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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Characterization of Materials Used as Face Coverings for Respiratory Protection

Use of masks is a primary tool to prevent the spread of the novel COVID-19 virus resulting from unintentional close contact with infected individuals. However, detailed characterization of the chemical properties and physical structure of common mask materials is lacking in the current literature. In this study, a series of commercial masks and potential mask materials, including 3M Particulate Respirator 8210 N95, a material provided by Oak Ridge National Laboratory Carbon Fiber Technology Facility (ORNL/CFTF), and a Filti Face Mask Material, were characterized by a suite of techniques, including scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Wetting properties of the mask materials were quantified by measurements of contact angle with a saliva substitute. Mask pass-through experiments were performed using a dispersed metal oxide nanoparticle suspension to model the SARS-CoV-2 virus, with quantification via spatially resolved X-ray fluorescence mapping. Notably, all mask materials tested provided a strong barrier against respiratory droplet breakthrough. The comparisons and characterizations provided in this study provide useful information when evaluating mask materials for respiratory protection.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Channel Scaling Dependent Photoresponse of Copper-Based Flexible Photodetectors Fabricated Using Laser-Induced Oxidation

Copper (Cu) oxide compounds (Cu x O), which include cupric (CuO) and cuprous (Cu 2 O) oxide, have been recognized as a promising p-channel material with useful photovoltaic properties and superior thermal conductivity. Typically, deposition methods or thermal oxidation can be used to obtain Cu x O. However, these processes are difficult to apply to flexible substrates because plastics have a comparatively low glass transition temperature. Also, additional patterning steps are needed to fabricate applications. In this work, we fabricated a metal–semiconductor–metal photodetector using laser-induced oxidation of thin Cu films under ambient conditions. Raman spectroscopy, scanning electron microscopy–energy-dispersive X-ray spectroscopy, and atomic force microscopy were used to study the composition and morphology of our devices. Moreover, the photoresponse of this device is reported herein. We performed an in-depth analysis of the relationship between the channel size and number of carriers using scanning photocurrent microscopy. The carrier transport behaviors were identified; the photocurrent decreased as the length and width of the channel increased. Furthermore, we verified the suitability of the device as a flexible photodetector using a variety of bending tests. Our in-depth analysis of this Cu-based flexible photodetector could play an important role in understanding the mechanisms of other flexible photovoltaic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Interfacial Reactivity of Silicon Electrodes: Impact of Electrolyte Solvent and Presence of Conductive Carbon

Silicon (Si) is a promising high-capacity material for lithium-ion batteries; however, its limited reversibility hinders commercial adoption. Approaches such as particle and crystallite size reduction, introduction of conductive carbon, and use of different electrolyte solvents have been explored to overcome these electrochemical limitations. Herein, operando isothermal microcalorimetry (IMC) is used to probe the influence of silicon particle size, electrode composition, and electrolyte additives fluoroethylene carbonate and vinylene carbonate on the heat flow during silicon lithiation. In this work, the IMC data are complemented by X-ray photoelectron and Raman spectroscopies to elucidate differences in solid electrolyte interphase (SEI) composition. Nanosized (~50 nm, n-Si) and micrometer-sized (~4 μm, μ-Si) silicon electrodes are formulated with and without amorphous carbon and electrochemically lithiated in ethylene carbonate (EC), fluoroethylene carbonate (FEC), or vinylene carbonate (VC) based electrolytes. Notably, n-Si electrodes generate 53–61% more normalized heat relative to their μ-Si counterparts, consistent with increased surface area and electrode/electrolyte reactivity. Introduction of amorphous carbon significantly alters the heat flow profile where multiple exothermic peaks and increased normalized heat dissipation are observed for all electrolyte types. Notably, the VC-containing electrolyte demonstrates the greatest normalized heat dissipation of the electrode compositions tested showing as much as a 50% increase compared to the EC or FEC counterparts. The results are relevant to the understanding of silicon negative electrode function in the presence of electrolyte additives and provide insight relative to silicon containing cell reactivity and safety.

