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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

A Method to Probe the Interfaces in La2−xSrxCuO4-LaSrAlO4-La2−xSrxCuO4 Trilayer Junctions

C-axis trilayer cuprate Josephson junctions are essential for basic science and digital circuit applications of high-temperature superconductors. We present a method for probing the interface perfection in La2−xSrxCuO4 (LSCO)-LaSrAlO4 (LSAO)-La2−xSrxCuO4 trilayer junctions. A series of LSCO-LSAO superlattices with atomically smooth surfaces and sharp interfaces were grown by the atomic-layer-by-layer molecular beam epitaxy (ALL-MBE) technique. We have systematically varied the thickness of LSCO and LSAO layers with monolayer precision. By studying the mutual inductance and electrical transport in these superlattices, we detect the non-superconducting (“dead”) layers at the interfaces and quantify their thicknesses. Our results indicate that two optimally doped LSCO monolayers just above and below the one monolayer LSAO barrier are no longer superconducting, rendering the actual barrier thickness of five monolayers. Next, we have shown that introducing a protective highly-overdoped LSCO layer reduces the thickness of dead layers by one or two monolayers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

The Quest for High-Temperature Superconductivity in Nickelates under Ambient Pressure

Recently, superconductivity with Tc ≈ 80 K was discovered in La3Ni2O7 under extreme hydrostatic pressure (>14 GPa). For practical applications, we needed to stabilize this state at ambient pressure. It was proposed that this could be accomplished by substituting La with Ba. To put this hypothesis to the test, we used the state-of-the-art atomic-layer-by-layer molecular beam epitaxy (ALL-MBE) technique to synthesize (La1−xBax)3Ni2O7 films, varying x and the distribution of La (lanthanum) and Ba (barium). Regrettably, none of the compositions we explored could be stabilized epitaxially; the targeted compounds decomposed immediately into a mixture of other phases. So, this path to high-temperature superconductivity in nickelates at ambient pressure does not seem promising.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Exploring internal structures and properties of terpolymer fibers via real-space characterizations

While significant research has investigated the processing and properties of high-performance terpolymer fibers, much remains to be understood about the internal nano- and microstructures of these fibers, and how these morphologies relate to fiber properties. Here we use a focused ion beam notch technique and multifrequency atomic force microscope mapping to characterize the internal structure and local mechanical properties within Technora ® fibers. We find a highly fibrillated structure that appears to connect with both the fiber’s molecular chemistry and full-fiber mechanical properties. In addition, through detailed comparisons with Kevlar ® K29 fibers, we find remarkable differences between the internal structures of the two fibers, and posit connections between our measurements and multifunctional performance studies from the literature.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Accurate determination of the electron spin polarization in magnetized iron and nickel foils for Møller polarimetry

The Møller polarimeter in Hall A at Jefferson Lab in Newport News, VA, has provided reliable measurements of electron beam polarization for the past two decades. Past experiments have typically required polarimetry at the 1% level of absolute uncertainty which the Møller polarimeter has delivered. However, the upcoming proposed experimental program including MOLLER and SoLID have stringent requirements on beam polarimetry precision at the level of 0.4% (The MOLLER Collaboration, 2014; The SoLID collaboration, 2019), requiring a systematic re-examination of all the contributing uncertainties. Møller polarimetry uses the double polarized scattering asymmetry of a polarized electron beam on a target with polarized atomic electrons. The target is a ferromagnetic material magnetized to align the spins in a given direction. In Hall A, the target is a pure iron foil aligned perpendicular to the beam and magnetized out of plane parallel or antiparallel to the beam direction. The acceptance of the detector is engineered to collect scattered electrons close to 90° in the center of mass frame where the analyzing power is a maximum (-7/9). One of the leading systematic errors comes from determination of the target foil polarization. Polarization of a magnetically saturated target foil requires knowledge of both the saturation magnetization and g', the electron g-factor which includes components from both spin and orbital angular momentum from which the spin fraction of magnetization is determined. Target foil polarization has been previously addressed in a 1997 publication “A precise target for Møller polarimetry” by de Bever et al. (1997) at a level of precision sufficient for experiments up to this point. Several shortcomings with the previous published value require revisiting the result prior to MOLLER. Here, we utilize the existing world data to provide a best estimate for target polarization for both nickel and iron foils including uncertainties in magnetization, high-field and temperature dependence, and fractional contribution to magnetization from orbital effects. We determine the foil electron spin polarization at 294 K to be 0.08020 ± 0.00018 (@4 T applied field) for iron and 0.018845+/-0.000053 (@2 T applied field) for nickel. Finally, we conclude with a brief discussion of additional systematic uncertainties to Møller polarimetry using this technique.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Site-specific plan-view (S)TEM sample preparation from thin films using a dual-beam FIB-SEM

