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Sensor nodes have been assigned a lot of tasks in a connected environment that is growing rapidly. The power supply remains a challenge that is not answered convincingly. Energy harvesting is an emerging solution that is being studied to integrate in low power applications such as internet of things (IoT) and wireless sensor networks (WSN). In this work an interface circuit for a novel fluttering wind energy harvester is presented. The system consists of a switching converter controlled by a low power microcontroller. Optimization techniques on the hardware and software level have been implemented, and a prototype is developed for testing. Experiments have been done with generated input signals resulting in up to 67% efficiency for a constant voltage input. Other experiments were conducted in a wind tunnel that showed a transient output that is compatible with the target applications.

A new type of soft composite is syntetized by the use of two grade of commercially available Pt-catalyzed silicone elastomers and organic nanoclays (montmorillonite). A complete characterization underlines their attractive performances: lower Young modulus, higher dielectric permittivity, but without compromising important properties such as low dielectric losses and lower viscous losses, higher dielectric breakdown strength, and thereby maintaining the mechanical integrity of the elastomers. A figure of merit is introduced to compare all the innovative synthesized soft composites, characterized by a bimodal network. These achievements can be exploited for both the actuation and the energy generation purposes.

Flapping states of an energy harvesting device have been investigated by means of experiments, numerical simulations and a phenomenological model. The main aim is to predict the geometrical/physical properties of the system allowing sustained flapping limit cycles to emerge. These latter regimes are interesting when the system is used to harvest energy from flows. The main argument to identify flapping states is based on a simple resonance condition between the characteristic (elastic) time of the system and the flow time-scale. Similar arguments have been successful in other fields of fluid dynamics and fluid-structure interactions including turbulent flows of dilute polymer solutions and interactions between the wake originated by bluff bodies and elastic structures. The predictions of the geometrical/physical properties associated to critical conditions (i.e. those separating stable stages from flapping regimes) have been compared against the results of experiments, numerical simulations and a phenomenological model based on a set of ordinary differential equations. Results clearly confirm the expectations from the resonance condition. Discussions on how to extend our analysis in situations where the extraction stage is taken into account are also provided: this latter is indeed expected to influence the flapping stage and thus the critical conditions for flapping.

Aeroelastic phenomena are gaining significant attention from the perspective of energy harvesting (EH) with promising applications in supplying low-power remote sensors. Besides the development of individual EH devices, further issues are posed when considering multiple objects for realizing arrays of devices and magnifying the extracted power. Due to nonlinear mutual interactions, the resulting dynamics is generally different from that of single devices and the setup optimization turns out to be nontrivial. In this work, we investigate the problem focusing on a flutter-based EH system consisting of a rigid plate anchored by elastic elements and invested by a uniform laminar flow, undergoing regular limit-cycle oscillations and flapping motions of finite amplitude. We consider a simplified, yet general, physical model and employ three-dimensional direct numerical simulations based on a finite-difference Navier–Stokes solver combined with a moving-least-squares immersed boundary method. Focusing on main kinematic and performance-related quantities, we first report on the dynamics of the single device and then on multiple devices, considering different arrangements (i.e.: in-line, staggered and side-by-side). A parametric exploration is performed by varying the mutual distance between the devices and insights are provided. For the in-line arrangement, a recovery in performance for downstream devices is achieved by tuning their elasticity. Moreover, cooperative effects in the side-by-side arrangement are found to be substantially beneficial in terms of resulting power, with increases (i.e. constructive interference) up to 100% with respect to the single-device configuration. In order to confirm this numerical evidence, complementary results from wind-tunnel experiments are presented. Finally, we describe the system behaviour when increasing further the number of devices, outlining the ultimate goal of developing a high-performance EH network of numerous aeroelastic energy harvesters.