25 ENERGY STORAGE↗
DOE OSTI2022

High Entropy Oxide Relaxor Ferroelectrics

Relaxor ferroelectrics are important in technological applications due to strong electromechanical response, energy storage capacity, electrocaloric effect, and pyroelectric energy conversion properties. Current efforts to discover and design materials in this class generally rely on substitutional doping as slight changes to local compositional order can significantly affect the Curie temperature, morphotropic phase boundary, and electromechanical responses. In this work, we demonstrate that moving to the strong limit of compositional complexity in an ABO 3 perovskite allows stabilization of relaxor responses that do not rely on a single narrow phase transition region. Entropy-assisted synthesis approaches are utilized to synthesize single-crystal Ba(Ti 0.2 Sn 0.2 Zr 0.2 Hf 0.2 Nb 0.2 )O 3 [Ba(5B)O] films. The high levels of configurational disorder present in this system are found to influence dielectric relaxation, phase transitions, nanopolar domain formation, and Curie temperature. Temperature-dependent dielectric, Raman spectroscopy, and second-harmonic generation measurements reveal multiple phase transitions, a high Curie temperature of 570 K, and the relaxor ferroelectric nature of Ba(5B)O films. The first-principles theory calculations are used to predict possible combinations of cations to design relaxor ferroelectrics and quantify the relative feasibility of synthesizing these highly disordered single-phase perovskite systems. Further, the ability to stabilize single-phase perovskites with various cations on the B-sites offers possibilities for designing high-performance relaxor ferroelectric materials for piezoelectric, pyroelectric, and electrocaloric applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Unveiling the Degradation Mechanism of High-Temperature Superconductor Bi 2 Sr 2 CaCu 2 O 8+δ in Water-Bearing Environments

We report the physical properties of copper oxide high-temperature superconductors have been studied extensively, such as its band structure, and doping effects of Bi 2 Sr 2 CaCu 2 O 8+δ (Bi-2212). However, some chemical-related properties of these superconductors are rarely reported, such as their stability in air. Here, we report experiments combined with ab initio calculations that address the effects of water in contact with Bi-2212. The evolution of Bi-2212 flake with exposure to water for different time intervals were tested and characterized by optical microscopy (OM), atomic force microscopy (AFM), Raman spectroscopy, transmission electron microscopy (TEM) and electrical measurements. The thickness of Bi-2212 flakes is gradually decreased in water, and some thin flakes can be completely etched away after a few days. The stability of Bi-2212 in other solvents is also evaluated, including alcohol, acetone, HCl and KOH. The morphology of Bi-2212 flakes is relatively stable in organic solvents. However, the flakes are etched relatively quick in HCl and KOH, especially in acidic environment. Our results imply that hydrogen ion is primarily responsible for the deterioration of their properties. Both TEM and calculation results demonstrate that the atoms in Bi-O plane is relatively stable when compared to the inner atoms in Sr-O, Ca-O and Cu-O planes. This work contributes towards understanding the chemical stability of Bi-2212 superconducting device in environmental medium, which is important for both fundamental studies and practical applications of copper oxide high-temperature superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

MoVN-Cu Coatings for In Situ Tribocatalytic Formation of Carbon-Rich Tribofilms in Low-Viscosity Fuels

Inhibiting the tribological failure of mechanical assemblies which rely on fuels for lubrication is an obstacle to maintaining the lifetime of these systems with low-viscosity and low-lubricity fuels. Here in the present study, a MoVN-Cu nanocomposite coating was tribologically evaluated for durability in high- and low-viscosity fuels as a function of temperature, load, and sliding velocity conditions. The results indicate that the MoVN-Cu coating is effective in decreasing wear and friction relative to an uncoated steel surface. Raman spectroscopy, transmission electron microscopy, and electron-dispersive spectroscopy analysis of the MoVN-Cu worn surfaces confirmed the presence of an amorphous carbon-rich tribofilm which provides easy shearing and low friction during sliding. Further, the characterization of the formed tribofilm revealed the presence of nanoscale copper clusters overlapping with the carbon peak intensities supporting the tribocatalytic origin of the surface protection. The tribological assessment of the MoVN-Cu coating reveals that the coefficient of friction decreased with increasing material wear and initial contact pressure. These findings suggest that MoVN-Cu is a promising protective coating for fuel-lubricated assemblies due to its adaptive ability to replenish lubricious tribofilms from hydrocarbon environments.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Electric-Field-Induced Assembly of an Ionic Liquid–Water Interphase Enables Efficient Heavy Metal Electrosorption

