1,720,987 research outputs found
Effects of the mixing of charge transfer and molecular excitations on the resonance Raman properties of symmetric radical dimers
No full textCOUPLING 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 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 TTF2W6O19) and TTF2 Mo6 O19) whose structures contain almost isolated TTF ) 2 dimers. The RRS spectra of TTF2W6O19), measured in resonance with the CT absorption band centered at 832 nm, show 1 three phonon modes located at 55, 90, and 116 cm 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 TTF2W6O19) 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 TTF2W6O19), 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
Coupling of charge transfer transitions to low frequency phonons in quasi-one-dimensional radical ion salts: resonance Raman study of tetraethylammonium-DDQ
No full textDevelopment of a Passive Skin for Glass Building Surfaces in a Smart Electromagnetic Environment
No full textElectromagnetic metasurfaces (MTS), also referred to as Reconfigurable Intelligent Surfaces (RIS) in their dynamic form, have the potential to actively shape the wireless communication environment, particularly in 5G and 6G systems. They help overcome significant path loss issues, especially at millimeter-wave (mmWave) frequencies within the FR2 band. Our study focuses on MTS from a fabrication standpoint, highlighting the microfabrication methods employed to create a static and passive MTS prototype on a 6′′-optically transparent wafer substrate. This MTS design is intended for integration onto large glass surfaces commonly found in urban settings
Long-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
Aluminum doped Zinc Oxide coatings at Low Temperature by Atmospheric Pressure Plasma Jet
No full textPure and aluminum-doped zinc oxide thin films were produced with an atmospheric pressure plasma (APP) deposition process. Chemical, structural, morphological, electrical and optical analyses were carried out on samples coated with a plasma deposition process and with a spray pyrolysis process for comparison, respectively. The coatings were characterized by a compact layered structure of oxide islands, with a quite uniform distribution of Al in the network. Electrical measurements confirmed the active role and the dispersion of dopant in the zinc oxide network with an observed increase of conductivity even if high resistance values indicated a highly defective microstructure. In comparison to the spray pyrolysis coating the atmospheric pressure plasma coatings show a uniform substrate coverage and a higher chemical purity
Precise dot inkjet printing thought multifactorial statistical optimization of the piezoelectric actuator waveform
No full textInkJet printing is a technique that in the last decades has attracted the attention of the scientific community because it allows producing customized patterns with a variety of inks and substrates, making it suitablemethod for the production of flexible circuits. However, the optimization of this technique is still problematic due to a large number of process variables. Among them the modification of the waveform parameters of the piezoelectric actuator that allows the ejections of the ink can be effective in tuning the printing quality. This work reports a study by a statistical method, namely Design of Experiments (DOE), to optimize the inkjet printing parameters for a nanoparticle-based silver (Ag) ink. This method showed the interplay of the waveform parameters into the definition of optimal drop reproducibility and the achievement of the optimal resolution. In particular, it is shown that mixed terms of the model have a statistical significance and therefore the proposed multifactorial approach provides a benefit in the optimization with respect to the more commonly used one-factor-at-a-time models (OFAT). For the first time, empirical equations have been reported within the corresponding 95% confidence intervals. These equations can be used as a tool to directly tune the properties of the printed dot by modifying the waveform parameters. As case study, we proposed the combinations of a commercial Ag nanoparticles ink with Kapton, a commonly used substrate for flexible electronics
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Multiparametric Microwave Sensor for Environmental Measurements
No full textIn this paper, we propose the use of multiple passive microwave sensors to monitor several environmental parameters simultaneously. The system can be easily integrated into a chipless RFID system to obtain sensing and identification in a single, simple tag, which is also inexpensive, completely passive, suitable for harsh environments and easy to fabricate. We demonstrate the capability to detect humidity, NO2, ozone and ammonia. The main challenges, related to the selection of suitable sensing materials and the detection system, are also discussed, together with possible directions for future work
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