Energy Harvesting is the main solution to ensure the powering of sensors and micro-processors, especially in extreme environmental conditions where the use of batteries can be expensive or even impractical. In this work, a coupled-mode aero elastic fluttering system, exploiting self-sustained oscillations to harvest electrical energy from the mechanical one, is proposed. An airfoil can freely turn around its rotational axis, bounded to two elastomers parallel to the flow: in the presence of a fluid in motion, under particular mechanical conditions, the system exhibits limit cycle oscillations characterized by noteworthy amplitude and frequency. Moving in the space of parameters every flow speed range is theoretically achievable for the purposes of electrical extraction; this work will focus on low wind speed conditions. By positioning a pair of coils at the ends of the rotational axis of the wing and fixing magnets in an alternated polarity in front of their quasi-vertical harmonic motion, an electro-magnetic coupling (EMc) is obtained: during the oscillations an alternated voltage at the ends of the coils is measured. Dielectric Elastomer Generators (DEGs), composite material formed by coupling two stretchable electrodes to a high permittivity rubber, forming a capacitor in which the capacitance changes with the stretching, replace traditional elastomers: this permits, by charging the DEGs in the maximal stretched status and discharging it in the pre-stretch status, to amplify the input voltage. DEGs cannot be an autonomous powering, because they need an external electrical energy source. Synergistically, the use of an integrated circuit designed for storing efficiently the charges from the EMc in a supercapacitor (SC), and electronics able to manage the DEGs by a ‘charge pumping’ process supplying a second SC, allows to ensure an excellent and adaptable autonomous powering. A further synergy is introduced exploiting intrinsic effects of the two electrical extraction strategies adopted in the system: EM damping due to the resistance load, and the change in stiffness of DEGs when a voltage is applied, can extend the operating speed range, increasing its global efficiency. Centimeter-sized devices exploiting EMc and DEGs, and an overview about DEGs materials are presented in this work.

Significant efforts are being devoted in order to develop efficient and reliable energy harvesters based on interactions between structures and environmental fluid flows such as wind or marine currents. In this framework, a fully-passive energy harvester of centimetric size employing an elastically bounded wing has been developed. The system exploits the coupled-mode flutter, leading in certain conditions to finite amplitude and self-sustained oscillations. Electrical output power levels up to 15[mW] have been reached by an experimental prototype within a wind range between 2 and 5 [m/s] by means of electromagnetic coupling as the conversion strategy. Focusing on the aeroelastic point of view, it is crucial to investigate how the kinematics (i.e. flapping amplitude and frequency, phase between the pitch and plunge motion DoFs) varies with the main parameters (e.g. wind velocity and wing geometry), in order to identify the optimal conditions for potential harvesting. With this goal in mind, we present and discuss the results for a representative configuration of the device (first without the extraction mechanism), exploring the behavior within the design wind range, combining wind-tunnel experiments, three-dimensional CFD simulations and the development of a quasi-steady phenomenological model. We find that both the amplitude and the frequency of the flapping motion are maximised for a certain wind velocity. Moreover, the phase between pitch and plunge changes abruptly when close to this condition. Hence, we estimate the mechanical power that the wing is able to collect and the Betz efficiency, e.g. the ratio between the latter and the power available in the flow. The mathematical model is then enriched by additional terms mimicking an electrical resistive circuit and predictions are made regarding the extracted power and global efficiency of the system, showing the presence of optimal conditions for which these quantities are maximised. Finally, we outline future challenges in the harvester development towards a realistic deployment.

We present experimental results on simultaneous surface nanostructuring and optical activation of lithium fluoride crystals by 800 eV off-normal Ar + sputtering. Our data demonstrate that the formation of periodic nanostructures is accompanied by the efficient production of stable electronic defects, optically active in the green and red parts of the visible spectra, thus providing the possibility to conceive and fabricate advanced insulating substrates.

A new energy harvester, based on the fluttering phenomenon, is presented. The device is done with a wing connected to a support via two elastomers. When a fluid in motion impinges on this elastic structure, an amount of kinetic energy is transferred to the system, inducing large amplitude oscillations if few mechanical parameters are correctly set. In order to transform the mechanical energy in electrical energy, an electromagnetic coupling is adopted. In this way, it is possible to produce several mW in a wind of 4 m/s with a centimeter-sized device. The device is conceived as an autonomous power source for distributed sensors to be used in Internet of Things.

