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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

High-Resolution Three-Dimensional Sculpting of Two-Dimensional Graphene Oxide by E-Beam Direct Write

On demand switchable additive/subtractive patterning of 2D nanomaterials is an essential capability for developing new concepts of functional nanomaterials and their device realizations. Traditionally, this is performed via a multi-step process using photoresist coating and patterning by conventional photo or electron beam lithography, which is followed by bulk dry/wet etch or deposition. This limits the range of functionalities and structural topologies that can be achieved, as well as increases the complexity, cost, and possibility of contamination which are significant barriers to device fabrication from highly sensitive 2D materials. Focused electron beam induced processing (FEBIP) enables a material chemistry/site-specific, high-resolution multi-mode atomic scale processing and provides unprecedented opportunities for direct-write, single-step surface patterning of 2D nanomaterials with an in-situ imaging capability. It allows for realizing a rapid multi-scale/multi-mode approach, ranging from an atomic scale manipulation (e.g., via targeted defect introduction as an active site) to a large-area surface modification on nano and micro scales, including patterned doping and material removal/deposition with 2D (in-plane)/3D (out-of-plane) control. In this work, we report on a new capability of FEBIP for nanoscale patterning of graphene oxide via removal of oxygenated carbon moieties with no use of reactive gas required for etching complemented by carbon atom deposition using focused electron beam. The mechanism of experimentally observed phenomena is explored using the density functional theory (DFT) calculations, revealing that interactions of e-beam liberated reactive oxygen radicals with carbon atoms on graphene basal plane lead to creation of atomic vacancies in the material. The reaction by-products are volatile carbon di-oxides, which are dissociated and volatilized from the graphene oxide surface functional groups by interactions with an energetic focused electron beam. Along with selective “subtractive” patterning of graphene oxide, the same electron beam with increased irradiation doses can deposit out-of-plane 3D carbon nanostructures on top of or around the 2D etched pattern, thus forming a hybrid 2D/3D nanocomposite with feature control down to a few nanometers. Furthermore, this in-operando dual nanofabrication capability of FEBIP is unmatched by any other nanopatterning techniques and opens a new design window for forming 2D/3D complex nanostructures and functional nanodevices.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ionic Control over Ferroelectricity in 2D Layered van der Waals Capacitors

The van der Waals layered material CuInP 2 S 6 features interesting functional behavior, including the existence of four uniaxial polarization states, polarization reversal against the electric field through Cu ion migration, a negative-capacitance regime, and reversible extraction of Cu ions. At the heart of these characteristics lies the high mobility of Cu ions, which also determines the spontaneous polarization. Therefore, Cu migration across the lattice results in unusual ferroelectric behavior. Here, we demonstrate how the interplay of polar and ionic properties provides a path to ionically controlled ferroelectric behavior, achieved by applying selected DC voltage pulses and subsequently probing ferroelectric switching during fast triangular voltage sweeps. Using current measurements and theoretical calculations, we observe that increasing DC pulse duration results in higher ionic currents, the buildup of an internal electric field that shifts polarization loops, and an increase in total switchable polarization by ~50% due to the existence of a high polarization phase which is stabilized by the internal electric field. Apart from tuning ferroelectric behavior by selected square pulses, hysteretic polarization switching can even be entirely deactivated and reactivated, resulting in three-state systems where polarization switching is either inhibited or can be performed in two different directions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

van der Waals Epitaxy, Superlubricity, and Polarization of the 2D Ferroelectric SnS

Tin monosulfide (SnS) is a two-dimensional layered semiconductor that exhibits in-plane ferroelectric order at very small thicknesses and is of interest in highly scaled devices. Here, in this study, we report the epitaxial growth of SnS on hexagonal boron nitride (hBN) using a pulsed metal-organic chemical vapor deposition process. Lattice matching is observed between the SnS($100$) and hBN{$1\bar{10}$} planes, with no evidence of strain. Atomic force microscopy reveals superlubricity along the commensurate direction of the SnS/hBN interface, and first-principles calculations suggest that friction is controlled by the edges of the SnS islands, rather than interface interactions. Differential phase contrast imaging detects remnant polarization in SnS islands with domains that are not dictated by step-edges in the SnS. The growth of ferroelectric SnS on high quality hBN substrates is a promising step toward electrically switchable ferroelectric semiconducting devices.

