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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Tethered tertiary amines as solid-state n-type dopants for solution-processable organic semiconductors

A scarcity of stable n-type doping strategies compatible with facile processing has been a major impediment to the advancement of organic electronic devices. Localizing dopants near the cores of conductive molecules can lead to improved efficacy of doping. We and others recently showed the effectiveness of tethering dopants covalently to an electron-deficient aromatic molecule using trimethylammonium functionalization with hydroxide counterions linked to a perylene diimide core by alkyl spacers. In this work, we demonstrate that, contrary to previous hypotheses, the main driver responsible for the highly effective doping observed in thin films is the formation of tethered tertiary amine moieties during thin film processing. Furthermore, we demonstrate that tethered tertiary amine groups are powerful and general n-doping motifs for the successful generation of free electron carriers in the solid-state, not only when coupled to the perylene diimide molecular core, but also when linked with other small molecule systems including naphthalene diimide, diketopyrrolopyrrole, and fullerene derivatives. Our findings help expand a promising molecular design strategy for future enhancements of n-type organic electronic materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Room-temperature cycling of metal fluoride electrodes: Liquid electrolytes for high-energy fluoride ion cells

Fluoride ion batteries are potential “next-generation” electrochemical storage devices that offer high energy density. At present, such batteries are limited to operation at high temperatures because suitable fluoride ion–conducting electrolytes are known only in the solid state. We report a liquid fluoride ion–conducting electrolyte with high ionic conductivity, wide operating voltage, and robust chemical stability based on dry tetraalkylammonium fluoride salts in ether solvents. Pairing this liquid electrolyte with a copper–lanthanum trifluoride (Cu@LaF 3 ) core-shell cathode, we demonstrate reversible fluorination and defluorination reactions in a fluoride ion electrochemical cell cycled at room temperature. Fluoride ion–mediated electrochemistry offers a pathway toward developing capacities beyond that of lithium ion technology.

Davis, Victoria K.↗
DOE OSTI2016

Monitoring and Control of Chemical Composition of InGaN Layers During MOCVD

This Department of Energy SBIR Phase II grant targets the inefficiency of the epitaxial processes used to deposit wide band-gap semiconductor thin films that are an essential part of the next generation high-brightness LEDs for solid state lighting. Non-uniformity of the layers over a single wafer and non-repeatability over the wafers in a single batch, separate batches and separate reactors are some of the primary source of reduced manufacturing yield. The team performed extensive research, development and validation of an in-situ spectroscopic optical monitoring and epitaxial process control system. The system monitors the LED thin films as they grow on the individual wafers inside the epitaxial reactor, records the signal in a broad spectral range and processes the information to retrieve essential film quality parameters and their variation over a single wafer, all the wafers in a batch and multiple batches. A novel software algorithm is implemented, which performs real-time spectral pattern recognition and displays any abnormalities or differences in the deposition, which is used by the engineer to optimize the epitaxial process. The project resulted in the optimization of the LED film growth and improvement of its uniformity and repeatability, reducing the cost of the final LED devices.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Probing and controlling oxygen impurity diffusion in h -BN semi-bulk crystals

Combining its unique features of ultrawide bandgap (UWBG) and two-dimensional nature, h-BN has been explored for emerging applications such as deep ultraviolet optoelectronic devices and single photon emitters. One of the unusual applications of h-BN is for solid-state neutron detectors by utilizing the property of high thermal neutron capture cross section of B-10 as well as its UWBG properties. Although a record high detection efficiency of 59% has been attained by h-BN detectors, the understanding/minimization of defects and impurities is still needed to further advance the h-BN material and detector technologies. We report metal organic chemical vapor deposition growth and oxygen (O) impurity diffusion in thick h-BN. The diffusion coefficient (D) of O impurities has been measured via the evolution of an oxygen related emission with the etching depth, providing a value of D of ∼ 2 × 10−13 cm2/s at 1450 °C and supporting the interpretation that oxygen in h-BN is a substitutional donor. A multiple-buffer-layer approach was employed to mitigate to a certain degree the issue of oxygen diffusion from sapphire substrate during growth. It was demonstrated that the performance of h-BN neutron detectors fabricated from the wafer incorporating multiple buffer layers was significantly improved, as manifested by the enhanced thermal neutron detection efficiency. The advancement of the crystal growth technology of h-BN semi-bulk crystals creates applications in optoelectronic and power electronic devices utilizing the UWBG semiconductor properties of h-BN, while high efficiency h-BN neutron detectors have the potential to supplant the traditional He-3 gas detectors in various application areas by offering the obvious advantages of UWBG semiconductor technologies.

