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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Spatial filter based light-sheet laser interference technique for three-dimensional nanolithography

We propose a laser interference technique for the fabrication of 3D nano-structures. This is possible with the introduction of specialized spatial filter in a 2π cylindrical lens system (consists of two opposing cylindrical lens sharing a common geometrical focus). The spatial filter at the back-aperture of a cylindrical lens gives rise to multiple light-sheet patterns. Two such interfering counter-propagating light-sheet pattern result in periodic 3D nano-pillar structure. This technique overcomes the existing slow point-by-point scanning, and has the ability to pattern selectively over a large volume. The proposed technique allows large-scale fabrication of periodic structures. Computational study shows a field-of-view (patterning volume) of approximately 12.2 mm{sup 3} with the pillar-size of 80 nm and inter-pillar separation of 180 nm. Applications are in nano-waveguides, 3D nano-electronics, photonic crystals, and optical microscopy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Effect of dislocation pile-up on size-dependent yield strength in finite single-crystal micro-samples

Recent research has explained that the steeply increasing yield strength in metals depends on decreasing sample size. In this work, we derive a statistical physical model of the yield strength of finite single-crystal micro-pillars that depends on single-ended dislocation pile-up inside the micro-pillars. We show that this size effect can be explained almost completely by considering the stochastic lengths of the dislocation source and the dislocation pile-up length in the single-crystal micro-pillars. The Hall–Petch-type relation holds even in a microscale single-crystal, which is characterized by its dislocation source lengths. Our quantitative conclusions suggest that the number of dislocation sources and pile-ups are significant factors for the size effect. They also indicate that starvation of dislocation sources is another reason for the size effect. Moreover, we investigated the explicit relationship between the stacking fault energy and the dislocation “pile-up” effect inside the sample: materials with low stacking fault energy exhibit an obvious dislocation pile-up effect. Our proposed physical model predicts a sample strength that agrees well with experimental data, and our model can give a more precise prediction than the current single arm source model, especially for materials with low stacking fault energy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Analysis of hydrogen plasma in a microwave plasma chemical vapor deposition reactor

The aim of this work is to build a numerical model of hydrogen plasma inside a microwave plasma chemical vapor deposition system. This model will help in understanding and optimizing the conditions for the growth of carbon nanostructures. A 2D axisymmetric model of the system is implemented using the finite element high frequency Maxwell solver and the heat transfer solver in COMSOL Multiphysics. The system is modeled to study variation in parameters with reactor geometry, microwave power, and gas pressure. The results are compared with experimental measurements from the Q-branch of the H{sub 2} Fulcher band of hydrogen using an optical emission spectroscopy technique. The parameter γ in Füner's model is calibrated to match experimental observations at a power of 500 W and 30 Torr. Good agreement is found between the modeling and experimental results for a wide range of powers and pressures. The gas temperature exhibits a weak dependence on power and a strong dependence on gas pressure. The inclusion of a vertical dielectric pillar that concentrates the plasma increases the maximum electron temperature by 70%, the maximum gas temperature by 50%, and the maximum electron number density by 70% when compared to conditions without the pillar at 500 W and 30 Torr. Experimental observations also indicate intensified plasma with the inclusion of a pillar.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Development of plasma bolometers using fiber-optic temperature sensors

Measurements of radiated power in magnetically confined plasmas are important for exhaust studies in present experiments and expected to be a critical diagnostic for future fusion reactors. Resistive bolometer sensors have long been utilized in tokamaks and helical devices but suffer from electromagnetic interference (EMI). Results are shown from initial testing of a new bolometer concept based on fiber-optic temperature sensor technology. A small, 80 μm diameter, 200 μm long silicon pillar attached to the end of a single mode fiber-optic cable acts as a Fabry–Pérot cavity when broadband light, λ{sub o} ∼ 1550 nm, is transmitted along the fiber. Changes in temperature alter the optical path length of the cavity primarily through the thermo-optic effect, resulting in a shift of fringes reflected from the pillar detected using an I-MON 512 OEM spectrometer. While initially designed for use in liquids, this sensor has ideal properties for use as a plasma bolometer: a time constant, in air, of ∼150 ms, strong absorption in the spectral range of plasma emission, immunity to local EMI, and the ability to measure changes in temperature remotely. Its compact design offers unique opportunities for integration into the vacuum environment in places unsuitable for a resistive bolometer. Using a variable focus 5 mW, 405 nm, modulating laser, the signal to noise ratio versus power density of various bolometer technologies are directly compared, estimating the noise equivalent power density (NEPD). Present tests show the fiber-optic bolometer to have NEPD of 5-10 W/m{sup 2} when compared to those of the resistive bolometer which can achieve <0.5 W/m{sup 2} in the laboratory, but this can degrade to 1-2 W/m{sup 2} or worse when installed on a tokamak. Concepts are discussed to improve the signal to noise ratio of this new fiber-optic bolometer by reducing the pillar height and adding thin metallic coatings, along with improving the spectral resolution of the interrogator.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Design and fabrication of a high-density multilayer metal-insulator-metal capacitor based on selective etching