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

Nanoscale Surface Structure of Nanometer-Thick Ferroelectric BaTiO 3 Films Revealed by Synchrotron X-ray Scanning Tunneling Microscopy: Implications for Catalytic Adsorption Reactions

Ferroelectric nanomaterials are of interest in catalysis, non-volatile memory, and neuromorphic computing among other applications because of their switchable structure that can alter electronic and interface properties of a single material. The investigation of the role of polarization on the surface structure and chemistry of ferroelectric nanomaterials is a longstanding challenge, as it ideally requires a combination of both nanoscale imaging and chemical spectroscopy. In this work we study a model ferroelectric BaTiO 3 thin film by synchrotron X-ray scanning tunneling microscopy (SX-STM), a unique method which integrates nanoscale surface imaging and chemically sensitive spectroscopy. We find that polarization switching from downward to upward in (001)single crystalline BaTiO 3 thin films increases the intensity of X-ray absorption across Ba M, Ti L and O K edges. Chemical mapping of nanometer sized domains further demonstrates the modulation of surface structures upon polarization switching, as well as confirming the trends observed in single point experiments across the surface. Here, we complement these measurements with ab-initio computational absorption spectroscopy to elucidate the effect of polarization switching on the core-hole excitations using the Bethe-Salpeter equation approach. Our experimental and theoretical results thus confirm a stronger binding strength for the upward polarized surface with molecular O 2 as a model reactant, offering mechanistic evidence that supports previous reports. This work advances the understanding of the surface chemistry and electronic structure of ferroelectrics, which can ultimately aid strategies to design interfaces with tailored properties.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Dynamic Activation of Single-Atom Catalysts by Reaction Intermediates: Conversion of Formic Acid on Rh/Fe 3 O 4 (001)

The stability and activity of supported single-atom catalysts (SACs) represent critical yet opposing factors limiting our ability to explore and exploit their unique properties. Here, this study demonstrates the operation of a switchable catalyst that is activated in the presence of surface intermediates and reverts back to a stable but inactive form when the reaction is completed. We employ atomically defined Rh-Fe 3 O 4 (001) catalysts to demonstrate how structurally stable Rh, bound in surface octahedral Fe sites, gets destabilized to form highly active Rh adatoms and small clusters. Conversion of formic acid, leading initially to surface formate and hydroxyl species, is employed as a model reaction to probe the dynamics of such processes. We find that surface hydroxyl recombination to water through the Mars van Krevelen mechanism reduces Rh coordination, triggering its conversion to active Rh adatoms. Since such lattice oxygen exchange is observed in many acid-base and redox chemistries, the process can be broadly applicable to controlling the activation of the range of SACs.

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

Engineered pH-Sensitive Protein G/IgG Interaction

While natural protein–protein interactions have evolved to be induced by complex stimuli, rational design of interactions that can be switched-on-demand still remain challenging in the protein design world. Here, we demonstrate that a computationally redesigned natural interface for improved binding affinity could further be mutated to adopt a pH switchable interaction. The redesigned interface of Protein G/human IgG Fc domain (referred to as PrG/hIgG), when incorporated with histidine and glutamic acid on PrG (PrG-EHHE), showed a switch in binding affinity by 50-fold when the pH was altered from mild acidic to mild basic. The wild-type (WT) interface showed a negligible switch. The overall binding affinity under mild acidic pH for PrG-EHHE outperformed the wild-type PrG (PrG-WT) interaction. Overall, we find that the new reagent PrG-EHHE can be revolutionary in IgG purification, since the standard method of using an extreme acidic pH for elution can be circumvented.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Redox-Responsive, Reconfigurable All-Liquid Constructs

Using host-guest chemistries in a biphasic system, a novel supramolecular nanoparticle surfactant (s-NPS) with redox-responsiveness is presented to structure liquids. Additionally, the in situ assembly/jamming and disassembly/unjamming of s-NPSs at the oil-water interface are reversibly controlled by a switchable redox process, imparting a nanoscale redox-responsiveness, affecting the assemblies on all length scales. "Smart" all-liquid constructs including structured emulsions and programmable liquid devices are easily prepared, showing promising applications in responsive delivery, release, and reaction systems.

