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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Surrogate models to optimize plasma-assisted atomic layer deposition in high aspect ratio features

In this work, we explore surrogate models to optimize plasma enhanced atomic layer deposition (PEALD) in high aspect ratio features. In plasma-based processes such as PEALD and atomic layer etching (ALE), surface recombination can dominate the reactivity of plasma species with the surface, which can lead to unfeasibly long exposure times to achieve full conformality inside nanostructures like high aspect ratio vias. Using a synthetic dataset based on simulations of PEALD, we train artificial neural networks to predict saturation times based on cross section thickness data obtained for partially coated conditions. The results obtained show that just two experiments in undersaturated conditions contain enough information to predict saturation times within 10% of the ground truth. A surrogate model trained to determine whether surface recombination dominates the plasma–surface interactions in a PEALD process achieves 99% accuracy. This demonstrates that machine learning can provide a new pathway to accelerate the optimization of PEALD processes in areas such as microelectronics. Our approach can be easily extended to ALE and more complex structures.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Insights from high-fidelity modeling of industrial rotary bell atomization

The global automotive industry sprayed over 2.6 billion liters of paint in 2018, much of which through electrostatic rotary bell atomization, a highly complex process involving the fluid mechanics of rapidly rotating thin films tearing apart into micrometer-thin filaments and droplets. Coating operations account for 65% of the energy usage in a typical automotive assembly plant, representing 10,000s of gigawatt-hours each year in the United States alone. Optimization of these processes would allow for improved robustness, reduced material waste, increased throughput, and significantly reduced energy usage. Here, we introduce a high-fidelity mathematical and algorithmic framework to analyze rotary bell atomization dynamics at industrially relevant conditions. Our approach couples laboratory experiment with the development of robust non-Newtonian fluid models; devises high-order accurate numerical methods to compute the coupled bell, paint, and gas dynamics; and efficiently exploits high-performance supercomputing architectures. These advances have yielded insight into key dynamics, including i) parametric trends in film, sheeting, and filament characteristics as a function of fluid rheology, delivery rates, and bell speed; ii) the impact of nonuniform film thicknesses on atomization performance; and iii) an understanding of spray composition via primary and secondary atomization. These findings result in coating design principles that are poised to improve energy- and cost-efficiency in a wide array of industrial and manufacturing settings.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Primary Radiation Damage Formation in Solids

The processes that give rise to changes in the microstructure and the physical and mechanical properties of solid metals and ceramics exposed to energetic particles are initiated by essentially elastic collisions between atoms in what has been called an atomic displacement cascade. These processes are similar in metals and ceramics, with some differences related to the ionic and covalent bonding in ceramics compared to metallic bonding. The formation and evolution of primary radiation damage mechanisms are described to provide an overview of how stable defects are formed by displacement cascades, as well as the nature and morphology of the defects themselves. The impact of the primary variables cascade energy and irradiation temperature are discussed, along with a range of secondary factors that can influence damage formation.

Zarkadoula, Eva↗
DOE OSTI2020

Two-Photon Spontaneous Emission in Atomically Thin Plasmonic Nanostructures

The ability to harness light-matter interactions at the few-photon level plays a pivotal role in quantum technologies. Single photons—the most elementary states of light—can be generated on demand in atomic and solid state emitters. Two-photon states are also key quantum assets, but achieving them in individual emitters is challenging because their generation rate is much slower than competing one-photon processes. We demonstrate that atomically thin plasmonic nanostructures can harness two-photon spontaneous emission, resulting in giant far field two-photon production, a wealth of resonant modes enabling tailored photonic and plasmonic entangled states, and plasmon-assisted single-photon creation orders of magnitude more efficient than standard one-photon emission. We unravel the two-photon spontaneous emission channels and show that their spectral line shapes emerge from an intricate interplay between Fano and Lorentzian resonances. Enhanced two-photon spontaneous emission in two-dimensional nanostructures paves the way to an alternative efficient source of light-matter entanglement for on-chip quantum information processing and free-space quantum communications.

36 MATERIALS SCIENCE↗
NASA NTRS1975

Dissociation of CH4 and CD4 by electron impact - Production of metastable and high-Rydberg hydrogen and carbon fragments

Production of hydrogen and carbon atoms in metastable and high-lying Rydberg states by electron-impact dissociation of methane and deuterated methane is investigated for incident electron energies ranging from threshold values to 300 eV. Threshold energies for five different processes resulting in metastable hydrogen and carbon atoms are determined in the energy range from 20 to 70 eV, and it is shown that metastable hydrogen atoms are produced in four of these collisional processes while metastable carbon atoms are produced in the other. The nature of each collisional process is described, differential cross sections are derived for the dissociative excitation of both types of atoms to metastable and high-Rydberg states at 100 eV, and the onset energy for UV photon production is measured. Much of the data is interpreted in terms of the ion core model suggested by Kupriyanov (1968) and developed by Freund (1971).

