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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Synthesis of nickel selenide thin films for high performance all-solid-state asymmetric supercapacitors

As a significant semiconductor, nickel selenide shows enormous potential and extensive application prospects in the field of sensor, photocatalysis and supercapacitor. In this paper, nickel selenide (Ni 3 Se 2 , NiSe) thin films were successfully fabricated on stainless-steel sheet using a facile, effective electrodeposition technique. The morphologies, microstructures and chemical compositions of the thin films are characterized systematically. Electrochemical tests exhibit that the Ni3Se2 and NiSe possess high specific capacitance of 581.1 F/g and 1644.7 F/g, respectively. A flexible, all-solid-state asymmetric supercapacitor is assembled by utilizing NiSe film as positive electrode and activated carbon as negative electrode. The solid device delivers a high areal capacitance of 27.0 mF/cm 2 at the current density of 0.7 mA/cm 2 . Furthermore, the maximum volumetric energy density and power density of the NiSe//AC asymmetric SCs can achieve 0.26 mWh/cm 3 and 33.35 mW/cm 3 , respectively. The device shows robust cycling stability with 84.6% capacitance retention after 10000 cycles, outstanding flexibility and satisfactory mechanical stability. Moreover, two devices in series can light up a red light-emitting diode, which displayed great potential applications for energy storage.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Bidentate Ligand-Induced Oriented Transformation of CsPbBr 3 Perovskite Nanocrystals into Nanowires for X-ray Photodetectors

We report shape and dimensionality control by ligands is an efficient way to fabricate high-quality perovskite nanocrystals (NCs) with optoelectronic properties. Herein, to realize oriented transformations between different morphologies of CsPbBr 3 nanocrystals, we conceived of the use of defects and bidentate ligands to synergistically drive the reorientation of CsPbBr3nanocrystals into CsPbBr 3 nanowires (NWs). By employing aminocaproic acid as the bidentate ligand, CsPbBr 3 NWs were reconstructed from the CsPbBr 3 NCs (~7 nm) with 20-60 nm in width and several micrometers in length, as well as a 527 nm photoluminescence (PL) peak, 59% PL quantum yield, and 98.5 ns PL lifetime. The bidentate ligand-directed anisotropic shape evolution and growth of perovskite NWs from NCs was elucidated by transmission electronmicroscopy and PL studies. The photodetectors fabricated with the reconstructed CsPbBr 3 NWs displayed a photocurrent enhancement (2.75 × 10 -11 A) compared with that of the devices based on solution-synthesized NWs (2.28 × 10 -11 A). The device also showed a short response time, indicating its more sensitive photoelectric response. This process provides a viable approach to engineering diverse morphologies of perovskite nanocrystals for optoelectronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Simulating the non-monotonic strain response of nanoporous multiferroic composites under electric field control

In this work, we simulate and analyze the mechanical response of a class of multiferroic materials consisting of a templated porous nanostructure made out of cobalt ferrite (CFO) partially filled by atomic layer deposition (ALD) with a ferroelectric phase of lead zirconate titanate (PZT). The strain in the device is measured when an electric field is applied for varying ALD thicknesses, displaying a non-monotonic dependence with a maximum strain achieved for a coating thickness of 3 nm. To understand this behavior, we apply finite element modeling to the smallest repeatable unit of the nanoporous template and simulate the mechanical response as a function of PZT coating thickness. We find that this non-monotonic response is caused by the interplay between two driving forces opposing one another. First, increased porosity works toward increasing the strain due to a reduced system stiffness. Second, decreased porosity involves a larger mass fraction of PZT, which drives the electro-mechanical response of the structure, thus leading to a larger strain. The balance between these two driving forces is controlled by the shear coupling at the CFO/PZT interface and the effective PZT cross section along the direction of the applied electric field. Here, our numerical results show that considering a nonlinear piezoelectric response for PZT leads to an improved agreement with the experimental data, consistent with ex situ poling of the nanostructure prior to magnetic measurements.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Flexible and high-performance electrochromic devices enabled by self-assembled 2D TiO 2 /MXene heterostructures

Transition metal oxides (TMOs) are promising electrochromic (EC) materials for applications such as smart windows and displays, yet the challenge still exists to achieve good flexibility, high coloration efficiency and fast response simultaneously. MXenes (e.g. Ti 3 C 2 T x ) and their derived TMOs (e.g. 2D TiO 2 ) are good candidates for high-performance and flexible EC devices because of their 2D nature and the possibility of assembling them into loosely networked structures. Here we demonstrate flexible, fast, and high-coloration-efficiency EC devices based on self-assembled 2D TiO 2 /Ti 3 C 2 T x heterostructures, with the Ti 3 C 2 T x layer as the transparent electrode, and the 2D TiO 2 layer as the EC layer. Benefiting from the well-balanced porosity and connectivity of these assembled nanometer-thick heterostructures, they present fast and efficient ion and electron transport, as well as superior mechanical and electrochemical stability. We further demonstrate large-area flexible devices which could potentially be integrated onto curved and flexible surfaces for future ubiquitous electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2021

