Manufacturing & Prototyping

3D Microwave Print Head System for Melting Materials

This approach has applications in industry where solid materials need to be melted. NASA’s Jet Propulsion Laboratory, Pasadena, California There is a need to develop an efficient method for processing lunar regolith in support of future missions to colonize the Moon. A system for heating lunar regolith (“moon soil”) using microwaves for processing has been developed. It relies on an enhanced heating effect based on a large temperature gradient forming when a sample of lunar regolith under microwave radiation emits heat from its surface rapidly as the core is melting. Once the core melts, the sample absorbs microwave energy more readily. This molten lunar regolith would then exit the sample tube, and the lunar regolith could then be introduced into molds for forming a desired structure or building block.

Posted in: Manufacturing & Prototyping, Briefs

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Novel Chemistry for Deposition of MgF2 Thin Films

NASA’s Jet Propulsion Laboratory, Pasadena, California Magnesium fluoride (MgF2) thin films are useful for many different optics applications. In particular, they are useful for ultraviolet anti-reflective and protective coatings. However, in the far UV, one needs a very small, controllable amount of material to get the best optical performance. That is difficult to achieve with conventional methods. Atomic layer deposition (ALD) is an ideal UV-compatible thin-film deposition technique due to its ability to deposit uniform, pin-hole free films with angstrom-level thickness control. Therefore, it is an ideal technique to use to deposit protective thin films in the 2-nm thickness range. However, conventional ALD-MgF2 reactions are very unpredictable due to the low reactivity and volatility of the precursors.

Posted in: Manufacturing & Prototyping, Briefs, TSP

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Self-Aligning Lug for Adapting Carbon Fiber Rods to a Bolted Metallic Connection

Joint strength is controlled through precise bond line control. Ames Research Center, Moffett Field, California The enormous strength of unidirectional carbon fiber composite rods is difficult to take advantage of at their ends because of inadequate joining technology. Bolting does not work with unidirectional composites, and bonding is difficult due to stiffness mismatches between the metallic and composite connections. Ideally, a thick bond is desired so that the relatively softer adhesive can shear and distribute shear stresses instead of peaking at the ends of the bond. Thick bonds are difficult to obtain and repeatedly control with conventional methods of beads, bonding wire, shim, or tooling. Most of these methods control the minimum thickness of the bond, but do not control the maximum thickness. In addition, traditional joint types such as lap, strap, and scarf are not ideal for this application.

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Growth Method for Chalcongenide Phase-Change Nanostructures

Nanometer-scale materials can provide smaller devices than those currently available. Ames Research Center, Moffett Field, California Recently, one-dimensional (1-D) nanostructures such as nanowires and nanotubes have become the focal point of research in nanotechnology due to their fascinating properties. These properties are intrinsically associated with low dimensionality and small diameters, which may lead to unique applications in various nanoscale devices. It is generally accepted that 1-D nanostructures provide an excellent test ground for understanding the dependence of physical, electrical, thermal, optical, and mechanical properties on material dimensionality and physical size. In particular, 1-D semiconductor nanostructures, which exhibit different properties as compared with their bulk or thin film counterparts, have shown great potential in future nanoelectronics applications in data storage, computing, and sensing devices.

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Integrated PEMFC Flow Field Design for Gravity-Independent Passive Water Removal

The design solves safety as well as reliability issues. A gravity-independent PEM (proton exchange membrane) fuel cell stack has been developed that will operate at high-pressure H2 and O2 conditions with the requirement for relatively modest H2 and O2 gas circulation. Until now, in order to get higher efficiency, excess reactant gas flow was required to prevent water slug formation in gas channels, thus reducing fuel cell performance. In addition, this excess gas flow is typically supported by mechanical pumps and/or a high-pressure ejector system. All of these in a closed space environment contributed to potential safety as well as reliability issues due to the potential failure of mechanical pumps and ejectors.

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Metal-Assisted Fabrication of Biodegradable Porous Silicon Nanostructures

Silicon nanostructures are fabricated from single-crystal silicon by an electroless chemical etch process. Porous silicon nanowires are fabricated by two-step, metal-assisted electroless chemical etching of p-type or n-type silicon wafers. This method, in combination with nanolithography or nanopatterning, can be applied to fabricate porous silicon nanostructures of different shapes and sizes, such as nanorods, nanobelts, nanostrips, and nanochains. The specific resistivity of the silicon substrate, and composition of the etching solution, determine the porosity and pore size or lack thereof of the resulting nanostructures. Silicon doping, type of metal catalyst, concentrations of H2O2, and solvent all affect the formation of porous nanostructures at various resistivity ranges of silicon. A phase diagram summarizing the relation of porosification and doping, metal, concentrations of H2O2, and solvent can be generated. In this innovation, high-aspect-ratio porous silicon nanostructures, such as those previously mentioned, were fabricated from single-crystal silicon by an electroless chemical etch process. A metal film, metal nanofeatures, or metal nanoparticles were coated on the silicon substrate first, and a solution of HF and hydrogen peroxide was then used to anisotropically etch the silicon to form the porous silicon nanostructures. Up to hundreds of micron-long high-aspect-ratio porous silicon nanostructures can be fabricated, and the patterns of the cross-section of porous silicon structures can be controlled by photolithography, nanolithography, or nanoparticle-assisted patterning. The porosity is related to the resistivity range of the silicon substrate, the metal catalysts, the chemical concentration, and the additive solvent. The fabricated porous silicon nanostructure is biodegradable, and the degradation time can be controlled by surface treatments. Porous silicon nanowires can be fabricated with a two-step process. A nanostructured metal layer can be deposited on a silicon substrate by an electroless chemical deposition or electrochemical deposition. This step determines the shape of the final nanowires. Alternatively, metal nanoparticles can be spun on the silicon surface to form a metal layer, or a metal layer can be physically or chemically deposited on the silicon through a nanopatterned mask. The metal-coated silicon can be etched in a solution of HF, water, and H2O2 to produce porous silicon nanowires. Solvent can be added to the solution to modulate the features of the porous silicon nanowires. This work was done by Mauro Ferrari, Xuewu Liu, and Ciro Chappini of the University of Texas Health Science Center at Houston for Johnson Space Center. For further information, contact the JSC Innovation Partnerships Office at (281) 483-3809. In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:   The University of Texas  Health and Science Center at Houston  Office of Technology Management  7000 Fannin Street, Suite 720  Houston, TX 77030 MSC-24690-1

Posted in: Manufacturing & Prototyping, Semiconductors & ICs, Briefs

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Post-Growth, In Situ Adhesion of Carbon Nanotubes to a Substrate for Robust CNT Cathodes

This technology can be used down-hole in oil wells, and in high-temperature, high-pressure, corrosive environments in the automotive industry. The field emission electron sources using carbon nanotubes (CNTs) are being targeted for low-power vacuum microelectronic applications for harshenvironment operation (high temperature, pressure, and corrosive atmosphere). While CNTs have demonstrated excellent properties in terms of low threshold field, low-power operation, and high current densities, one problem with vacuum electronic applications is poor adhesion of CNTs to the substrate on which they are synthesized. The chemical vapor deposition (CVD) process used to grow CNTs on silicon or other metallic substrates using an iron catalyst with a thin oxide diffusion barrier layer has consistently provided reproducible growth. The CNTs are only surface- adhering in these cases, and are easily removed from the surface with the application of minor forces — typically pressures of 20 to 60 kPa. This causes catastrophic failures of CNT field emitters since the applied field could exceed the adhesion strength of CNTs to the substrate.

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