To fully evaluate the atomic structure, and associated properties of materials using transmission electron microscopy, examination of samples from three non-collinear orientations is needed. This is particularly challenging for thin films and nanoscale devices built on substrates due to limitations with plan-view sample preparation. In this work, a new method for preparation of high-quality, site-specific, plan-view TEM samples from thin-films grown on substrates, is presented and discussed. Here, it is based on using a dual-beam focused ion beam scanning electron microscope (FIB-SEM) system. To demonstrate the method, the samples were prepared from thin films of perovskite oxide BaSnO 3 grown on a SrTiO 3 substrate and metal oxide IrO 2 on a TiO 2 substrate, ranging from 20–80 nm in thicknesses using molecular beam epitaxy. While the method is optimized for the thin films, it can be extended to other site-specific plan-view samples and devices build on wafers. Aberration-corrected STEM was used to evaluate the quality of the samples and their applicability for atomic-resolution imaging and analysis.

BaSnO3↗
DOE OSTI2020

Doping transition-metal atoms in graphene for atomic-scale tailoring of electronic, magnetic, and quantum topological properties

Atomic-scale fabrication is an outstanding challenge and overarching goal for the nanoscience community. The practical implementation of moving and fixing atoms to a structure is non-trivial considering that one must spatially address the positioning of single atoms, provide a stabilizing scaffold to hold structures in place, and understand the details of their chemical bonding. Free-standing graphene offers a simplified platform for the development of atomic-scale fabrication and the focused electron beam in a scanning transmission electron microscope can be used to locally induce defects and sculpt the graphene. In this scenario, the graphene forms the stabilizing scaffold and the experimental question is whether a range of dopant atoms can be attached and incorporated into the lattice using a single technique and, from a theoretical perspective, we would like to know which dopants will create technologically interesting properties. Here in this paper, we demonstrate that the electron beam can be used to selectively and precisely insert a variety of transition metal atoms into graphene with highly localized control over the doping locations. We use first-principles density functional theory calculations with direct observation of the created structures to reveal the energetics of incorporating metal atoms into graphene and their magnetic, electronic, and quantum topological properties.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Directed Gas-Phase Formation of The Propargyl Family of Resonance-Stabilized Radicals in The Reactions of Ground-State Carbon Atoms (C; 3 P j ) with Butene Isomers (C 4 H 8 ): Dimethylpropargyl and Ethylpropargyl

The propargyl radical (C 3 H 3 ) is the simplest resonance-stabilized free radical (RSFR), but how does stepwise methyl substitution in the alkene reactant affect its dynamics of their formation? We report a crossed molecular beam study of the reactions of atomic carbon (C, 3 P j ) with four butene isomers (C 4 H 8 ) under single collision conditions at a collision energy of 28 ± 2 kJ mol −1 . Barrierless addition of atomic carbon to the alkene C=C bond triggers ring opening to triplet substituted allenes—a de facto insertion mechanism—followed by unimolecular decomposition via atomic hydrogen (H), methyl (CH 3 ) or ethyl (C 2 H 5 ) loss, yielding a family of propargyl‑type RSFRs. RRKM calculations reveal that the branching ratios are highly sensitive to the alkene structure. While the methyl loss channel, affording 1‑methylpropargyl, dominates for 2 butenes (80–90%), the predicted hydrogen atom loss channel (≈10%) leading to 1,3 dimethylpropargyl is identified in the experiment by comparison with theoretical energetics. For isobutene, a near‑equal competition is seen, with the reaction producing 3‑methylpropargyl (≈50%) and 1,1‑dimethylpropargyl (≈40%), along with 2‑vinylallyl (≈5%), whose formation is supported by the experimental data. Most notably, the reaction with 1 butene uniquely favors an enthalpically driven hydrogen shift, eventually producing 1 vinylallyl (≈38%), which is assigned based on the excellent agreement between the measured and calculated reaction exothermicity. Rapid entropically favored fragmentation channels yield ≈40% of propargyl type species (propargyl, 1- and 3-ethylpropargyls), slightly outcompeting the allyl type product. Furthermore, these results establish a systematic progression from C 2 H 4 to C 4 H 8 , where the increasing alkyl substitution unlocks new fragmentation channels, providing a versatile gas phase route to alkylated RSFRs—key intermediates in the growth of methylated and ethylated PAHs and aliphatic chains in combustion and cold interstellar environments (molecular clouds).