Finn, T. G.↗
DOE OSTI2023

Automated phase segmentation and quantification of high-resolution TEM image for alloy design

In the alloy design and development process, a wealth of atomically resolved structural high-resolution transmission electron microscopy (HRTEM) images are produced. Identifying the different nano-precipitate phases and tracking their evolution under various compositions and during manufacturing or post-processing requires hundreds of HRTEM images and thousands of precipitates. The nanoscopic phase information labeling and analysis purely relies on humans are prohibitively costly and time-consuming, sometimes not reliable because of the lack of authoritative knowledge. Here, in this work, we develop a novel unsupervised machine learning approach coupled with adaptive computer vision techniques with features in the Fourier space to automatically determine the number of phases and segment/quantify the phases with nanoscale resolution, allowing for quantitative correlation between nanostructure formation, processing and functional properties. To automate the phase extraction/quantification and ascertain its applicability, we have applied the developed framework to the HRTEM images from several alloy systems, processing conditions, image magnifications, and phase types and morphologies (precipitates, nano-twins, stacking faults, crystalline matrix, and amorphous structures) for verification. This study paves the road for compression, visualization, and translation of raw image structural data into physically relevant information in real-time with minimal human supervision. It shows the promise of enabling high-throughput materials characterization for the acceleration of alloy manufacturing and design.

36 MATERIALS SCIENCE↗
NASA NTRS2001

Meteoric Ions in Planetary Ionospheres

Solar system debris, in the form of meteoroids, impacts every planet. The flux, relative composition and speed of the debris at each planet depends on the planet's size and location in the solar system. Ablation in the atmosphere evaporates the meteoric material and leaves behind metal atoms. During the ablation process metallic ions are formed by impact ionization. For small inner solar system planets, including Earth, this source of ionization is typically small compared to either photoionization or charge exchange with ambient molecular ions. For Earth, the atmosphere above the main deposition region absorbs the spectral lines capable of ionizing the major metallic atoms (Fe and Mg) so that charge exchange with ambient ions is the dominant source. Within the carbon dioxide atmosphere of Mars (and possibly Venus), photoionization is important in determining the ion density. For a heavy planet like Jupiter, far from the sun, impact ionization of ablated neutral atoms by impacts with molecules becomes a prominent source of ionization due to the gravitational acceleration to high incident speeds. We will describe the processes and location and extent of metal ion layers for Mars, Earth and Jupiter, concentrating on flagging the uncertainties in the models at the present time. This is an important problem, because low altitude ionosphere layers for the planets, particularly at night, probably consist predominantly of metallic ions. Comparisons with Earth will be used to illustrate the differing processes in the three planetary atmospheres.

Pesnell, W. D.↗
DOE OSTI2020

Molecular Layer Etching of Metalcone Films Using Lithium Organic Salts and Trimethylaluminum

Advances in semiconductor device manufacturing are limited by our ability to precisely add and remove thin layers of material in multistep fabrication processes. Recent reports on atomic layer etching (ALE) have provided the means for the precise removal of inorganic thin films deposited by atomic layer deposition (ALD), opening new avenues for nanoscale device design. Here, we report on a new technique for the precise removal of metal organic thin films deposited by molecular layer deposition (MLD), which we term molecular layer etching. This etching process employs sequential exposures of lithium organic salt (LOS) and trimethylaluminum (TMA) precursors to produce self-limiting etching behavior. We employ quartz crystal microbalance experiments to demonstrate (i) etching of alucone films preloaded with LOS upon TMA exposures and (ii) layer-by-layer etching of alucone films using alternating exposures of LOS and TMA. We also identify the selectivity of these etching mechanisms. We probe the mechanism for the layer-by-layer etching of alucone using a quartz crystal microbalance and Fourier transform infrared spectroscopy and identify that the etching proceeds via heterolytic cleaving of Al-O bonds in alucone upon LOS exposure followed by methylation to produce volatile species upon TMA exposure. The etching process results in the removal of 0.4 nm/cycle of alucone at 160 °C and up to 3.6 nm/cycle of alucone at 266 °C in ex situ etching experiments on silicon wafers. This halogen-free etching process enables etching of MLD films and provides new fabrication pathways for the control of material geometries at the nanoscale.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1987

Opacity project - Astrophysical and fusion applications

An overview is presented of a project to calculate large quantities of accurate atomic data for radiative processes of importance in the precise determination of opacities in stellar atmospheres, and for astrophysical and laboratory applications in general. Work is in progress on the oscillator strengths, photoionization cross sections, damping constants, etc., for all atoms and ions in hydrogen through neon isoelectronic sequences going up to iron.

