Search NASA⌕ Search

SEARCH · Search NASA

Results for “CONTROL SURFACE”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Optimization of Magnesium-Doped Lithium Metal Anode for High Performance Lithium Metal Batteries through Modeling and Experiment

Lithium (Li)-magnesium (Mg) alloy with limited Mg amount, which can also be called Mg-doped Li (Li-Mg), has been considered as a potential alternative anode for high energy density rechargeable Li metal batteries. However, the optimum doping-content of Mg in Li-Mg anode and the mechanism of the improved performance are not well understood. In this study, density functional theory (DFT) calculations are used to investigate the effect of Mg amount in Li-Mg anode. The Li-Mg with about 5 wt. % Mg (abbreviated as Li-Mg5) has the lowest absorption energy of Li, thus all the surface area can be “controlled” by Mg atoms, leading to the smooth and continuous deposition of Li on the surface around the Mg center. A localized high concentration electrolyte enables Li-Mg5 to exhibit the best cycling stability in Li metal batteries with high-loading cathode and lean electrolyte under 4.4 V high-voltage, which is approaching the demand of practical application. This electrolyte also helps generate an inorganic-rich solid electrolyte interphase, which leads to smooth, compact and less corrosion layer on the Li-Mg5 surface. Both theoretical simulations and experimental results prove that Li-Mg5 has optimum Mg content and gives best battery cycling performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Ultra-compact and efficient heat exchanger for solar desalination with unprecedented scaling resistance

The objective is to design, prototype, and test a heat exchanger technology with an efficiency improvement of more than 150% compared to state-of-the-art heat exchanger technology (UA/volume), with significantly improved fouling/scaling resistance at elevated temperatures (>120°C) when compared to existing technology where scaling is a major performance-limiting issue, as well as at lower operating-temperatures (~63-110°C). We now report our overall progress on the project. An ultra-compact, efficient heat exchanger geometry has been developed that can maximize surface-area-to-volume ratio so that proposed target (UA/volume). Advanced manufacturing techniques, such additive manufacturing, have made it possible to create complex structures cost effectively. In addition to traditional manufacturing methods, additive manufacturing has been successfully used for the development of high-performance geometries. These methods allow the ability to create custom surface textures, which are deployed to dramatically control wettability and create energy-gradient surfaces. These techniques allow fouling/scaling nucleation to be spatially controlled, such that as the fouling layer grows it will be broken and removed by flow forces.

42 ENGINEERING↗
DOE OSTI2020

Small Polarons and Surface Defects in Metal Oxide Photocatalysts Studied Using XUV Reflection–Absorption Spectroscopy

In photocatalytic transition metal oxides, the surface electronic structure and carrier kinetics are complicated by both charge trapping at defects and self-trapping by small polaron formation. These effects are specific to both the material and the type of defect or surface states involved. Here we review recent studies on ultrafast photoexcited charge carrier dynamics at the surfaces of alpha-Fe 2 O 3 (hematite) and NiO and at the interface of a alpha-Fe 2 O 3 /NiO heterojunction using extreme ultraviolet (XUV) reflection-absorption spectroscopy. We study dynamics of small polaron formation at hematite surfaces showing that the rate of carrier self-trapping is slower than in the bulk due to a greater lattice reorganization energy required for surface polaron formation. We also show that surface dynamics of hematite can be systematically tuned to control carrier transport properties through surface functionalization. To better understand the impact of defects on carrier events, we study charge carrier recombination of NiO. It is shown that O vacancies have no detrimental effect on carrier lifetime while grain boundaries cause fast recombination. Finally, we study a model heterojunction consisting of alpha-Fe 2 O 3 and NiO and find that interfacial charge transfer across these two materials occurs by a two-step mechanism where the interfacial electric field drives fast exciton dissociation followed by hole injection from alpha-Fe2O3 to NiO. Finally, these examples illustrate future opportunities to observe surface electron dynamics in photocatalytic materials with element and chemical state resolution using ultrafast XUV spectroscopy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Needle-Like Ferroelastic Domains in Individual Ferroelectric Nanoparticles