Starting from their discovery in 1991, carbon nanotubes have attracted a great attention, thanks to their peculiar mechanical, electrical and elastic properties that could be used to realize new devices in many different fields. For nanotechnology applications it is very important to be able to control not only shape and position but also alignment and orientation of carbon nanotubes, both during the growth and after it. Here we present preliminary results obtained by depositing carbon nanotubes (CNT) solutions on ion sputtered quartz substrates. Atomic force microscopy (AFM) images allow to study both CNTs positioning on the “ripples” generated by Ar+ sputtering on the SiO2 surface and their radial deformation induced by the “rough” surface. Work is now in progress to optimize the sputtering parameters and solution treatment (purification and functionalization) in order to get single CNTs regularly arranged on a patterned surface.

The smoothening process of nanometer-scale ripples grown on the (1 1 0) surface of silver is investigated using thermal energy He atom scattering. Morphological equilibration the corrugated surface is followed in real time in the temperature range between 205 and 230 K. The mean ripple wavelength, Λ , is observed to increase during surface recovery. To take this effect into account the decay time is assumed to scale as Λ 3 . Within this approximation the ripple amplitude is observed to decay linearly with time. The activation energy of the mechanism driving surface relaxation is estimated as (0.46 ± 0.02) eV. The underlying rate limiting process, i.e. adatom detachment from the open 〈0 0 1〉 step edges is evidenced.

We investigated the contact mechanics and friction forces between atomic force microscope (AFM) probes and self-affine fractal carbon films. We studied single-asperity contacts by means of conventional nanometric conical tips whilst custom-designed micrometric flat tips were adopted to form multiple junctions between the probe and the sample. By varying the externally applied load we found that the average frictional force follows a power-law behavior in the single-asperity regime and a linear behavior in the multi-asperity regime. The friction coefficient was the same for carbon specimens having different fractality. We also acquired quasi-static load–displacement curves on micrometric scale, revealing a strong dependence of the average indentation depth on the values of fractal parameters. A comparison of experimental data with contact theories for randomly rough surfaces is provided. © 2003 Elsevier Science B.V. All rights reserved.

We present a novel experimental technique devoted to the investigation of contact mechanics on mesoscopic scale. It consists of an atomic force microscope (AFM) equipped with custom-designed probes with integrated flat micrometric tips. Samples are normally compressed by the flat tips and load–displacement curves are acquired. The latter allow to investigate the mechanical response under a multi-asperity regime not accessible by conventional AFM. Preliminary results are reported for the contact mechanics of nanostructured carbon-based films having a self-affine fractal morphology.

The morphology of the surface of single‐crystalline silicon as a function of the degree of oxidation has been investigated by the method of atomic‐force microscopy. The roughness of the surface at different stages of treatment has been evaluated with the use of topographic images. It has been found that the standard deviation characterizing the distribution of microroughnesses by height, or the roughness, increases with oxidation of the sample. A histogram of the distribution of structural surface elements has been presented. The data obtained can be employed in specifying boundary conditions to gasdynamic problems.

Recent developments of low-power microprocessors open to new applications such as wireless sensor networks (WSN) with the consequent problem of autonomous powering. For this purpose, a possible strategy is represented by energy harvesting from wind or other flows exploiting fluid–structure interactions. In this work, we present an updated picture of a flutter-based device characterized by fully passive dynamics and a simple constructive layout, where limit cycle oscillations are undergone by an elastically bounded wing. In this case, the conversion from mechanical to electrical energy is performed by means of an electromagnetic coupling between a pair of coils and magnets. A centimetric-size prototype is shown to harvest energy from low wind velocities (between 2 and 4 m s−1), reaching a power peak of 14 mW, representing a valuable amount for applications related to WSN. A mathematical description of the nonlinear dynamics is then provided by a quasi-steady phenomenological model, revealing satisfactory agreement with the experimental framework within a certain parametric range and representing a useful tool for future optimizations.

The submonolayer homoepitaxial growth on Ag(1 1 0) is studied by using a variable-temperature ultrahigh vacuum scanning tunneling microscope. The evolution of island density is studied as a function of temperature at given flux (≈0.0025 ML s −1 ) and coverage (0.16 ML) to evaluate the energy barriers and the binding energies for the in-channel and cross-channel diffusion. The experimental results are compared with kinetic Monte Carlo simulation.

