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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 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Transforming Boron Carbon Nitride: A Carbon-to-Oxygen Switch to Boost Propane Oxidative Dehydrogenation

Hexagonal boron nitride (h-BN) catalysts exhibit high alkene selectivity in the oxidative dehydrogenation of propane (ODHP). Nevertheless, the conversion-selectivity trade-off persisted primarily due to the low density of oxygen-containing boron active species, while simple and controllable modification strategies for h-BN still face challenges. Herein, we developed an in situ carbon-to-oxygen switch strategy within a tailored boron carbon nitride (BCN) framework, in which uniformly embedded B–C 3 were transformed into B–O 3 via oxidative treatment (denoted as BNO x ). The structural evolution from B–C 3 to B–O 3 was well characterized by spectroscopy and soft X-ray absorption techniques. The resulting BNO x catalysts, enriched with B–O 3 units, demonstrated performance in ODHP, achieving a propane conversion of 50.4% with 32.7% olefin yield at 500 °C. Density functional theory (DFT) calculations confirmed that B–O 3 species preferentially lower activation barriers, rendering the process thermodynamically more favorable. In conclusion, this work introduced an in situ reconstruction method for atomic-level heteroatom-engineered h-BN catalysts, opening an avenue for advanced catalyst design across energy conversion systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Real-Time Corrective Switching in Response to Simultaneous Contingencies

The standard optimal power flow (OPF) problem is an economic dispatch (ED) problem combined with transmission constraints, which are based on a static topology. Prior research has demonstrated that cooptimization of generation dispatch and transmission topology results in cost savings. However, the computational complexity associated with topology control (TC) has been a major deterrent to its implementation. The proposed work investigates the application of a heuristic, a greedy algorithm, to improve the computational time for the TC problem while still maintaining the ability to find quality solutions. An expression is derived, which indicates the impact on the objective for a marginal change in the state of a transmission line. This expression is used to generate a priority list with potential candidate lines for switching, which may provide huge improvements to the system. The advantage of this method is that it is a fast heuristic as compared to using mixed integer programming (MIP) to find a solution. The heuristic is tested on real-time applications such as N-1 events, N - m events (m simultaneous contingencies), and cascading events. The proposed algorithm specifically targets cases that lead to load shedding in the system and provides a quick and efficient method to restore the loads by improving the deliverability of reserves via TC. Simulation results on the IEEE 73 bus test system and the IEEE 118 bus test system suggest a significant improvement in the amount of load served to the system with TC as opposed to without TC with minimal time and computation.

Electric power systems↗
DOE OSTI2013

Enlarged band gap and electron switch in graphene-based step-barrier structure

We study the transmission through a step-barrier in gapped graphene and propose a method to enlarge the band gap. The step-barrier structure consists of two or more barriers with different strengths. It is found that the band gap could be effectively enlarged and controlled by adjusting the barrier strengths in the light of the mass term. Klein tunneling at oblique incidence is suppressed due to the asymmetry of step-barrier, contrary to the cases in single-barrier and superlattices. Furthermore, a tunable conductance channel could be opened up in the conductance gap, suggesting an application of the structure as an electron switch.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Multi-channel conduction in redox-based resistive switch modelled using quantum point contact theory

A simple analytic model for the electron transport through filamentary-type structures in Si-rich silica (SiO{sub x})-based resistive switches is proposed. The model is based on a mesoscopic description and is able to account for the linear and nonlinear components of conductance that arise from both fully and partially formed conductive channels spanning the dielectric film. Channels are represented by arrays of identical scatterers whose number and quantum transmission properties determine the current magnitude in the low and high resistance states. We show that the proposed model not only reproduces the experimental current-voltage (I-V) characteristics but also the normalized differential conductance (dln(I)/dln(V)-V) curves of devices under test.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Acoustically assisted spin-transfer-torque switching of nanomagnets: An energy-efficient hybrid writing scheme for non-volatile memory