Superior structural, physical and electronic properties make ferroelectric nanocrystals essential in enabling a range of next-generation devices. Ferroelectric responses are determined by crystal structure and domain morphology. The ability to reversibly displace, create and annihilate elastic domains is critical to device applications. Whereas electric-field control has been demonstrated for ferroelectric 180° surface domain walls and vortices, similar control of ferroelastic domains and domain boundaries within individual nanocrystals remains challenging. Using controlled external compressive and tensile axial stress, deterministic and reversible control of highly mobile ferroelastic domains and axial polarization in three dimensions is demonstrated in this study. While many studies exist on ferroelastic domains in thin films and bulk, little is known about ferroelastic interactions at the single nanoparticle level, especially involving domain boundaries. Through combining Bragg coherent X-ray diffractive imaging and Landau theory, strain gradients in individual BaTiO3 nanocrystals are shown to stabilize needle-like ferroelastic twin domains. These domains are highly labile under applied axial stress, producing a locally enhanced electric polarization mediated by a ferroelectric phase transition. The efficacy of Bragg coherent X-ray diffractive imaging in studying in operando domains in three-dimensions is demonstrated, while synergy with theory provides a paradigm for domain boundary engineering and potential for nanoscale functional devices.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Global fire modelling and control attributions based on the ensemble machine learning and satellite observations

Contemporary fire dynamics is one of the most complex and least understood land surface phenomena. Global fire controls related to climate, vegetation, and anthropogenic activity are usually intertwined, and difficult to disentangle in a quantitative way. Here, we leveraged an ensemble of five machine learning (ML) models and multiple satellite-based observations to conduct global fire modeling for three fire metrics (burned area, fire number, and fire size), and quantified driving mechanisms underlying annual fire changes in a spatially resolved manner for the period 2003–2019. Ensemble learning is a meta-approach that combines multiple ML predictions to improve accuracy, robustness, and generalization performance. We found that the optimized ensemble ML well reproduced annual dynamics of global burned area (R 2 = 0.90, P < 0.001), total fire numbers (R 2 = 0.86, P < 0.001), and averaged fire size (R 2 = 0.70, P < 0.001). Additionally, the ensemble ML captured key spatial patterns of multi-year mean magnitudes, annual variabilities, anomalies, and trends for different fire metrics. Our ML-based fire attributions further highlighted the dominant role of enhanced anthropogenic activity in reducing global burned area (–1.9 Mha/yr, P < 0.01), followed by climate control (–1.3 Mha/yr, P < 0.01) and insignificant positive vegetation control (0.4 Mha/yr, P = 0.60). Spatially, climate dominated a much larger burned area (53.7%) than human (23.4%) or vegetation control (22.9%); however, the counteracting effects from regional wetting and drying trends weakened the net climate impacts on global burned area. The fire number and fire size exhibited similar spatial control patterns with burned area; globally, however, fire number tended to be more affected by climate while fire size more influenced by human activities. Overall, our study confirmed the feasibility and efficiency of ensemble ML in global fire modeling and subsequent control attributions, providing a better understanding of contemporary fire regimes and contributing to robust fire projections in a changing environment.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Self-healing Growth of LaNiO 3 on a Mixed-Terminated Perovskite Surface

Developing atomic-scale synthesis control is a prerequisite for understanding and engineering the exotic physics inherent to transition-metal oxide heterostructures. Thus, far, however, the number of materials systems explored has been extremely limited, particularly with regard to the crystalline substrate, which is routinely SrTiO 3 . Here, we investigate the growth of a rare-earth nickelate-LaNiO 3 -on (LaAlO 3 )(Sr 2 AlTaO 6 ) (LSAT) (001) by oxide molecular beam epitaxy (MBE). Whereas the LSAT substrates are smooth, they do not exhibit the single surface termination usually assumed necessary for control over the interface structure. Performing both nonresonant and resonant anomalous in situ synchrotron surface X-ray scattering during MBE growth, we show that reproducible heterostructures can be achieved regardless of both the mixed surface termination and the layer-by-layer deposition sequence. The rearrangement of the layers occurs dynamically during growth, resulting in the fabrication of high-quality LaNiO 3 /LSAT heterostructures with a sharp and consistent interfacial structure. This is due to the thermodynamics of the deposition window as well as the nature of the chemical species at interfaces-here, the flexible charge state of nickel at the oxide surface. This has important implications regarding the use of a wider variety of substrates for fundamental studies on complex oxide synthesis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Numerical study to predict the effect of surface roughness on the thermal and hydraulic performance of additively manufactured heat exchangers