This paper presents a novel and cost-effective method for fabricating high-density multilayer metal-insulator-metal (MIM) integrated capacitors. To eliminate the usage of numerous photolithography steps when parallel stacking multiple capacitors layers, a unique process has been developed based on depositing the MIM layers onto a substrate with two protruding pillars, polishing down the pillars to expose the multilayer cross sections and then selectively etching the metal layers on each pillar to form the alternating capacitor plate electrodes. For demonstration purpose, only capacitors with two dielectric layers were fabricated, and the measurement results were verified by a compact analytical model together with finite element simulations. With 200 nm thick silicon nitride/oxide dielectric layers, a capacitance density of 0.6 fF mu m(-2) was achieved, which can be easily increased by scaling down the layer thicknesses and/or stacking more layers. A low equivalent series resistance (ESR) of 300-700 m Omega was measured, and the self-resonance frequency was above measurement limits (> 100 MHz). Further design optimization shows that the ESR can be reduced to below 80 m Omega, while the operation frequency extended to above 2.6 GHz.

Tseng, VFG↗
DOE OSTI2017

Kinetics of Domain Switching by Mechanical and Electrical Stimulation in Relaxor-Based Ferroelectrics

Ferroelectric materials have been extensively explored for applications in high-density nonvolatile memory devices because of their ferroelectric-ferroelastic domain-switching behavior under electric loading or mechanical stress. However, the existence of ferroelectric and ferroelastic backswitching would cause significant data loss, which affects the reliability of data storage. In this work, we apply in situ transmission electron microscopy and phase-field modeling to explore the unique ferroelastic domain-switching kinetics and the origin of this in relaxor-based Pb(Mg 1/3 Nb 2/3 )O 3 -33%PbTiO 3 single-crystal pillars under electrical and mechanical stimulations. Results showed that the electric-mechanical hysteresis loop shifted for relaxor-based single-crystal pillars because of the low energy levels of domains in the material and the constraint on the pillars, resulting in various mechanically reversible and irreversible domain-switching states. The phenomenon can potentially be used for advanced bit writing and reading in nonvolatile memories, which effectively overcomes the backswitching problem and broadens the types of ferroelectric materials for nonvolatile memory applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

1 kV Self-Aligned Vertical GaN Superjunction Diode

This work demonstrates vertical GaN superjunction (SJ) diodes fabricated via a novel self-aligned process. The SJ comprises n-GaN pillars wrapped by the charge-balanced p-type nickel oxide (NiO). After the NiO sputtering around GaN pillars, the self-aligned process exposes the top pillar surfaces without the need for additional lithography or a patterned NiO etching which is usually difficult. The GaN SJ diode shows a breakdown voltage (B V) of 1100 V, a specific on-resistance (R ON ) of 0.4 mΩ· cm2, and a SJ drift-region resistance ( R dr ) of 0.13 mΩ· cm2. Further, the device also exhibits good thermal stability with B V retained over 1 kV and R ON dropped to 0.3 mΩ· cm2 at 125°C. The trade-off between B V and R dr is superior to the 1D GaN limit. These results show the promise of vertical GaN SJ power devices. The self-aligned process is applicable for fabricating the heterogeneous SJ based on various wide- and ultra-wide bandgap semiconductors.

42 ENGINEERING↗
DOE OSTI2024

Field-Emission Properties of Vertically Aligned Carbon Nanotube Cathodes of Varying Geometries