We show that the energy dissipated to write bits in spin-transfer-torque random access memory can be reduced by an order of magnitude if a surface acoustic wave (SAW) is launched underneath the magneto-tunneling junctions (MTJs) storing the bits. The SAW-generated strain rotates the magnetization of every MTJs' soft magnet from the easy towards the hard axis, whereupon passage of a small spin-polarized current through a target MTJ selectively switches it to the desired state with > 99.99% probability at room temperature, thereby writing the bit. The other MTJs return to their original states at the completion of the SAW cycle.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Conduction paths in Cu/amorphous-Ta{sub 2}O{sub 5}/Pt atomic switch: First-principles studies

We have examined the structure of Cu filaments in Cu/amorphous-Ta{sub 2}O{sub 5} (a-Ta{sub 2}O{sub 5})/Pt atomic switch from first principles. We have found that the Cu single atomic chains are unstable during the molecular dynamics (MD) simulation and thus cannot work as conduction paths. On the other hand, Cu nanowires with various diameters are stable and can form conductive paths. In this case, the Cu-Cu bonding mainly contributes to the conductive, delocalized defect state. These make a sharp contrast with the case of single Cu chains in crystalline Ta{sub 2}O{sub 5}, which can be conductive paths through the alternant Cu-Ta bonding structure. A series of MD simulations suggest that even Cu nanowires with a diameter of 0.24 nm can work as conduction paths. The calculations of the transport properties of Cu/a-Ta{sub 2}O{sub 5}/Pt heterostructures with Cu nanowires between two electrodes further confirm the conductive nature of the Cu nanowires in the a-Ta{sub 2}O{sub 5}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Resistive switching of a TaO{sub x}/TaON double layer via ionic control of carrier tunneling

Resistance random access memory (RRAM) is an attractive candidate for future non-volatile memory due to its superior features. As the oxide thickness is scaled down, the charge transport mechanism is also subject to the transition from hopping to tunneling dominant process, which is critically related to the interfacial electronic band structure. A TaO{sub x}/TaON double layer-based RRAM is fabricated and characterized in this work. Upon TaON insertion at the lower interface, the improved switching behavior is observed. The TaON at the bottom electrode interface blocks oxygen vacancy percolation due to strong N-O bonds and also modifies interfacial band alignment to lower the injected electron energy from bottom electrode due to higher tunneling barrier height than that of TaO{sub x}/Pt. This study suggested that a defect-minimized insertion layer like TaON with a proper interfacial band alignment is pivotal in RRAM for the effective ionic control of carrier tunneling resulting in non-linear I-V behavior with improved properties.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Note: Switching crosstalk on and off in Kelvin probe force microscopy

In Kelvin Probe Force Microscopy (KPFM) electronic crosstalk can occur between the excitation signal and probe deflection signal. Here, we demonstrate how a small modification to our commercial instrument enables us to literally switch the crosstalk on and off. We study in detail the effect of crosstalk on open-loop KPFM and compare with closed-loop KPFM. We measure the pure crosstalk signal and verify that we can correct for it in the data-processing required for open-loop KPFM. We also demonstrate that open-loop KPFM results are independent of the frequency and amplitude of the excitation signal, provided that the influence of crosstalk has been eliminated.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Numerical simulations of output pulse extraction from a high-power microwave compressor with a plasma switch

Numerical simulations of the process of electromagnetic energy release from a high-power microwave pulse compressor comprising a gas-filled cavity and interference switch were carried out. A microwave plasma discharge in a rectangular waveguide H-plane tee was modeled with the use of the fully electromagnetic particle-in-cell code MAGIC. The gas ionization, plasma evolution, and interaction with RF fields accumulated within the compressor were simulated using different approaches provided by the MAGIC code: particle-in-cell approach accounting for electron-neutral collisions, gas conductivity model based on the concept of mobility, and hybrid modeling. The dependences of the microwave output pulse peak power and waveform on parameters that can be controlled in experiments, such as an external ionization rate, RF field amplitude, and background gas pressure, were investigated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Metallic filament formation by aligned oxygen vacancies in ZnO-based resistive switches