Physics↗
DOE OSTI2020

Solid-State Ionic Rectification in Perovskite Nanowire Heterostructures

Halide perovskites have attracted increasing research attention with regard to their potential for optoelectronic applications. Because of its low activation energy, ion migration is implicated in the long-term stability and many unusual transport behaviors of halide perovskite devices. However, direct observation and precise control of the ionic transport in halide perovskite crystals remain challenging. Here, we have designed an axial CsPbBr 3 -CsPbCl 3 nanowire heterostructure, in which electric-field-induced halide ion migration was clearly visualized and quantified. We demonstrated that halide ion migration is dependent on the applied electric field and exhibits ionic rectification in this solid-state system, which is due to the nonuniform distribution of the ionic vacancies in the nanowire that results from a competition between electrical screening and their creation/destruction at the electrodes' interfaces. Furthermore, the asymmetric heterostructure characteristics add an additional knob to control the ion movement in the design of advanced ionic circuits with halide perovskites as building blocks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Solid electrolytes for solid-state and lithium-sulfur batteries

The stringent demands placed on batteries by emerging vehicle technologies such as plug-in and battery electric vehicles suggest that improvements in the safety and performance of electrochemical energy storage devices, as well as concurrent reductions in their cost, are highly desirable. Current strategies for improving performance have largely focused on Li-ion battery chemistries. In this project went beyond the state of the art by pursuing electrolyte chemistries that will enable the use of Li metal anodes and sulfur cathodes, either concurrently in a solid state Li-S battery, or as a means to achieve a Li metal anode which is stable upon cycling. More specifically, our effort advanced strategies to enable Li metal anodes for myriad beyond Li-ion chemistries . LLZO garnet (Li 7 La 3 Zr 2 O 12 ) is the first bulk-scale ceramic electrolyte to exhibit the combination of superionic conductivity (1mS/cm at 298K), high shear modulus (61 GPa) to suppress Li dendrite penetration, and apparent electrochemical stability (0-6V vs Li/Li + ), thus enabling Li metal anodes. However, to date there are no reports confirming LLZO can tolerate current densities > 1mA/cm 2 , thus demonstrating relevance to PHEV/EV batteries. Our goal was to investigate the mechanisms that govern the Li-LLZO interfacial stability as a function of current density. We determined that defects in polycrystalline LLZO reduce the critical current density (CCD). Primarily contaminants on the LLZO surface and grain boundaries were the primary defects the limited the CCD. Using our experience with synthesis and processing (Sakamoto and Wolfenstine) and sophisticated materials characterization (Nanda), we precisely controlled atomistic and microstructural defects and correlated their effects on controlling the critical current density. These data fed into multi-scale computation models (Siegel and Monroe) to isolate and quantify the roles that each defect played in controlling the critical current density. Bridging this knowledge gap allowed us to demonstrate that LLZO can withstand > 1mA/cm 2 .

25 ENERGY STORAGE↗
DOE OSTI2016

Solid-state electrochemistry on the nanometer and atomic scales: the scanning probe microscopy approach

Energy technologies of the 21st century require an understanding and precise control over ion transport and electrochemistry at all length scales – from single atoms to macroscopic devices. Our short review provides a summary of recent studies dedicated to methods of advanced scanning probe microscopy for probing electrochemical transformations in solids at the meso-, nano- and atomic scales. In this discussion we present the advantages and limitations of several techniques and a wealth of examples highlighting peculiarities of nanoscale electrochemistry.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Unexpectedly Strong Auger Recombination in Halide Perovskites

The emergence of halide perovskites for photovoltaic applications has triggered great interest in these materials for solid-state light emission. Higher order electron–hole recombination processes can critically affect the efficiency of such devices. In the present work, the Auger recombination coefficients are computed in the prototypical halide perovskite, CH 3 NH 3 PbI 3 (MAPbI 3 ), using first-principles calculations. It is demonstrated that Auger recombination is responsible for the exceptionally high third-order recombination coefficient observed in experiment. The large Auger coefficient is attributed to a coincidental resonance between the bandgap and interband transitions to a complex of higher-lying conduction bands. It is also found that the distortions of PbI 6 octahedra contribute significantly to the high Auger coefficient, offering potential avenues for materials design.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Identification and Mitigation of Generated Solid By-Products during Advanced Electrode Materials Processing