Alkyls↗
DOE OSTI2025

An integrated photonic engine for programmable atomic control

Abstract Solutions for scalable, high-performance optical control are important for the development of scaled atom-based quantum technologies. Modulation of many individual optical beams is central to applying arbitrary gate and control sequences on arrays of atoms or atom-like systems. At telecom wavelengths, miniaturization of optical components via photonic integration has pushed the scale and performance of classical and quantum optics far beyond the limitations of bulk devices. However, material platforms for high-speed telecom integrated photonics lack transparency at the short wavelengths required by leading atomic systems. Here, we propose and implement a scalable and reconfigurable photonic control architecture using integrated, visible-light modulators based on thin-film lithium niobate. We combine this system with techniques in free-space optics and holography to demonstrate multi-channel, gigahertz-rate visible beamshaping. When applied to silicon-vacancy artificial atoms, our system enables the spatial and spectral addressing of a dynamically-selectable set of these stochastically-positioned point emitters.

Science & Technology - Other Topics↗
DOE OSTI2025

Learning and Controlling Silicon Dopant Transitions in Graphene Using Scanning Transmission Electron Microscopy

A machine learning approach is introduced to determine the transition dynamics of silicon atoms on a single layer of carbon atoms, when stimulated by the electron beam of a scanning transmission electron microscope (STEM). This method is data-centric, leveraging data collected on a STEM. The data samples are processed and filtered to produce symbolic representations, which is used to train a neural network to predict transition probabilities. These learned transition dynamics are then leveraged to guide a single silicon atom throughout the lattice to pre-determined target destinations. Empirical analyses are presented that demonstrate the efficacy and generality of the approach.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Atomistic Positioning of Defects in Helium Ion Treated Single-Layer MoS 2

Structuring materials with atomic precision is the ultimate goal of nanotechnology and is becoming increasingly relevant as an enabling technology for quantum electronics/spintronics and quantum photonics. Here, we create atomic defects in monolayer MoS 2 by helium ion (He-ion) beam lithography with a spatial fidelity approaching the single-atom limit in all three dimensions. Using low-temperature scanning tunneling microscopy (STM), we confirm the formation of individual point defects in MoS 2 upon He-ion bombardment and show that defects are generated within 9 nm of the incident helium ions. Atom-specific sputtering yields are determined by analyzing the type and occurrence of defects observed in high-resolution STM images and compared with Monte Carlo simulations. Both theory and experiment indicate that the He-ion bombardment predominantly generates sulfur vacancies.

Two-dimensional materials↗
DOE OSTI2021

Improved optical standing-wave beam splitters for dilute Bose–Einstein condensates

Bose–Einstein condensate (BEC)-based atom interferometry exploits low temperatures and long coherence lengths to facilitate high-precision measurements. Progress in atom interferometry promises improvements in navigational devices like gyroscopes and accelerometers, as well as applications in fundamental physics such as accurate determination of physical constants. Previous work demonstrates that beam splitters and mirrors for coherent manipulation of dilute BEC momentum in atom interferometers can be implemented with sequences of non-resonant standing-wave light pulses. While previous work focuses on the optimization of the optical pulses’ amplitude and duration to produce high-order momentum states with high fidelity, we explore how varying the shape of the optical pulses affects optimal beam-splitter performance, as well as the effect of pulse shape on the sensitivity of optimized parameters in achieving high fidelity in high-momentum states. Here, in simulations of two-pulse beam splitters utilizing optimized square, triangle, and sinc-squared pulse shapes applied to dilute BECs, we, in some cases, reduce parameter sensitivity by an order of magnitude while maintaining fidelity.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Atom-by-Atom Direct Writing

