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Results for “Capacitance”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Low-temperature capacitive sensor based on perovskite oxides

Energy, environmental and social issues drive towards the green political economy and the development of advanced technologies, promoting renewable energy sources, improving energy conversion efficiency and reducing exhaust gas emissions. The development of sustainable technologies requires strategic research in the area of gas sensors for monitoring air quality, controlling gas emissions and optimizing combustion processes. Solid state sensors are the most attractive one because of their simplicity in function, small size and low cost. The aim of this work is to synthetize and characterize strontium titanate and test its sensing performance. The prepared sensor device shows significant sensitivity and response rate at room-temperature. However, because of the low recovery rate, the regeneration of the sensor has to be made at high temperature for promoting the decomposition of the carbonates formed on the perovkite surface.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Capacitive coupling in hybrid graphene/GaAs nanostructures

Coupled hybrid nanostructures are demonstrated using the combination of lithographically patterned graphene on top of a two-dimensional electron gas (2DEG) buried in a GaAs/AlGaAs heterostructure. The graphene forms Schottky barriers at the surface of the heterostructure and therefore allows tuning the electronic density of the 2DEG. Conversely, the 2DEG potential can tune the graphene Fermi energy. Graphene-defined quantum point contacts in the 2DEG show half-plateaus of quantized conductance in finite bias spectroscopy and display the 0.7 anomaly for a large range of densities in the constriction, testifying to their good electronic properties. Finally, we demonstrate that the GaAs nanostructure can detect charges in the vicinity of the heterostructure's surface. This confirms the strong coupling of the hybrid device: localized states in the graphene ribbon could, in principle, be probed by the underlying confined channel. The present hybrid graphene/GaAs nanostructures are promising for the investigation of strong interactions and coherent coupling between the two fundamentally different materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Electron heating mode transition induced by mixing radio frequency and ultrahigh frequency dual frequency powers in capacitive discharges

Electron heating mode transitions induced by mixing the low- and high-frequency power in dual-frequency nitrogen discharges at 400 mTorr pressure are presented. As the low-frequency (13.56 MHz) power decreases and high-frequency (320 MHz) power increases for the fixed power of 200 W, there is a transition of electron energy distribution function (EEDF) from Druyvesteyn to bi-Maxwellian type characterized by a distinguished warm electron population. It is shown that this EEDF evolution is attributed to the transition from collisional to collisionless stochastic heating of the low-energy electrons.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Publisher's Note: “Differential voltage amplification from ferroelectric negative capacitance” [Appl. Phys. Lett. 111, 253501 (2017)]

This article was originally published online on 18 December 2017. Due to a production error, the initially-published version contained several typographical errors not corrected during proof revisions, none of which affected the substance of the article. AIP Publishing apologizes for this error. All online versions of the article were corrected on 21 December 2017, and it now appears correctly in print.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2020

Similarity of capacitive radio-frequency discharges in nonlocal regimes

Similarity transformations are essential for correlating discharges at different scales, which are mostly utilized with local field or local energy approximations. In this work, we report the fully kinetic results from particle-in-cell/Monte Carlo collision simulations that unambiguously demonstrate the similarity of radio frequency (rf) discharges in nonlocal regimes where the electron energy relaxation length is much larger than the gap dimension. It is found that at a constant rf voltage amplitude, discharges will be similar if the gas pressure, inverse of gap distance, and rf driving frequency are all changed by the same scaling factor. The scaling relations of fundamental parameters are illustrated for rf discharges in the alpha-mode with secondary electron emission ignored, and the temporal electron kinetics are shown to have invariance in similar discharges. The results explicitly validate the scaling laws in nonlocal kinetic regimes, indicating promising application potentials of the similarity transformations across a wide range of kinetic regimes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Ionization by Drift and Ambipolar Electric Fields in Electronegative Capacitive Radio Frequency Plasmas

Unlike {alpha}- and {gamma}-mode operation, electrons accelerated by strong drift and ambipolar electric fields in the plasma bulk and at the sheath edges are found to dominate the ionization in strongly electronegative discharges. These fields are caused by a low bulk conductivity and local maxima of the electron density at the sheath edges, respectively. This drift-ambipolar mode is investigated by kinetic particle simulations, experimental phase-resolved optical emission spectroscopy, and an analytical model in CF{sub 4}. Mode transitions induced by voltage and pressure variations are studied.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