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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Method for Fabricating Composite Structures Using Pultrusion Processing

A method for fabricating composite structures at a low-cost, moderate-to-high production rate. A first embodiment of the method includes employing a continuous press forming fabrication process. A second embodiment of the method includes employing a pultrusion process for obtaining composite structures. The methods include coating yarns with matrix material, weaving the yarn into fabric to produce a continuous fabric supply and feeding multiple layers of net-shaped fabrics having optimally oriented fibers into a debulking tool to form an undebulked preform. The continuous press forming fabrication process includes partially debulking the preform, cutting the partially debulked preform and debulking the partially debulked preform to form a netshape. An electron-beam or similar technique then cures the structure. The pultrusion fabric process includes feeding the undebulked preform into a heated die and gradually debulking the undebulked preform. The undebulked preform in the heated die changes dimension until a desired cross-sectional dimension is achieved. This process further includes obtaining a net-shaped infiltrated uncured preform, cutting the uncured preform to a desired length and electronbeam curing (or similar technique) the uncured preform. These fabrication methods produce superior structures formed at higher production rates, resulting in lower cost and high structural performance.

Farley, Gary L.↗
NASA NTRS1981

Development and fabrication of a solar cell junction processing system

The major component fabrication program was completed. Assembly and system testing of the pulsed electron beam annealing machine are described. The design program for the transport reached completion, and the detailed drawings were released for fabrication and procurement of the long lead time components.

Kiesling, R.↗
NASA NTRS2018

Nanoscale Fabrication of Microwave Detectors from Commercially-Available CVD-Grown Monolayer Graphene

Using commercially-available monolayer graphene, synthesized by means of chemical vapor deposition, microwave power sensing elements have been nanofabricated and integrated with microwave-grade test structures suitable for on-wafer probing. The graphene, situated on a thermal oxide, was first cleaned of stray contaminants in a forming gas environment briefly held at 250 degrees Celsius using a rapid thermal annealer. Immediately following this step, the graphene was passivated with a protective aluminum oxide layer (approximately S nm in thickness). Micrometer-scale Corbino disc test structures were then fabricated in direct contact with the graphene using a self-aligned process, which relies on the fact that tetramethylammonium hydroxide develops the photoresist while removing the aluminum oxide. Graphene nanoribbons (with widths as small 400 nm) were then fabricated across the Corbino disc gaps using electron-beam writing in conjunction with a negative tone resist. The same developer exposed the majority of the graphene while defining nanometer-scale lines of photoresist stacked upon aluminum oxide. These stacks served as etch-stops while the unprotected graphene was ion-milled in an oxygen plasma. Finally, the photoresist was removed leaving behind passivated graphene nanoribbons. Damage caused by the fabrication was evaluated by comparing the Raman spectra of the grapheme before and after processing.

detectors↗
NASA NTRS2008

Fabrication Capabilities Utilizing In Situ Materials

The National Aeronautics and Space Administration (NASA) has a Space Exploration Policy that lays out a plan that far exceeds the earlier Apollo goals where landing on the moon and taking those first historic steps fulfilled the mission. The policy states that we will set roots on the moon by establishing an outpost. This outpost will be used as a test bed for residing in more distant locales, such as Mars. In order to become self-sufficient, the occupants must have the capability to fabricate component parts in situ. Additionally, in situ materials must be used to minimize valuable mission upmass and to be as efficient as possible. In situ materials can be found from various sources such as raw lunar regolith whereby specific constituents can be extracted from the regolith (such as aluminum, titanium, or iron), and existing hardware already residing on the moon from past Apollo missions. The Electron Beam Melting (EBM) process lends itself well to fabricating parts, tools, and other necessary items using in situ materials and will be discussed further in this paper.

McLemore, Carole A.↗
NASA NTRS1972

Composite overwrapped metallic tanks

Work is reported for fabricating and testing the fiberglass overwrapped titanium pressure vessel for cryogenic service. Difficulties encountered in the tank liner fabrication phase involved explosive forming, vacuum annealing, chemical milling and electron beam welding. While each of these processes and the nondestructive test methods employed are normally considered to be individually reliable, the combination of poor material together with fabrication and development reversals prevented the full achievement of the desired end results. Eight tanks plus a prototype and tool proofing article were produced. Six of the vessels failed during the hydrostatic sizing operation. One of the remaining tanks was hydrostatically pressurized to burst and the other was pressurized repeatedly at 75 F from 100 psi to the operating pressure until failure occurred. As a result, it is not possible to draw firm conclusions as to the true value of the design concept due to the problems encountered in the program.

