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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 OSTI2025

Preserving the Josephson Coupling of Twisted Cuprate Junctions via Tailored Silicon Nitride Circuits Boards

Controlled fabrication of twisted van der Waals heterostructures is essential to unlock the full potential of moiré materials. However, achieving reproducibility remains a major challenge, particularly for air-sensitive materials such as Bi 2 Sr 2 CaCu 2 O 8 + δ (BSCCO), where it is crucial to preserve the intrinsic and delicate superconducting properties of the interface throughout the entire fabrication process. Here, a dry, inert and cryogenic assembly method is presented that combines silicon nitride nanomembranes (NMBs) with pre-patterned electrodes and the cryogenic stacking technique (CST) to fabricate high-quality twisted BSCCO Josephson junctions (JJs). This protocol prevents thermal and chemical degradation during both interface formation and electrical contact integration. It is also found that asymmetric membrane designs, such as a double cantilever, effectively suppress vibration-induced disorder due to wire bonding, resulting in sharp and hysteretic current–voltage characteristics. The junctions exhibit a twist-angle-dependent Josephson coupling with magnitudes comparable to the highest-performing devices reported to date, but achieved through a straightforward and versatile contact method, offering a scalable and adaptable platform for future applications. These findings highlight the importance of both interface and contact engineering in addressing reproducibility in superconducting van der Waals heterostructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Correlating aluminum layer deposition rates, Josephson junction microstructure, and superconducting qubits’ performance

An ultra-thin aluminum oxide layer is a key component for Josephson junctions (JJ) in superconducting quantum bits (qubits). This layer serves as a barrier layer for Cooper pairs tunneling between the superconducting electrodes and significantly influences the overall performance of the junction. In this study, we investigate the impact of aluminum deposition rates on the microstructure and chemical variation of the aluminum oxide layer, as well as the device's yields and qubits’ lifetimes. Surprisingly, although the oxide layer roughness and thickness variation improve noticeably with an increasing Al deposition rate from 0.5 Å/s to 5 Å/s, the qubit's coherence time is almost unchanged. We attribute this to the fact that Cooper pairs tunnel only through the thinnest region of the barrier. Additionally, we revealed a stress-induced grain boundary sliding short-circuit failure mechanism in the JJ. Our discovery provides a vital understanding of oxide microstructure and JJ functionality, which are critical for improving the coherence time of superconducting qubits.

Coherence time↗
DOE OSTI2020

A plausible method of preparing the ideal p-n junction interface of a thermoelectric material by surface doping

Recent advances in two-dimensional (2D) crystals make it possible to realize an ideal interface structure that is required for device applications. Specifically, a p-n junction made of 2D crystals is predicted to exhibit an atomically well-defined interface that will lead to high device performance. Using angle-resolved photoemission spectroscopy, a simple surface treatment was shown to allow the possible formation of such an interface. Furthermore, Ta adsorption on the surface of a p-doped SnSe shifts the valence band maximum towards the higher binding energy due to the charge transfer from Ta to SnSe that is highly localized at the surface due to the layered structure of SnSe. As a result, the charge carriers of the surface are changed from holes of its bulk characteristics to electrons, while the bulk remains as a p-type semiconductor. This observation suggests that the well-defined interface of a p-n junction with an atomically thin n-region is formed between Ta-adsorbed surface and bulk.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Neuromuscular Junction Model Optimized for Electrical Platforms

Neuromuscular junctions (NMJs), specialized synapses between motor neurons and muscle fibers, are essential for muscle activity. A simple and reproducible cell-based in vitro NMJ platform is needed to test the impact of chemicals on the neuron-muscle communication. Our platform utilizes genetically modified neurons and muscle cells, optimized culture conditions, and commercially available multielectrode array system for recording action potentials. Neuronal cells (NSC34) were optogenetically modified with channelrhodopsin chimera to allow for simultaneous, light-mediated, millisecond-precise activation of neuronal population. This signal is propagated through functional synapses to the muscle fibers. Muscle cells (C2C12) were modified by incorporating gap junction protein (Connexin-43) to improve intracellular communication without affecting muscle differentiation. This communication between muscle fibers resulted in better signal propagation and signal strength. Optimized culture medium facilitated the growth and differentiation of both cell types together. Our system was validated using vecuronium, a muscle relaxant, which abolished the muscle response. This in vitro model provides a unique tool for establishing a NMJ platform that is easy to record and analyze. Potential applications include nondestructive long-term screening of drugs affecting the NMJ.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Spatial Mapping of Chiral-Induced Spin Selectivity in Chiral Perovskite via Spin-Schottky Junction