Heat exchangers are used in many industries to transfer thermal energy between two or more objects with an associated thermal and hydraulic performance indicated by thermal effectiveness and pressure drop respectively. Many investigations have aimed to enhance the thermal effectiveness of heat exchangers by introducing turbulent flow inducers that increase the heat transfer rate at the expense of increasing pressure drop. Flow inducers like surface roughness can be controlled with advanced manufacturing methods like additive manufacturing for heat exchanger production. Selecting and manufacturing an optimal surface roughness for heat exchangers requires a more comprehensive approach that accounts for the surface roughness effect on the thermal and hydraulic performance of a sample. Since fabricating samples with additive manufacturing to a desired surface roughness can be an extensive experimental process, this study will fundamentally investigate the effect of surface roughness on the thermal and velocity boundary layers for various surface roughness profiles with physics-based computational modeling. To accurately model the surface roughness effect on thermohydraulic performance, correlations like roughness ratio, friction factor, and Nusselt number are investigated. This study expects to indicate correlations for different flow regimes which can successfully predict the effect of surface roughness on thermohydraulic performance. Results generated from modeling surface roughness effect with unique correlations are then compared to experimental data obtained from literature for validation. The results of this study will provide insight to understand the thermal fluid physics associated with surface roughness and design guidelines for heat exchangers produced with additive manufacturing.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Oxygen Evolution on Mechanically Strained TiO2/NiTi: Implications of Compositional Heterogeneity at (Photo)Electrocatalytic Interfaces

The adsorption and activation energetics underpinning small molecule conversion on heterogeneous (photo)electrocatalysts are intrinsically tied to catalyst surface properties. Absent compositional characterization techniques with sufficient interface sensitivity, however, (photo)electrochemical performance can be misinterpreted in the context of bulk or near-surface material properties. Here we provide a fundamental investigation of the convoluting role of near-surface compositional heterogeneity in the interpretation of (photo)electrochemical alkaline oxygen evolution reaction (OER) activity, highlighting challenges in correlating composition measured by surface- and near-surface-sensitive probes. TiO2 thin films grown by air-annealing the superelastic alloy Nitinol (TiO2/NiTi) crack under tensile mechanical strain, increasing the number of electrochemically active Ni sites (Ni site density) that are probed via voltammetric features corresponding to Ni3+/Ni2+ redox events. (Photo)electrochemical OER kinetics trend with Ni site density, with overpotentials and Tafel slopes decreasing for Ni site densities < 1013 Ni/cm2geo and asymptotically approaching the performance of the base NiTi substrate for Ni site densities > 1013 Ni/cm2geo. Photoelectrochemical fill factors follow similar Ni site density dependent trends. When probing unstrained TiO2/NiTi, Ni site densities are two orders of magnitude higher when comparing near-surface-sensitive techniques (e.g., X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectrometry (TOF-SIMS), and scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS)) to surface-sensitive electrochemical measurements. This result highlights the challenge of correlating kinetic performance with intrinsic surface properties of electrochemical interfaces in the presence of near-surface compositional heterogeneity. Further, it reinforces the importance of fundamental investigations of surfaces with well-controlled composition and structure and the need for physically grounded and self-consistent interpretation of multiple near-surface characterization techniques.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Peak‐in‐Valley Metal Nano‐Architectures via E‐Beam‐Guided Metal Oxide Redox

