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At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Commercial and Human Settlement of the Moon and Cislunar Space – A Look Ahead at the Possibilities over the Next 50 Years

Over 50 years have passed since the movie 2001: A Space Odyssey debuted in April 1968. In the film, Dr. Heywood Floyd flies to a large artificial gravity space station orbiting Earth aboard a commercial space plane. He then embarks on a commuter flight to the Moon arriving there 25 hours later. Today, on the 50th anniversary of the Apollo 11 lunar landing, the images portrayed in 2001 still remain well beyond our capabilities. This paper examines key technologies and systems (in-situ resource utilization, fission power, advanced chemical and nuclear propulsion), and orbiting infrastructure elements (providing a propellant depot and cargo transfer function), that could be developed by NASA and the private sector in future decades allowing the operational capabilities presented in 2001 to be achieved, albeit on a more spartan scale. Lunar-derived propellants (LDPs) will be essential to reducing the launch mass requirements from Earth and developing a reusable lunar transportation system (LTS) that can allow initial outposts to evolve into settlements supporting a variety of commercial activities like in-situ propellant production. Deposits of icy regolith found within permanently shadowed craters at the lunar poles can supply the feedstock material to produce liquid oxygen (LO2) and hydrogen (LH2) propellant needed by surface-based lunar landing vehicles (LLVs) using chemical rocket engines. Along the Moon’s nearside equatorial corridor, iron oxide-rich volcanic glass beads from vast pyroclastic deposits, together with mare regolith, can provide the materials to produce lunar-derived LO2 plus other important solar wind implanted (SWI) volatiles, including H2 and helium-3. Megawatt-class fission power systems will be essential for providing continuous “24/7” power to processing plants, evolving human settlements, and other commercial activities that develop on the Moon and in orbit. Reusable LLVs will provide cargo and passenger “orbit-to-surface” access and will also be used to transport LDP to Space Transportation Nodes (STNs) located in lunar polar (LPO) and equatorial orbits (LLO). Spaced-based, reusable lunar transfer vehicles (LTVs), operating between STNs in low Earth orbit (LEO), LLO, and LPO, and able to refuel with LDPs, can offer unique mission capabilities including short transit time crewed cargo transports. Even a commuter shuttle service similar to that portrayed in 2001 appears possible, allowing 1-way trip times to and from the Moon as short as 24 hours. The performance of LTVs using both RL10B-2 chemical rockets, and a variant of the nuclear thermal rocket (NTR), the LO2-Augmented NTR (LANTR), are examined and compared. The bipropellant LANTR engine utilizes its divergent nozzle section as an afterburner into which oxygen is injected and supersonically combusted with reactor-heated hydrogen emerging from the engine’s sonic throat. If only 1% of the LDP obtained from icy regolith, volcanic glass, and SWI volatile deposits were available for use in lunar orbit, such a supply could support routine commuter flights to the Moon for many thousands of years! This paper provides a look ahead at what might be possible in the not too distant future, quantifies the operational characteristics of key in-space and surface technologies and systems, and provides conceptual designs for the various architectural elements discussed.