Controlling ion desolvation, transport, and charge transfer at the electrode-electrolyte interface (EEI) is critical to enabling the rational design of efficient and selective separation of targeted heavy metals and decontamination of industrial waste water. One challenge is to sufficiently resolve and interrogate the intermediate transformation steps between solvated metal cations and bare cations for electroreduction at the EEI and establish pathways to modulate these steps to achieve efficient energy transfer for targeted reactive separations. Herein, we obtained a predictive understanding of the effect of adding a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium chloride (EMIMCl), to an aqueous electrolyte on modulating the desolvation and electrosorption of Pb 2+ cations using a combination of experimental and theoretical techniques. Here, we reveal formation of a compact interphase layer consisting of EMIMCl-Pb complex clusters under an applied electric field using operando electrochemical Raman spectroscopy, atomic force microscopy, and electrochemical impedance spectroscopy measurements combined with classical molecular dynamics simulations. The application of a larger negative potential is shown to result in formation of a well oriented layer with the positive imidazolium ring of the EMIMCl lying on the electrode and the long hydrophobic alkyl chain extending into the bulk electrolyte. This oriented layer is demonstrated to facilitate desolvation of incoming solvated Pb 2+ cations and decrease the charge transfer resistance for Pb electrodeposition, which has important implications for selective removal of Pb from contaminated mixtures. Overall, our studies open up new opportunities to modulate ion desolvation using hydrophobic ionic liquids in aqueous electrolytes for efficient heavy metal separation.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Mixed-Anion Contact Ion-Pair Formation Enabling Improved Performance of Halide-Free Mg-Ion Electrolytes

In this article, discovery of stable and efficient electrolytes that are compatible with magnesium metal anodes and high-voltage cathodes is crucial to enabling energy storage technologies that can move beyond existing Li-ion systems. Many promising electrolytes for magnesium anodes have been proposed with chloride-based systems at the forefront; however, Cl-containing electrolytes lack the oxidative stability required by high-voltage cathodes. In this work, we report magnesium trifluoromethanesulfonate (triflate) as a viable coanion for Cl-free, mixed-anion magnesium electrolytes. The addition of triflate to electrolytes containing bis(trifluoromethane sulfonyl) imide (TFSI – ) anions yields significantly improved Coulombic efficiency, up to a 100 mV decrease in the plating/stripping overpotential, improved tolerance to trace H 2 O, and improved oxidative stability (0.35 V improvement compared to that of hybrid TFSI-Cl electrolytes). Based on 19 F nuclear magnetic resonance and Raman spectroscopy measurements, we propose that these improvements in performance are driven by the formation of mixed-anion contact ion pairs, where both triflate and TFSI – are coordinated to Mg 2+ in the electrolyte bulk. The formation of this mixed-anion magnesium complex is further predicted by the density functional theory to be thermodynamically driven. Collectively, this work outlines the guiding principles for the improved design of next-generation electrolytes for magnesium batteries.

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

Direct Laser Writing Crystal Polymorphs of Organic Semiconductors for Phase Change Electronics

The many diverse polymorphic behaviors observed in organic electronic materials offer opportunities to modulate electronic properties through reversibly switching crystal structures. Here, we access the prolific polymorphism observed in two-dimensional quinoidal terthiophene via laser writing to locally heat and direct the phase transitions. We access a metastable polymorph IV through rapid cooling and observe distinct symmetry as well as packing through grazing incidence X-ray diffraction (GIXD). Using our open-source PolyChemPrint patterning platform, we direct laser heating to initiate the IV-I transition, switching the conductance by >2 orders of magnitude. Here, this is confirmed via a combination of GIXD and Raman spectroscopy. Finally, we demonstrate switching of transistor devices as well as discrete tuning of conductance via laser writing.

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

The Roles of Oil–Water Interfaces in Forming Ultrasmall CaSO 4 Nanoparticles

In natural and engineered environmental systems, calcium sulfate (CaSO 4 ) nucleation commonly occurs at dynamic liquid–liquid interfaces. Although CaSO 4 is one of the most common minerals in oil spills and oil–water separation, the mechanisms driving its nucleation at these liquid–liquid interfaces remain poorly understood. Here, in this study, using in situ small-angle X-ray scattering (SAXS), we examined CaSO 4 nucleation at oil–water interfaces and found that within 60 minutes of reaction, short rod-shaped nanoparticles (with a radius of gyration (R g ) of 17.2 ± 2.7 nm and a length of 38.2 ± 5.8 nm) had formed preferentially at the interfaces. Wide-angle X-ray scattering (WAXS) analysis identified these nanoparticles as gypsum (CaSO 4 ·2H 2 O). In addition, spherial nanoparticles measuring 4.1 nm in diameter were observed at oil–water interfaces, where surface-enhanced Raman spectroscopy (SERS) revealed an elevated pH compared to the bulk solution. The negatively charged oil–water interfaces preferentially adsorb calcium ions, collectively promoting CaSO 4 formation there. CaSO 4 particle formation at the oil–water interface follows a nonclassical nucleation (N-CNT) pathway by forming ultrasmall amorphous spherical particles which then aggregate to form intermediate nanoparticles, subsequently growing into nanorod-shaped gypsum. These findings of this study provide insights into mineral scaling during membrane separation and can inform more efficient oil transport in energy recovery systems.

