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Results for “inverted pyramids”

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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13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Experimental Investigation of Composite Pressure Vessel Performance and Joint Stiffness for Pyramid and Inverted Pyramid Joints

The focus of this study is on the suitability in the application of classical laminate theory analysis tools for filament wound pressure vessels with adhesive laminated joints in particular: pressure vessel wall performance, joint stiffness and failure prediction. Two 18-inch diameter 12-ply filament wound pressure vessels were fabricated. One vessel was fabricated with a 24-ply pyramid laminated adhesive double strap butt joint. The second vessel was fabricated with the same number of plies in an inverted pyramid joint. Results from hydrostatic tests are presented. Experimental results were used as input to the computer programs GENLAM and Laminate, and the output compared to test. By using the axial stress resultant, the classical laminate theory results show a correlation within 1% to the experimental results in predicting the pressure vessel wall pressure performance. The prediction of joint stiffness for the two adhesive joints in the axial direction is within 1% of the experimental results. The calculated hoop direction joint stress resultant is 25% less than the measured resultant for both joint configurations. A correction factor is derived and used in the joint analysis. The correction factor is derived from the hoop stress resultant from the tank wall performance investigation. The vessel with the pyramid joint is determined to have failed in the joint area at a hydrostatic pressure 33% value below predicted failure. The vessel with the inverted pyramid joint failed in the wall acreage at a hydrostatic pressure within 10% of the actual failure pressure.

Verhage, Joseph M.↗
DOE OSTI2021

Pinhole Formation in Poly-Si/SiOx Passivating Contacts on Si(111)-Oriented Textures

Poly-Si/SiOx passivating contacts were grown on inverted pyramid and random pyramid textured wafers to investigate the hypothesis that pinhole formation is most susceptible at the valleys and edges of a textured surface. Tetramethylammonium hydroxide (TMAH) etching and electron beam induced current (EBIC) were used to assess pinhole formation and charge-carrier transport. Scanning electron microscopy revealed that TMAH etching can expose pinhole locations on textured surfaces. We show that pinholes may preferentially form at the vertices of inverted pyramids. Our TMAH and EBIC analyses on random pyramids show no preferential oxide breakup at the pyramid valleys.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2020

Experimental demonstration of broadband solar absorption beyond the lambertian limit in certain thin silicon photonic crystals

The tantalizing possibility of 31% solar-to-electric power conversion efficiency in thin film crystalline silicon solar cell architectures relies essentially on solar absorption well beyond the Lambertian light trapping limit (Bhattacharya and John in Nat Sci Rep 9:12482, 2019). Up to now, no solar cell architecture has exhibited above-Lambertian solar absorption, integrated over the broad solar spectrum. In this work, we experimentally demonstrate two types of photonic crystal (PhC) solar cells architectures that exceed Lambertian light absorption, integrated over the entire 300–1,200 nm wavelength band. These measurements confirm theoretically predicted wave-interference-based optical resonances associated with long lifetime, slow-light modes and parallel-to-interface refraction. These phenomena are beyond the realm of ray optics. Using two types of 10-μm thick PhC’s, first an Inverted Pyramid PhC with lattice constant a= 2,500 nm and second a Teepee PhC with a = 1,200 nm, we observe solar absorption well beyond the Lambertian limit over λ = 950–1,200 nm. Our absorption measurements correspond to the maximum-achievable-photocurrent-density (MAPD), under AM1.5G illumination at 4-degree incident angle, 41.29 and 41.52 mA/cm2 for the Inverted Pyramid and Teepee PhC, respectively, in agreement with wave-optics, numerical simulations. Both of these values exceed the MAPD (= 39.63 mA/cm2) corresponding to the Lambertian limit for a 10-μm thick silicon for solar absorption over the 300–1,200 nm band.

36 MATERIALS SCIENCE↗
NASA NTRS1988

Simulation of GaAs cluster formation on GaAs(00-1), AlAs(00-1), Si(001), and As1/Si(001) surfaces

Recently developed semiempirical potential energy functions for the Ga-As-Si and Ga-As-Al systems have been applied here to determine the excess formation energy for GaAs clusters on GaAs(00-1), AlAs(00-1), Si(001), and one atomic layer As-covered Si(001) substrates as a function of cluster size and cluster shape by the Monte Carlo technique. Pyramidal type ledges on the GaAs clusters are found to be the favored ledge for the first three layers while an inverted-pyramidal type ledge is also favored in certain cases for the As1/Si(001) substrate. Cluster formation at ledges is compared with cluster formation on a flat terrace for the Si(001) and the As1/Si(001) substrates.