The electronic structure of ZnO with defects of oxygen vacancies were investigated by using first-principles methods. Some structure models were constructed in order to investigate the effects of the distribution of oxygen vacancies on the electronic properties of ZnO. By analyzing the calculated results, we found that only the aligned oxygen vacancies can form the conducting channel in ZnO, and the transformation of the oxygen vacancy from charged state to neutral state is consistent with the energetics rule of the forming aligned oxygen vacancies. As for the heterojunction of Pt/ZnO/Pt, the oxygen vacancies near the interface of Pt/ZnO depress the local Schottky barrier effectively, and the aligned oxygen vacancies in ZnO form a conducting filament connecting two Pt electrodes. The metallic filament formation in Pt/ZnO/Pt resistive switching cells should be closely related to the carrier injection from Pt electrode into ZnO and the arrangement of oxygen vacancies in ZnO slab.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Spin switches for compact implementation of neuron and synapse

Nanomagnets driven by spin currents provide a natural implementation for a neuron and a synapse: currents allow convenient summation of multiple inputs, while the magnet provides the threshold function. The objective of this paper is to explore the possibility of a hardware neural network implementation using a spin switch (SS) as its basic building block. SS is a recently proposed device based on established technology with a transistor-like gain and input-output isolation. This allows neural networks to be constructed with purely passive interconnections without intervening clocks or amplifiers. The weights for the neural network are conveniently adjusted through analog voltages that can be stored in a non-volatile manner in an underlying CMOS layer using a floating gate low dropout voltage regulator. The operation of a multi-layer SS neural network designed for character recognition is demonstrated using a standard simulation model based on coupled Landau-Lifshitz-Gilbert equations, one for each magnet in the network.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Optimization of magnetic switches for single particle and cell transport

The ability to manipulate an ensemble of single particles and cells is a key aim of lab-on-a-chip research; however, the control mechanisms must be optimized for minimal power consumption to enable future large-scale implementation. Recently, we demonstrated a matter transport platform, which uses overlaid patterns of magnetic films and metallic current lines to control magnetic particles and magnetic-nanoparticle-labeled cells; however, we have made no prior attempts to optimize the device geometry and power consumption. Here, we provide an optimization analysis of particle-switching devices based on stochastic variation in the particle's size and magnetic content. These results are immediately applicable to the design of robust, multiplexed platforms capable of transporting, sorting, and storing single cells in large arrays with low power and high efficiency.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Low frequency noise in the unstable contact region of Au-to-Au microcontact for microelectromechanical system switches

The noise behavior of Au-to-Au microcontact for microelectromechanical system switches has been experimentally studied in the unstable contact region. The results suggest that the electrical conduction remains nonmetallic at the initial stage during contact formation due to the existence of alien films, and traps in the alien layer located at the contact interface could play an important role in determining the conduction noise. The conduction fluctuation induced by electron trapping-detrapping associated with the hydrocarbon layer is found to be an intrinsic noise source contributing to the low frequency noise in the unstable contact region.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Thermal analysis of an indirectly heat pulsed non-volatile phase change material microwave switch

We show the finite element simulation of the melt/quench process in a phase change material (GeTe, germanium telluride) used for a radio frequency switch. The device is thermally activated by an independent NiCrSi (nickel chrome silicon) thin film heating element beneath a dielectric separating it electrically from the phase change layer. A comparison is made between the predicted and experimental minimum power to amorphize (MPA) for various thermal pulse powers and pulse time lengths. By including both the specific heat and latent heat of fusion for GeTe, we find that the MPA and the minimum power to crystallize follow the form of a hyperbola on the power time effect plot. We also find that the simulated time at which the entire center GeTe layer achieves melting accurately matches the MPA curve for pulse durations ranging from 75–1500 ns and pulse powers from 1.6–4 W.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Metallic to hopping conduction transition in Ta{sub 2}O{sub 5−x}/TaO{sub y} resistive switching device

