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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Deep level study of chlorine-based dry etched β-Ga 2 O 3

Chlorine-based gases are used for the reactive ion etching (RIE) of β-Ga 2 O 3 . However, the effects of Cl-plasma on the electronic properties of β-Ga 2 O 3 are not known. In order to shed light on this topic, we carried out an experimental and theoretical study on β-Ga 2 O 3 epilayers treated with Cl 2 /Ar or BCl 3 /Ar plasma. We found four traps in the 0.2–0.8 eV energy range below the conduction band edge (EC). Two of these, located at E C -0.24 eV and E C -0.28 eV, arise only when the epilayers are treated with BCl 3 /Ar. While the involvement of Cl in their microscopic structure is not discarded, the possibility that these two levels might have an intrinsic nature seems more plausible. Our findings might explain the reported effects on the Schottky barrier diodes of β-Ga 2 O 3 when RIE is employed during processing.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Large aperture and durable glass-engraved optical metasurfaces using nanoparticle etching masks: prospects and future directions

Abstract Metasurfaces (MSs), or surfaces consisting of engineered spatially oriented sub-wavelength elements—also known as meta-atoms—are quickly becoming a burgeoning field of interest due to their seemingly unparalleled control over the propagation of light. This article will discuss the emergence of a MS technology that is based on dewetting thin metal films to form dry etching masks for MS fabrication. The novelty this process presents is the ability to spatially vary mask features—which translates into spatially varying index of the finished surface—in a way that, rather than writing subwavelength elements one-by-one, writes entire areas at once to provide a route to easily scale the process up to meter-sized optics. Glass-engraved MSs have shown to be laser damage resistant, with damage thresholds close to the parent substrate damage thresholds. Furthermore, these surfaces have proven to be mechanically durable and capable of handling normal loads two orders of magnitude higher than that of an average fingerprint pressure. This indicates that accidental handling contact is not detrimental to the MS optical performance. Also discussed are the foreseeable technological challenges, potential solutions for those obstacles, and some currently unexplored directions for future efforts.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Ultra-Fast 4H-SiC LGAD With Etched Termination and Field Plate

The design, fabrication, and demonstration of a novel Silicon Carbide Low Gain Avalanche Detector (4HSiC LGAD), exhibiting an ultra-fast time response and excellent time resolution, are reported. Here, the use of field plates is proposed to suppress the high electric field caused by the negative bevel-etched angle in 4H-SiC LGADs based on TCAD simulations. Experimental measurements confirm that the field plate significantly increases the breakdown voltage of the 4H-SiC LGADs. Gain and time resolution are measured by using the ultraviolet transient current technique (UV-TCT) showing that 4H-SiC LGADs possess excellent timing performance, with a time resolution better than 35 ps for the injected laser signal with single minimum ionizing particle (MIP) charges generation at room temperature. Additionally, the gain suppression effect in a 4H-SiC LGAD is observed for the first time.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Fabrication of Poly-Si on Locally Etched SiOx as Passivating Contacts for c-Si Solar Cells

Polysilicon on silicon oxide (poly-Si/SiO x ) passivating contacts with predominant charge-carrier transport via pinholes were prepared with room temperature metal-assisted chemical etching. Pinhole areal densities in the range of 2.8 x 10^4 to 4.5 x 10^7 cm^-2 were imaged by SEM. Contact resistivity of 32 m-ohm-cm^2 and implied open circuit voltage of 729 mV were obtained for symmetric n+ poly-Si/SiOx grown onto randomly textured n-Cz. We also show preliminary data pertaining boron-doped polysilicon on nitride/oxide passivating contacts, with which we achieved implied open circuit voltage above 730 mV and recombination current of 0.2 fA/cm^2.

amorphous Si↗
DOE OSTI2024

An examination of the performance of molecular dynamics force fields: Silicon and silicon dioxide reactive ion etching

Classical molecular dynamics (MD) simulations of plasma-surface interactions were performed of physical sputtering and reactive ion etching (RIE), with predictions based on several force fields. In this paper, we focus mainly on SiO 2 but include some results for Si substrates as well. Here, we compare predictions from these MD simulations to experimental studies of SiO 2 physical sputtering (by Ar + ions), RIE of Si, and RIE of SiO 2 (both using F atoms and Ar + ions). MD results using different published force fields are compared to reported yields from published vacuum beam experiments. The near-surface depth profiles predicted using different force fields are compared. One motivation for the present study is to document the nature and magnitude of differences in the predictions for selected systems and conditions of practical interest.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Shallow-etched thin-film lithium niobate waveguides for highly-efficient second-harmonic generation

High-fidelity periodic poling over long lengths is required for robust, quasi-phase-matched second-harmonic generation using the fundamental, quasi-TE polarized waveguide modes in a thin-film lithium niobate (TFLN) waveguide. Here, a shallow-etched ridge waveguide is fabricated in x-cut magnesium oxide doped TFLN and is poled accurately over 5 mm. The high fidelity of the poling is demonstrated over long lengths using a non-destructive technique of confocal scanning second-harmonic microscopy. We report a second-harmonic conversion efficiency of up to 939 %.W −1 (length-normalized conversion efficiency 3757 %.W −1 .cm −2 ), measured at telecommunications wavelengths. The device demonstrates a narrow spectral linewidth (1 nm) and can be tuned precisely with a tuning characteristic of 0.1 nm/°C, over at least 40 °C without measurable loss of efficiency.

Zhao, Jie (ORCID:0000000306230125)↗
DOE OSTI2021

Room temperature plasma-etching and surface passivation of far-ultraviolet Al mirrors using electron beam generated plasmas

The development of optical systems operating in the far ultraviolet range (FUV, λ=100-200 nm) is limited by the efficiency of passivated aluminum (Al) mirrors. Although it is presently possible to obtain high-reflectivity FUV mirrors through physical vapor deposition, the process involves deposition with substrates at high temperatures, which is technically challenging for large optical elements. A novel passivation procedure for bare Al mirrors is reported. The treatment consisted of using a low-temperature electron-beam generated plasma produced in a gas mixture of Ar and SF6 to etch away the native oxide layer from the Al film, while simultaneously promoting the generation of a thin aluminum tri-fluoride (AlF3) layer on the Al surface. In the first section we analyze the effect of varying both ion energy and SF6 concentration on the FUV reflectance, thickness, composition, and surface morphology of the resulting AlF3 protective layers. In the second section, the reflectivity of samples is optimized at selected important FUV wavelengths for astronomical observations. Notably, samples attained state-of-the-art reflectances of 75% at 108.5 nm (He Lyman γ), 91% at 121.6 nm (H Lyman α), 90% at 130.4 nm (OI), and of 95% at 155.0 nm (C IV). The stability over time of these passivated mirrors is also investigated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1968

Reaction rates of graphite with ozone measured by etch decoration

Etch-decoration technique of detecting vacancies in graphite has been used to determine the reaction rates of graphite with ozone in the directions parallel and perpendicular to the layer planes. It consists essentially of peeling single atom layers off graphite crystals without affecting the remainder of the crystal.

Hennig, G. R.↗