Choi, D. K.↗
DOE OSTI2022

Communication—Electrodeposition of Indium Directly on Silicon

Direct electrodeposition of indium onto silicon paves the way for advances in microelectronics, photovoltaics, and optoelectronics. Indium is generally electrodeposited onto silicon utilizing a physically or thermally deposited metallic seed layer. Eliminating this layer poses benefits in microelectronics by reducing resistive interfaces and in vapor-liquid-solid conversion to III-V material by allowing direct contact to the single-crystal silicon substrate for epitaxial conversion. We investigated conditions to directly electrodeposit indium onto n-type Si(100). We illustrate that a two-step galvanostatic plating at low temperatures can consistently produce smooth, continuous films of indium over large areas, in bump morphologies, and conformally into inverted pyramids.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1977

Spinoff 1977

The National Aeronautics & Space Administration has many missions but they can all be reduced to a common denominator: to explore Earth and its surroundings, conduct aeronautical research, and put the results to work for the benefit of mankind. At times the benefit may be dimly perceived. Take, for instance, last year's monumental triumph of exploration, the landing of robot spacecraft on Mars. How, some ask, does probing a neighbor planet improve the lot of Earth's people? In two ways: scientific gain and technological advancement. Though perhaps little understood, they are concrete benefits, assets as tangible as sunshine, more valuable than gold. Technological advancement, on the other hand, offers equally important but more immediate returns. Technology is science applied. It is the ability of a society to make things that improve the quality of human existence. It is compounded of intellect and skill, which draw upon the scientific base to bring forth new ideas, inventions, materials and processes. It is, in a word, knowledge. It builds like an inverted pyramid, each level broader than the one . before as successive generations contribute to the cumulative lore. Knowledge is readily transferable. If you build a better mousetrap, you may acquire experience in the course of the project that can be applied to a need totally unrelated to mouse-traping. This transfer process has been going on since the dawn of technology. In the last two decades it has accelerated enormously, spurred by the immense flow of aerospace-stimulated technology. There have been literally thousands of spinoffs, new products and processes that owe their origins to aerospace research. Collectively, they add up to significant gain in terms of personal convenience, human welfare, industrial efficiency, and economic value.

Haggerty, James J.↗
NASA NTRS2021

Anisotropic Wet Etching of Si as a Fabrication Tool Enabling 3-D Microphotonics Structures and Devices

It is shown that due to high speed and large volume of production, anisotropic wet etching of Si is a unique method of manufacturing high quality micropyramidal arrays for silicon photonics. Four types of arrays were fabricated: (i) square pyramids with the 54.7 slope of the sidewall surface, (ii) microcones with the 45 slope of sidewall surface, (iii) inverted square pyramids with 54.7 slope, and (iv) inverted triangular pyramids with different angles of the sidewalls. It is shown that the first type of arrays has a capability to produce tightly focused mid-wave infrared (MWIR) beams at the tips of the pyramids. Other arrays can be also used as light concentrators and various multifunctional microphotonic components.

Astratov, Vasily N.↗
DOE OSTI2023

Structure of V-defects in long wavelength GaN-based light emitting diodes

The V-defect is a naturally occurring inverted hexagonal pyramid structure that has been studied in GaN and InGaN growth since the 1990s. Strategic use of V-defects in pre-quantum well superlattices or equivalent preparation layers has enabled record breaking efficiencies for green, yellow, and red InGaN light emitting diodes (LEDs) utilizing lateral injection of holes through the semi-polar sidewalls of the V-defects. In this article, we use advanced characterization techniques such as scattering contrast transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy, x-ray fluorescence maps, and atom probe tomography to study the active region compositions, V-defect formation, and V-defect structure in green and red LEDs grown on (0001) patterned sapphire and (111) Si substrates. We identify two distinct types of V-defects. The “large” V-defects are those that form in the pre-well superlattice and promote hole injection, usually nucleating on mixed (Burgers vector b = ±a±c⁠) character threading dislocations. In addition, “small” V-defects often form in the multi-quantum well region and are believed to be deleterious to high-efficiency LEDs by providing non-radiative pathways. The small V-defects are often associated with basal plane stacking faults or stacking fault boxes. Furthermore, we show through scattering contrast transmission electron microscopy that during V-defect filling, the threading dislocation, which runs up the center of the V-defect, will “bend” onto one of the six {10$\overline{1}$1} semi-polar planes. In conclusion, this result is essential to understanding non-radiative recombination in V-defect engineered LEDs.