The electronic structure and growth mode of C 60 molecules deposited on Ag(001) have been studied as a function of deposition parameters and annealing temperature. The measurements show that C 60 molecules are chemically bound to the Ag(001) surface even when deposited at 150 K, and the bond properties do not change significantly after annealing up to 670 K. In the resulting ordered C 60 overlayer, a mixed contrast of the buckyballs, as seen by scanning tunneling microscopy, is discussed in terms of non-equivalent orientations of the adsorbed molecules.

Surface morphology of a Cu(110) crystal, generated by ion sputtering, has been investigated by scanning tunneling microscopy. Different from recent theoretical predictions and experimental results, normal sputtering produces a well defined ripple structure whose wave vector rotates from $〈001〉$ to $〈1\overline{1}0〉$ by increasing the substrate temperature. Off-normal sputtering at low temperature (180 K) generates ripples whose orientation depends on both ion direction and surface azimuthal orientation. These results are described by a continuum equation which includes both surface curvature dependent erosion terms and diffusion terms accounting for surface anisotropy and Ehrlich-Schwoebel barriers.

The growth of Ag–O rows on a Ag(110) surface has been studied at room temperature by using a UHV-STM. The evolution of the typical (n×1) (n=8,7,…,2) structures has been analyzed as a function of O2 exposure. At the beginning, the (Ag–O) rows are randomly distributed on the surface. Increasing the exposure, many (n×1) phases coexist. The evolution of the system is due to a global rearrangement of the existing rows, which can move along the [Formula: see text] direction. A model for this mechanism is proposed.

In this Letter, we present and discuss an energy harvesting device, based on a wing elastically bounded to a fixed support. Large amplitude and periodic oscillations can be induced when this system is subject to wind, if a few parameters are carefully set. A linear stability analysis as well as two-dimensional numerical simulations confirms the existence of instability regions in the parameter space. In order to harvest energy by using this system, different methods are considered. Preliminary results obtained by an electromagnetic coupling are presented.

We report on the dependence of the sticking coefficient S of O2 on Ag(110) on oxygen coverage, for molecular and dissociative adsorption. S is found to diminish strongly with increasing coverage. The initial dependence is linear and for dissociative adsorption the slope depends on crystal temperature. The data are indicative of a coverage dependence of the adsorption barrier height, which is caused by the change of the surface work function with coverage. The analysis of the temperature variation of the dependence of S on coverage allows to extract the variation of the ratio of the pre‐exponential factors and of the height of the barriers for desorption and dissociation from the molecularly chemisorbed state.

We studied the dissociation of molecular oxygen adsorbed on Ag(110) by electron-energy-loss spectroscopy. We observe that the dissociation of the adsorbed molecules at 150 K is connected to increased surface disorder. The elastic reflectivity is recovered at 200 K independently of coverage when the added row reconstruction of the substrate sets in.

Nanopatterns on metal surfaces can be easily created by ion sputtering. However, due to the fast diffusion processes characterizing these materials, the nanostructures are often unstable at room temperature and above. This effect prevents the use of such patterned substrates in nanotechnology applications. In this letter, we present a simple oxidation process able to stabilize these features durably. The method has been tested on Cu, but its generality suggests that it can be applied to many other metals.

With a quartz crystal microbalance (QCM) we have studied the nanofriction of neon and other simple gases deposited on lead at low temperature. Special care has been paid to the investigation of some artifacts in the QCM response encountered after the initial cooldown. Extensive results obtained with QCMs that have been thermally annealed confirm that Ne films slide on Pb below 10 K. However, no extra dissipation is observed when the Pb electrode is driven either magnetically or thermally into the metallic state. This means that the electronic contribution to friction is negligible for this system, probably, because of the small polarizability of Ne atoms. More polarizable adsorbates like N${}_{2}$, Kr, and Xe are instead found to be completely pinned to Pb below 10 K.