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

Insights into the Electrochemical Oxidation and Reduction of Nickel Oxide Surfaces

Surface oxidation/reduction processes, driven by varying electrochemical potentials, can substantially impact catalyst effectiveness and, consequently, electrolyzer performance. Here, this study combines theoretical and experimental approaches to explore the surface redox behavior of nickel oxides, which are cost-effective and efficient catalysts for many electrochemical reactions. Surface Pourbaix diagrams for three different phases of nickel oxides, i.e., nickel hydroxide (Ni(OH) 2 ), nickel oxyhydroxide (NiOOH), and nickel dioxide (NiO 2 ), were constructed using density functional theory-based simulations. Various experimental methods, including cyclic voltammetry, in situ Raman spectroscopy, and electrochemical titration, were employed to probe the surface redox processes of nickel oxide thin films. Our findings indicate that the ABAB stacking sequence of Ni(OH) 2 lacks stability under oxidizing conditions to host the surface oxidation (deprotonation) events, while the AABBCC stacking sequence of NiOOH is energetically favorable due to the presence of interlayer hydrogen bonding. Rapid charge transfer facilitated by interlayer hydrogen bonding accounts for the higher reactivity of partially oxidized/reduced NiOOH (001) surfaces compared to Ni(OH) 2 (001) and NiO 2 (001) surfaces with the same stoichiometry, where interlayer hydrogen bonding is absent. Insights presented in this work can offer guidelines for optimizing operational conditions and tailoring the surface structures and oxidation states of nickel oxides to enhance performance in applications such as electrocatalysis and supercapacitors.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Sputter-Coated TiO 2 Films as Passivation and Hole Transfer Layers for Improved Energy Conversion with Solar Fuel WO 3 /CuWO 4 Photoanodes

Atomic layer deposited (ALD) “leaky” TiO 2 have gained interest as charge-selective protection layers for semiconductor solar fuel electrodes. Here we demonstrate the use of sputter-deposited TiO 2 layers as hole selective contacts for WO 3 /CuWO 4 type 2 heterojunction water oxidation photoanodes for the first time. TiO 2 protection layers with varying thicknesses (2 to 128 nm) were deposited using the RF magnetron sputtering technique. The resulting TiO 2 films are amorphous based on Raman spectroscopy and powder XRD. Photoelectrochemical scans and Vibrating Kelvin probe photovoltage spectroscopy show that 2-8 nm TiO 2 layers nearly double the photocurrent to 0.97 mA cm -2 under AM 1.5 illumination (19% AQE at 350 nm), increase the surface photovoltage signal by 25%, and increase the WO 3 /CuWO 4 bandgap. These effects can be attributed to the selectivity of TiO 2 for photoholes. Additionally, SPV data suggest that TiO 2 overlayers suppress copper-based surface recombination defects. Reduced photocurrent and the photovoltage are seen in thicker TiO 2 films (16 to 128 nm) as a result of an increasing hole transfer resistance and because of light shading effects according to photoaction spectra. The TiO 2 films also improve the stability of the WO 3 /CuWO 4 photoelectrodes, allowing nearly constant O 2 evolution over 3 hours after an initial 20-35% loss. Overall, this work establishes RF magnetron sputtering as a useful method to install amorphous TiO 2 passivation layers for improved WO 3 /CuWO 4 solar fuel photoelectrodes. Furthermore, we show how the combination of PEC with SPV measurements provides insight into the function of the TiO 2 coatings.

