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At least 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Measurement of Poly-Si Film Thickness on Textured Surfaces by X-Ray Diffraction in Poly-Si/SiOx Passivating Contacts for Monocrystalline Si Solar Cells

Polycrystalline Silicon on tunneling silicon oxide (poly-Si/SiOx) passivating contacts have shown great potential for the next-generation monocrystalline Si (c-Si) industrial photovoltaic technology. However, these cells typically suffer from strong parasitic absorption in the thick front poly-Si layer, which is designed to reduce metal-induced recombination. In previous work, we demonstrated an improved short-circuit current density, Jsc, by thinning the front poly-Si film in an SF6 plasma using the front metal grids as a self-aligned mask, but the sub - 100 nm thick poly-Si film is difficult to measure on an alkaline textured surface. Conventional optical techniques such as spectroscopic ellipsometry cannot be used due to the high scattering nature of the random pyramids. At poly-Si thicknesses below 50 nm, secondary electron microscopy (SEM) has difficulty distinguishing the poly-Si from the underlying c-Si substrate. Here, we demonstrate X-ray diffraction as an effective method to quantitatively measure the front poly-Si thickness. The thickness calculated from the diffraction peak height of the Si(111) crystallographic plane agrees well with the cross-section SEM analysis and simulations using SunSolve. We show that by thinning the front poly-Si from 200 to 60 nm, Jsc increased by 2.4 mA/cm2, while maintaining the same Voc. This led to an absolute efficiency gain of 1.73%. In addition, we also discuss possible reasons for the premature loss of passivation before the removal of all poly-Si, which prevented an even higher gain in Jsc.

light/electron beam induced current↗
NASA NTRS1972

Alignment microscope for rotating laser scanner

Microscopic assembly for alignment of rotary laser focuses on small film area along scan line at oblique angle. Suitable choice of angle and location of optical components project laser beam line as X coordinate reticle. Coordination with horizontal recticle line included microscope facilitates Y coordinate position indexing.

Maciel, A., Jr.↗
NASA NTRS1986

High resolution observations of the L1551 bipolar outflow

The nearby dark cloud Lynds 1551 contains one of the closest examples of a well-collimated bipolar molecular outflow. This source has the largest angular size of any known outflow and was the first bipolar outflow to be detected. The outflow originates from a low-luminosity young stellar object, IRS-5. Optical and radio continuum observations show the presence of a highly collimated, ionized stellar wind orginating from close to IRS-5 and aligned with the molecular outflow. However, we have little information on the actual mechanism that generates the stellar wind and collimates it into opposed jets. The Very Large Array (VLA) observations indicate that the winds originate within 10(15) cm of IRS-5, unfortunately at a size scale difficult to resolve. For these reasons, observations of the structure and dynamics of the hypersonic molecular gas may provide valuable information on the origin and evolution of these outflows. In addition, the study of the impact of the outflowing gas on the surrounding molecular material is essential to understand the consequence these outflows have on the evolution and star formation history of the entire cloud. Moriarty-Schieven et al. (1986) obtained a oversampled map of the CO emission of a portion of both the blueshifted and redshifted outflows in LI551 using Five College Radio Astronomy Observatory 14 m telescope. The oversampled maps have been reconstructed to an effective angular resolution of 20 arcsec using a maximum entropy algorithm. A continuation of the study of Moriarty-Schieven et al. is presented. The entire L1551 outflow has now been mapped at 12 arcsec sampling requiring roughly 4000 spectra. This data has been constructed to 20 arcsec resolution to provide the first high resolution picture of the entire L1551 outflow. This new data has shown that the blueshifted lobe is more extended than previously thought and has expanded downstream sufficiently to break out of the dense molecular cloud, but the redshifted outflow is still confined within the molecular cloud. Details of the structure and kinematics of the high velocity gas are used to test the various models of the origin and evolution of outflows.