This work characterizes the bulk emission properties of carbon nanotube (CNT) forest cathodes fabricated with various geometries. Geometries explored include dense nanotube forests of varying height grown on 5×5 mm silicon (Si) substrates and discrete, patterned CNT pillars fabricated using UV photolithography. Dense forests heights ranged from 526 μ m to 1.41 mm, with packing fraction for dense forest calculated to be 4e10 nanotubes/cm2 based on an average nanotube separation distance of 100 nm for fixed growth dense forests. Patterned sample micro pillar heights ranged from 47 to 393 μ m with pillar widths on tested samples ranging from 250 to 270 μ m . Properties explored include emission current, turn-on field, and emission current performance over time. A parallel plate electron beam diode with a 100- μ m A-K gap and an automated test apparatus were developed to provide a configurable experiment that provides accurate and repeatable measurements for dc, dc sweep, and timed performance testing. Operating voltages for the voltage sweeps spanned from 0 to −350 V. Furthermore, testing has shown evidence of a hysteresis effect on the emission current tied to the applied field history as well as shifting of the turn-on field magnitude throughout the testing period, suggesting a conditioning effect during use. Three separate emission regions in the I–V curves during sweep testing have also been observed. In the geometric study, dense forests and patterned samples were sweep tested up to a peak applied voltage of −250 V, with the taller samples generally performing better. Currents produced in the geometric study from the dense forest emitters ranged from 36.8 to 572.34 μ A , with current densities ranging from 15 to 2.29 mA/cm2. Currents produced from the patterned micropillar emitters ranged from 39.4 to 317.51 μ A , with current densities ranging from 67 to 3 mA/cm2. DC time testing s...

36 MATERIALS SCIENCE↗
DOE OSTI2021

Optimization of three-dimensional metamaterials for terahertz energy harvesting

This work focuses on finite element modeling (FEM) of a three-dimensional metamaterial used as an absorber for terahertz energy harvesting. The metamaterial consists of patterned pillars of an SU-8 dielectric photoresist coupled to a copper metal overlayer. Here, our study shows that the electromagnetic performance of the metamaterial is dependent on the following characteristic design parameters of the SU-8 dielectric: pillar height, bottom side length, and spacing between adjacent pillars. Using FEM, the metamaterial geometry is successfully optimized and the surface plasmon can be tuned to a peak frequency of 1.2 THz and a maximum terahertz absorption amplitude of 30%.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Manipulation and statistical analysis of the fluid flow of polymer semiconductor solutions during meniscus-guided coating

Recent work in structure–processing relationships of polymer semiconductors have demonstrated the versatility and control of thin-film microstructure offered by meniscusguided coating (MGC) techniques. Here, we analyze the qualitative and quantitative aspects of solution shearing, a model MGC method, using coating blades augmented with arrays of pillars. The pillars induce local regions of high strain rates—both shear and extensional—not otherwise possible with unmodified blades, and we use fluid mechanical simulations to model and study a variety of pillar spacings and densities. We then perform a statistical analysis of 130 simulation variables to find correlations with three dependent variables of interest: thin-film degree of crystallinity and transistor field-effect mobilities for charge-transport parallel (Μ para ) and perpendicular (Μ perp ) to the coating direction. Our study suggests that simple fluid mechanical models can reproduce substantive correlations between the induced fluid flow and important performance metrics, providing a methodology for optimizing blade design.

36 MATERIALS SCIENCE↗
DOE OSTI2021

University of Missouri Research Reactor LEU Fuel Element Flow Test Conceptual Design—Hydraulic Reactor Design Parameters

The University of Missouri-Columbia Research Reactor (MURR®) is one of five U.S. high performance research reactors (USHPRR), plus one critical facility, that actively collaborates with the National Nuclear Security Administration (NNSA) Material Management and Minimization(M 3 ) Reactor Conversion Program to convert to the use of low-enriched uranium (LEU, < 20 wt.% U-235) fuel. A new type of LEU fuel with very high density, based on an alloy of uranium and 10 weight percent molybdenum (U-10Mo), is expected to allow the conversion to LEU of USHPRR that have been found unable to be converted with previously qualified uranium silicide-aluminum (U 3 Si 2 -Al) dispersion fuel. MURR has been working with the USHPRR Reactor Conversion (RC) Pillar at Argonne National Laboratory to perform fuel element design and fuel cycle performance analyses, steady-state thermal hydraulics safety analyses, and accident safety analyses in preparation for the conversion of MURR and to support a preliminary Safety Analysis Report (SAR) for conversion to LEU fuel. This work is performed in preparation for the flow test campaign that will be conducted by the USHPRR RC Pillar. The purpose of the hydraulic performance evaluation of the MURR LEU fuel element designed by the RC Pillar is to test a prototypic commercially fabricated LEU fuel element to determine whether any failure modes are observed or predicted in the fuel element, including significant deformations such as plate bending, twisting, or plate detachment from the side plate under selected safety-basis limits for reactor hydraulic conditions. To support the design of the flow test for MURR LEU fuel element hydraulic performance evaluation, design parameters for hydraulic testing of the LEU fuel element are laid out in this report.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