Focused electron beams enable nanoscale material modification via localized etching or deposition. In liquid-phase electron-beam-mediated processing, radiolysis-driven redox reactions present an opportunity to control both etching and deposition simultaneously. Here, this duality using a water-ammonia solvent as a tunable redox mediator on copper surfaces is demonstrated. At lower ammonia concentrations, the oxidation process dominates, etching copper to sub-50-nm depths. The copper ions and ion-complexes released during this initial oxidation step are reduced by solvated electrons resulting in metal deposition into the etched sites, over longer e-beam exposures, producing characteristic peak-in-valley nanostructures. Conversely, at higher ammonia concentrations copper-ammine ion complexation and radiolytic oxidizing species scavenging by ammonia occur at higher rates, creating a reducing environment conducive to rapid beam-guided copper deposition. Reaction-transport simulations and experiments are performed to show the effects of ammonia-mediated radiolysis chemistry, describing the direct influence of solvent concentration on redox balance and the outcome of e-beam guided processing. By uniting both etching and deposition within a single framework, this work provides a versatile route for controlled surface nanostructuring.

copper nanostructures↗
DOE OSTI2026

Theoretical background for a fast flow liquid metal divertor experiment

Tokamak Energy has developed a liquid metal experiment featuring a lithium loop that circulates lithium through the HIDRA stellarator at the University of Illinois at Urbana-Champaign. The loop includes a replaceable divertor module, designed to demonstrate fast, steady, open-surface liquid metal flow. The first-generation divertor module was deliberately kept simple—an open-surface chute—to enable modelling validation and establish a benchmark for future design iterations. This paper presents the theoretical foundations of the experimental design. Specifically, we identify module overflooding as the primary challenge and determine the limits of fluid velocity and magnetic field strength necessary to prevent it. The steady-state flow patterns are expected to exhibit relatively slow surface velocities, which do not fully align with the fast-flow concept. Nevertheless, the experiment is designed to achieve controllable, continuous open-surface flow within an operational fusion device, representing a significant step toward the development of liquid metal divertor technology.

Experiment↗
DOE OSTI2022

Molecular Design of Supported MoO x Catalysts with Surface TaO x Promotion for Olefin Metathesis

A series of supported 3% MoOx catalysts were synthesized by incipient-wetness impregnation of 5%-15% TaO x surface modified γ-Al 2 O 3 support. The catalysts were characterized by in situ spectroscopies (DRIFTS, Raman, UV-vis, XAS) and multiple chemical probes (C 2 H 4 /C 4 H 8 titration, C 3 H 6 -TPSR, steady state propylene metathesis, NH 3 -IR adsorption). The supported tantalum oxide phase was present as surface TaO x sites on the γ-Al 2 O 3 support that capped that Al 2 O 3 surface hydroxyls. The change in available surface hydroxyls caused the subsequent anchoring of MoOx species to occur at different surface hydroxyls. This shifted the anchoring of MoO x species from basic (Al-OH) to neutral (Al 2 -OH) to more acidic (Al 3 -OH) surface hydroxyls as well as perturbation of the remaining alumina surface hydroxyls by the surface TaO x sites. The TaO x surface modified γ-Al 2 O 3 support increased the number of activated surface MoO x sites (Ns) by ~6x and the TOF by ~10x resulting in an increased activity of ~60x. In conclusion, It was found that the specific anchoring surface hydroxyls rather than the extent of oligomerization of the surface MoO x sites control the number of activated MoO x sites and TOF for propylene metathesis. No relationship between the nature of the surface Lewis/Brønsted acid sites and Ns and TOF were found to be present.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Guest Editorial: Special section on Resilient Control of Cyber-Physical Power and Energy Systems

Our power and energy systems are becoming more and more integrated and interconnected. The increasing integration of edge devices and dependence on cyber infrastructure provides both the potential for benefits and risks. The integration enables more dynamic and flexible control paradigms while at the same time increasing the cyberattack surface and uncertainty of behavior. Control methodology in this new world must be designed for resilience and must have the ability to withstand, react, and respond to both physical faults and cyber-induced threats. Finally, understanding system resilience under adverse conditions requires studying control performance and how cyber infrastructure can integrate with and support the overall resilience of the system.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2025