Borowski, Stanley K.↗
NASA NTRS2013

NASA Tech Briefs, April 2013

Topics covered include: Fully Integrated, Miniature, High-Frequency Flow Probe Utilizing MEMS Leadless SOI Technology; Nanoscale Surface Plasmonics Sensor With Nanofluidic Control; Advanced Dispersed Fringe Sensing Algorithm for Coarse Phasing Segmented Mirror Telescopes; Neural Network Back-Propagation Algorithm for Sensing Hypergols; Bulk Moisture and Salinity Sensor; Change-Based Satellite Monitoring Using Broad Coverage and Targetable Sensing; Circularly Polarized Microwave Antenna Element with Very Low Off-Axis Cross-Polarization; Ultra-Low Heat-Leak, High-Temperature Superconducting Current Leads for Space Applications; Flash Cracking Reactor for Waste Plastic Processing; An Automated Safe-to-Mate (ASTM) Tester; Wireless Chalcogenide Nanoionic-Based Radio-Frequency Switch; Compute Element and Interface Box for the Hazard Detection System; DOT Transmit Module; Composite Aerogel Multifoil Protective Shielding; Li-Ion Electrolytes with Improved Safety and Tolerance to High-Voltage Systems; Polymer-Reinforced, Non-Brittle, Lightweight Cryogenic Insulation; Controlled, Site-Specific Functionalization of Carbon Nanotubes with Diazonium Salts; Regenerable Sorbent for CO2 Removal; Sprayable Aerogel Bead Compositions With High Shear Flow Resistance and High Thermal Insulation Value; Lexan Linear Shaped Charge Holder with Magnets and Backing Plate; Robotic Ankle for Omnidirectional Rock Anchors; Wind, Wave, and Tidal Energy Without Power Conditioning; An Active Heater Control Concept to Meet IXO Type Mirror Module Thermal-Structural Distortion Requirement; Waterless Clothes-Cleaning Machine; Integrated Electrical Wire Insulation Repair System; LVGEMS Time-of-Flight Mass Spectrometry on Satellites; Surface Inspection Tool for Optical Detection of Surface Defects; Per-Pixel, Dual-Counter Scheme for Optical Communications; Certification-Based Process Analysis; Surface Navigation Using Optimized Waypoints and Particle Swarm Optimization; Smart-Divert Powered Descent Guidance to Avoid the Backshell Landing Dispersion Ellipse; Estimating Foreign-Object-Debris Density from Photogrammetry Data; Adaptive Sampling of Spatiotemporal Phenomena with Optimization Criteria; Building a 2.5D Digital Elevation Model From 2D Imagery; Eyes on the Earth 3D; Target Trailing With Safe Navigation for Maritime Autonomous Surface Vehicles; Adams-Based Rover Terramechanics and Mobility Simulator - ARTEMIS; ISTP CDF Skeleton Editor; Uplink Summary Generator (ULSGEN) Version 1.0; Robotics On-Board Trainer (ROBoT); Software Engineering Tools for Scientific Models; Automatic Data Filter Customization Using a Genetic Algorithm; Tracker Toolkit; Towards Efficient Scientific Data Management Using Cloud Storage; On a Formal Tool for Reasoning About Flight Software Cost Analysis; A Nanostructured Composites Thermal Switch Controls Internal and External Short Circuit in Lithium Ion Batteries; Spacecraft Crew Cabin Condensation Control; and Functional Near-Infrared Spectroscopy Signals Measure Neuronal Activity in the Cortex.

Source record↗
DOE OSTI2026

3D probabilistic fracture mechanics / computational fluid dynamics simulation of a reactor pressure vessel under transient conditions

Reactor pressure vessels (RPVs) are safety-critical light-water-reactor components that, under irradiation, experience long-term material degradation in the form of embrittlement. This can increase their susceptibility to fracture under thermal-shock conditions, which could occur during off-normal transients such as loss-of-coolant accidents (LOCAs). During a LOCA, the most severe conditions for the RPV occur when emergency core cooling water is injected through the cold legs into the water-and-steam-filled RPV. The rapid cooling of the downcomer and internal RPV surface causes decreased temperature and elevated thermally driven tensile stresses in the RPV wall. This, combined with long-term material embrittlement, may cause fracture initiation at pre-existing flaws, challenging the integrity of the RPV. Assessing RPV integrity during transients with a large spatial variation in the coolant temperature requires a modeling approach that considers the effects of spatially varying coolant temperature on the fracture probability of a population of flaws distributed throughout the RPV, accounting for spatially varying embrittlement. Here, the present study addresses this need by demonstrating first-of-its-kind coupling of a high-fidelity 3D computational fluid dynamics code with 3D probabilistic fracture mechanics This was accomplished using representative models of a pressurized-water reactor subjected to small- and medium-break LOCA conditions, both of which can result in large spatial temperature variations. While the observed impact of accounting for 3D effects was minimal under the small-break LOCA this study indicates a significant increase in the probability of fracture initiation under the medium-break LOCA when 3D effects are considered, relative to a spatially uniform cooling scenario.

22 - GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2024

Formation and transformation of iron oxy-hydroxide precursor clusters to ferrihydrite