Spatially Resolved Near Field Spectroscopy of Vibrational Polaritons at the Small N Limit

Vibrational polaritons, which have been primarily studied in Fabry–Pérot cavities with a large number of molecules (N ~ 10 6 –10 10 ) coupled to the resonator mode, exhibit various experimentally observed effects on chemical reactions. However, the exact mechanism is elusively understood from the theoretical side, as the large number of molecules involved in an experimental strong coupling condition cannot be represented completely in simulations. This discrepancy between theory and experiment arises from computational descriptions of polariton systems typically being limited to only a few molecules, thus failing to represent the experimental conditions adequately. To address this mismatch, we used surface phonon polariton (SPhP) resonators as an alternative platform for vibrational strong coupling. SPhPs exhibit strong electromagnetic confinement on the surface and thus allow for coupling to a small number of molecules. As a result, this platform can enhance nonlinearity and slow down relaxation to the dark modes. In this study, we fabricated a pillar-shaped quartz resonator and then coated it with a thin layer of cobalt phthalocyanine (CoPc). By employing scattering-type scanning near-field optical microscopy (s-SNOM), we spatially investigated the dependency of vibrational strong coupling on the spatially varying electromagnetic field strength and demonstrated strong coupling with 38,000 molecules only–reaching to the small N limit. Through s-SNOM analysis, we found that strong coupling was observed primarily on the edge of the quartz pillar and the apex of the s-SNOM tip, where the maximum field enhancement occurs. In contrast, a weak resonance signal and lack of coupling were observed closer to the center of the pillar. This work demonstrates the importance of spatially resolved polariton systems in nanophotonic platforms and lays a foundation to explore polariton chemistry and chemical dynamics at the small N limit–one step closer to reconcile with high-level quantum calculations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1981

Percutaneous connectors

A surface possessing a regular array of micro-pillars was evaluated with regard to its ability to control epithelial downgrowth at the percutaneous interface. A range of pillar sizes were applied to the vertical segment of T shaped Biomer (R) implants. These percutaneous tabs were implanted into the dorsum of cats for a period of 6 weeks using a standardized surgical technique. Comments were made post-operatively and at the time of retrieval. A quantitative scoring system was applied to these observations as well as histological results. As observed, the pillar morphology used displayed the ability to control epithelial downgrowth. Collagen ingrowth into the interpillar spaces and possibly direct interactions of the epithelial cells with the morphology may account for the inhibition. The reproducibility of epithelial inhibition is, however, limited by other factors which are currently not well understood. These factors and potential methods of assessment are discussed.

Picha, G. J.↗
NASA NTRS2003

The National Aerospace Initiative (NAI): Technologies For Responsive Space Access

The Secretary of Defense has set new goals for the Department of Defense (DOD) to transform our nation's military forces. The Director for Defense Research and Engineering (DDR&E) has responded to this challenge by defining and sponsoring a transformational initiative in Science and Technology (S&T) - the National Aerospace Initiative (NAI) - which will have a fundamental impact on our nation's military capabilities and on the aerospace industry in general. The NAI is planned as a joint effort among the tri-services, DOD agencies and National Aeronautics and Space Administration (NASA). It is comprised of three major focus areas or pillars: 1) High Speed Hypersonics (HSH), 2) Space Access (SA), and 3) Space Technology (ST). This paper addresses the Space Access pillar. The NAI-SA team has employed a unique approach to identifying critical technologies and demonstrations for satisfying both military and civilian space access capabilities needed in the future. For planning and implementation purposes the NAI-SA is divided into five technology subsystem areas: Airframe, Propulsion, Flight Subsystems, Operations and Payloads. Detailed technology roadmaps were developed under each subsystem area using a time-phased, goal oriented approach that provides critical space access capabilities in a timely manner and involves subsystem ground and flight demonstrations. This S&T plan addresses near-term (2009), mid-term (2016), and long-term (2025) goals and objectives for space access. In addition, system engineering and integration approach was used to make sure that the plan addresses the requirements of the end users. This paper describes in some detail the technologies in NAI-Space Access pillar. Some areas of emphasis are: high temperature materials, thermal protection systems, long life, lightweight, highly efficient airframes, metallic and composite cryotanks, advanced liquid rocket engines, integrated vehicle health monitoring and management, highly operable systems and payloads. Implementation strategies for NAI are also described.