OPERATING EXPERIENCE AND ITS RELATIONSHIP TO EMBEDDED DIGITAL DEVICES IN SAFETY SYSTEMS

Interest in embedded digital devices (EDDs) for monitoring and providing control of components is increasing and the added functionality digital brings such as diagnostics, displays, control functions is welcomed in both the nuclear and other industries. As a result, pure analog-based components continue to disappear from the industrial I&C marketplace. Equipment with EDDs, also known by related terms such as smart devices, intelligent devices, and digital devices of limited functionality, can include sensors, breakers, priority logic modules, time delay relays, pumps, valve actuators, motor control centers, and uninterruptible power supplies. Not only is equipment consisting of analog and older digital technology being replaced with commercial grade products containing EDDs, but EDDs can also be retrofitted to work with existing components. EDDs may be installed physically within a component, such as in a relay. There are also external devices that some would not consider an EDD, but that operate in almost all technical ways identically to one internal to a component such as in a valve controller. In fact, the digital portions may be located hundreds of feet from the actual component.Due to the potential of being used in an identical manner and without alteration from their application in other industries, operating experience (OpE) for EDDs may be much more applicable than in the case of other more system level devices. Clear separation and independence of functionality provided with EDDs may also allow greater applicability of existing OpE from industry for changes that can be shown not to affect its safety function. However, OpE also demonstrates issues with different conditions between other industries and nuclear power plants, such as issues with undeclared changes or undeclared digital devices and the new failure modes they may introduce, issues with the reporting of OpE in industry, and a lack of transparency into OpE for EDDs.Understanding and addressing these issues will be key in the future use of EDDs in nuclear power plants, but failure rate data is difficult to obtain for EDDs, and lessons learned from the use of EDDs are difficult to collect and identify.Key words: embedded digital device, smart device, operating experience, failure modes

Muhlheim, Michael↗
DOE OSTI2023

Salts as Additives: A Route to Improve Performance and Stability of n-Type Organic Electrochemical Transistors

Organic electrochemical transistors (OECTs) are becoming increasingly ubiquitous in various applications at the interface with biological systems. However, their widespread use is hampered by the scarcity of electron-conducting (n-type) backbones and the poor performance and stability of the existing n-OECTs. Here, we introduce organic salts as a solution additive to improve the transduction capability, shelf life, and operational stability of n-OECTs. We demonstrate that the salt-cast devices present a 10-fold increase in transconductance and achieve at least one year-long stability, while the pristine devices degrade within four months of storage. The salt-added films show improved backbone planarity and greater charge delocalization, leading to higher electronic charge carrier mobility. These films show a distinctly porous morphology where the interconnectivity is affected by the salt type, responsible for OECT speed. The salt-based films display limited changes in morphology and show lower water uptake upon electrochemical doping, a possible reason for the improved device cycling stability. Our work provides a new and easy route to improve n-type OECT performance and stability, which can be adapted for other electrochemical devices with n-type films operating at the aqueous electrolyte interface.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Diazirine-based photo-crosslinkers for defect free fabrication of solution processed organic light-emitting diodes

The fabrication of solution deposited OLEDs is fraught with difficulties, largely due to the interlayer mixing and surface erosion during sequential deposition of the layers. We demonstrate that these problems can be circumvented by using photopolymerizable diazirine-based cross-linker capable of converting soluble organic materials into highly cross-linked insoluble networks. 3-Trifluoromethyl(aryl)diazirines photolyze readily upon the 10–15 min exposure of 365 nm UV irradiation to generate carbenes, which react with polymers or small molecules via C–H bond insertion producing highly cross-linked materials. This photo-generated cross-linking does not require any catalyst, initiator or short-wavelength UV light and is performed at room temperature, releasing molecular nitrogen as the only byproduct. To show the cross-linked polymer layers do not display inter-layer mixing, we deposited red-emitting regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) over cross-linked (10% cross-linker) blue emitting dioctyl polyfluorene (PFO) layer. The overlaid layers showed clear and well-defined boundary with no interlayer mixing. The surface morphology of the solution deposited layers was investigated by AFM to show that the cross-linked layers exhibited significant decrease in surface roughness. This is also shown on the example of the hole transporting material 4,4'-bis[N-(1-naphthyl)-N-phenylamino]-biphenyl (NPB) which displayed roughness average to decrease from 6.4 nm to 1.0 nm. The effect of decreased surface roughness on the performance of phosphorescent OLEDs was investigated by fabricating devices with configuration of ITO/PEDOT:PSS/NPB:(0%/5%/10%) cross-linker/MCP:6% Ir(mppy) 3 /TPBI/CsF/Al. Furthermore, following the diazirine-mediated cross-linking, the OLEDs displayed a decrease in turn-on voltage from 3.8 V to 3.0 V along with a six-fold enhancement of external quantum efficiency (EQE max ) from 1.1% to 6.8% and maximum luminous efficiency increase from 3.8 cd A -1 to 22.9 cd A -1 . These results demonstrate that the simple diazirine mediated photo-cross-linking using mild conditions compatible with organic layers is a promising strategy for improving the performance of the solution-processed OLEDs.