Snell, R.↗
NASA NTRS1990

An Optimal Design For Steerable Dish Antenna With BWG

New design proposed for highly-efficient 34-m-diameter millimeter-wavelength antennas of NASA's Deep Space Network. Incorporates axial beam waveguide, BWG, and improved structure to maintain shape and alignment of reflecting surfaces. General approach to conceptual construction of structure to modularize overall system so critical constraint conditions pertaining to microwave optics and structural performance satisfied. Design retrofitted to existing NASA Deep Space Network 34-m antennas, or used as basis to build large ground-based steerable antennas. Engineering concepts involved in design adapted to design of other large, steerable antennas for telecommunications, radio astronomy, and military uses.

Chuang, K. L.↗
NASA NTRS1990

Microwave structure of the quiet sun at 8.5 GHz

Multifrequency VLA observations of the quiet sun near 8.5 GHz are presented. Two regions of the sun were observed, one dominated by an enhanced network corresponding to a decayed active region, and the other corresponding to an enhanced network with no active features. The full-day synthesis maps for both show nearly perfect correspondence to H-alpha images, and to longitudinal magnetograms. The coronal loops were observed to appear as regions of radio emission with no underlying longitudinal magnetic fields, being aligned with H-alpha fibrils in the photosphere, and connecting regions of opposite magnetic polarity. The emission can be modeled as optically thin free-free emission from a coronal loop with a peak axial density of approximately 2.4-2.8 x 10 to the 9th/cu cm, for an assumed coronal temperature of 1-2 x 10 to the 6th K. The quiet chromosphere sources are measured, and the significance of these measurements for existing chromospheric models is discussed.

Gary, Dale E.↗
NASA NTRS1990

The Hubble Space Telescope optical systems failure report

The findings of the Hubble Space Telescope Optical Systems Board of Investigation are reported. The Board was formed to determine the cause of the flaw in the telescope, how it occurred, and why it was not detected before launch. The Board conducted its investigation to include interviews with personnel involved in the fabrication and test of the telescope, review of documentation, and analysis and test of the equipment used in the fabrication of the telescope's mirrors. The investigation proved that the primary mirror was made in the wrong shape (a 0.4-wave rms wavefront error at 632.8 nm). The primary mirror was manufactured by the Perkin-Elmer Corporation (Hughes Danbury Optical Systems, Inc.). The critical optics used as a template in shaping the mirror, the reflective null corrector (RNC), consisted of two small mirrors and a lens. This unit had been preserved by the manufacturer exactly as it was during the manufacture of the mirror. When the Board measured the RNC, the lens was incorrectly spaced from the mirrors. Calculations of the effect of such displacement on the primary mirror show that the measured amount, 1.3 mm, accounts in detail for the amount and character of the observed image blurring. No verification of the reflective null corrector's dimensions was carried out by Perkin-Elmer after the original assembly. There were, however, clear indications of the problem from auxiliary optical tests made at the time. A special optical unit called an inverse null corrector, designed to mimic the reflection from a perfect primary mirror, was built and used to align the apparatus; when so used, it clearly showed the error in the reflective null corrector. A second null corrector was used to measure the vertex radius of the finished primary mirror. It, too, clearly showed the error in the primary mirror. Both indicators of error were discounted at the time as being themselves flawed. The Perkin-Elmer plan for fabricating the primary mirror placed complete reliance on the reflective null corrector as the only test to be used in both manufacturing and verifying the mirror's surface with the required precision. This methodology should have alerted NASA management to the fragility of the process and the possibility of gross error. Such errors had been seen in other telescope programs, yet no independent tests were planned, although some simple tests to protect against major error were considered and rejected. During the critical time period, there was great concern about cost and schedule, which further inhibited consideration of independent tests.

Source record↗
NASA NTRS1992

Controlled retroreflection - A technique for understanding and eliminating parasitic lasing

Parasitic lasing is examined with an emphasis on understanding and quantifying its effect on high-gain laser systems. Parasitic lasing is unwanted stimulated emission commonly found in high-gain optical systems. A general technique was developed that carefully retroreflects light back into the optical system, thereby creating an externally induced oscillator. Discrepancies between experimental data and threshold calculations for the externally induced oscillator are direct evidence of optical misalignment or of component performance problems. Any changes in the optical system can be directly measured as a change in threshold for the externally induced oscillator. This technique also enables one to align the system for maximum parasitic suppression with the system fully operational. Experimental data illustrating the utility of this technique are presented.

