecular probes being fixed to a respective resonator;; and by the fact that the identification of at least one target analyte is carried out through the analysis of the total emission spectrum coming from said plurality of photonic crystals resonators, in order to detect possible wavelength resonance peaks generated as a result of the binding of said target analyte, bound to the common luminescent marker, to one or more of said molecular probes.