A scalable, solid-state elevated temperature process was developed to produce high capacity carbonaceous electrode materials for energy storage devices via decomposition of starch-based precursor in an inert atmosphere. The fabricated carbon-based architectures are useful as an excellent electrode material for lithium-ion, sodium-ion and lithium-sulfur batteries. This article focuses on the study and analysis of the formed nanometer-sized byproducts during the lab-scale production of carbonaceous electrode materials in the process design phase. The complete material production process was studied by operation, namely during heating, holding the reaction at elevated temperature, followed by cooling. The unknown downstream particles in the process exhaust were collected and characterized via aerosol and liquid suspensions, and they were quantified using direct-reading instruments for number and mass concentrations. The airborne emissions were collected on polycarbonate filters and TEM grids using the Tsai diffusion sampler (TDS) for characterization and further analysis. Released byproduct aerosols collected in a deionized (DI) water trap were analyzed using a Nanosight real time nanoparticle characterization system and the aerosols emitted post water suspension were collected and characterized. Individual particles in the nanometer size range were found in exhaust aerosols, however, crystal structured aggregates were formed on the sampling substrate after a long-term sampling of emitted exhaust. After characterizing the released aerosol byproducts, methods were also identified to mitigate possible human and environmental exposures upon the industrial implementation of such a process.

25 ENERGY STORAGE↗
DOE OSTI2024

Upconversion on the Micrometer Scale: Impact of Local Heterogeneity

The properties of perovskite/naphtho[2,3-a]pyrene (NaPy) upconversion devices are investigated by a combination of atomic force microscopy and photoluminescence mapping to understand the role of microscopic heterogeneity in the ensemble device properties. The results emphasize strong microscopic inhomogeneity across the perovskite/NaPy upconversion device due to local formation of NaPy microcrystals. NaPy shows emission from three distinct states in the solid state: S 1 ′ emission at 520 nm, excimer emission at 560 nm, and S 1 ″ emission at 620 nm. Clear spatial differences in the emission spectrum under 405 nm excitation are found, highlighting that there is a strong microcrystal-to-microcrystal variation in the optical properties─emphasizing a need for multimodal measurements. Furthermore, our results indicate that microcrystals with strong emission from the strongly coupled low-energy state S 1 ″ (J-dimer) show much higher upconversion intensity than those with dominant emission from the high-energy S 1 ′ state (I-aggregate). Hence, our results suggest that microcrystals with strong emission from the low-energy state S 1 ″ act as isolated hotspots for upconversion.

Crystals↗
DOE OSTI2022

High-Cooperativity Coupling of Rare-Earth Spins to a Planar Superconducting Resonator

The interfacing of a superconducting microwave resonator with rare-earth-doped crystals presents a promising hybrid quantum system for applications including spin-assisted transducers and memories. The coupling strength between the spins of the rare-earth ions and the microwave photons is characterized by the cooperativity. Here, we report an ultrahigh cooperativity of C~650 between rare-earth spins and a planar superconducting microwave resonator that features a highly uniform magnetic field for harnessing the strong anisotropic coupling strength of erbium-doped yttrium orthosilicate. This cooperativity rivals that from a bulk dielectric resonator and may pave a path for efficient coupling of spins with microwave photons on an integrated platform.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Phonon-Assisted Intertube Electronic Transport in an Armchair Carbon Nanotube Film

The electrical conductivity of a macroscopic assembly of nanomaterials is determined through a complex interplay of electronic transport within and between constituent nano-objects. Phonons play dual roles in this situation: their increased populations tend to reduce the conductivity via electron scattering, while they can boost the conductivity by assisting electrons to propagate through the potential-energy landscape. Here, we identified a phonon-assisted coherent electron transport process between neighboring nanotubes in temperature-dependent conductivity measurements on a macroscopic film of armchair single-wall carbon nanotubes. Through atomistic modeling of electronic states and calculations of both electronic and phonon-assisted junction conductances, we conclude that phonon-assisted conductance is the dominant mechanism for observed high-temperature transport in armchair carbon nanotubes. The unambiguous manifestation of coherent intertube dynamics proves a single-chirality armchair nanotube film to be a unique macroscopic solid-state ensemble of nano-objects promising for the development of room-temperature coherent electronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