Chiral halide perovskite (c-HP) semiconductors exhibit on average a large chiral-induced spin selectivity (CISS) effect. Nevertheless, the microscopic details of CISS and its integration in opto-spintronic constructs remain nascent. Reliable reporting of CISS performance characteristics represents a significant challenge in providing the necessary design rules. We show a Kelvin probe force microscopy (KPFM) method that can quantitatively evaluate and spatially map the chirality-dependent surface contact potential difference resulting from the formation of a spin-Schottky junction. We revealed inhomogeneity in the CISS response, where low-CISS regions in the c-HP films reduce the overall macroscopic average, likely serving as a key factor in optimizing macroscopic performance. We also observed that although c-HP films made from higher precursor concentrations lead to thicker films and higher carrier concentrations with subsequent larger barrier heights in the Schottky junction, stronger spin relaxation due to non-ideal film quality reduces spin polarization.

14 SOLAR ENERGY↗
DOE OSTI2026

Indirect tunneling enabled spontaneous time-reversal symmetry breaking and Josephson diode effect in TiN/Al 2 ⁢O 3 /Hf 0.8 ⁢Zr 0.2 ⁢O 2 /Nb tunnel junctions

Josephson diode (JD) effect in Josephson tunnel junctions (JTJs) has attracted a great deal of attention due to its importance for developing superconducting-circuitry-based quantum technologies. Even though the preparation of high-quality JTJs by techniques employed in the semiconductor industry has been demonstrated, which was an important milestone because JTJs are the building blocks of superconducting electronics even before the quantum era, the JD effect has not been accomplished in them, nor has the highly desirable electrical control of the effect. We report here the fabrication of JTJs featuring a composite tunnel barrier of Al 2 ⁢O 3 and Hf 0.8 ⁢Zr 0.2 ⁢O 2 using complementary-metal-oxide-semiconductor compatible atomic layer deposition. These JTJs were found to show the JD effect in nominally zero magnetic fields with nonreciprocity controllable via an electric training current, yielding a surprisingly large diode efficiency. The quasiparticle tunneling, through which the Josephson coupling in a JTJ is established, was found to show theoretically expected gap features but no nonreciprocity. We attribute these observations to the simultaneous presence of positive and negative local Josephson couplings in the JTJs, with the negative Josephson coupling originating from indirect tunneling, which results in spontaneous time-reversal symmetry breaking. Finally, the double-minima washboard potential for the ensemble-averaged phase difference in the resistively and capacitively shunted junction model is shown to fully account for the experimentally observed JD effect.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Majorana bound states in a d -wave superconductor planar Josephson junction

We study phase-controlled planar Josephson junctions comprising a two-dimensional electron gas with strong spin-orbit coupling and d-wave superconductors, which have an advantage of a high critical temperature. We show that a region between the two superconductors can be tuned into a topological state by the in-plane Zeeman field, and can host Majorana bound states. The phase diagram as a function of the Zeeman field, chemical potential, and the phase difference between superconductors exhibits the appearance of Majorana bound states for a wide range of parameters. We further investigate the behavior of the topological gap and its dependence on the type of d-wave pairing, i.e., d, d+is, or d+id', and note the difficulties that can arise due to the presence of gapless excitations in pure d-wave superconductors. On the other hand, the planar Josephson junctions based on superconductors with d+is and d+id' pairings can potentially lead to realizations of Majorana bound states. Furthermore, our proposal can be realized in cuprate superconductors, e.g., in a twisted bilayer, combined with the layered semiconductor Bi 2 O 2 Se.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Direct Measurement of the Be 7 L / K Capture Ratio in Ta-Based Superconducting Tunnel Junctions