The investigation of the initial sticking coefficent S 0 for non-dissociative adsorption of oxygen on Ag(110) along 〈 1 1 0 〉 at low temperature (83 K) is presented. The data were recorded as a function of the incident energy and of the impact angle of the molecules. S 0 is found to vary from 10 −3 to 1 in the normal energy range from 20 meV to 600 meV. The barrier is the same as with the crystal at room temperature. An evaluation of the electric dipole moment and of the charge transfer from the substrate to the adsorbed molecule is given.

With a quartz crystal microbalance technique we have studied the nanofriction of neon monolayers deposited on a lead surface at a temperature around 7 K. Unlike heavier adsorbates, Ne is found to systematically slide at such low temperatures without any evidence of pinning. The crossing of the Pb superconducting-metal transition is not accompanied by any change in dissipation, suggesting that the electronic contribution to friction is negligible for this system.

The controlled production of nanostructures endowed with well-selected shapes and reduced dimensionality represents a multidisciplinary key activity in nanotechnology. In particular, a great effort is currently oriented at the development of metal nanoparticle arrays in order to exploit the strong field-enhancement effects associated with the excitation of localized surface plasmon resonances. Here we demonstrate that ion-beam sputtering can be successfully employed to convert a polycrystalline metal film into a disconnected array of nanowires supported on a flat dielectric substrate. The nanowire arrays exhibit spectrally selective dichroic absorption due to the excitation of localized plasmon oscillations. The possibility to tailor the broadband plasmonic response has been demonstrated by finely tuning the morphological parameters of the arrays.

With a quartz-crystal microbalance technique we have studied the nanofriction of Ne monolayers at temperatures below 6.5 K and in ultrahigh-vacuum conditions deposited on metallic surfaces plated with heavy rare-gases multilayers. Covering the electrode with one layer of Kr or Xe increases the slippage of a Ne monolayer by a factor close to 3. Such a behavior has been observed with smooth lead electrodes as well as with rougher gold ones. The lubrication effect does not improve with thicker overlayers.

The self-organized formation of high aspect ratio dielectric nanostructures can be guided and sped-up recurring to a sacrificial metal film during ion beam sputtering. Following ion irradiation, the metal film evolves into a disconnected array of laterally ordered nanowires, which guide etching of the dielectric substrate. While the amplification rate of large scale features can be described simply in terms of the ratio of the sputtering yields of substrate and film, for small scale features the amplification rate depends on the interplay and lateral range of the smoothing and erosive mechanisms of the two materials.

Nano-patterned metal surfaces on dielectric substrates are become very important in nanoscale optical devices such as molecular sensors, second harmonic emitters, negative index materials. Among these, self-organised approaches are a promising alternative to the conventional lithographic or scanning lithography methods, since allow low cost patterning of large macroscopic surface in a single step event. The possibility to construct tailored artificial nanostructures by acting on simple experimental parameters opens new exciting possibilities in the nanoscale technology. In this work we explored the second harmonic emission properties in transmission of self-organized gold nanowires on dielectric substrates. Second harmonic emission from thin metal surfaces is limited by several constrains: for example the emission is forbidden at normal incidence and the emission is always polarized along the plane of incidence of the pumping light. In our samples selected morphology allows to overcome such constrains leading to high emission at normal incidence, polarization of the emission guided by the wires orientation. The angular dependence of the generation efficiency was measured on test samples whose thicknesses of the wires range from 5 nm to 40 nm. The efficiency results of a value larger with respect to samples with equivalent thickness and different morphology.

Ion beam sputtering (IBS) can induce the formation of ordered nanostructures, whose properties depend on ion flux, sputtering angle, sample temperature, sample structure, surface symmetry, etc. For the comprehension of the time evolution of the formed nanostructure morphology it is necessary to perform in situ real time studies. In this review we shall describe results obtained using x-ray based techniques at synchrotron facilities to study in situ the time and temperature evolution of metal surfaces nanopatterned by ion sputtering. Different techniques, such as x-ray reflectivity, grazing incidence small angle x-ray scattering and x-ray surface diffraction have been used, each of them providing complementary information for the determination of the surface structure and morphology. In this review, we present some experiments done in recent years to show how these methods contributed to our understanding of the IBS process on metal surfaces.