Storm, Mark E.↗
NASA NTRS1994

Numerical aperture limits on efficient ball lens coupling of laser diodes to single-mode fibers with defocus to balance spherical aberration

The potential capabilities and limitations of single ball lenses for coupling laser diode radiation to single-mode optical fibers have been analyzed; parameters important to optical communications were specifically considered. These parameters included coupling efficiency, effective numerical apertures, lens radius, lens refractive index, wavelength, magnification in imaging the laser diode on the fiber, and defocus to counterbalance spherical aberration of the lens. Limiting numerical apertures in object and image space were determined under the constraint that the lens perform to the Rayleigh criterion of 0.25-wavelength (Strehl ratio = 0.80). The spherical aberration-defocus balance to provide an optical path difference of 0.25 wavelength units was shown to define a constant coupling efficiency (i.e., 0.56). The relative numerical aperture capabilities of the ball lens were determined for a set of wavelengths and associated fiber-core diameters of particular interest for single-mode fiber-optic communication. The results support general continuing efforts in the optical fiber communications industry to improve coupling links within such systems with emphasis on manufacturing simplicity, system packaging flexibility, relaxation of assembly alignment tolerances, cost reduction of opto-electronic components and long term reliability and stability.

Wilson, R. Gale↗
NASA NTRS2010

Fabrication of Single, Vertically Aligned Carbon Nanotubes in 3D Nanoscale Architectures

Plasma-enhanced chemical vapor deposition (PECVD) and high-throughput manufacturing techniques for integrating single, aligned carbon nanotubes (CNTs) into novel 3D nanoscale architectures have been developed. First, the PECVD growth technique ensures excellent alignment of the tubes, since the tubes align in the direction of the electric field in the plasma as they are growing. Second, the tubes generated with this technique are all metallic, so their chirality is predetermined, which is important for electronic applications. Third, a wafer-scale manufacturing process was developed that is high-throughput and low-cost, and yet enables the integration of just single, aligned tubes with nanoscale 3D architectures with unprecedented placement accuracy and does not rely on e-beam lithography. Such techniques should lend themselves to the integration of PECVD grown tubes for applications ranging from interconnects, nanoelectromechanical systems (NEMS), sensors, bioprobes, or other 3D electronic devices. Chemically amplified polyhydroxystyrene-resin-based deep UV resists were used in conjunction with excimer laser-based (lambda = 248 nm) step-and-repeat lithography to form Ni catalyst dots = 300 nm in diameter that nucleated single, vertically aligned tubes with high yield using dc PECVD growth. This is the first time such chemically amplified resists have been used, resulting in the nucleation of single, vertically aligned tubes. In addition, novel 3D nanoscale architectures have been created using topdown techniques that integrate single, vertically aligned tubes. These were enabled by implementing techniques that use deep-UV chemically amplified resists for small-feature-size resolution; optical lithography units that allow unprecedented control over layer-to-layer registration; and ICP (inductively coupled plasma) etching techniques that result in near-vertical, high-aspect-ratio, 3D nanoscale architectures, in conjunction with the use of materials that are structurally and chemically compatible with the high-temperature synthesis of the PECVD-grown tubes. The techniques offer a wafer-scale process solution for integrating single PECVD-grown nanotubes into novel architectures that should accelerate their integration in 3D electronics in general. NASA can directly benefit from this technology for its extreme-environment planetary missions. Current Si transistors are inherently more susceptible to high radiation, and do not tolerate extremes in temperature. These novel 3D nanoscale architectures can form the basis for NEMS switches that are inherently less susceptible to radiation or to thermal extremes.