Caudill, C. L.↗
NASA NTRS2010

Low-Cost High-Precision PIAA Optics for High Contrast Imaging with Exo-Planet Coronagraphs

PIAA optics for high contrast imaging present challenges in manufacturing and testing due to their large surface departures from aspheric profiles at the aperture edges. With smaller form factors and consequent smaller surface deformations (<50 microns), fabrication of these mirrors with diamond turning followed by electron beam lithographic techniques becomes feasible. Though such a design reduces the system throughput to approx.50%, it still provides good performance down to 2 lambda/D inner working angle. With new achromatic focal plane mask designs, the system performance can be further improved. We report on the design, expected performance, fabrication challenges, and initial assessment of such novel PIAA optics.

pupil remapping↗
NASA NTRS2006

Ion Milling On Steps for Fabrication of Nanowires

Arrays of nanowires having controlled dimensions can now be fabricated on substrates, optionally as integral parts of multilayer structures, by means of a cost-effective, high-yield process based on ion milling on steps. Nanowires made, variously, of semiconductors or metals are needed as components of sensors and high-density electronic circuits. Unlike prior processes used to fabricate nanowires, the present process does not involve electron-beam lithography, manipulation of nanoscopic objects by use of an atomic-force microscope, or any other technique that is inherently unsuitable for scaling up to mass production. In comparison with the prior processes, this process is rapid and simple. Wires having widths as small as a few tens of nanometers and lengths as long as millimeters have been fabricated by use of this process. The figure depicts a workpiece at different stages of the process. A silicon dioxide substrate is coated with a photoresist or poly(methyl methacrylate) [PMMA] to a thickness of as much as 500 nm. The photoresist or PMMA is patterned to form edges where wires are to be formed. A metal - either Pt or Ti - is deposited, by sputtering, to a thickness of as much as 200 nm. By ion milling at normal incidence, the thickness of the metal deposit is reduced until the only metal that remains is in the form of wall-like nanowires along the edges of the photoresist or PMMA. Finally, an oxygen plasma is used to remove the photoresist or PMMA, leaving only the nanowires on the substrate.

Yun, Minhee↗
NASA NTRS1984

Planar techniques for fabricating X-ray diffraction gratings and zone plates

The state of current planar techniques in the fabrication of Fresnel zone plates and diffraction gratings is reviewed. Among the fabrication techniques described are multilayer resist techniques; scanning electron beam lithography; and holographic lithography. Consideration is also given to: X-ray lithography; ion beam lithography; and electroplating. SEM photographs of the undercut profiles obtained in a type AZ 135OB photoresistor by holographic lithography are provided.

Smith, H. I.↗
NASA NTRS1994

Silicon Technologies Adjust to RF Applications

Silicon (Si), although not traditionally the material of choice for RF and microwave applications, has become a serious challenger to other semiconductor technologies for high-frequency applications. Fine-line electron- beam and photolithographic techniques are now capable of fabricating silicon gate sizes as small as 0.1 micron while commonly-available high-resistivity silicon wafers support low-loss microwave transmission lines. These advances, coupled with the recent development of silicon-germanium (SiGe), arm silicon integrated circuits (ICs) with the speed required for increasingly higher-frequency applications.

Reinecke Taub, Susan↗
NASA NTRS1972

Thermal Skin fabrication technology

Advanced fabrication techniques applicable to Thermal Skin structures were investigated, including: (1) chemical machining; (2) braze bonding; (3) diffusion bonding; and (4) electron beam welding. Materials investigated were nickel and nickel alloys. Sample Thermal Skin panels were manufactured using the advanced fabrication techniques studied and were structurally tested. Results of the program included: (1) development of improved chemical machining processes for nickel and several nickel alloys; (2) identification of design geometry limits; (3) identification of diffusion bonding requirements; (4) development of a unique diffusion bonding tool; (5) identification of electron beam welding limits; and (6) identification of structural properties of Thermal Skin material.

