A novel approach for the fabrication and assembly of a solid oxide fuel cell system is described which enables effective scaling of the fuel delivery, manifold, and fuel cell stack components for applications in miniature and microscale energy conversion. Scaling towards miniaturization is accomplished by utilizing thin film deposition combined with novel micromachining approaches which allow manifold channels and fuel delivery system to be formed within the substrate which the thin film fuel cell stack is fabricated on, thereby circumventing the need for bulky manifold components which are not directly scalable. Results demonstrating the generation of electrical current in the temperature range of 200 - 400 degrees Celsius for a thin film solid oxide fuel cell stack fabricated on a silicon wafer will be presented.
Superconducting devices operate at speeds where coaxial copper cables can be a limiting factor. Coaxial cables can limit frequency response and impose significant thermal loading on a cyrogenic system. The high bandwidth of optical fibers and their low thermal conductivity make them good candidates for providing data into and out of superconducting circuits. In this paper, we present the results of our experience in operating photodetectors and laser diodes together with superconducting circuits in the same low temperature (4.2 K) environment. Using these photodetectors, we demonstrate the input of optical signals to an analog superconducting circuit at 6 GHz. Output from a superconducting circuit operating at 500 MHz is fed into a laser diode, and optically coupled to room temperature electronics. By combining these two techniques, we demonstrate a fully operational superconducting shift register with both input and output signals supplied by optical fiber.
This paper reports on the operation of lithium niobate electro-optic waveguide modulators at temperatures down to 15 degree(s)K. Commercial and laboratory fiber pigtailed devices have successfully been cooled without any increases in insertion loss from temperature induced stresses in device packaging. Three x-cut devices exhibited a linear increase in Vpi voltage of 8% +/- 1% when cooled from room temperature to approximately 20 degree(s)K. The broadband frequency response improved at lower temperatures. A velocity-matched experimental modulator has shown increased bandwidth when cooled to liquid nitrogen temperature.
The saturation and power scaling of terahertz radiation produced by large-aperture photoconducting antennas under high electric fields and high optical fluences are described. From the saturation behavior, a large-aperture transmitter can be designed to produce the maximum pulse energy of terahertz radiation for a given photoconductor, optical pulse energy and electric field.
Picoseccond photoconductivity has been achieved for a variety of semiconductor materials by techniques which have now become almost standard1. Enhanced scattering by the excessive amount of deep level defects which provide for picosecond recombination lifetimes significantly reduces the mobility, degrading the responsivity of the photoconductor. This paper will present a concept where improved responsivity is achievable by utilizing a graded bandgap AlxGaixAs active detecting layer grown on a high defect density GaAs layer by molecular beam epitaxy (MBE).
GaAs layers have been grown on silicon subsirates by Molecular Beam Epitaxy (MBE), from which
photoconductive circuit elements (PCE) have been fabricated. A fabrication procedure will be described which is fully
compatible with standard siicdn IC processing technology. Results will be presented demonstrating the reliance of
GaAs PCE performance on epitaxial growth conditions and subsequent processing steps. PCE response speeds ranging
from <10 to 60 P5 have been observed.
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