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

Direct Observation of Modulated Radical Spin States in Metal–Organic Frameworks by Controlled Flexibility

Owing to their switchable spin states and dynamic electronic character, organic-based radical species have been invoked in phenomena unique to a variety of fields. When incorporated in solid state materials, generation of organic radicals proves challenging due to aggregation. Metal–organic frameworks (MOFs) are promising candidates for immobilization and stabilization of organic radicals because of the tunable spatial arrangement of organic linkers and metal nodes, which sequesters the reactive species. Herein, a flexible, redox-active tetracarboxylic acid linker bearing two imidazole units was chosen to construct a new Zr 6 -MOF, NU-910, with scu topology. By exploiting the structural flexibility of NU-910, we successfully modulate the dynamics between an isolated organic radical species and an organic radical π-dimer species in the MOF system. Single-crystal X-ray diffraction analysis reveals that through solvent exchange from N,N-diethylformamide to acetone, NU-910 undergoes a structural contraction with interlinker distances decreasing from 8.32 Å to 3.20 Å at 100 K. Organic radical species on the bridging linkers are generated via UV light irradiation. Direct observation of temperature-induced spin switches from an isolated radical species to a magnetically silent radical π-dimer in NU-910 after irradiation in the solid state was achieved via variable-temperature single-crystal X-ray diffraction and variable-temperature electron paramagnetic resonance spectroscopy. Ultraviolet–visible–near infrared spectroscopy and density functional theory calculations further substantiated the formation of a radical cation π-dimer upon irradiation. As a result, this work demonstrates the potential of using flexible MOFs as a platform to modulate radical spin states in the solid phase.

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

Broad Electronic Modulation of Two-Dimensional Metal–Organic Frameworks over Four Distinct Redox States

Two-dimensional (2D) inorganic materials have emerged as exciting platforms for (opto)electronic, thermoelectric, magnetic, and energy storage applications. However, electronic redox tuning of these materials can be difficult. Instead, 2D metal–organic frameworks (MOFs) offer the possibility of electronic tuning through stoichiometric redox changes, with several examples featuring one to two redox events per formula unit. Here, we demonstrate that this principle can be extended over a far greater span with the isolation of four discrete redox states in the 2D MOFs Li x Fe 3 (THT) 2 (x = 0–3, THT = triphenylenehexathiol). This redox modulation results in 10,000-fold greater conductivity, p- to n-type carrier switching, and modulation of antiferromagnetic coupling. Physical characterization suggests that changes in carrier density drive these trends with relatively constant charge transport activation energies and mobilities. Furthermore, this series illustrates that 2D MOFs are uniquely redox flexible, making them an ideal materials platform for tunable and switchable applications.

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

Reversible Emulsions from Polyoxometalate–Polymer: A Robust Strategy to Cyclic Emulsion Catalysis and High-Internal-Phase Emulsion Materials

Reversible Pickering emulsions, achieved by switchable, interfacially active colloidal particles, that enable on-demand emulsification/demulsification or phase inversion, hold substantial promise for biphasic catalysis, emulsion polymerization, cutting fluids, and crude oil pipeline transportation. However, particles with such a responsive behavior usually require complex chemical syntheses and surface modifications, limiting their extensive use. Herein, we report a simple route to generate emulsions that can be controlled and reversibly undergo phase inversion. The emulsions are prepared and stabilized by the interfacial assembly of polyoxometalate (POM)–polymer, where their electrostatic interaction at the interface is dynamic. The wettability of the POMs that dictates the emulsion type can be readily regulated by tuning the number of polymer chains bound to POMs, which, in turn, can be controlled by varying the concentrations of both components and the water/oil ratio. In addition, the number of polymer chains anchored to the POMs can be varied by controlling the number of negative charges on the POMs through an in situ redox reaction. As such, a reversible inversion of the emulsions can be triggered by switching between exposure to ultraviolet light and the introduction of oxygen. Combining the functions of POM itself, a cyclic interfacial catalysis system was realized. Inversion of the emulsion also affords a pathway to high-internal-phase emulsions. Finally, the diversity of the POMs, the polymers, and the responsive switching groups open numerous new, simple strategies for designing a wide range of responsive soft matter for cargo loading, controlled release, and delivery in biomedical and engineering applications without time-consuming particle syntheses.

