RESUMEN
The eruption of the Hunga-Tonga volcano in the South Pacific Ocean on January 15, 2022, at about 4:15 UTC, generated a violent explosion, which created atmospheric pressure disturbances in the form of Rayleigh-Lamb waves detected all over the globe. Here we discuss the observation of the Hunga-Tonga shock-wave performed at the Ny-Ålesund Research Station on the Spitsbergen island, by the detectors of the PolarquEEEst experiment and their ancillary sensors. Online pressure data as well as the results of dedicated offline analysis are presented and discussed in details. Results include wave arrival times, wave amplitude measurements and wave velocity calculation. We observed five passages of the shock wave with a significance larger than 3 [Formula: see text] and an amplitude up to 1 hPa. The average propagation velocity resulted to be (308 ± 0.6) m/s. Possible effects of the atmospheric pressure variation associated with the shock-wave multiple passages on the cosmic-ray rate at ground level are also investigated. We did not find any significant evidence of this effect.
RESUMEN
We have investigated the macroscopic and microscopic properties of large sets of Ba0.7Sr0.3TiO3 thin films including several substitution rates of manganese. Thanks to a high degree of control of the processing parameters at each stage we have been able to find a link between the dc leakage current and the low and high frequency dielectric permittivity and losses. We supplemented these macroscopic observations with in depth investigations of the defect states through x-ray photoelectron spectroscopy. We found that both the leakage current and the extrinsic dielectric parameters arise from a large density of charged point defects related to oxygen vacancies. At the outer surfaces of the films, the density of such charged defects is so high that it can raise the Fermi level to close to the conduction band. Such degradation of the films' performance can be relieved by appropriate manganese substitution for the titanium host ions. Such doping is able to move back the Fermi level to close to the center of the bandgap thus changing the conduction process from interfacial Schottky to bulk Poole Frenkel and decreasing the extrinsic losses. This beneficial effect was already inferred in ceramics and thin films but we have established a clear link between the macroscopic parameters and the microscopic defect state. This model can be transferred to many high permittivity oxides.
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This work presents a novel characterization methodology for the dielectric charging phenomenon in electrostatically driven MEMS devices using Kelvin probe force microscopy (KPFM). It has been used to study plasma-enhanced chemical vapor deposition (PECVD) silicon nitride thin films in view of application in electrostatic capacitive RF MEMS switches. The proposed technique takes the advantage of the atomic force microscope (AFM) tip to simulate charge injection through asperities, and then the induced surface potential is measured. The impact of bias amplitude, bias polarity, and bias duration employed during charge injection has been explored. The influence of various parameters on the charging/discharging processes has been investigated: dielectric film thickness, SiN(x) material deposition conditions, and under layers. Fourier transform infrared spectroscopy (FT-IR) and x-ray photoelectron spectroscopy (XPS) material characterization techniques have been used to determine the chemical bonds and compositions, respectively, of the SiN(x) films being investigated. The required samples for this technique consist only of thin dielectric films deposited over planar substrates, and no photolithography steps are required. Therefore, the proposed methodology provides a low cost and quite fast solution compared to other available characterization techniques of actual MEMS switches. Finally, the comparison between the KPFM results and the discharge current transients (DCT) measurements shows a quite good agreement.
RESUMEN
In this work, for the first time different stiction mechanisms in electrostatic micro-electromechanical systems (MEMS) switches were studied. In these devices stiction can be caused by two main mechanisms: dielectric charging and meniscus formation resulting from the adsorbed water film between the switch bridge and the dielectric layer. The effect of each mechanism and their interaction were investigated by measuring the adhesive and friction forces under different electrical stress conditions and relative humidity levels. An atomic force microscope (AFM) was used to perform force-distance and friction measurements on the nanoscale. A novel technique was proposed to measure the induced surface potential over the dielectric surface and was used to explain the obtained adhesive and friction results. The evolution of adhesive force with time was monitored in order to study the charging/discharging processes in the dielectric film. The assessment methodology is employed for application in RF-MEMS switches and could be extended to other electrostatic MEMS devices. The study provides an in-depth understanding of different stiction mechanisms, and explanation for the literature reported device level measurements for electrostatic capacitive MEMS switches.
RESUMEN
In this paper, we investigate the impact of environment gases and relative humidity on dielectric charging phenomenon in electrostatically actuated micro- and nano-electromechanical systems (MEMS and NEMS). The research is based on surface potential measurements using Kelvin probe force microscopy (KPFM). Plasma-enhanced chemical vapor deposition (PECVD) silicon nitride films were investigated in view of applications in electrostatic capacitive RF MEMS switches. Charges were injected through the atomic force microscope (AFM) tip, and the induced surface potential was measured using KPFM. Experiments have been performed in air and in nitrogen environments, both under different relative humidity levels ranging from 0.02% to 40%. The impact of oxygen gas and hydrocarbon contaminants has been studied for the first time by using different gas purifiers in both air and nitrogen lines. Voltage pulses with different bias amplitudes have been applied during the charge injection step under all investigated environmental conditions in order to investigate the effect of bias amplitude. The investigation reveals a deeper understanding of charging and discharging processes and could further lead to improved operating environment conditions in order to minimize the dielectric charging. Finally, the nanoscale KPFM results obtained in this study show a good correlation with the device level measurements for capacitive MEMS switches reported in the literature.
RESUMEN
Many social, technological, and biological interactions involve network relationships whose outcome intimately depends on the structure of the network and on the strengths of the connections. Yet, although much information is now available concerning the structure of many networks, the strengths are more difficult to measure. Here we show that, for one particular social network, notably the e-mail network, a suitable measure of the strength of the connections can be available. We also propose a simple mechanism, based on positive feedback and reciprocity, that can explain the observed behavior and that hints toward specific dynamics of formation and reinforcement of network connections. Network data from contexts different from social sciences indicate that power-law, and generally broad, distributions of the connection strength are ubiquitous, and the proposed mechanism has a wide range of applicability.