Kaul, Anupama B.↗
DOE OSTI2024

Corrosion Testing Of Additively Manufactured Stainless Steel 316H In Molten Salt Environments

The development of a new ASTM standard for evaluating the corrosion resistance of additive manufactured (AM) stainless steel (SS) 316H in chloride molten salts is critical for the use of these materials in extreme environments such as molten salt reactors (MSRs). This report pertains to a work package of the Advaned Materials and Manufacturing Technologies (AMMT) developing a systematic methodology to link changes in AM fabrication parameters, namely surface finishing, porosity, microstructure, and chemical heterogeneity, to corrosion performance in NaCl-MgCl2 salt, a proposed secondary coolant for MSRs. During Fiscal Year 2024, Idaho National Laboratory investigators in the AMMT program, utilized SS316H bars, fabricated with laser bed powder fusion at Los Alamos National Laboratory, to establish and optimize the workflow for evaluating these process-to-performance relationships. Standard practices for specimen preparation were established using these specimens, with particular focus on descaling and sectioning methods that align with ASTM guidelines. A comprehensive experimental design for static corrosion testing was developed, with pre- and post-exposure analysis utilizing optical microscopy and scanning electron microscopy. So far standard descaling techniques were optimized, one static corrosion test was conducted on the LANL AM SS316H specimens, and pre- and post-corrosion practices were established. In addition, the work package yielded a review paper on corrosion testing gaps for AM materials in nuclear applications and submitted a proposal for a rapid-turnaround experiment to the Nuclear Science User Facilities Program to investigate the combined effects of proton irradiation and corrosion on AM SS316H. This work package establishes a foundation for evaluating processing-to-performance relationships for AM SS316H in harsh conditions, contributing to the safe and efficient design of components for next-generation nuclear reactors. The creation of a standardized methodology and the generation of relevant publications and future research pathways represent significant strides towards integrating AM materials into critical applications where corrosion resistance is paramount.

36 MATERIALS SCIENCE↗
NASA NTRS1978

The scanning modulation collimator experiment on the HEAO-1

The purpose of this experiment is to localize celestial sources of X-rays to a precision of 5 to 20 arcsec, so that they may be identified with optical or radio counterparts. We also study their angular size and structure, to elucidate the X-ray emission mechanism. Four grids, wound with nickel alloy wires, are aligned to produce a modulated X-ray signal when the spacecraft rotation carries the collimator field of view across an X-ray source. An image dissector star camera and rate integrating gyroscopes are used to deduce the celestial position from which a peak X-ray signal arises. On-orbit performance and thermal stability have been very good. Based on the first six weeks of quick look data, we have the following results: the location of an X-ray burst source within a globular cluster; the location of 4U1608-52, a unique object which shows bursting, transient, and steady X-ray behavior and is also an optical source; the location of the X-ray transient H1705-25, which provided Anglo-Australian astronomers the basis for an optical identification with a nova-like object; the location of the X-ray transient H1743-32 in the galactic center; and a precise measurement of the angular extent of the Crab Nebula.

Schwartz, D. A.↗
DOE OSTI2022

Tailored approach to study Legionella infection using a lattice light sheet microscope (LLSM)

Legionella is a genus of ubiquitous environmental pathogens found in freshwater systems, moist soil, and composted materials. More than four decades of Legionella research has provided important insights into Legionella pathogenesis. Although standard commercial microscopes have led to significant advances in understanding Legionella pathogenesis, great potential exists in the deployment of more advanced imaging techniques to provide additional insights. The lattice light sheet microscope (LLSM) is a recently developed microscope for 4D live cell imaging with high resolution and minimum photo-damage. We built a LLSM with an improved version for the optical layout with two path-stretching mirror sets and a novel reconfigurable galvanometer scanner ( RGS ) module to improve the reproducibility and reliability of the alignment and maintenance of the LLSM. We commissioned this LLSM to study Legionella pneumophila infection with a tailored workflow designed over instrumentation, experiments, and data processing methods. Our results indicate that Legionella pneumophila infection is correlated with a series of morphological signatures such as smoothness, migration pattern and polarity both statistically and dynamically. Our work demonstrates the benefits of using LLSM for studying long-term questions in bacterial infection. Our free-for-use modifications and workflow designs on the use of LLSM system contributes to the adoption and promotion of the state-of-the-art LLSM technology for both academic and commercial applications.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1995