We report a high-statistics measurement of the L / K orbital electron capture ratio in 7 Be embedded in cryogenic Ta. The thin Ta film formed part of a high-resolution superconducting tunnel junction radiation detector that was used to identify the signals from different decay channels. The measured L/K capture ratio of 0.070(7) is significantly larger than the only previous measurement of this quantity and the theoretical predictions that include in-medium effects. This value is a uniquely sensitive probe of the 1s and 2s orbital overlaps with the nucleus and is of relevance to nuclear and atomic physics, as well as Li production in novae and other astrophysical scenarios. Furthermore, this is the first experiment that uses superconducting tunnel junctions for nuclear-recoil detection, opening a new experimental avenue for low-energy precision measurements with rare isotopes.

6 ≤ A ≤ 19↗
DOE OSTI2020

Three-Terminal Bipolar Junction Bottom Cell as Simple as PERC: Towards Lean Tandem Cell Processing

Silicon-based tandem cells are a potential upgrade for the dominating PERC technology and can greatly increase the conversion efficiency. A novel approach, the three-terminal (3T) tandem using interdigitated back-contact (IBC) cells, was shown to combine the advantages of four- and two-terminal tandem cells at the expense of a more complex bottom cell fabrication process. In this paper, we propose a simplified and lean PERC-like 3T bipolar junction bottom cell featuring two minority-carrier selective contacts and a single majority-carrier selective contact, and thus resembling a bipolar junction transistor architecture. We present the lean PERC-like fabrication process and explain the working principle by using current-voltage measurements of illuminated 3T IBC cells.

14 SOLAR ENERGY↗
DOE OSTI2020

Measurements of Six-Junction Concentrator Solar Cells

Accurate measurements of six-junction inverted metamorphic concentrator solar cells under AM1.5 direct spectrum are obtained by adjusting the spectrum of a tunable high-intensity solar simulator with custom mirrors. Isotype reference cells and broadband InGaAs QE calibration cells were developed for accurate measurements. Modeling and varying the illumination show that an unavoidable 15% - 17% overillumination on the sixth junction does not result in significant error of these 6J IMM devices. Spectrally adjusted flash measurements are independently confirmed by NREL's Cell and Module Performance team. Concentration measurements of a 6J IMM solar cell resulted in 47.1 ± 3.2% (absolute) efficiency at 143 suns.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2021

Electrical and Thermal Performance of Ga₂O₃–Al₂O₃–Diamond Super-Junction Schottky Barrier Diodes

The design space of Ga 2 O 3 -based devices is severely constrained due to its low thermal conductivity and absence of viable p-type dopants. In this work, we discuss the limits of operation of a novel Ga 2 O 3 –Al 2 O 3 –diamond-based super-junction device concept, which can alleviate the constraints associated with Ga 2 O 3 -based devices. The improvements achieved using the proposed device concept are demonstrated through electrical and thermal simulations of Ga 2 O 3 –Al 2 O 3 –diamond-based super-junction Schottky barrier diodes (SJ-SBDs) and non-punch-through or conventional Schottky barrier diodes (NP-SBDs). The SJ-SBD enables operation below the R ON -breakdown voltage limit of Ga 2 O 3 NP-SBD, enabling >4 kV blocking voltage at R ON of 1–3 mΩ cm 2 . Here, the maximum switching frequency of SJ-SBD may be only a few kHz, as it is limited by the activation energy of acceptors (0.39 eV) in the diamond. Crucially, compared with NP-SBD, the use of diamond also results in ~60% reduction in temperature rise during static power dissipation. Polycrystalline diamond (PCD) properties depend on detailed microstructure and benefits compared to ideal Ga 2 O 3</sub NP-SBD arise for diamond critical fields ≥6 MV/cm and thermal conductivities as low as 50–150 W/(m • K).