High performance devices enabled by epitaxial, preferentially oriented, nanodots and/or nanorods

Novel articles and methods to fabricate same with self-assembled nanodots and/or nanorods of a single or multicomponent material within another single or multicomponent material for use in electrical, electronic, magnetic, electromagnetic, superconducting and electrooptical devices is disclosed. Self-assembled nanodots and/or nanorods are ordered arrays wherein ordering occurs due to strain minimization during growth of the materials. A simple method to accomplish this when depositing in-situ films is also disclosed. Device applications of resulting materials are in areas of superconductivity, photovoltaics, ferroelectrics, magnetoresistance, high density storage, solid state lighting, non-volatile memory, photoluminescence, thermoelectrics and in quantum dot lasers.

36 MATERIALS SCIENCE↗
DOE OSTI2012

High performance electrical, magnetic, electromagnetic and electrooptical devices enabled by three dimensionally ordered nanodots and nanorods

Novel articles and methods to fabricate same with self-assembled nanodots and/or nanorods of a single or multicomponent material within another single or multicomponent material for use in electrical, electronic, magnetic, electromagnetic and electrooptical devices is disclosed. Self-assembled nanodots and/or nanorods are ordered arrays wherein ordering occurs due to strain minimization during growth of the materials. A simple method to accomplish this when depositing in-situ films is also disclosed. Device applications of resulting materials are in areas of superconductivity, photovoltaics, ferroelectrics, magnetoresistance, high density storage, solid state lighting, non-volatile memory, photoluminescence, thermoelectrics and in quantum dot lasers.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

High performance superconducting devices enabled by three dimensionally ordered nanodots and/or nanorods

Novel articles and methods to fabricate same with self-assembled nanodots and/or nanorods of a single or multicomponent material within another single or multicomponent material for use in electrical, electronic, magnetic, electromagnetic and electrooptical devices is disclosed. Self-assembled nanodots and/or nanorods are ordered arrays wherein ordering occurs due to strain minimization during growth of the materials. A simple method to accomplish this when depositing in-situ films is also disclosed. Device applications of resulting materials are in areas of superconductivity, photovoltaics, ferroelectrics, magnetoresistance, high density storage, solid state lighting, non-volatile memory, photoluminescence, thermoelectrics and in quantum dot lasers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Microfabrication of a gadolinium-derived solid-state sensor for thermal neutrons

Neutron sensing is critical in civilian and military applications. Conventional neutron sensors are limited by size, weight, cost, portability and helium supply. Here in this study, the microfabrication of gadolinium (Gd) conversion material–based heterojunction diodes for detecting thermal neutrons using electrical signals produced by internal conversion electrons (ICEs) is described. Films with negligible stress were produced at the tensile-compressive crossover point, enabling Gd coatings of any desired thickness by controlling the radiofrequency sputtering power and using the zero-point near p(Ar) of 50 mTorr at 100 W. Post-deposition Gd oxidation–induced spallation was eliminated by growing a residual stress-free 50 nm neodymium-doped aluminum cap layer atop Gd. The resultant coatings were stable for at least 6 years, demonstrating excellent stability and product shelf-life. Depositing Gd directly on the diode surface eliminated the air gap, leading to a 200-fold increase in electron capture efficiency and facilitating monolithic microfabrication. The conversion electron spectrum was dominated by ICEs with energies of 72, 132 and 174 keV. Results are reported for neutron reflection and moderation by polyethylene for enhanced sensitivity, and γ- and X-ray elimination for improved specificity. The optimal Gd thickness was 10.4 μm for a 300 μm-thick partially depleted diode of 300 mm 2 active surface area. Fast detection (within 10 min) at a neutron source-to-diode distance of 11.7 cm was achieved with this configuration. All ICE energies along with γ-ray and K α ,β X-rays were modeled to emphasize correlations between experiment and theory. Semi-conductor thermal neutron detectors offer advantages for field-sensing of radioactive neutron sources.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