Iron (Fe) oxy-hydroxide minerals such as ferrihydrite (Fh) are ubiquitous in Earth-surface environments and important in biogeochemical element cycling. Recent research has suggested that their formation is preceded by the precipitation of ultrasmall (~1 nm) Keggin-like Fe oxy-hydroxide clusters. However, relatively little is understood about the structure of the precursor clusters and the impacts of pH and time on their growth and transformation to more stable phases. Here, we used a new method that involves mixed flow reactors (MFR) to synthesize these Fe oxy-hydroxide precursor clusters at pH 1.0, 1.5, 2.5, and 4.5. In situ and ex situ synchrotron scattering measurements and laboratory small-angle X-ray scattering (SAXS) were used to study the structure and size of Fe oxy-hydroxide clusters and their transformation products, respectively. Results show that with increasing pH, the particle size and structural order of samples increase, forming solids that resemble 2-line Fh at pH 4.5. The experimental data were compared with X-ray pair distribution functions (PDF) calculated for a range of Fe(III) oxyhydroxide clusters, including Fe 13 Keggin isomers computed previously using density functional theory (DFT), which yielded at best only partial agreement at short range (<5 Å). Aging of the clusters synthesized at pH 1.5 and 2.5 results in growth and transformation via Ostwald ripening to mixtures of goethite (Gt) and lepidocrocite (Lp). This process was inhibited by immediately reacting the early-formed clusters with phosphate (PO 4 3– ), suggesting that oxyanion surface complexes can stabilize the initial clusters by preventing growth and crystallization to more stable phases.

58 GEOSCIENCES↗
DOE OSTI2024

Physical and Electrochemical Characterization of Aluminum Electrodes during Electrocoagulation

Electrocoagulation (EC) of synthetic groundwater was conducted using a sacrificial aluminum electrode in a flow-through EC reactor with short retention times (<1 min) under varying hydrodynamic and electrochemical conditions. The treated water was allowed to settle for 24 h and achieved silicate removal of up to 50 ± 4%, and hardness removal of 11 ± 1%. Physical, chemical, and electrochemical characterization was performed to explore changes in electrode surface morphology and composition. Electrochemical impedance spectroscopy (EIS) showed that chemical reactions at the electrode/water interface are sensitive to changes in the immediate chemical environment. We demonstrate that the most energy-intensive step in EC is aluminum dissolution at the anode, which remained fairly constant due to the continuous renewal of the anode’s surface, a result of aluminum dissolution. At the cathode, a structural change in the oxide layer, from γ-Al 2 O 3 to gibbsite, was detected by grazing-incidence X-ray diffraction, which decreased the resistance to charge transfer at the cathode surface, resulting in decreased electrode resistance. The high flow rate in the system minimized the accumulation of aluminum hydroxide solids and aluminum ions at the electrode/water interface, which minimized the formation of thick scalants and amorphous Al(OH) 3 on the cathode and anode, respectively. In conclusion, it was further demonstrated by EIS that under these conditions the resistance to charge transfer was constant throughout the duration of the experiment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Structural Tolerance of Zirconium Diboride under Electron Irradiation through in-situ Convergent Beam Electron Diffraction and Energy-dispersive X-ray Spectroscopy

Zirconium diboride (ZrB 2 ) is a ultra-high temperature ceramic with high melting temperature (>3000 K), super strength and hardness, good thermal conductivity, and excellent resistance to plasma erosion and chemical erosion, being widely applied in hypersonic flight, arc-electrodes, refractory materials, and plasma-facing materials in fusion reactors. Therefore, the structural stability of the material is essential for the applications. Up to now, the material was investigated under neutron irradiation and high-energy ion irradiations. It was reported that the neutron irradiation caused swelling and catastrophic cracking. High-energy ions (30 keV He + ) changed the surface morphology and caused the bright blue and brown colors on ZrB 2 surfaces between 920 K and 1120 K. The electron irradiation tolerance of the material has not been reported yet. Here we used convergent beam electron diffraction (CBED) and energy-dispersive X-ray spectroscopy (EDS) to investigate structural tolerances of ZrB 2 crystals under high-energy electrons at room temperature under vacuum. Finally, the investigation would benefit the understanding of its structural tolerance at microscales.

42 ENGINEERING↗
DOE OSTI2024

Abstract for CRADA between Capture6 CORP and NETL

The National Energy Technology Laboratory (NETL) and Capture6 CORP (Participant) will collaborate to refine Capture6’s transformative air contactor design for optimal direct air capture (DAC) under an awarded project from the Department of Energy’s Direct Air Capture Pre-Commercialization Technology Prize. Current cooling tower designs require exponentially more resources as the concentration of CO 2 in the gas phase decreases, resulting in a low conversion rate of carbonates, a large physical footprint, and high evaporation of water, which consequently limits the energy and water benefits that a DAC process can create. Capture6’s innovative tower design AURA (Absorption Unit Reactor for Ambient air) seeks to improve the mass transfer characteristics of legacy cooling towers and reduces total energy demand by: (1) introducing laminar and turbulent flow to increase mass transfer, (2) generating a solvent gradient to improve CO 2 absorption, (3) leveraging venturi and packed towers to increase the surface for the mass-transfer process, (4) adding charged/cool plates to reduce overall water loss in the system, and (5) utilizing surfactant additives to increase mass transfer. The collaboration will facilitate the deployment of technologies that reduce the total energy required and carbon footprint of solvent-based carbon dioxide removal (CDR) technologies. The anticipated results support NETL’s goal of fostering rapid development and commercialization pathways for technologies that remove CO 2 from the atmosphere.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2024