We propose a method for the separation of long DNA molecules, based on elastomeric nanochannels with tunable cross section. These nanoconfinement structures can be used to stretch DNA molecules and lower their conformational entropy. The sieving mechanism of entropic recoil, proposed by Cabodi et al. [1], will be implemented using an array of elastomeric nanocheannels. Structures of various dimensions are fabricated taking advantage of replica molding techniques, starting from Focused Ion Beam (FIB) patterned silicon substrates. Poly(dimethylsiloxane) (PDMS) and hard-PDMS [2] are used to replicate the features on the silicon mold. After plasma oxidation the nanochannels are sealed using a glass cover slip. A piezoelectric system will be integrated on the device in order to exploit the elastomeric propertis of PDMS, reversibly deform the nanochannels and tune their cross section. This system will allow a dynamic variation of the confinement conditions affecting molecules mobility inside the nanochannels.

A thin metal film can exist in a metastable state with respect to breaking into small clusters. In this paper we report on grazing incidence small-angle x-ray scattering studies carried out in situ during the annealing of thin Ni films, between 2 and 10 nm thick, deposited on an amorphous ${\text{SiO}}_{2}$ substrate. Our results show the presence of two different regimes which depend on the initial film thickness. For thicknesses less than 5 nm the annealing results in the formation of small, compact clusters on top of a residual Ni wetting layer. For thicknesses greater than 5 nm the film breaks into large, well-separated clusters and the substrate shows an uncovered clean surface.

Here we report on the development of an unconventional approach for the physical synthesis of laterally ordered self-organized arrays of metallic nanowires supported on nanostructured dielectric templates. The method, based on a combination of nanoscale patterning of the glass substrate by ion beam sputtering with shadow deposition of the metal nanoparticles, provides a viable alternative to time consuming serial nanopatterning approaches. Far-field optical characterization demonstrates that the nanowire arrays exhibit tunable anisotropic properties in the visible range due to the excitation of localized plasmon resonances.

We have experimentally determined the magnitude of the in-plane magnetocrystalline anisotropy of monatomic Fe steps on the surface of nanopatterned $\mathrm{Fe}∕\mathrm{Ag}(001)$ films. The films have been nanopatterned by the ion-sculpting technique, in which grazing-incidence ion sputtering is exploited to induce the formation of nanometer-scale surface ripples oriented along the ion-beam direction. We quantitatively assessed the ripple morphology in order to determine the density of Fe monatomic steps parallel to the ripple ridges. By correlating the morphology with the measured uniaxial magnetic anisotropy, we obtained the strength of the magnetocrystalline anisotropy of Fe monatomic steps ${\ensuremath{\kappa}}_{u}^{\mathit{mc}}=(6.5\ifmmode\pm\else\textpm\fi{}1.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\phantom{\rule{0.3em}{0ex}}\mathrm{erg}∕\mathrm{cm}$.

We report for the first time on muscovite mica surfaces nanostructured by a low-energy defocused Ar ion beam: ripple structures self-organize on macroscopic areas, with wavelength and roughness in the range 40-140 nm and 0.5-15 nm respectively, according to ions dose. In detail we address structural and chemical variations of the surface layer induced by sputtering. X-ray Photoelectron Spectroscopy (XPS) survey spectra reveal selective sputtering and Al surface enrichment whereas Atomic Force Microscopy (AFM) force-spectroscopy experiments indicate reduced charging of irradiated specimens under aqueous electrolyte solutions. Such experimental evidences contribute to clarify the chemical and physical properties of nanostructured mica samples, in view of their potential use as templates for aligned deposition of organic molecules and investigations on nanolubrication phenomena. (C) 2006 Elsevier B.V. All rights reserved.

Using a quartz crystal microbalance technique, we have measured the interfacial viscosity of nitrogen monolayers deposited on very homogeneous Pb(111) surfaces. At temperatures below 15?K, no dissipation is detected, suggesting that the N2 films are rigidly coupled to the oscillating electrode. By raising the temperature close to 20?K, we find sliding of the nitrogen film for coverages above about 0.5?nominal layers. The observed temperature dependence is in good qualitative agreement with recent calculations on the static friction of a nitrogen slab in contact with a crystalline Pb substrate.