36 MATERIALS SCIENCE↗
DOE OSTI2020

2-D moving mesh modeling of lithium dryout in open surface liquid metal flow applications

Liquid lithium displays increasing promise as a replacement for solid plasma facing components (PFCs) in fusion device applications. The Liquid Metal Infused Trench (LiMIT) system, developed at the University of Illinois (UIUC), has demonstrated how thermoelectric magnetohydrodynamics (TEMHD) can be harnessed to drive liquid lithium flow in an open surface PFC. However, in the highest heat flux applications, large local acceleration is created via TEMHD, and the sudden increase in velocity can cause the liquid level to expose the underlying solid, eliminating the protective benefits of the lithium. In order to study potential mitigation strategies, a 2-D COMSOL Multiphysics model was developed using the moving mesh module to capture free surface flow. The model depicts the development of the dryout phenomenon for 2 test cases – slow (1 cm/s) and medium (10 cm/s) flow in 5 mm deep trenches – including the liquid level reduction under the high heat flux and the pileup of slower flow both upstream and downstream of the heat stripe. The effectiveness of trench shaping dryout mitigation strategies is examined. For the slow flow case, it is shown that a 1.8 mm ledge placed under the heat stripe will stop dryout, and for the medium flow case, a 2.7 mm ledge is required to mitigate the effect. This model can be used to identify strategies for increasing the viable heat load for open surface liquid lithium PFCs.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Rapid, Sensitive, Label-Free Electrical Detection of SARS-CoV-2 in Nasal Swab Samples

Rapid diagnosis of coronavirus disease 2019 (COVID-19) is key for the long-term control of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) amid renewed threats of mutated SARS-CoV-2 around the world. Here, we report on an electrical label-free detection of SARS-CoV-2 in nasopharyngeal swab samples directly collected from outpatients or in saliva-relevant conditions by using a remote floating-gate field-effect transistor (RFGFET) with a 2-dimensional reduced graphene oxide (rGO) sensing membrane. RFGFET sensors demonstrate rapid detection (<5 min), a 90.6% accuracy from 8 nasal swab samples measured by 4 different devices for each sample, and a coefficient of variation (CV) < 6%. Also, RFGFET sensors display a limit of detection (LOD) of pseudo-SARS-CoV-2 that is 10 000-fold lower than enzyme-linked immunosorbent assays, with a comparable LOD to that of reverse transcriptionpolymerase chain reaction (RT-PCR) for patient samples. To achieve this, comprehensive systematic studies were performed regarding interactions between SARS-CoV-2 and spike proteins, neutralizing antibodies, and angiotensin-converting enzyme 2, as either a biomarker (detection target) or a sensing probe (receptor) functionalized on the rGO sensing membrane. Finally, taken together, this work may have an immense effect on positioning FET bioelectronics for rapid SARS-CoV-2 diagnostics.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Synthesis and exceptional operational durability of polyaniline-inspired conductive ladder polymers

Ladder-type structures can impart exceptional stability to polymeric electronic materials. This article introduces a new class of conductive polymers featuring a fully ladder-type backbone. A judicious molecular design strategy enables the synthesis of a low-defect ladder polymer, which can be efficiently oxidized and acid-doped to achieve its conductive state. The structural elucidation of this polymer and the characterization of its open-shell nature are facilitated with the assistance of studies on small molecular models. An autonomous robotic system is used to optimize the conductivity of the polymer thin film, achieving over 7 mS cm −1 . Impressively, this polymer demonstrates unparalleled stability in strong acid and under harsh UV-irradiation, significantly surpassing commercial benchmarks like PEDOT:PSS and polyaniline. Moreover, it displays superior durability across numerous redox cycles as the active material in an electrochromic device and as the pseudocapacitive material in a supercapacitor device. This work provides structural design guidance for durable conductive polymers for long-term device operation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Geometrical quasi-ballistic effects on thermal transport in nanostructured devices