Direct-write processes enable the alteration or deposition of materials in a continuous, directable, sequential fashion. Here, in this work, we demonstrate an electron beam direct-write process in an aberration-corrected scanning transmission electron microscope. This process has several fundamental differences from conventional electron-beam-induced deposition techniques, where the electron beam dissociates precursor gases into chemically reactive products that bond to a substrate. Here, we use elemental tin (Sn) as a precursor and employ a different mechanism to facilitate deposition. The atomic-sized electron beam is used to generate chemically reactive point defects at desired locations in a graphene substrate. Temperature control of the sample is used to enable the precursor atoms to migrate across the surface and bond to the defect sites, thereby enabling atom-by-atom direct writing.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Buffer-layer-controlled nickeline vs zinc-blende/wurtzite-type MnTe growths on c -plane Al 2 O 3 substrates

In the recent past, MnTe has proven to be a crucial component of the intrinsic magnetic topological insulator (IMTI) family [MnTe] m [Bi2Te 3 ] n , which hosts a wide range of magneto-topological properties depending on the choice of m and n. However, bulk crystal growth allows only a few combinations of m and n for these IMTIs due to the strict limitations of the thermodynamic growth conditions. One way to overcome this challenge is to utilize atomic layer-by-layer molecular beam epitaxy (MBE) technique, which allows arbitrary sequences of [MnTe]m and [Bi 2 Te 3 ] n to be formed beyond the thermodynamic limit. For such MBE growth, finding optimal growth templates and conditions for the parent building block, MnTe, is a key requirement. Here, we report that two different hexagonal phases of MnTe - nickeline (NC) and zinc-blende/wurtzite (ZB-WZ) structures, with distinct in-plane lattice constants of 4.20 ± 0.04 Å and 4.39 ± 0.04 Å, respectively - can be selectively grown on c-plane Al 2 O 3 substrates using different buffer layers and growth temperatures. Moreover, we provide the first comparative studies of different MnTe phases using atomic-resolution scanning transmission electron microscopy and show that ZB and WZ-like stacking sequences can easily alternate between the two. Surprisingly, In 2 Se 3 buffer layer, despite its lattice constant (4.02 Å) being closer to that of the NC phase, fosters the ZB-WZ instead, whereas Bi 2 Te 3 , sharing the same lattice constant (4.39 Å) with the ZB-WZ phase, fosters the NC phase. Furthermore, these discoveries suggest that lattice matching is not always the most critical factor determining the preferred phase during epitaxial growth. Overall, this will deepen our understanding of epitaxial growth modes for chalcogenide materials and accelerate progress toward new IMTI phases as well as other magneto-topological applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

High-performance silicon photonic single-sideband modulators for cold-atom interferometry

The laser system is the most complex component of a light-pulse atom interferometer (LPAI), controlling frequencies and intensities of multiple laser beams to configure quantum gravity and inertial sensors. Its main functions include cold-atom generation, state preparation, state-selective detection, and generating a coherent two-photon process for the light-pulse sequence. To achieve substantial miniaturization and ruggedization, we integrate key laser system functions onto a photonic integrated circuit. Our study focuses on a high-performance silicon photonic suppressed-carrier single-sideband (SC-SSB) modulator at 1560 nanometers, capable of dynamic frequency shifting within the LPAI. By independently controlling radio frequency (RF) channels, we achieve 30-decibel carrier suppression and unprecedented 47.8-decibel sideband suppression at peak conversion efficiency of –6.846 decibels (20.7%). We investigate imbalances in both amplitudes and phases between the RF signals. Using this modulator, we demonstrate cold-atom generation, state-selective detection, and atom interferometer fringes to estimate gravitational acceleration, g ≈ 9.77 ± 0.01 meters per second squared, in a rubidium ( 87 Rb) atom system.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Aberration-corrected STEM imaging of 2D materials: Artifacts and practical applications of threefold astigmatism