Milam, T. B.↗
NASA NTRS2001

Composite Structures and Materials Research at NASA Langley Research Center

A summary of recent composite structures and materials research at NASA Langley Research Center is presented. Fabrication research to develop low-cost automated robotic fabrication procedures for thermosetting and thermoplastic composite materials, and low-cost liquid molding processes for preformed textile materials is described. Robotic fabrication procedures discussed include ply-by-ply, cure-on-the-fly heated placement head and out-of-autoclave electron-beam cure methods for tow and tape thermosetting and thermoplastic materials. Liquid molding fabrication processes described include Resin Film Infusion (RFI) Resin Transfer Molding (RTM) and Vacuum-Assisted Resin Transfer Molding (VARTM). Results for a full-scale composite wing box are summarized to identify the performance of materials and structures fabricated with these low-cost fabrication methods.

Starnes, James H., Jr.↗
NASA NTRS1994

A combined electron beam/optical lithography process step for the fabrication of sub-half-micron-gate-length MMIC chips

Advanced radar and communication systems rely heavily on state-of-the-art microelectronics. Systems such as the phased-array radar require many transmit/receive (T/R) modules which are made up of many millimeter wave - microwave integrated circuits (MMIC's). The heart of a MMIC chip is the Gallium Arsenide (GaAs) field-effect transistor (FET). The transistor gate length is the critical feature that determines the operating frequency of the radar system. A smaller gate length will typically result in a higher frequency. In order to make a phased array radar system economically feasible, manufacturers must be capable of producing very large quantities of small-gate-length MMIC chips at a relatively low cost per chip. This requires the processing of a large number of wafers with a large number of chips per wafer, minimum processing time, and a very high chip yield. One of the bottlenecks in the fabrication of MIMIC chips is the transistor gate definition. The definition of sub-half-micron gates for GaAs-based field-effect transistors is generally performed by direct-write electron beam lithography (EBL). Because of the throughput limitations of EBL, the gate-layer fabrication is conventionally divided into two lithographic processes where EBL is used to generate the gate fingers and optical lithography is used to generate the large-area gate pads and interconnects. As a result, two complete sequences of resist application, exposure, development, metallization and lift-off are required for the entire gate structure. We have baselined a hybrid process, referred to as EBOL (electron beam/optical lithography), in which a single application of a multi-level resist is used for both exposures. The entire gate structure, (gate fingers, interconnects and pads), is then formed with a single metallization and lift-off process. The EBOL process thus retains the advantages of the high-resolution E-beam lithography and the high throughput of optical lithography while essentially eliminating an entire lithography/metallization/lift-off process sequence. This technique has been proven to be reliable for both trapezoidal and mushroom gates and has been successfully applied to metal-semiconductor and high-electron-mobility field-effect transistor (MESFET and HEMT) wafers containing devices with gate lengths down to 0.10 micron and 75 x 75 micron gate pads. The yields and throughput of these wafers have been very high with no loss in device performance. We will discuss the entire EBOL process technology including the multilayer resist structure, exposure conditions, process sensitivities, metal edge definition, device results, comparison to the standard gate-layer process, and its suitability for manufacturing.

Sewell, James S.↗
NASA NTRS1981

Three-axis electron-beam test facility

An electron beam test facility, which consists of a precision multidimensional manipulator built into an ultra-high-vacuum bell jar, was designed, fabricated, and operated at Lewis Research Center. The position within the bell jar of a Faraday cup which samples current in the electron beam under test, is controlled by the manipulator. Three orthogonal axes of motion are controlled by stepping motors driven by digital indexers, and the positions are displayed on electronic totalizers. In the transverse directions, the limits of travel are approximately + or - 2.5 cm from the center with a precision of 2.54 micron (0.0001 in.); in the axial direction, approximately 15.0 cm of travel are permitted with an accuracy of 12.7 micron (0.0005 in.). In addition, two manually operated motions are provided, the pitch and yaw of the Faraday cup with respect to the electron beam can be adjusted to within a few degrees. The current is sensed by pulse transformers and the data are processed by a dual channel box car averager with a digital output. The beam tester can be operated manually or it can be programmed for automated operation. In the automated mode, the beam tester is controlled by a microcomputer (installed at the test site) which communicates with a minicomputer at the central computing facility. The data are recorded and later processed by computer to obtain the desired graphical presentations.