Pradhan, A. K.↗
NASA NTRS1957

Basic Considerations in the Combustion of Hydrocarbon Fuels with Air

Basic combustion research is collected, collated, and interpreted as it applies to flight propulsion. The following fundamental processes are treated in separate chapters: atomization and evaporation of liquid fuels, flow and mixing processes in combustion chambers, ignition and flammability of hydrocarbon fuels, laminar flame propagation, turbulent flames, flame stabilization, diffusion flames, oscillations in combustors, and smoke and coke formation in the combustion of hydrocarbon-air mixtures. Theoretical background, basic experimental data, and practical significance to flight propulsion are presented.

Barnett, Henry C↗
NASA NTRS1987

The physics of interstellar shock waves

This review discusses the observations and theoretical models of interstellar shock waves, in both diffuse cloud and molecular cloud environments. It summarizes the relevant gas dynamics, atomic, molecular and grain processes, radiative transfer, and physics of radiative and magnetic precursors in shock models. It then describes the importance of shocks for observations, diagnostics, and global interstellar dynamics. It concludes with current research problems and data needs for atomic, molecular and grain physics.

Shull, J. Michael↗
DOE OSTI2020

Photothermal alternative to device fabrication using atomic precision advanced manufacturing techniques

The attachment of dopant precursor molecules to depassivated areas of hydrogen-terminated silicon templated with a scanning tunneling microscope (STM) has been used to create electronic devices with sub-nanometer precision, typically for quantum physics demonstrations, and to dope silicon past the solid-solubility limit, with potential applications in microelectronics and plasmonics. However, this process, which we call atomic precision advanced manufacturing (APAM), currently lacks the throughput required to develop sophisticated applications because there is no proven scalable hydrogen lithography pathway. Here, we demonstrate and characterize an APAM device workflow where STM lithography has been replaced with photolithography. An ultraviolet laser is shown to locally heat silicon controllably above the temperature required for hydrogen depassivation. STM images indicate a narrow range of laser energy density where hydrogen has been depassivated, and the surface remains well-ordered. A model for photothermal heating of silicon predicts a local temperature which is consistent with atomic-scale STM images of the photo-patterned regions. Finally, a simple device made by exposing photo-depassivated silicon to phosphine is found to have a carrier density and mobility similar to that produced by similar devices patterned by STM.

42 ENGINEERING↗
NASA NTRS1980

Molecule formation and infrared emission in fast interstellar shocks. II - Dissociation speeds for interstellar shock waves

The postshock destruction of molecules is examined, including the processes of (1) collisions with neutral hydrogen atoms and molecules, (2) electronic collisions, and (3) neutral chemical reactions with atoms, particularly atomic hydrogen. By using conservative estimates of collisional dissociation rates from individual vibrational states, it is found that process (1) leads to the destruction of molecular hydrogen behind shocks with speeds equal to or greater than 25 km/s if the preshock molecular gas has hydrogen nucleus densities of equal to or greater than 10 to the 4th/cu cm. At lower densities (100 per cu cm), destruction occurs for shock speeds equal to or greater than 50 km/s and process (2) dominates. Dissociation of molecules such as CO, H2O, and O2 follows the destruction of H2, as the resultant hydrogen atoms chemically dissociate the metal atoms from their bonds (process 3) in the hot postshock gas. These results demonstrate that many of the observed high-speed interstellar molecules, if shock accelerated, must have dissociated and reformed in the postshock gas.