In this work, we employ thermoreflectance thermal imaging to directly measure the steady-state two-dimensional (2D) temperature field generated by nanostructured heat sources deposited on silicon substrate with different geometrical configurations and characteristic sizes down to 400nm. The analysis of the results using Fourier’s law not only breaks down as size scales down, but it also fails to capture the impact of the geometry of the heat source. The substrate effective Fourier thermal conductivities fitted to wire-shaped and circular-shaped structures with identical characteristic lengths are found to display up to 40% mismatch. Remarkably, a hydrodynamic heat transport model reproduces the observed temperature fields for all device sizes and shapes using just intrinsic Si parameters, i.e., a geometry and size-independent thermal conductivity and nonlocal length scale. The hydrodynamic model provides insight into the observed thermal response and of the contradictory Fourier predictions. We discuss the substantial Silicon hydrodynamic behavior at room temperature and contrast it to InGaAs, which shows less hydrodynamic effects due to dominant phonon-impurity scattering.

42 ENGINEERING↗
DOE OSTI2026

Achieving ultrahigh modulus of resilience and enhanced thermal stability in ZnO x /SU-8 interpenetrating network polymer nanocomposite nanopillars

The modulus of resilience, a mechanical property that quantifies the maximum strain energy density a material can store during elastic deformation, is a crucial parameter for materials used in flexible displays, micro/nano-electro-mechanical system (M/NEMS) actuators, and ultra-sensitive pressure sensors. In this study, ZnO x /SU-8 nanocomposite nanopillars with a diameter of 300 nm, fully infiltrated with a uniformly distributed, interpenetrating amorphous ZnO x filler network, were synthesized via vapor-phase infiltration (VPI). In-situ uniaxial nano-compression tests revealed that the modulus of resilience of ZnO x /SU-8 reaches ∼ 12 MJ/m 3 , which is an ultrahigh value among all engineering materials with comparable strength. In addition, the synthesis fidelity, inorganic infiltration depth, and mechanical performance were all significantly improved compared to VPI-synthesized AlO x nanocomposites. Thermal stability, another key requirement for M/NEMS device materials operating under extreme environments, was also notably enhanced. Furthermore, partial crystallization of the amorphous ZnO x fillers during annealing contributed to an additional increase in modulus of resilience, reaching up to ∼ 13.9 MJ/m 3 . This work presents an effective fabrication strategy for producing nanostructured organic–inorganic hybrid nanocomposites with ultrahigh modulus of resilience and superior thermal stability, paving the way for their integration into next-generation flexible displays and high-performance M/NEMS devices working under harsh environments.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Complete Stokes vector analysis with a compact, portable rotating waveplate polarimeter

Accurate calibration of polarization dependent optical elements is often necessary in optical experiments. A versatile polarimeter device to measure the polarization state of light is a valuable tool in these experiments. Here we report a rotating waveplate-based polarimeter capable of complete Stokes vector analysis of collimated light. Calibration of the device allows accurate measurements over a range of wavelengths, with a bandwidth of >30 nm in this implementation. A photo-interrupter trigger system supplies the phase information necessary for full determination of the Stokes vector. An Arduino microcontroller performs rapid analysis and displays the results on a liquid crystal display. The polarimeter is compact and can be placed anywhere on an optical table on a single standard post. The components to construct the device are only a fraction of the cost of commercially available devices while the accuracy and precision of the measurements are of the same order of magnitude.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Diagnosing and Destroying Non-Markovian Noise

Nearly every protocol used to analyze the performance of quantum information processors is based on an assumption that the errors experienced by the device during logical operations are constant in time and are insensitive to external contexts. This assumption is pervasive, rarely stated, and almost always wrong. Quantum devices that do behave this way are termed "Markovian:' but nearly every system we have ever probed has displayed drift or crosstalk or memory effects they are all non-Markovian. Strong non-Markovianity introduces spurious effects in characterization protocols and violates assumptions of the fault-tolerance threshold theorems. This SAND report details a three year laboratory-directed research and development (LDRD) project entitled, "Diagnosing and Destroying non-Markovian Noise in Quantum Information Processors." This program was initiated to build tools to study non-Markovian dynamics and quantum systems and develop robust methodologies for eliminating it. The program achieved a number of notable successes, including the first statistically rigorous protocol for identifying and characterizing drift in quantum systems, a formalism for modeling memory effects in quantum devices, and the successful suppression of drift in a Sandia trapped-ion quantum processor.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Thermally Activated Delayed Fluorescence Sensitization for Highly Efficient Blue Fluorescent Emitters