CuWO4↗
DOE OSTI2025

Atomic Structure, Dynamics, Changes in Chemical Bonding and Semiconductor-Metal Transition in Sb 2 Se 3 : A Remarkable Material for Quantum Networks and Energy Applications

Antimony sesquiselenide has become an outstanding functional material for photovoltaics, energy storage and transformation, memory and photonic applications. Sb 2 Se 3 is one of the most successful emerging solar light absorbers and has also been identified as a highly promising ultralow-loss phase-change material (PCM) for next-generation coherent nanophotonic processors, photonic tensor cores, quantum and neuromorphic networks. Unlike benchmark telluride PCMs, Sb 2 Se 3 features a quasi-one-dimensional (1D) crystalline structure consisting of (Sb 4 Se 6 ) ∞ ribbons, lacks the typical PCM chemical bonding, and undergoes an extended semiconductor-metal transition above the melting point. Consequently, the origin of high optical contrast between crystalline (SET) and amorphous (RESET) logic states remains elusive and presents a significant challenge. Using high-energy X-ray diffraction and Raman spectroscopy over a wide temperature range, supported by first-principles simulations and complemented by thermal, optical and electrical measurements, as well as by 121 Sb-Mossbauer spectroscopy, the quasi-1D network of orthorhombic antimony sesquiselenide was found to undergo significant evolution in amorphous and supercooled Sb 2 Se 3 , leading to lower coordination, shorter interatomic distances and a higher p-electron density on antimony, indicating changes in chemical bonding. The observed novel Sb 2 Se 3 nanocrystalline polymorph, characterized by trigonal antimony coordination and more isolated Sb-Se ribbons, could help reduce multiple trapping defect states in the bandgap, which are typical of orthorhombic Sb 2 Se 3 , thereby enhancing the power-conversion efficiency of photovoltaic devices. Semimetallic and metallic liquid Sb 2 Se 3 exhibit a gradual transformation into a denser 2D and/or 3D network with higher antimony coordination. Localized electron states in the pseudogap are becoming extended, leading to an increase in electronic conductivity σ following the relationship σ ∝ N(E F ) 2 . Liquid Sb 2 Se 3 also appears to be strongly fragile, with a nonmonotonic change in viscosity and higher atomic mobility in the metallic liquid. Furthermore, these results explain extraordinary functionalities of Sb 2 Se 3 for photonic and energy applications.

antimony↗
DOE OSTI2025

Evidence for In-Plane Electrical Polarization in 3R-β’-In 2 Se 3 Thin Films Grown by Molecular Beam Epitaxy

β-In 2 Se 3 has been identified as a potential ferroelectric. This work describes the growth of β-In 2 Se 3 via molecular beam epitaxy along with a description of its properties, including the search for switchable polarization in 3R-β’-In2Se3. The thin-film morphology, crystal structure, and phase maps of β-In 2 Se 3 on Si(111) and Al 2 O 3 (0001) were evaluated by atomic force microscopy, X-ray diffraction, and Raman spectroscopy as a function of the atomic Se/In flux ratio and growth temperature. Smooth β-In 2 Se 3 thin films were successfully realized on Si(111) at a substrate temperature of 150 °C using a Se/In flux ratio of 5.7, as well as on Al 2 O 3 (0001) at 450 °C using a Se/In flux ratio of 5.5. Scanning transmission electron microscopy (STEM) confirms the 3R polytype of β-In 2 Se 3 in films on both substrates, with a minor disorder associated with the 2H polytype at the interface. Indications of in-plane Se atom displacements characteristic of the 3R-β’-In 2 Se 3 polytype were found by STEM and second harmonic generation analysis in films on Al 2 O 3 (0001), but not in films on Si(111). Furthermore, attempts at electrical polarization switching did not produce compelling evidence for ferroelectricity. Instead, electrical transport measurements demonstrated locally varying anisotropic responses with the applied electric fields along different in-plane directions, with some hysteresis associated with the trapping of charges.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Encapsulation of Monolayer 2D Materials Using Kinetic Energy-Controlled Pulsed Laser Deposition

The integration of monolayer (ML) two-dimensional (2D) materials into next-generation microelectronics, optoelectronics, and sensors is hindered by their sensitivity to environmental exposure. Deposition of additional layers for encapsulation or growth on ML 2D materials by versatile but energetic plasma techniques such as pulsed laser deposition (PLD) has not been considered at the monolayer level because of potential damage caused by hyperthermal species with kinetic energies (KEs) exceeding the threshold displacement energy (TDE) of the ML. Here, we describe a general strategy to understand and mitigate damage during PLD by reducing the incident KE of ablated species below the TDE of the 2D monolayer using background gas collisions. Ion flux diagnostics, combined with in situ Raman spectroscopy of monolayer graphene during PLD of amorphous boron nitride (a-BN) as a dielectric encapsulation layer, show that damage is primarily correlated with fast ions that penetrate the background gas in accordance with Beer’s Law and are often overlooked in ICCD imaging due to the dominance of the bright, delayed plasma luminescence. Significantly, if fast ions are eliminated and a ∼2 nm-thick a-BN layer is “soft landed”, the monolayer graphene is effectively protected from damage by high KE species in the boron nitride plasma plume. Deposited a-BN films display a characteristic dielectric constant of 3.6 at 100 kHz and tunable charge injection properties. Our results enable PLD as a viable option for encapsulation and thin film growth onto ML 2D materials, with implications for both fundamental research and device integration.