36 MATERIALS SCIENCE↗
DOE OSTI2023

Adroit Materials Final Scientific/Technical Report kV-class GaN-based Junction Barrier Schottky diodes using ion implantation

The primary aim of this research was to develop GaN-based Junction Barrier Schottky (JBS) diodes using an innovative ion implantation process previously established in ARPA-E funded projects. The central focus of our proposed technology revolves around selective area p-type doping, accomplished through the implantation of Mg ions. This approach builds upon our successes in the ARPA-E PNDIODES program, advancing towards commercial device integration. Selective area p-doping plays a pivotal role in realizing the next generation of GaN-based power devices, capable of significantly reducing the carbon footprint in the United States by several million tons. While ion implantation is a well-established technique for achieving selective area doping in SiC and Si materials, its feasibility in GaN had not been demonstrated until now. To fabricate high voltage GaN JBS diodes, we initially created thick n-type drift layers with high carrier concentrations ranging from 5×1015 cm-3 to 2×1016 cm-3 and very high mobilities. Subsequently, Mg ions were selectively implanted to form p-type islands within the n-type drift layer. To reduce electric field crowding at the edge of the diode and to achieve high breakdown voltage, junction edge termination (JTE) and floating field rings (FFRs) were formed using Mg implantation. A high temperature, high-pressure post-implantation annealing process was carried out to activate the implanted Mg ions. As a result, we were able to demonstrate GaN JBS diodes with a breakdown voltage of 915 V and an on-resistance of 0.6 mΩ·cm2. These diodes exhibited a forward bias current density of 1 kA/cm2 at 1.5 V. Subsequently, we achieved GaN JBS diodes with a remarkable breakdown voltage of 1900 V and an on-resistance of 1.9 mΩ·cm2, capable of sustaining a forward bias current density of 0.5 kA/cm2 at 1.5 V. Importantly, the ON and OFF state performance of these GaN JBS diodes surpassed that of Si and SiC-based power diodes reported in existing literature. Lastly, we successfully grew 60 μm thick GaN:Si layers using HVPE with a carrier concentration of approximately 3 to 5×1015 cm-3. Based on simulation and empirical data these devices represent 5 kV GaN JBS power diodes, leveraging the developed processes in this project.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Light-Driven Charge Transport and Optical Sensing in Molecular Junctions

Probing charge and energy transport in molecular junctions (MJs) has not only enabled a fundamental understanding of quantum transport at the atomic and molecular scale, but it also holds significant promise for the development of molecular-scale electronic devices. Recent years have witnessed a rapidly growing interest in understanding light-matter interactions in illuminated MJs. These studies have profoundly deepened our knowledge of the structure–property relations of various molecular materials and paved critical pathways towards utilizing single molecules in future optoelectronics applications. In this article, we survey recent progress in investigating light-driven charge transport in MJs, including junctions composed of a single molecule and self-assembled monolayers (SAMs) of molecules, and new opportunities in optical sensing at the single-molecule level. We focus our attention on describing the experimental design, key phenomena, and the underlying mechanisms. Specifically, topics presented include light-assisted charge transport, photoswitch, and photoemission in MJs. Emerging Raman sensing in MJs is also discussed. Finally, outstanding challenges are explored, and future perspectives in the field are provided.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Selective Heating Through Y-Junction Waveguide Designed by Acoustic Shape Optimization

Unlike phononic crystals or systems designed by topology optimization, waveguides designed by shape optimization do not have voids or internal defects, making the fabrication process more suitable for additive manufacturing. By designing a Y-junction waveguide through shape optimization, an ultrasonic wave can be controlled so that it propagates to a predetermined location just by adjusting its frequency. These demultiplexed ultrasonic waves can be used to transport signals or stimulate nearby materials. As an example, the ultrasonic wave is converted to heat at different locations, which can be applied to mechanisms that can take advantage of heating. First, shape optimization is performed on a cylindrical structure to selectively propagate ultrasonic waves of a particular frequency while attenuating others, which is analyzed through a finite element model. The numerical study results are compared with experimental measurements from samples fabricated through additive manufacturing methods. After verifying the concept, the Y-junction waveguide is fabricated to demultiplex the wave and selectively heat different locations. Here the results show that the method of combining shape optimization with additive manufacturing is exceptionally simple and capable of demultiplexing ultrasonic waves, which can replace complex electrical components with single-material waveguides.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Large Magnetoresistance in Scandium Nitride Magnetic Tunnel Junctions Using First Principles