Hollenbach, D.↗
NASA NTRSDate not supplied

Apatite Nanoresponse to Acidic Dissolution

Phosphorus uptake by plants and organisms is one of the most important life-sustaining processes occurring in the critical zone (CZ). Because 95% of Earth’s reserves is relatively immobile in the form of apatite, plants and organisms rely on molecular scale solubilization process to extract available P. As the world experiences a global P shortage, influencing food production, it becomes increasingly important to understand apatite dissolution. The detailed study of chemically weathered apatite surfaces at the μm to nm-scale is key to understanding P solubilization and uptake in the CZ, allowing for better crop management and efficient fertilization. Apatite weathering is generally viewed in terms of a pH-dependent process where protons weaken atomic bonds, this leading to the disintegration of the apatite structure. A general feature of apatite weathering in acid and near neutral pH conditions is an apparent non-stoichiometric dissolution characterized by [Ca/P]aq > 1.66 in both fluorapatites (FAP) and hydroxyapatites (HAP). This process leads to the formation of a surface altered layer (SAL) with a different composition from the bulk, which many have argued is a Ca-depleted “leached layer.” We investigated apatite weathering at the nanoscale using FIB-prepared TEM-foils. Our preliminary results based on laboratory-altered FAP at ambient T and pH 3 show the formation of amorphous SALs with a maximum thickness of ~10 nm. High resolution chemical mapping and profiling using STEM-EELS and STEM-EDXS indicate that the SALs are generally, but not always, depleted in Ca and enriched in P. These results provide an alternate view of the mechanism of apatite dissolution with stoichiometric breakdown of the apatite structure, followed by the reprecipitation of an amorphous surface layer depleted in Ca. This mechanism can be described in terms of coupled interfacial dissolution-reprecipitation (CIDR), which is increasingly viewed as a universal mechanism of silicate mineral and glass dissolution. Our observation that apatite may dissolve similarly to silicates implies not only that apatite weathering may be more complex than originally thought, but also that the CIDR mechanism may extend beyond silicates.

mineralogy↗
DOE OSTI2022

Design and construction of a quantum matter synthesizer

The quantum matter synthesizer (QMS) is a new quantum simulation platform in which individual particles in a lattice can be resolved and re-arranged into arbitrary patterns. The ability to spatially manipulate ultracold atoms and control their tunneling and interactions at the single-particle level allows full control of a many-body quantum system. We present the design and characterization of the QMS, which integrates into a single ultra-stable apparatus a two-dimensional optical lattice, a moving optical tweezer array formed by a digital micromirror device, and site-resolved atomic imaging. We demonstrate excellent mechanical stability between the lattice and tweezer array with relative fluctuations below 10 nm, diffraction-limited imaging at a resolution of 655 nm, and high-speed real-time control of the tweezer array at a 2.52 kHz refresh rate, which will be adopted to realize fast rearrangement of atoms. The QMS also features new technologies and schemes, such as nanotextured anti-reflective windows and all-optical long-distance transport of atoms.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Uncertainty-aware molecular dynamics from Bayesian active learning for phase transformations and thermal transport in SiC

Abstract Machine learning interatomic force fields are promising for combining high computational efficiency and accuracy in modeling quantum interactions and simulating atomistic dynamics. Active learning methods have been recently developed to train force fields efficiently and automatically. Among them, Bayesian active learning utilizes principled uncertainty quantification to make data acquisition decisions. In this work, we present a general Bayesian active learning workflow, where the force field is constructed from a sparse Gaussian process regression model based on atomic cluster expansion descriptors. To circumvent the high computational cost of the sparse Gaussian process uncertainty calculation, we formulate a high-performance approximate mapping of the uncertainty and demonstrate a speedup of several orders of magnitude. We demonstrate the autonomous active learning workflow by training a Bayesian force field model for silicon carbide (SiC) polymorphs in only a few days of computer time and show that pressure-induced phase transformations are accurately captured. The resulting model exhibits close agreement with both ab initio calculations and experimental measurements, and outperforms existing empirical models on vibrational and thermal properties. The active learning workflow readily generalizes to a wide range of material systems and accelerates their computational understanding.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Strategies to overcome electron-beam issues in liquid phase TEM: Study of chemical processes

Abstract Liquid phase (or liquid cell) transmission electron microscopy (TEM) has become a powerful platform for in situ investigation of various chemical processes at the nanometer or atomic level. The electron beam for imaging can also induce perturbation to the chemical processes. Thus, it has been a concern that the observed phenomena in a liquid cell could deviate from the real-world processes. Strategies have been developed to overcome the electron-beam-induced issues. This article provides an overview of the electron-beam effects, and discusses various strategies in liquid cell TEM study of nucleation, growth, and self-assembly of nanoscale materials, where an electron beam is often used to initiate the reactions, and highly electron-beam-sensitive electrochemical reactions. Graphical abstract

Zheng, Wenjing↗
NASA NTRSDate not supplied

Effect of Alloying Additions on Twinning in Ni-based Superalloys

Micro-twinning is the dominant creep deformation mechanism in Ni-based superalloys at temperatures above 700 °C. We use atomistic simulations to study two mechanisms of twin nucleation and growth that are characterized by qualitatively different rate limiting processes. In case of the mechanism proposed by Kolbe, the rate limiting process is diffusion-mediated atomic reshuffling. In case of the other mechanism, we proposed recently, the rate limiting process is nucleation of Shockley partial dislocation. We demonstrate the effects of alloying additions on functionality of these mechanisms.

Valery V Borovikov↗