2D materials↗
DOE OSTI2026

Dynamics of Radiation Damage Buildup in Ultrathin Hexagonal Boron Nitride Films under Ion Bombardment

Two-dimensional hexagonal boron nitride (hBN) is attractive for several emerging applications. Ion bombardment can be used to modify the hBN properties. However, the understanding of radiation damage buildup in hBN remains limited. Here, we investigate the effects of the dose rate and ion mass on radiation damage buildup by studying 40 nm-thick hBN films bombarded at room temperature with 500 keV 4 He, 15 N, 40 Ar, and 129 Xe ions and comparing with results for ion bombardment of polycrystalline hBN ceramics. Raman spectroscopy is used to quantify damage buildup, and transmission electron microscopy is used for microstructural analysis. Experiments are complemented by molecular dynamics simulations of the formation and evolution of point defects. Lighter ions are found to be more efficient at disordering hBN than heavier ions. This observation points to a critical role of intracascade defect processes. In contrast, a negligible dose rate effect observed suggests limited intercascade defect dynamic annealing processes for these irradiation conditions. These findings provide a fundamental basis for hBN defect engineering.

2D materials↗
DOE OSTI2026

Ultrafast Reactive Laser Sintering of Highly Conductive Garnet-Type LLZTO Solid Electrolytes

Rapid and scalable fabrication of garnet-type solid electrolytes remains a major challenge for the practical deployment of lithium metal batteries. Here, we report reactive laser sintering (RLS) as an ultrafast and potentially scalable strategy for fabricating garnet-type Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) solid electrolytes. RLS of LLZTO enables simultaneous reaction and densification, achieving ∼95% relative density while minimizing lithium loss and suppressing secondary phase formation. Compared to conventional furnace sintering, RLS promotes enhanced grain growth and improved densification, leading to improved ionic conductivity (0.36 ± 0.08 mS cm −1 ) while maintaining comparable activation energies for Li + transport. Structural characterization by X-ray diffraction (XRD), Raman spectroscopy, and solid-state 6 Li/ 7 Li NMR confirms the formation of cubic garnet LLZTO with homogeneous microscale elemental distribution. In addition, nanoindentation measurements demonstrate that RLS preserves the mechanical properties of the garnet framework despite ultrafast localized thermal processing. By integrating simultaneous reaction and densification with tunable microstructural control, reactive laser sintering provides a promising manufacturing pathway for high-performance garnet solid electrolytes toward next-generation solid-state batteries.

CO2 laser↗
DOE OSTI2024

Millimeter-Scale Exfoliation of hBN with Tunable Flake Thickness for Scalable Encapsulation

As a two-dimensional (2D) dielectric material, hexagonal boron nitride (hBN) is in high demand for applications in photonics, nonlinear optics, and nanoelectronics. Unfortunately, the high-throughput preparation of macroscopic-scale, high-quality hBN flakes with controlled thickness is an ongoing challenge, limiting device fabrication and technological integration. In this report we present a metal thin-film exfoliation method to prepare hBN flakes with millimeter-scale dimension, near-unity yields, and tunable flake thickness distribution from 1-7 layers, a substantial improvement over scotch tape exfoliation. The single crystallinity and high quality of the exfoliated hBN are demonstrated with optical microscopy, atomic force microscopy, Raman spectroscopy, and second harmonic generation. We further explore a possible mechanism for the effectiveness and selectivity based on thin-film residual stress measurements, density functional theory calculations, and transmission electron microscopy imaging of the deposited metal films. We find that the magnitude of the residual tensile stress induced by thin film deposition plays a key role in determining exfoliated flake thickness in a manner which closely resembles 3D semiconductor spalling. Lastly, we demonstrate that our exfoliated, large-area hBN flakes can be readily incorporated as encapsulating layers for other 2D monolayers. Altogether, this method brings us one step closer to the high throughput, mass production of hBN-based 2D photonic, optoelectronic, and quantum devices.

2D materials↗