Hyperfluorescence is emerging as a powerful strategy to develop optoelectronic devices with high-color purity and enhanced stability. It requires appropriate integration of a sensitizer displaying efficient thermally activated delayed fluorescence (TADF) and an emitter displaying strong, narrow-band fluorescence. Here, through a joint computational and experimental approach, we provide an unprecedented, end-to-end systems level description of the electronic and optical processes that take place in a hyperfluorescent emissive layer composed of a TADF sensitizer, bis(2,5-di(9H-carbazol-9-yl)phenyl)-1,3,4-oxadiazole (4CzDPO), and a fluorescent emitter, 2,5,8,11-tetra-tert-butylperylene (TBPe). We combine the photophysical properties measurement of the emissive layer with the computational determination of the electronic properties, film morphology, and excitation transfer phenomena. The Förster resonance energy transfer rates from 4CzDPO to TBPe are on the order of 1011 s–1, considerably higher than the radiative and non-radiative recombination rates for 4CzDPO. These features ensure nearly complete energy transfer to TBPe, leading to a five-fold increase in the photoluminescence quantum yields in the 4CzDPO:TBPe system in comparison to neat films of 4CzDPO. Furthermore, our approach highlights the factors that can provide efficient energy transfer from TADF molecules to fluorescent emitters, suppress energy transfer among TADF molecules, and avoid the need for a host material within the emissive layer.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Incorporation of Alloy Fluctuation Effects for Accurate Modeling of GaN/InGaN/GaN Light Emitting Diodes

III-Nitride light emitting diodes (LEDs) are widely used in a range of high efficiency lighting and display applications, which have enabled significant energy savings in the last decade[1]. To improve the device performance of LEDs, it is imperative to understand the carrier transport, and how it affects forward voltage, extraction efficiency, and other LED characteristics. Despite the wide application of GaN LEDs, transport mechanisms across InGaN/GaN heterostructures in these devices are not well-explained. Fixed polarization sheet charges at InGaN/GaN interfaces lead to large interface dipole charges, which creates large potential barriers to overcome. One-dimensional models for transport across such heterostructures predict turn-on voltages that are significantly higher than that found in real devices. As a result, conventional models for transport cannot be used to design more efficient devices, or to understand the underlying transport and recombination phenomena in InGaN/GaN light emitting diodes. In this work, we show that incorporating low and high Indium compositions within quantum wells at the submicron scale can provide accurate prediction of the characteristics of GaN/InGaN light emitting diodes.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Multicolor Photonic Pigments for Rotation-Asymmetric Mechanochromic Devices

Photonic crystals are extensively explored to replace inorganic pigments and organic dyes as coloring elements in printing, painting, sensing, and anti-counterfeiting due to their brilliant structural colors, chemical stability, and environmental friendliness. However, most existing photonic-crystal-based pigments can only display monochromatic colors once made, and generating multicolors has to start with designing different building blocks. In this work, a novel photonic pigment featuring highly tunable structural colors in the entire visible spectrum, made by the magnetic assembly of monodisperse nanorods into body-centered-tetragonal photonic crystals, is reported. Their prominent magnetic and crystal anisotropy makes it efficient to generate multicolors using one photonic pigment by magnetically controlling the crystal orientation. Further, the combination of angle-dependent diffraction and magnetic orientation control enables the design of rotation-asymmetric photonic films that display distinct patterns and encrypted information in response to rotation. The efficient multicolor generation through precise orientational control makes this novel photonic pigment promising in developing high-performance structural-colored materials and optical devices.

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

Dynamics of superconducting qubit relaxation times

Superconducting qubits are a leading candidate for quantum computing but display temporal fluctuations in their energy relaxation times T 1 . This introduces instabilities in multi-qubit device performance. Furthermore, autocorrelation in these time fluctuations introduces challenges for obtaining representative measures of T 1 for process optimization and device screening. These T 1 fluctuations are often attributed to time varying coupling of the qubit to defects, putative two level systems (TLSs). In this work, we develop a technique to probe the spectral and temporal dynamics of T 1 in single junction transmons by repeated T 1 measurements in the frequency vicinity of the bare qubit transition, via the AC-Stark effect. Across 10 qubits, we observe strong correlations between the mean T 1 averaged over approximately nine months and a snapshot of an equally weighted T 1 average over the Stark shifted frequency range. These observations are suggestive of an ergodic-like spectral diffusion of TLSs dominating T 1 , and offer a promising path to more rapid T 1 characterization for device screening and process optimization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