84 research outputs found
Porous silicon microcavities as optical chemical sensors
No full textThe optical properties of porous silicon microcavities are strongly dependent on the environment. For highly luminescent samples, both the luminescence intensity and the peak position are affected by organic substances, giving the possibility to obtain dual-parameter optical sensors. While the peak position depends on the organic compound refractive index, luminescence intensity depends on its low-frequency dielectric constant. This allows the discrimination between different organic substances. This sensor is particularly interesting for solvents with low dielectric constant, where the response of electrical sensors is very weak
Coupling of electrons to intermolecular phonons in molecular charge transfer dimers: a resonance Raman study
No full textWe report resonance Raman scattering (RRS) spectra and Raman excitation profiles (REP) of a system containing π dimers of identical molecular radical ions measured with laser excitation in resonance with the charge transfer (CT) transition. A Peierls–Hubbard (PH) Hamiltonian has been used to model the investigated system and to calculate its optical and RRS properties. Results are reported for two polyoxometallate salts of tetrathiafulvalene (TTF), namely (TTF)2(W6O19) and (TTF)2(Mo6O19) whose structures contain almost isolated (TTF+)2 dimers. The RRS spectra of (TTF)2(W6O19), measured in resonance with the CT absorption band centered at 832 nm, show three phonon modes located at 55, 90, and 116 cm−1 which are strongly resonance enhanced. These modes have been associated to the out‐of‐phase combinations of the translational motions of the two molecules composing the dimer. Such modes are effective in modulating the intradimer transfer integral, thus providing an efficient mechanism for coupling with the electronic system and for enhancement of the scattering intensity at resonance with the CT transition. The REP for the three strongly coupled modes of (TTF)2(W6O19) have been measured with laser excitation wavelengths ranging from 740 to 930 nm. Quantitative analysis of the REP data has been performed based on a perturbative solution of the PH model to second order in the electron‐molecular‐vibration (EMV) and electron‐intermolecular‐phonon (EIP) interactions. The CT absorption profile and the REP’s have been calculated using a time correlator technique and the model parameters have been optimized in order to fit the experimental REP data. Infrared vibronic absorptions of (TTF)2(W6O19), originated by the EMV coupling, have been measured and independent information on the electronic parameters of the PH model have been derived. This has made the choice of the fitting parameters used for the REP calculations rather unambiguous and has allowed us to obtain, for the first time, reliable experimental estimates of the EIP coupling constants
Effects of the mixing of charge transfer and molecular excitations on the resonance Raman properties of symmetric radical dimers
No full textLong-term lifetime prediction for RF-MEMS switches
No full textTime to failure estimations of RF-MEMS (radio-frequency microelectromechanical system) switches under prolonged actuation is particularly interesting for satellite applications, where the devices have to retain their functionality for years. At present, a well-assessed methodology to predict RF-MEMS lifetime is still lacking, probably because, in the case of MEMS, failure may originate from either electrical or mechanical sources. Temperature is the most common failure accelerating factor, but it accelerates all failure mechanisms at the same time. In this paper, we take into account the effect of temperature on three different failure mechanisms, namely charge trapping, mechanical creep, and contact degradation. Short-term and long-term continuous actuation measurements for an ohmic clamped–clamped switch are reported and analyzed, showing that failure is strongly accelerated by temperature in the
range of temperatures investigated. The maximum temperature exploitable is, however, quite low, around 75 °C, because of structural modifications due to internal stress variations and buckling. Based on the experimental data, a prediction model is presented and discussed.
While failure at 55 °C has been measured after a few days, the extrapolated lifetimes at 25 °C are around five years. Contact deterioration has been found to be the reason of failure, but the switch fails only when the spring constant has been sufficiently lowered by mechanical creep
Nitrogen influence on the photoluminescence properties of silicon nanocrystals
No full textWe have performed photoluminescence analysis of silicon rich oxide (SRO) and silicon rich oxynitride (SRON) samples deposited by plasma enhanced chemical vapor deposition (PECVD) and thermally annealed to cause the formation of silicon nanocrystals (Si-nc). Our purpose was to investigate the influence of nitrogen embedded into the oxide matrix on the photoluminescence properties of Si-nc. We found a large incorporation of silicon and a decrease of its diffusivity when the oxide is nitrogen rich. As a consequence the rate of crystallization for Si aggregates is slowed down when nitrogen is present in the oxide matrix
A continuous flow microelectrophoretic module for protein separation
No full textIn the framework of our research work, we are developing a microfluidic system that can be used as a pre-treatment device for the sample preparation in analytical microsystems, as biosensors, for instance. Sample pre-treatment phase is usually envisaged before chemical and biological analysis. For example, if we want to perform contaminants detection in a complex matrix as milk, we must consider that the sample consists in a solution of butterfat globules and water with dissolved carbohydrates and protein complexes. If we want a bio-sensor to perform a label free detection of some target-contaminants in milk, interferents in the matrix must be removed. Proteins are an important part of these interferents, and their concentration needs to be reduced, in order to avoid fouling and consequently the inhibition of the sensor, or false positive results in the analysis. We have designed and fabricated a SPLITT flow thin fractionation device for protein separation that is now under testing with a BSA solution
Electrochemically oxidised porous silicon microcavities
No full textAgeing effects in porous silicon microcavities result in emission enhancement and resonance peak blueshift. In this paper we propose electrochemical oxidation as a method to control these effects. Properties of porous silicon microcavities obtained after anodic oxidation are compared to those of microcavities aged in air for several months. This evidences that emission enhancement and resonance peak shift are two different phenomena and the effects of anodic and naturally oxidation are not the same. A significant suppression of peak shift due to ageing is achieved, and the extent of this stabilisation increases with the oxidation time, but for long oxidation times the microcavity properties are degraded
Continuous binary protein separation in a microfabricated electrical split-flow thin fractionation (SPLITT) device
No full textHigh-Resolution Fabrication Procedure for an Optically-Transparent Modular Smart Electromagnetic Skin
No full textA Smart ElectroMagnetic Environment (SEME) is enabled by introducing smart electromagnetic (EM) skins, or metasurfaces, with the final aim of manipulating the reflection and/or transmission properties to improve the wireless interconnectivity in non-line-of-sight areas. We focus on manufacturing of passive and static smart EM skins for wavefront manipulation, to enable optically transparent and conformable solutions. The most significant technological innovation of this contribution is the creation of a metasurface by means of micro-manufactured modules on a transparent medium, which allows us to reach high-resolution standards and to work on unconventional substrates. Indeed, micro-fabrication of smart skins offers many advantages, e.g. choice of materials as in this case (i.e. transparent), miniaturization and, in turn, operation at higher frequencies. This constitutes a valuable counterpart to most literature works, which exploit “standard” technologies and substrates, such as classic PCB, severely limiting the manufacturing degrees of freedom (DoF) and material variety
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