Materials & Coatings

Silicon Nanowire Growth at Chosen Positions and Orientations

There are numerous potential applications in highly miniaturized sensors and electronic devices. It is now possible to grow silicon nanowires at chosen positions and orientations by a method that involves a combination of standard microfabrication processes. Because their positions and orientations can be chosen with unprecedented precision, the nanowires can be utilized as integral parts of individually electronically addressable devices in dense arrays.

Posted in: Briefs, TSP, Materials, Fabrication, Nanotechnology, Semiconductors, Silicon alloys

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Detecting Airborne Mercury by Use of Palladium Chloride

These sensors can be regenerated under relatively mild conditions. Palladium chloride films have been found to be useful as alternatives to the gold films heretofore used to detect airborne elemental mercury at concentrations of the order of parts per billion (ppb). Somewhat more specifically, when suitably prepared palladium chloride films are exposed to parts-per-billion or larger concentrations of airborne mercury, their electrical resistances change by amounts large enough to be easily measurable. Because airborne mercury adversely affects health, it is desirable to be able to detect it with high sensitivity, especially in enclosed environments in which there is a risk of leakage of mercury from lamps or other equipment.

Posted in: Briefs, TSP, Materials

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Detecting Airborne Mercury by Use of Gold Nanowires

Mercury has been detected at concentrations as low as 2 ppb. Like the palladium chloride (PdCl2) films described in the immediately preceding article, gold nanowire sensors have been found to be useful for detecting airborne elemental mercury at concentrations on the order of parts per billion (ppb). Also like the PdCl2 films, gold nanowire sensors can be regenerated under conditions much milder than those necessary for regeneration of gold films that have been used as airborne-Hg sensors. The interest in nanowire sensors in general is prompted by the expectation that nanowires of a given material covering a given surface may exhibit greater sensitivity than does a film of the same material because nanowires have a greater surface area.

Posted in: Briefs, TSP, Materials, Sensors and actuators, Air pollution, Metals, Nanotechnology, Hazardous materials

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Electrolytes for Low-Temperature Operation of Li-CFₓ Cells

A report describes a study of electrolyte compositions selected as candidates for improving the low-temperature performances of primary electrochemical cells that contain lithium anodes and fluorinated carbonaceous (CFx) cathodes. This study complements the developments reported in “Additive for Low-Temperature Operation of Li-(CF)n Cells” (NPO-43579) and Li/CFx Cells Optimized for Low-Temperature Operation (NPO-43585), which appear elsewhere in this issue of NASA Tech Briefs.

Posted in: Briefs, TSP, Materials

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Polyimide-Foam/Aerogel Composites for Thermal Insulation

These composites may also afford enhanced acoustic attenuation. Composites of specific types of polymer foams and aerogel particles or blankets have been proposed to obtain thermal insulation performance superior to those of the neat polyimide foams. These composites have potential to also provide enhanced properties for vibration dampening or acoustic attenuation. The specific type of polymer foam is denoted “TEEK-H,” signifying a series, denoted “H,” within a family of polyimide foams that were developed at NASA’s Langley Research Center and are collectively denoted “TEEK” (an acronym of the inventors’ names).

Posted in: Briefs, Materials, Thermal management, Performance upgrades, Composite materials, Foams, Insulation

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Yb₁₄MnSb₁₁ as a High- Efficiency Thermoelectric Material

This material could supplant the state-of-theart material, SiGe.Yb14MnSb11 has been found to be well-suited for use as a p-type thermoelectric material in applications that involve hot-side temperatures in the approximate range of 1,200 to 1,300 K. The figure of merit that characterizes the thermal-to-electric power-conversion efficiency is greater for this material than for SiGe, which, until now, has been regarded as the state-of-the art high-temperature p-type thermoelectric material. Moreover, relative to SiGe, Yb14MnSb11 is better suited to incorporation into a segmented thermoelectric leg that includes the moderate-temperature p-type thermoelectric material CeFe4Sb12 and possibly other, lower-temperature p-type thermoelectric materials.

Posted in: Briefs, Materials

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Room-Temperature Ionic Liquids for Electrochemical Capacitors

A document discusses room-temperature ionic liquids (RTILs) used as electrolytes in carbon-nanotube-based, electrochemical, double-layer capacitors. Unlike the previous electrolyte (EtNB4 in acetonitrile), the RTIL used here does not produce cyanide upon thermal decomposition and does not have a moisture sensitivity.

Posted in: Briefs, TSP, Materials, Capacitors, Electrolytes, Nanotechnology

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