Isolated Single Metal Atoms Supported on Silica for One Step Non-Oxidative Methane Upgrading to Hydrogen and Value-Added Hydrocarbons

Natural gas in the United States offers substantial economic opportunities due to its abundance but its transportation is challenging because its primary component, methane (CH 4 ), does not liquefy at ambient temperature and typical pressures. As a result, a significant portion of natural gas is either used for heat, flared in remote locations, or remains unutilized, presenting a lost economic opportunity and an environmental harm. Converting natural gas to larger hydrocarbons in an economically competitive manner would enable transportation of products and further boost the economy and reduce environmental footprint. Our research goal is to enable efficient non-oxidative methane conversion (NMC) via catalyst innovation to convert CH 4 in one-step to olefins and aromatics and hydrogen (H 2 ) co-product. The catalysts are made of supported single metal atoms and operated at medium-high temperatures. The single metal atoms achieve methane activation by heterogeneous surface dehydrogenation to generate a hydrocarbon pool and importantly limit coke formation. The integration of novel single atom catalysts in a short contact time microreactor enable unprecedented NMC performance that could lead to economically-feasible, distributed natural gas upgrading by advanced manufacturing and process intensification. Our innovated catalyst and reactor technology promise to tap into previously uneconomic natural gas resources, such as stranded, vented, and flared methane.

03 NATURAL GAS↗
NASA NTRS1992

Natural circulation decay heat removal from an SP-100, 550 kWe power system for a lunar outpost

This research investigated the decay heat removal from the SP-100 reactor core of a 550-kWe power system for a lunar outpost by natural circulation of lithium coolant. A transient model that simulates the decay heat removal loop (DHRL) of the power system was developed and used to assess the system's decay heat removal capability. The effects of the surface area of the decay heat rejection radiator, the dimensions of the decay heat exchanger (DHE) flow duct, the elevation of the DHE, and the diameter of the rise and down pipes in the DHRL on the decay heat removal capability were examined. Also, to determine the applicability of test results at earth gravity to actual system performance on the lunar surface, the effect of the gravity constant (1 g and 1/6 g) on the thermal behavior of the system after shutdown was investigated.

El-Genk, Mohamed S.↗
NASA NTRS2022

Recent Concept Study for Cryogenic Fluid Management to Support Opposition Class Crewed Missions to Mars

NASA recently completed a mission concept study to evaluate the feasibility and propulsion technology development requirements for reduced travel duration crewed missions to Mars. A high-level goal of the study was to minimize the health impact on the crew caused by the space environment. This was implemented in the study by limiting the crew to a total of approximately-two years of in-space operations and travel time. For the initial mission, the crew would stay about 30 days on the Martian surface. The propulsive demands of such a mission are immense, and the study identified two advanced propulsion options with the potential to meet the mission requirements—both options rely on nuclear fission to provide efficient propulsive energy. One propulsion option was a nuclear electric propulsion (NEP)/Chem Hybrid, with a reactor and energy conversion system powering xenon propellant ion thrusters to provide an efficient, but lower-thrust, push for most of the mission duration. This concept also relied on a liquid oxygen/liquid methane (LO2/LCH4) chemical propulsion stage to provide high thrust for maneuvers while near the Earth and Mars. The second propulsion option was nuclear thermal propulsion (NTP), in which the reactor heats liquid hydrogen (LH2) propellant to expand through a nozzle for thrust at about twice the efficiency of the best chemical propulsion systems. Both vehicle concepts rely on storing large amounts of cryogenic propellant (either LO2/LCH4 or LH2) for multiple years in space without loss, far exceeding state-of-the-art capability. To enable this new capability, the team assumed the use of several advanced cryogenic fluid management (CFM) technologies and analyzed the integrated system performance. This included considering the vehicle-level effects of the size, mass, and power requirements of these CFM elements. Further, the team evaluated the development required to enable such a mission in the mid-2030 s and determined that it was feasible. The paper elaborates on the assumed CFM technologies, provides key analysis results, and illustrates the feasibility of technology development for the proposed solutions to the CFM challenges for each propulsion concept.