Solid State Transformer Architecture and Control Compensation for Common Mode Currents

A high-altitude electromagnetic pulse (HEMP) or similar geomagnetic disturbance (GMD) has the potential to impact the operation of large-scale electric power grids. By introducing low-frequency common-mode (CM) currents, these events can degrade the performance of critical system components, such as large power transformers by introducing CM currents which can lead to magnetic saturation of the transformer core. In this work, a solid-state transformer (SST) is developed to replace susceptible equipment and improve grid resiliency by safely absorbing these CM disturbances. This device will be referred to as a common-mode solid-state transformer (CM-SST). An SST architecture based on a four-legged AC/DC converter is developed. This architecture enables active control of CM signals without disturbing the AC voltages or the real and reactive power delivery capabilities. A system-level model of this architecture is created, and time-domain simulations are performed to evaluate the SST’s performance in response to simulated CM disturbances. A control strategy for mitigating CM current is also investigated. Hamiltonian surface shaping and power flow control (HSSPFC) is used to design a nonlinear controller for the SST’s output inverter. The objectives of the controller are to suppress CM-induced AC current offsets and regulate AC currents to desired setpoints. Nonlinear system analysis is applied to design and validate the controller. Two cases are tested: (a) the proposed four-leg inverter and (b) a standard three-leg inverter. The results show that the proposed controller rapidly mitigates CM disturbances while maintaining high-quality AC current waveforms in the four-leg configuration. Finally, the hardware performance of an SST prototype is evaluated. In particular, the ability of the SST to safely redirect and absorb CM currents is demonstrated, showing how it can protect neighboring conventional transformers in the system. The study confirms that appropriate control laws allow the SST to protect both itself and adjacent transformers during a HEMP or GMD event.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2020

Photometric Analyses of Saturn’s Small Moons: Aegaeon, Methone, and Pallene Are Dark; Helene and Calypso Are Bright

We examine the surface brightnesses of Saturn’s smaller satellites using a photometric model that explicitly accounts for their elongated shapes and thus facilitates comparisons among different moons. Analyses of Cassini imaging data with this model reveal that the moons Aegaeon, Methone, and Pallene are darker than one would expect given trends previously observed among the nearby mid-sized satellites. On the other hand, the trojan moons Calypso and Helene have substantially brighter surfaces than their co-orbital companions Tethys and Dione. These observations are inconsistent with the moons’ surface brightnesses being entirely controlled by the local flux of E-ring particles, and therefore strongly imply that other phenomena are affecting their surface properties. The darkness of Aegaeon, Methone, and Pallene is correlated with the fluxes of high-energy protons, implying that high-energy radiation is responsible for darkening these small moons. Meanwhile, Prometheus and Pandora appear to be brightened by their interactions with the nearby dusty F ring, implying that enhanced dust fluxes are most likely responsible for Calypso’s and Helene’s excess brightness. However, there are no obvious structures in the E ring that would preferentially brighten these two moons, so there must either be something subtle in the E-ring particles’ orbital properties that leads to asymmetries in the relevant fluxes, or something happened recently to temporarily increase these moons’ brightnesses.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Re-evaluating cloud chamber constraints on depositional ice growth in cirrus clouds – Part 1: Model description and sensitivity tests