155- and 213-GHz AlInAs/GaInAs/InP HEMT MMIC oscillators

We report on the design and measurement of monolithic 155- and 213-GHz quasi-optical oscillators using AlInAs/GaInAs/InP HEMTs (high-electron mobility transistors). These results are believed to be the highest frequency three-terminal oscillators reported to date. The indium concentration in the channel was 80% for high sheet charge and mobility. The HEMT gates were fabricated with self-aligned sub-tenth-micrometer electron-beam techniques to achieve gate lengths on the order of 50 nm and drain-source spacing of 0.25 micron. Planar antennas were integrated into the fabrication process resulting in a compact and efficient quasi-optical Monolithic Millimeter-wave Integrated Circuit (MMIC) oscillator.

TRT-EXPERIMENTAL↗
DOE OSTI2021

Dynamics of filaments during the edge-localized mode crash on NSTX

Edge localized modes (ELMs) are routinely observed in H-mode plasma regimes of the National Spherical Torus Experiment (NSTX). Due to the explosive nature of the instability, only diagnostics with high temporal and spatial resolution could provide a detailed insight into the dynamics associated with the ELMs. Gas-puff imaging at NSTX provides 2D measurements of the magnetic field aligned fluctuations (e.g., ELM filaments) in the scrape-off layer and at the plasma edge with 2.5 μs temporal and 10 mm optical resolution. A novel analysis technique was developed to estimate the frame-by-frame velocities and the spatial parameters of the dominant structures associated with the ELMs. The analysis was applied to single ELM events to characterize the ELM crash dynamics and then extended to a database of 159 ELM events. Statistical analysis was performed in order to find the characterizing dynamics of the ELM crash. The results show that on average, an ELM crash consists of a filament with a circular cross section, which is propelled outward with a characterizing peak radial velocity of ~3.3 km/s. The radial velocity was found to be linearly dependent on the distance of the filament from the separatrix, which has never been seen before. The ELM filament is characterized by propagation in the ion-diamagnetic direction poloidally with a peak velocity of 11.4 km/s. The ELM crash lasts for approximately 100 μs until the radial propulsion settles back to the pre-ELM level. Furthermore, the experimental findings were compared with analytical theory. Two possible mechanisms were identified for explaining the observations: the curvature interchange model and the current–filament interaction model.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1978

Structural alignment sensor

Comparative Michelson interferometers are discussed as well as the operating range potential of a structural alignment sensor (SAS) which requires only one laser mode. Schematics are presented for the distance measurement logic, the basic SAS system, the SAS optical layout, the coarse measurement signal processor, and the measured range resolution.

Davis, L.↗
NASA NTRS1988

Improved docking alignment system

Improved techniques are provided for the alignment of two objects. The present invention is particularly suited for 3-D translation and 3-D rotational alignment of objects in outer space. A camera is affixed to one object, such as a remote manipulator arm of the spacecraft, while the planar reflective surface is affixed to the other object, such as a grapple fixture. A monitor displays in real-time images from the camera such that the monitor displays both the reflected image of the camera and visible marking on the planar reflective surface when the objects are in proper alignment. The monitor may thus be viewed by the operator and the arm manipulated so that the reflective surface is perpendicular to the optical axis of the camera, the roll of the reflective surface is at a selected angle with respect to the camera, and the camera is spaced a pre-selected distance from the reflective surface.

Monford, Leo G.↗
NASA NTRS1993

Pinhole Calibrator For Particle-Sizing Instrument

Rotating-pinhole calibrator designed for use in calibrating and testing optical instrument measuring sizes of cloud droplets, dust particles, and other small particles suspended in flowing air. Easily attachable to particle-size-measuring instrument and suitable for both quick verification of calibration in field and detailed calibration studies in laboratory. Calibrator used to determine such operating parameters of instrument as optical collection angles, depth of field, profile of laser beam used to measure particles, and response to trajectory of particle. Also used to align instrument. Pinhole reused any number of times without risk of variation in diffraction pattern. Furthermore, size of pinhole chosen precisely and at will.

Hovenac, Edward↗