42 ENGINEERING↗
NASA NTRS1983

Mechanical design of a low concentration ratio solar array for a space station application

This paper describes a preliminary study and conceptual design of a low concentration ratio solar array for a space station application with approximately a 100 kW power requirement. The baseline design calls for a multiple series of inverted, truncated, pyramidal optical elements with a geometric concentration ratio (GCR) of 6. It also calls for low life cycle cost, simple on-orbit maintainability, 1984 technology readiness date, and gallium arsenide (GaAs) of silicon (Si) solar cell interchangeability. Due to the large area needed to produce the amount of power required for the baseline space station, a symmetrical wing design, making maximum use of the commonality of parts approach, was taken. This paper will describe the mechanical and structural design of a mass-producible solar array that is very easy to tailor to the needs of the individual user requirement.

Biss, M. S.↗
NASA NTRS1981

Superplastically formed diffusion bonded metallic structure

A metallic sandwich structure particularly suited for use in aerospace industries comprising a base plate, a cover plate, and an orthogonally corrugated core is described. A pair of core plates formed of a superplastic alloy are interposed between the base plate and the cover plate and bonded. Each of the core plates is characterized by a plurality of protrusions comprising square-based, truncated pyramids uniformly aligned along orthogonally related axes perpendicularly bisecting the legs of the bases of the pyramids and alternately inverted along orthogonally related planes diagonally bisecting the pyramids, whereby an orthogonally corrugated core is provided.

Ko, W. L.↗
DOE OSTI2023

Using the Gerchberg-Saxton algorithm to reconstruct nonmodulated pyramid wavefront sensor measurements

Adaptive optics (AO) is a technique to improve the resolution of ground-based telescopes by correcting, in real-time, optical aberrations due to atmospheric turbulence and the telescope itself. With the rise of Giant Segmented Mirror Telescopes (GSMT), AO is needed more than ever to reach the full potential of these future observatories. One of the main performance drivers of an AO system is the wavefront sensing operation, consisting of measuring the shape of the above mentioned optical aberrations. Aims. The non-modulated pyramid wavefront sensor (nPWFS) is a wavefront sensor with high sensitivity, allowing the limits of AO systems to be pushed. The high sensitivity comes at the expense of its dynamic range, which makes it a highly non-linear sensor. We propose here a novel way to invert nPWFS signals by using the principle of reciprocity of light propagation and the Gerchberg-Saxton (GS) algorithm. We test the performance of this reconstructor in two steps: the technique is first implemented in simulations, where some of its basic properties are studied. Then, the GS reconstructor is tested on the Santa Cruz Extreme Adaptive optics Laboratory (SEAL) testbed located at the University of California Santa Cruz. This new way to invert the nPWFS measurements allows us to drastically increase the dynamic range of the reconstruction for the nPWFS, pushing the dynamics close to a modulated PWFS. The reconstructor is an iterative algorithm requiring heavy computational burden, which could be an issue for real-time purposes in its current implementation. However, this new reconstructor could still be helpful in the case of many wavefront control operations. In conclusion, this reconstruction technique has also been successfully tested on the Santa Cruz Extreme AO Laboratory (SEAL) bench where it is now used as the standard way to invert nPWFS signal.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Synthesis and Crystal Structure of the Zintl Phases NaSrSb, NaBaSb and NaEuSb

This work details the synthesis and the crystal structures of the ternary compounds NaSrSb, NaBaSb and NaEuSb. They are isostructural and adopt the hexagonal ZrNiAl-type structure (space group P6¯2m; Pearson code hP9). The structure determination in all three cases was performed using single-crystal X-ray diffraction methods. The structure features isolated Sb3– anions arranged in layers stacked along the crystallographic c-axis. In the interstices, alkali and alkaline-earth metal cations are found in tetrahedral and square pyramidal coordination environments, respectively. The formal partitioning of the valence electrons adheres to the valence rules, i.e., Na+Sr2+Sb3–, Na+Ba2+Sb3– and Na+Eu2+Sb3– can be considered as Zintl phases with intrinsic semiconductor behavior. Electronic band structure calculations conducted for NaBaSb are consistent with this notion and show a direct gap of approx. 0.9 eV. Additionally, the calculations hint at possible inverted Dirac cones, a feature that is reminiscent of topological quantum materials.

36 MATERIALS SCIENCE↗