High-resolution scanning transmission electron microscopy (HR-STEM) with spherical aberration correction enables researchers to peer into two-dimensional (2D) materials and correlate the material properties with those of single atoms. The maximum intensity of corrected electron beam is confined in the area having sub-angstrom size. Meanwhile, the residual threefold astigmatism of the electron probe implies a triangular shape distribution of the intensity, whereas its tails overlap and thus interact with several atomic species simultaneously. The result is the resonant modulation of contrast that interferes the determination of phase transition of 2D materials. Here, we theoretically reveal and experimentally determine the origin of resonant modulation of contrast and its unintended impact on violating the power-law dependence of contrast on coordination modes between transition metal and chalcogenide atoms. The finding illuminates the correlation between atomic contrast, spatially inequivalent chalcogenide orientation, and residual threefold astigmatism on determining the atomic structure of emerging 2D materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Electron beam injection from a hollow cathode plasma into a downstream reactive environment: Characterization of secondary plasma production and Si 3 N 4 and Si etching

A material etching system was developed by combining beam electron injection from a direct current (DC) hollow-cathode (HC) electron source with the downstream reactive environment of a remote CF 4 /O 2 low temperature plasma. The energy of the injected beam electrons is controlled using an acceleration electrode biased positively relative to the HC Argon discharge. For an acceleration voltage greater than the ionization potential of Ar, the extracted primary electrons can produce a secondary plasma in the process chamber. We characterized the properties of the secondary plasma by performing Langmuir probe measurements of the electron energy probability function (EEPF) 2.5 cm below the extraction ring. The data indicate the existence of two major groups of electrons, including electrons with a primary beam electron energy which varies as the acceleration voltage is varied, along with low energy electrons produced by ionization of the Ar gas atoms in the process chamber by the injected beam electrons. When combining the HC Ar beam electron with a remote CF 4 /O 2 electron cyclotron wave resonance (ECWR) plasma, the EEPF of both the low energy plasma electron and beam electron components decreases. Additionally, we studied surface etching of Si3N4 and poly-crystalline Si (poly-Si) thin films as a function of process parameters, including the acceleration voltage (0-70 V), discharge current of the HC discharge (1-2 A), pressure (2- 100 mTorr), source to substrate distance (2.5 to 5 cm), and feed gas composition (with or without CF 4 /O 2 ). The direction of the incident beam electrons was perpendicular to the surface. Si 3 N 4 and poly-crystalline silicon etching are seen and indicate an electronneutral synergy effect. No/little remote plasma spontaneous etching was observed for the conditions used in this study, and the etching is confined to the substrate area irradiated by the injected beam electrons. The electron etched Si 3 N 4 surface etching rate profile distribution is confined within a ~30 mm diameter circle, which is slightly broader than the area for which poly-Si etching is seen, and coincides closely with the spatial profile of beam electrons as determined by the Langmuir probe measurements. The magnitude of poly-Si etching rate is by a factor of two times smaller than the Si 3 N 4 etching rate. In this paper, we discuss possible explanations of the data and the role of surface charging.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Single-Layer Magnet Phase in Intrinsic Magnetic Topological Insulators, [MnTe][Bi 2 Te 3 ] n , Far beyond the Thermodynamic Limit

The intrinsic magnetic topological insulator (IMTI) family [MnTe][Bi 2 Te 3 ]n has demonstrated magneto-topological properties dependent on n, making it a promising platform for advanced electronics and spintronics. However, due to technical barriers in sample synthesis, their properties in the large n limit remain unknown. To overcome this, we utilized the atomic layer-by-layer molecular beam epitaxy (ALL-MBE) technique and achieved IMTIs with n as large as 15, far beyond that previously reported in bulk crystals or thin films. Then, we discover that the “single-layer magnet (SLM)” phase, primarily determined by intralayer ferromagnetic coupling, emerges for n > ∼4 and remains little affected up to n = 15. Nonetheless, still, nonzero, interlayer ferromagnetic coupling is necessary to stabilize the SLM phase, suggesting that the SLM phase eventually disappears in the n → ∞ limit. This study uncovers the secrets of IMTIs beyond the thermodynamic limit and opens a door to diverse magneto-topological applications.

2D ferromagnets↗