Abstract The state‐of‐the‐art magnetic tunnel junction, a cornerstone of spintronic devices and circuits, uses a magnesium oxide tunnel barrier that provides a uniquely large tunnel magnetoresistance at room temperature. However, the wide bandgap and band alignment of magnesium oxide‐iron systems increases the resistance‐area product and creates variability and breakdown challenges. Here, the authors study using first principles narrower‐bandgap scandium nitride (ScN) transport properties in magnetoresistive junctions in comparison to magnesium oxide. The results show a high magnetoresistance in Fe/ScN/Fe via Δ 1 and symmetry filtering with low wave function decay rates, suggesting scandium nitride could be a new barrier material for spintronic devices.

Karki, Suyogya↗
DOE OSTI2024

Organic Nano-Junctions: Linking Nanomorphology and Charge Transport in Organic Semiconductor Nanoparticles for Organic Photovoltaic Devices

In this study, innovative nanoscale devices are developed to investigate the charge transport in organic semiconductor nanoparticles. Using different steps of lithography techniques and dielectrophoresis, planar organic nano-junctions are fabricated from which hole mobilities are extracted in a space charge-limited current regime. Subsequently, these devices are used to investigate the impact of the composition and morphology of organic semiconductor nanoparticles on the charge mobilities. Pure donor nanoparticles and composite donor:acceptor nanoparticles with different donor compositions in their shell are inserted in the nanogap electrode to form the nano-junctions. The results highlight that the hole mobilities in the composite nanoparticles decrease by two-fold compared to pure donor nanoparticles. However, no significant change between the two kinds of composite nanoparticle morphologies is observed, indicating that conduction pathways for the holes are as efficient for donor proportion in the shell from 40% to 60%. Organic photovoltaic (OPV) devices are fabricated from water-based colloidal inks containing the two composite nanoparticles (P3HT:eh-IDTBR and P3HT:o-IDTBR) and no significant change in the performances is observed in accordance with the mobility results. Through this study, the performance of OPV devices have been successfully correlated to the transport properties of nanoparticles having different morphology via innovative nanoscale devices.

42 ENGINEERING↗
DOE OSTI2022

Direct Fabrication of Vertically Stacked Double Barrier Tunnel Junctions Based on Graphene and h-BN

Direct manufacturing of two-dimensional material-based double barrier (DB) tunnel junctions, based on a lithography-free approach was developed. Graphene/h-BN/Graphene/h-BN/Graphene devices were deposited on Si/SiO2 substrates by employing a plasma enhanced chemical vapor deposition technique in a sequential manner. DB tunneling junctions with varying barrier widths (by varying the thickness of the second graphene layer) were studied. Samples were characterized using Raman, Atomic Force Microscopy and X-ray photoemission spectroscopy. The I–V characteristics of tunneling current showed resonant tunneling behavior at room temperature with a negative differential conductance. The behavior could be explained with quantum mechanical double barrier tunneling model in which analytic solutions to Schrödinger’s equation were obtained in each region of the system. Resonances in transmission probability coefficient for varying barrier widths were evaluated and compared with the experimental results.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Highly efficient bifacial single-junction perovskite solar cells

Bifacial photovoltaics (PV) harvest solar irradiance from both their front and rear surfaces, boosting energy conversion efficiency to maximize their electrical power production. For single-junction perovskite solar cells (PSCs), the performance of bifacial configurations is still far behind that of their state-of-the-art monofacial counterparts. Here, in this paper, we report on highly efficient, bifacial, single-junction PSCs based on the p-i-n (or inverted) architecture. We used optical and electrical modeling to design a transparent conducting rear electrode for bifacial PSCs to enable optimized efficiency under a variety of albedo illumination conditions. The bifaciality of the PSCs was about 91%–93%. Under concurrent bifacial measurement conditions, we obtained equivalent, stabilized bifacial power output densities of 26.9, 28.5, and 30.1 mW/cm 2 under albedos of 0.2, 0.3, and 0.5, respectively. We further showed that bifacial perovskite PV technology has the potential to outperform its monofacial counterparts with higher energy yields and lower levelized cost of energy (LCOE).

14 SOLAR ENERGY↗