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

Dynamic Atomistic Polar Structure Underpins Ultrahigh Linear Electro-Optic Coefficient in Transparent Ferroelectric Ceramics

Transparent ferroelectrics with high linear electro-optic (EO) coefficients are critical for advanced electro-optical devices. However, achieving optical transparency in ferroelectric ceramics remains challenging due to visible light scattering caused by defects such as domain walls, grain boundaries, and pores. Here, we report the successful fabrication of transparent ferroelectric ceramics through innovative chemical composition design and an advanced two-step sintering process in the La-doped Pb(Mg 1/3 Nb 2/3 )O 3 –PbTiO 3 system. The optical transparency, which is near the theoretical upper limit, can be attributed to the wide band gap and the minimization of light scattering of defects. By minimizing porosity and engineering grain/domain sizes to differ significantly from the wavelengths of visible light, we suppress scattering, achieving optical transparency near the theoretical upper limit. Strikingly, these ceramics exhibit an ultrahigh linear EO coefficient of ∼1417 pm/V, over 65 times greater than that of LiNbO 3 single crystals, the current industry standard. We attribute this exceptional performance to dynamic atomistic polar structures within switchable, thermally stable domains, which enhance electronic polarization sensitivity. This mechanism is corroborated by dielectric spectroscopy, high-resolution transmission electron microscopy and simulation. Our findings offer insights into the design of cost-effective transparent materials with exceptional EO properties, paving the way for next-generation electro-optical devices.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Surface-Functionalized, Two-Dimensional Polymer Electrochromic Layers as Ultrafast, Multi-State Infrared Optical Gates

Electrochromic devices have widespread application potential, but the currently available switching speeds limit broad real-world implementation of this technology. Here, we report surface-engineered two-dimensional polymers with ionophilic pores that offer unprecedented switching speeds in solid-state, two-terminal, electrochromic devices. In particular, we demonstrate that a crystalline donor–acceptor 2DP functionalized with ethylene glycol oligomers exhibits multistate infrared absorption that is 4× faster (t c = 320 ms) with 3× coloration efficiency (491 cm 2 C –1 ) compared to an alkyl functionalized 2DP constructed from the same chromophores. The functionalized nanoporous surfaces enable rapid switching in these materials under either oxidative or reductive conditions, allowing us to access a range of robust, stable optical responses in a single electrochromic layer. These attributes led us to leverage surface-functionalized 2DPs as multistate infrared logic gates. Collectively, this work demonstrates that surface engineering of nanoporous crystalline lattices is a promising approach to co-optimize the electronic and ionic conductivities required to achieve rapidly switchable electrochromic layers. Beyond speed and efficiency, the demonstration of multistate infrared characteristics shows that electrochromic frameworks are useful in integrated optoelectronic circuits. This positions surface-engineered 2DPs as improved electrochromic coatings and a new material platform for photonic information processing and adaptive devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Three-State Electrochiroptical Switches Derived from Chiral Stable Carbenes

Chiral redox switches have been used to develop stimuli-responsive materials and organic electronics wherein small molecule chirality produces new functionality. Despite the widespread use of stable carbenes in redox-active materials and asymmetric synthesis, their integration into chiral redox switches remains largely unexplored. Herein, we show that chiral stable carbenes can be used to construct helically chiral overcrowded alkenes which function as three-state electrochiroptical switches. Redox-driven (de)aromatization triggers the reversible exchange of helical and axial chirality via a helically chiral π-radical cation. Due to dramatic changes in both electronic and geometric structure, including the inversion of helical chirality, each state exhibits distinct chiroptical properties. As a proof of concept, we demonstrate multiple cycles of electrochemical ON–OFF switching and sign inversion of the electronic circular dichroism response. Overall, this work establishes chiral stable carbenes as promising building blocks for chiral and redox-switchable materials.