cryogenic propellant↗
DOE OSTI2021

Initial Developments in Modeling Graphite Behavior

Graphite is used in High Temperature Reactor designs as a moderator, reflector and core material responsible for protecting the fuel and maintaining structural stability. From a safety perspective, it is imperative to be able to predict how graphite will behave under reactor operating conditions which may compromise the core’s structural integrity or fuel’s safety performance. The following report summarizes recent modeling work undertaken at Idaho National Laboratory which focuses on graphite degradation behavior. One phenomenon which is explored in this report and can cause significant degradation to graphite properties is oxidation. Oxidation behavior in graphite is highly temperature dependent. At low temperatures, oxygen can fully penetrate a component and cause a homogeneous damage profile. At high temperatures, only the graphite near the surface of a component is affected. Understanding and modeling this temperature dependence is essential to predicting graphite behavior. In this report, three graphite models are discussed. The first model is used to investigate strength loss after low temperature oxidation. It does this by generating an approximate graphite microstructure then determining the required load to cause crack propagation. It has been shown that the model reproduces the quasi brittle stress versus strain relationship observed in graphite. Strength loss results from the model are shown to match experimental values. The second model investigates strength loss under high temperature oxidation conditions. This model is more applicable to full scale graphite components where the oxidation damage is often inhomogeneous throughout a component. The third model computes stresses in graphite under reactor conditions. Specifically, the model incorporates the effect of creep, irradiation dose, thermal strains, and oxidation in order to predict internal stresses in a component. All of these models are implemented in the Multiphysics Object-Oriented Simulation Environment (MOOSE), an open source, parallel finite element framework.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Status of Eddy Current Developments at INL

Both standard and advanced Light Water Reactor (LWR) fuel systems are composed of fuel pellets enclosed in a metallic cladding. The fuel cladding represents the first containment of the fission products and the first safety barrier. Upon progression of irradiation, the cladding properties deteriorate, mainly due to the pick-up of hydrogen, which causes embrittlement, and the consequence corrosion that reduced the metallic substrate. Those changes in the properties combined with the harsh environment, e.g., fatigue and fretting occurring during operation, might eventually lead to loss of hermeticity. Therefore, it is important to be able to quantify the amount of corrosion taking place and to detect and size structural discontinuity that can promote cladding failure. Eddy current testing is one of the non-destructive methods employed for this purpose. Inspections are carried out using special probes, which are designed and optimized to inspect a tube with well-defined geometrical and physical characteristics, i.e. external diameter, wall thickness, material electric conductivity and magnetic permeability. The inspection goals are mainly twofold: first, the determination of the amount of corrosion by measurement of the external oxide thickness; second, the detection of flaws in the tube wall, ether on the external or the internal surface of the tube. This report summarizes the available capabilities for eddy current testing of LWR fuel claddings, identifies needs and are of developments for testing of ATF claddings.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2022

Multifunctional intensified reactor device with integrated heat and mass transfer

A packing device for mass and heat transfer with a subject fluid includes a housing having opposing ends, and subject fluid openings at each opposing end defining a subject fluid flow path for at least one subject fluid flowing through the packing device. A plurality of mass and heat transfer plates each include an interior heat exchange fluid channel disposed between interior heat transfer surfaces of the mass and heat transfer plates. A heat exchange fluid inlet and fluid outlet can supply and remove heat exchange fluid to the heat exchange fluid channels of the mass and heat transfer plates. The mass and heat transfer plates can be oriented to define there between fluid flow channels for the subject fluid. A method and system for mass and heat transfer with a subject fluid, and a method and system for the removal of CO2 from a gas stream are disclosed.

Lai, Canhai↗
DOE OSTI2023

Characterization of Fe and Cr Dissolution and Reaction Product Formation in Molten Chloride Salts With and Without Impurities

There is considerable interest in molten chloride salts for several applications including thermal storage and next-generation molten salt reactors (MSRs). Several studies have concluded that Cl salts are highly corrosive to structural materials. Using Oak Ridge National Laboratory’s established methodology, Cl salt compatibility was assessed for candidate Ni-based alloys 230, 600 and 740 H at 600°–800°C in static welded capsules and in flowing thermal convection loop (TCL) salt experiments. Simply drying commercial Cl salt at 550°–650°C and adding~0.05 wt.%Mg was able to produce small specimen mass changes and limited surface attack after 100–1000 h exposures. Intentional additions of H 2 O, NiCl 2 and undried salt were used to better understand the role of impurities and achieve the>50 µm levels of attack reported in other studies. Further, characterisation of Cr depletion and oxide formation in conjunction with pre- and post-test salt chemistry measurements are being used to understand salt compatibility of structural materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