Culbertson, Andrew↗
NASA NTRS1988

Luminal surface fabrication for cardiovascular prostheses

A method is provided for forming a mold surface with microscopic upstanding pillars for molding the inside surface of a vascular prostheses (synthetic blood vessel). The mold article is formed from a quantity of Teflon (polytetrafluoroethylene) which has a polished, flat surface on which a gold film has been sputter deposited. A photoresist layer, which cannot adhere directly to Teflon, adheres to the gold. The photoresist is exposed and developed leaving a sputter resistant mask defining the desired pillar locations, and the resulting workpiece is ion etched to form the pillars in the Teflon. A synthetic blood vessel material is cast against the Teflon mold to form blind recesses on the inside of the synthetic blood vessel, with the recesses being of predetermined uniform cross section and present in a predetermined uniform pattern.

Deininger, William D.↗
NASA NTRS2008

Protective coating and hyperthermal atomic oxygen texturing of optical fibers used for blood glucose monitoring

Disclosed is a method of producing cones and pillars on polymethylmethacralate (PMMA) optical fibers for glucose monitoring. The method, in one embodiment, consists of using electron beam evaporation to deposit a non-contiguous thin film of aluminum on the distal ends of the PMMA fibers. The partial coverage of aluminum on the fibers is randomly, but rather uniformly distributed across the end of the optical fibers. After the aluminum deposition, the ends of the fibers are then exposed to hyperthermal atomic oxygen, which oxidizes the areas that are not protected by aluminum. The resulting PMMA fibers have a greatly increased surface area and the cones or pillars are sufficiently close together that the cellular components in blood are excluded from passing into the valleys between the cones and pillars. The optical fibers are then coated with appropriated surface chemistry so that they can optically sense the glucose level in the blood sample than that with conventional glucose monitoring.

Banks, Bruce A.↗
NASA NTRS2005

Precision Cryogenic Dilatometer

A dilatometer based on a laser interferometer is being developed to measure mechanical creep and coefficients of thermal expansion (CTEs) of materials at temperatures ranging from ambient down to 15 K. This cryogenic dilatometer has been designed to minimize systematic errors that limit the best previously available dilatometers. At its prototype stage of development, this cryogenic dilatometer yields a strain measurement error of 35 ppb or 1.7 ppb/K CTE measurement error for a 20-K thermal load, for low-expansion materials in the temperature range from 310 down to 30 K. Planned further design refinements that include a provision for stabilization of the laser and addition of a high-precision sample-holding jig are expected to reduce the measurement error to 5-ppb strain error or 0.3-ppb/K CTE error for a 20-K thermal load. The dilatometer (see figure) includes a common-path, differential, heterodyne interferometer; a dual-frequency, stabilized source bench that serves as the light source for the interferometer; a cryogenic chamber in which one places the material sample to be studied; a cryogenic system for cooling the interior of the chamber to the measurement temperature; an ultra-stable alignment stage for positioning the chamber so that the sample is properly positioned with respect to the interferometer; and a data-acquisition and control system. The cryogenic chamber and the interferometer portion of the dilatometer are housed in a vacuum chamber on top of a vibration isolating optical table in a cleanroom. The sample consists of two pieces a pillar on a base both made of the same material. Using reflections of the interferometer beams from the base and the top of the pillar, what is measured is the change in length of the pillar as the temperature in the chamber is changed. In their fundamental optical and electronic principles of operation, the laser light source and the interferometer are similar to those described in Common-Path Heterodyne Interferometers (NPO-20786), NASA Tech Briefs, Vol. 25, No. 7 (July 2001), page 12a, and Interferometer for Measuring Displacement to Within 20 pm (NPO- 21221), NASA Tech Briefs, Vol. 27, No. 7 (July 2003), page 8a. However, the present designs incorporate a number of special geometric, optical, and mechanical features to minimize optical and thermal-expansion effects that contribute to measurement errors. These features include the use of low-thermal expansion materials for structural components, kinematic mounting and symmetrical placement of optical components, and several measures taken to minimize spurious reflections of laser beams.

Dudik, Matthew↗
NASA NTRS2016

Photonic Waveguide Choke Joint with Absorptive Loading

A photonic waveguide choke includes a first waveguide flange member having periodic metal tiling pillars, a dissipative dielectric material positioned within an area between the periodic metal tiling pillars and a second waveguide flange member disposed to be coupled with the first waveguide flange member and in spaced-apart relationship separated by a gap. The first waveguide flange member has a substantially smooth surface, and the second waveguide flange member has an array of two-dimensional pillar structures formed therein.

Wollack, Edward J.↗