Abstract. Ice growth from vapor deposition is an important process for the evolution of cirrus clouds, but the physics of depositional ice growth at the low temperatures (<235 K) characteristic of the upper troposphere and lower stratosphere is not well understood. Surface attachment kinetics, generally parameterized as a deposition coefficient αD, control ice crystal habit and also may limit growth rates in certain cases, but significant discrepancies between experimental measurements have not been satisfactorily explained. Experiments on single ice crystals have previously indicated the deposition coefficient is a function of temperature and supersaturation, consistent with growth mechanisms controlled by the crystal's surface characteristics. Here we use observations from cloud chamber experiments in the Aerosol Interactions and Dynamics in the Atmosphere (AIDA) aerosol and cloud chamber to evaluate surface kinetic models in realistic cirrus conditions. These experiments have rapidly changing temperature, pressure, and ice supersaturation such that depositional ice growth may evolve from diffusion limited to surface kinetics limited over the course of a single experiment. In Part 1, we describe the adaptation of a Lagrangian parcel model with the Diffusion Surface Kinetics Ice Crystal Evolution (DiSKICE) model (Zhang and Harrington, 2014) to the AIDA chamber experiments. We compare the observed ice water content and saturation ratios to that derived under varying assumptions for ice surface growth mechanisms for experiments simulating ice clouds between 180 and 235 K and pressures between 150 and 300 hPa. We found that both heterogeneous and homogeneous nucleation experiments at higher temperatures (>205 K) could generally be modeled consistently with either a constant deposition coefficient or the DiSKICE model assuming growth on isometric crystals via abundant surface dislocations. Lower-temperature experiments showed more significant deviations from any depositional growth model, with different ice growth rates for heterogeneous and homogeneous nucleation experiments.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Controllable strain-driven topological phase transition and dominant surface-state transport in HfTe5

Abstract The fine-tuning of topologically protected states in quantum materials holds great promise for novel electronic devices. However, there are limited methods that allow for the controlled and efficient modulation of the crystal lattice while simultaneously monitoring the changes in the electronic structure within a single sample. Here, we apply significant and controllable strain to high-quality HfTe 5 samples and perform electrical transport measurements to reveal the topological phase transition from a weak topological insulator phase to a strong topological insulator phase. After applying high strain to HfTe 5 and converting it into a strong topological insulator, we found that the resistivity of the sample increased by 190,500% and that the electronic transport was dominated by the topological surface states at cryogenic temperatures. Our results demonstrate the suitability of HfTe 5 as a material for engineering topological properties, with the potential to generalize this approach to study topological phase transitions in van der Waals materials and heterostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Direct visualization of radiation-induced transformations at alkali halide–air interfaces

Radiation driven reactions at mineral/air interfaces are important to the chemistry of the atmosphere, but experimental constraints (e.g. simultaneous irradiation, in situ observation, and environmental control) leave process understanding incomplete. Using a custom atomic force microscope equipped with an integrated X-ray source, transformation of potassium bromide surfaces to potassium nitrate by air radiolysis species was followed directly in situ at the nanoscale. Radiolysis initiates dynamic step edge dissolution, surface composition evolution, and ultimately nucleation and heteroepitaxial growth of potassium nitrate crystallites mediated by surface diffusion at rates controlled by adsorbed water. Finally, in contrast to in situ electron microscopy and synchrotron-based imaging techniques where high radiation doses are intrinsic, our approach illustrates the value of decoupling irradiation and the basis of observation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Methods for Color Center Preserving Hydrogen‐Termination of Diamond

Abstract Chemical functionalization of diamond surfaces by hydrogen is an important method for controlling the charge state of near‐surface fluorescent color centers, an essential process in fabricating devices such as diamond field‐effect transistors and chemical sensors, and a required first step for realizing families of more complex terminations through subsequent chemical processing. In all these cases, termination is typically achieved using hydrogen plasma sources that can etch or damage the diamond, as well as deposited materials or embedded color centers. This work explores alternative methods for lower‐damage hydrogenation of diamond surfaces, specifically the annealing of diamond samples in high‐purity, non‐explosive mixtures of nitrogen and hydrogen gas, and the exposure of samples to microwave hydrogen plasmas in the absence of intentional stage heating. The effectiveness of these methods are characterized by x‐ray photoelectron spectroscopy (XPS), and comparison of the results to density‐functional modelling of the surface hydrogenation energetics implicates surface oxygen ligands as the primary factor limiting the termination quality of annealed samples. Finally, photoluminescence (PL) spectroscopy is used to verify that both the annealing and reduced sample temperature plasma methods are non‐destructive to near‐surface ensembles of nitrogen‐vacancy (NV) centers, in stark contrast to plasma treatments that use heated sample stages.

36 MATERIALS SCIENCE↗