HFIR SiC-SiC Composite Clad Tube Bowing Test: Pre-Irradiation Characterization

This report describes the pre-irradiation characterization of the SiC-SiC composite clad tube bowing experiment that will be irradiated in the High Flux Isotope Reactor (HFIR). There are concerns that SiCSiC fuel cladding in light water reactors could undergo bowing because of the non-uniform fast neutron flux profiles. This experiment is combined with the SiC-SiC channel box experiment, which has similar concerns regarding control blade movements in boiling water reactors. The HFIR experiment aims to validate the predicted deformation and stresses in the composite clad specimen after the exposure of fast neutron flux gradients. Significant radial fast neutron flux gradients that exist in the permanent reflector of HFIR were thoroughly characterized by using detailed 3D neutronic calculations. The 3D displacement damage dose rate profile and the resulting volumetric swelling in SiC were used as inputs to structural analyses to determine the predicted deformation that will affect the specimens. The tube specimens were characterized by using traditional dimensional inspection and surface profilometry to provide detailed information regarding the pre-irradiation condition as the first step to evaluate the radiation-induced deformation. Furthermore, fine engraving markers were inscribed along all outer surfaces of the specimen and mapped by using a digital microscope and a multidimensional stage. This allows marker spacings to be accurately measured and compared with similar measurements that will be made post-irradiation to provide local radiation-induced strain mapping. The experiment successfully completed two HFIR cycle irradiations, cycles 492 and 493, which finished on July 25, 2021.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2021

Erosion of focus rings in capacitively coupled plasma etching reactors

In plasma etching reactors, the structure surrounding the wafer, often called a focus ring (FR), plays an important role in maintaining uniform fluxes of reactants across the wafer. The FR is typically made of dielectric materials. During the plasma etching process, the sheath that forms over the wafer to accelerate ions anisotropically into the surface extends over the FR. Electrical charging of the FR modifies the sheath relative to that over the wafer. On the one hand, one wants the sheath to be uniform across the wafer-FR boundary to enable uniform fluxes to the edge of the wafer. On the other hand, maintaining a high voltage sheath over the FR will erode the FR, which is undesirable as the FR is a consumable component that must be periodically replaced in high volume manufacturing. In this work, we computationally investigated the consequences of dielectric constant ε of the FR materials on erosion of the FR. The series capacitance of the FR and its underlying structure is typically smaller than that of the wafer and its underlying structure. As a result, the FR charges quickly relative to the wafer, which then reduces the voltage across the sheath on top of the FR. The ion energy and angular distributions (IEADs) striking the FR are, therefore, generally lower in energy with a broader angular distribution. With ε = 2, the ion energies striking the middle to the outer edge of the FR are 30–180 eV, whereas for ε = 100, the ion energies are 120–380 eV. At the transition between the wafer and the FR, there is a skew in the IEAD as large as 15° that results from the difference in sheath thickness above the wafer and the FR. This skew and the erosion rate across the FR are functions of the dielectric constant of the FR material. With low ε, the FR charges quickly, less plasma is produced above the FR, and there is less voltage across the sheath that results in less FR erosion. Increasing ε of the FR produces a higher sheath voltage as well as higher ion fluxes over the FR, which increases erosion, while the skew at the edge of the wafer is less severe. Further, the material of the subsurface portion of the FR, which dominates its capacitance, is an important consideration in the design of the substrate assembly.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Driving energetically unfavorable dehydrogenation dynamics with plasmonics

Nanoparticle surface structure and geometry generally dictate where chemical transformations occur, with higher chemical activity at sites with lower activation energies. Here, we show how optical excitation of plasmons enables spatially modified phase transformations, activating otherwise energetically unfavorable sites. We have designed a crossed-bar Au-PdH x antenna-reactor system that localizes electromagnetic enhancement away from the innately reactive PdH x nanorod tips. Using optically coupled in situ environmental transmission electron microscopy, we track the dehydrogenation of individual antenna-reactor pairs with varying optical illumination intensity, wavelength, and hydrogen pressure. Our in situ experiments show that plasmons enable new catalytic sites, including dehydrogenation at the nanorod faces. Molecular dynamics simulations confirm that these new nucleation sites are energetically unfavorable in equilibrium and only accessible through tailored plasmonic excitation.

36 MATERIALS SCIENCE↗