Chirality↗
DOE OSTI2020

Development of light-responsive protein binding in the monobody non-immunoglobulin scaffold

Abstract Monobodies are synthetic non-immunoglobulin customizable protein binders invaluable to basic and applied research, and of considerable potential as future therapeutics and diagnostic tools. The ability to reversibly control their binding activity to their targets on demand would significantly expand their applications in biotechnology, medicine, and research. Here we present, as proof-of-principle, the development of a light-controlled monobody (OptoMB) that works in vitro and in cells and whose affinity for its SH2-domain target exhibits a 330-fold shift in binding affinity upon illumination. We demonstrate that our αSH2-OptoMB can be used to purify SH2-tagged proteins directly from crude E. coli extract, achieving 99.8% purity and over 40% yield in a single purification step. By virtue of their ability to be designed to bind any protein of interest, OptoMBs have the potential to find new powerful applications as light-switchable binders of untagged proteins with the temporal and spatial precision afforded by light.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Chemical trends of deep levels in van der Waals semiconductors

Abstract Properties of semiconductors are largely defined by crystal imperfections including native defects. Van der Waals (vdW) semiconductors, a newly emerged class of materials, are no exception: defects exist even in the purest materials and strongly affect their electrical, optical, magnetic, catalytic and sensing properties. However, unlike conventional semiconductors where energy levels of defects are well documented, they are experimentally unknown in even the best studied vdW semiconductors, impeding the understanding and utilization of these materials. Here, we directly evaluate deep levels and their chemical trends in the bandgap of MoS 2 , WS 2 and their alloys by transient spectroscopic study. One of the deep levels is found to follow the conduction band minimum of each host, attributed to the native sulfur vacancy. A switchable, DX center - like deep level has also been identified, whose energy lines up instead on a fixed level across different hosts, explaining a persistent photoconductivity above 400 K.

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

Superconducting diode effect via conformal-mapped nanoholes

A superconducting diode is an electronic device that conducts supercurrent and exhibits zero resistance primarily for one direction of applied current. Such a dissipationless diode is a desirable unit for constructing electronic circuits with ultralow power consumption. However, realizing a superconducting diode is fundamentally and technologically challenging, as it usually requires a material structure without a centre of inversion, which is scarce among superconducting materials. Here, we demonstrate a superconducting diode achieved in a conventional superconducting film patterned with a conformal array of nanoscale holes, which breaks the spatial inversion symmetry. We showcase the superconducting diode effect through switchable and reversible rectification signals, which can be three orders of magnitude larger than that from a flux-quantum diode. The introduction of conformal potential landscapes for creating a superconducting diode is thereby proven as a convenient, tunable, yet vastly advantageous tool for superconducting electronics. This could be readily applicable to any superconducting materials, including cuprates and iron-based superconductors that have higher transition temperatures and are desirable in device applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Beam steering at the nanosecond time scale with an atomically thin reflector

Techniques to mold the flow of light on subwavelength scales enable fundamentally new optical systems and device applications. The realization of programmable, active optical systems with fast, tunable components is among the outstanding challenges in the field. Here, we experimentally demonstrate a few-pixel beam steering device based on electrostatic gate control of excitons in an atomically thin semiconductor with strong light-matter interactions. By combining the high reflectivity of a MoSe 2 monolayer with a graphene split-gate geometry, we shape the wavefront phase profile to achieve continuously tunable beam deflection with a range of 10°, two-dimensional beam steering, and switching times down to 1.6 nanoseconds. Our approach opens the door for a new class of atomically thin optical systems, such as rapidly switchable beam arrays and quantum metasurfaces operating at their fundamental thickness limit.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