In this Letter, a comprehensive analysis of how the metallic behavior transition to hopping was presented by studying the transport mechanisms of low resistance states (LRS) in Ta{sub 2}O{sub 5−x}/TaO{sub y} resistive switching devices at very low temperatures. Three types of conduction behaviors were reported through temperature-dependent measurements ranging from 5 K to 250 K. Memory cells at low LRS show metallic behavior due to the formation of metallic filament. The temperature dependence of resistance at medium LRS exhibits an interesting phenomenon that a positive temperature coefficient transfers into a negative one at temperature of 20 K. Detailed analysis reveals that this phenomenon is caused by the coexistence of extended and localized states, with metallic conduction at higher temperatures and variable-range hopping at lower temperatures. Carrier transport at high LRS is dominated by electrons hopping conduction with nearest-neighboring hopping conduction changing into variable-range hopping as temperature decreases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Effects of ZrO{sub 2} doping on HfO{sub 2} resistive switching memory characteristics

A resistive switching (RS) random access memory device with ZrO{sub 2}-doped HfO{sub 2} exhibits better RS performance than that with pure HfO{sub 2}. In particular, I{sub res}, V{sub res}, and V{sub set} are reduced by approximately 58%, 38%, and 39%, respectively, when HfO{sub 2} is doped with ZrO{sub 2} (9 at. %). In addition, the ZrO{sub 2} doping in HfO{sub 2} makes the distribution of most parameters steeper. Transmission electron microscopy (TEM) analysis reveals that the deposited zirconium-doped hafnium oxide (HZO) (9 at. %) is polycrystalline. Elemental mapping results by scanning TEM–energy dispersive spectroscopy also prove that ZrO{sub 2} is uniformly distributed in the HZO (9 at. %) film. The possible mechanism for the improvement in the RS characteristics is also suggested on the basis of the X-ray photoelectron spectroscopy results and filamentary RS mechanism. These results suggest that the ZrO{sub 2} doping into HfO{sub 2} likely not only will reduce power consumption but also will improve cyclic endurance by controlling the nonstoichiometric phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Multiphoton photoluminescence contrast in switched Mg:LiNbO{sub 3} and Mg:LiTaO{sub 3} single crystals

We observed a multiphoton luminescence contrast between virgin and single-switched domains in Mg-doped LiNbO{sub 3} (LNO) and LiTaO{sub 3} (LTO) single crystals with different doping levels of 0–7 mol. % and 0–8 mol. %, respectively. A luminescence contrast in the range of 3% was measured between as-grown and electrically inverted domain areas in Mg:LNO samples, while the contrast reaches values of up to 30% for the Mg:LTO case. Under annealing, an exponential decay of the domain contrast was observed. The activation energy of about 1 eV being determined for the decay allowed a comparison with reported activation energies of associated defects, clearly illustrating a strong connection between thermal contrast decay and the H{sup +} and Li{sup +}-ion mobility. Finally, performing similar experiments on oxidized samples undoubtedly demonstrated that the origin of the reported luminescence contrast is strongly connected with lithium ions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Role of oxygen vacancies in resistive switching in Pt/Nb-doped SrTiO{sub 3}

Oxygen vacancies at the metal/oxide interface, driven by an electric field, have been considered responsible for the switching to the low-resistance state. We studied the electrical properties, along with microscopic observations, of the Pt/Nb-doped SrTiO{sub 3} (001) single-crystal system. Electron energy loss spectroscopy revealed highly accumulated oxygen vacancies at the interface in the high-resistance state, contrasting to common explanation. Higher resistance state by more oxygen vacancies was further confirmed in Pt/H{sub 2}-annealed SrTiO{sub 3}. These results suggest the presence of an interfacial state which dominantly determined the resistivity by changing the barrier height at the interface.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