Dayton, J. A., Jr.↗
NASA NTRS1981

Development and fabrication of a solar cell junction processing system

Modifications to the ground plane, to insure a good electrical return path during the pulse discharge, were made using a ring of beryllium copper finger stock attached to the underside of the aluminum ground plate. Experiments on annealing of wafers with ion implantation damage continued. The entire surface of 100 mm diameter wafers were annealed by one pulse for the standard implant (10 keV, phosphorus, 2x10 to the 15th power ions/sq cm). While samples are being fabricated into solar cells for electrical characterization, work is continuing on improvement of the electron beam uniformity and the optimization of the diode parameters. The engineering design was completed and the manufacturing detail drawings were released for fabrication. Assembly of the subcomponents for the exit and entrance locks is almost complete. These components include the cassettes, the indexing mechanisms, main doors, and wafer carrier transfer modules. The 'Y' track and three phase transition track sections are under final assembly and test.

Giesling, R.↗
NASA NTRS1975

Advances in superconducting quantum electronic microcircuit fabrication

Standard microelectronic fabrication techniques have been utilized to produce batch quantities of superconducting quantum electronic devices and circuits. The overall goal is a fabrication technology yielding circuits that are rugged and stable and capable of being fabricated controllably and reproducibly in sizeable quantities. Our progress toward this goal is presented, with primary emphasis on the most recent work, which includes the use of electron-beam lithography and techniques of hybrid microelectronics. Several prototype microcircuits have been successfully fabricated. These microcircuits are formed in a thin-film parent material consisting of layers of superconducting and normal metals, and use proximity-effect structures as the active circuit elements.

Kirschman, R. K.↗
NASA NTRS1991

Effect of thermal exposure, forming, and welding on high-temperature, dispersion-strengthened aluminum alloy: Al-8Fe-1V-2Si

The feasibility of applying conventional hot forming and welding methods to high temperature aluminum alloy, Al-8Fe-1V-2Si (FVS812), for structural applications and the effect of thermal exposure on mechanical properties were determined. FVS812 (AA8009) sheet exhibited good hot forming and resistance welding characteristics. It was brake formed to 90 deg bends (0.5T bend radius) at temperatures greater than or equal to 390 C (730 F), indicating the feasibility of fabricating basic shapes, such as angles and zees. Hot forming of simple contoured-flanged parts was demonstrated. Resistance spot welds with good static and fatigue strength at room and elevated temperatures were readily produced. Extended vacuum degassing during billet fabrication reduced porosity in fusion and resistance welds. However, electron beam welding was not possible because of extreme degassing during welding, and gas-tungsten-arc welds were not acceptable because of severely degraded mechanical properties. The FVS812 alloy exhibited excellent high temperature strength stability after thermal exposures up to 315 C (600 F) for 1000 h. Extended billet degassing appeared to generally improve tensile ductility, fatigue strength, and notch toughness. But the effects of billet degassing and thermal exposure on properties need to be further clarified. The manufacture of zee-stiffened, riveted, and resistance-spot-welded compression panels was demonstrated.

Kennedy, J. R.↗
NASA NTRS1992

Radiation sensitivity of quartz crystal oscillators experiment for the Long Duration Exposure Facility (LDEF)

Factors determining the radiation sensitivity of quartz crystal oscillators were studied on NASA's LDEF. Quartz materials were examined in the transmission electron microscope (TEM) and classified as to their sensitivity to radiation damage by establishing the rate of damage caused by the electron beam in the microscope. Two types of materials, i.e., swept premium Q quartz and natural quartz were chosen because clear differences were observed in their response to the electron beam in the TEM studies. Quartz resonators were then fabricated from them, tested for frequency stability over a greater than 6 mo. period and flown on the LDEF satellite. After retrieval (more than 7 yrs in space) the stability of the resonators was again determined. All of the space exposed resonators fabricated with swept premium Q material exhibited a frequency shift above that of the control resonators: none of the resonators fabricated from the natural quartz materials exhibited such a shift. The significant differences observed between the two types of materials in both the ground-based TEM studies and the space radiation induced frequency changes suggest that there may be a correlation between the two observations.

Ahearn, J. S.↗