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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
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 OSTI2016

Large Spatially Resolved Rectification in a Donor–Acceptor Molecular Heterojunction

Here, we demonstrate that rectification ratios (RR) of ≳250 (≳1000) at biases of 0.5 V (1.2 V) are achievable at the two-molecule limit for donor–acceptor bilayers of pentacene on C 60 on Cu using scanning tunneling spectroscopy and microscopy. Using first-principles calculations, we show that the system behaves as a molecular Schottky diode with a tunneling transport mechanism from semiconducting pentacene to Cu- hybridized metallic C 60 . Low-bias RRs vary by two orders-of-magnitude at the edge of these molecular heterojunctions due to increased Stark shifts and confinement effects.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Controlling the rectification properties of molecular junctions through molecule–electrode coupling

The development of molecular components functioning as switches, rectifiers or amplifiers is a great challenge in molecular electronics. A desirable property of such components is functional robustness, meaning that the intrinsic functionality of components must be preserved regardless of the strategy used to integrate them into the final assemblies. Here, this issue is investigated for molecular diodes based on N-phenylbenzamide (NPBA) backbones. The transport properties of molecular junctions derived from NPBA are characterized while varying the nature of the functional groups interfacing the backbone and the gold electrodes required for break-junction measurements. Furthermore, combining experimental and theoretical methods, it is shown that at low bias (<0.85 V) transport is determined by the same frontier molecular orbital originating from the NPBA core, regardless of the anchoring group employed. The magnitude of rectification, however, is strongly dependent on the strength of the electronic coupling at the gold–NPBA interface and on the spatial distribution of the local density of states of the dominant transport channel of the molecular junction.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Spatially resolved, substrate-induced rectification in C 60 bilayers on copper

Here, we demonstrate rectification ratios ( RR ) of ≳1000 at biases of 1.3 V in bilayers of C 60 deposited on copper. Using scanning tunneling spectroscopy and first-principles calculations, we show that the strong coupling between C 60 and the Cu(111) surface leads to the metallization of the bottom C 60 layer, while the molecular orbitals of the top C60 are essentially unaffected. Due to this substrate-induced symmetry breaking and to a tunneling transport mechanism, the system behaves as a hole-blocking layer, with a spatial dependence of the onset voltage on intra-layer coordination. Together with previous observations of strong electron-blocking character of pentacene/C 60 bilayers on Cu(111), this work further demonstrates the potential of strongly hybridized, C 60 -coated electrodes to harness the electrical functionality of molecular components.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Dynamic Characteristics and Test Results of a Wave Power Take-off System with Mechanical Motion Rectification and Transmission

An innovative ocean wave power takeoff (PTO) system is presented here to enhance electrical energy generation from oscillating wave motions. This PTO system, mainly consisting of dual ball screws, gearbox with mechanical motion rectification (MMR) and a permanent magnet synchronous generator (PMSG), can convert bidirectional irregular motions from a floating wave buoy into unidirectional regular generator rotations. Systematical operating principles, design and prototyping details of the PTO system are presented and analyzed. A hydrodynamics-mechanical-electrical model of the system is established by reasonably representing power switches attached to the PMSG as an equivalent external resistance. The overall dynamics of the system are then analyzed in the frequency-domain. Three power control strategies are proposed to maximize the wave power absorption by changing the equivalent external resistance. The effectiveness and relatively high energy conversion efficiency of the PTO system have been demonstrated based on lab bench test results. The levelized cost of energy of a full scale wave energy converter system is also calculated based on the proposed PTO system.

16 TIDAL AND WAVE POWER↗
NASA NTRS1963

The rectification process

Rectification process concerned with observation of accuracy in computation of osculating orbit

ORBIT CALCULATION↗
DOE OSTI2017

Choice of Fine Packing for Rectification of Uranium Hexafluoride

Coefficients are proposed for the Bain–Hougen equation for calculating the limit velocity of vapor in a column filled with fine packing for the rectification of metal hexafluorides and their mixtures. It is shown that a simple method of comparing different packings in terms of the kinetic and hydrodynamic parameters is possible by using the effective throughput per unit volume of the packing, equivalent to one transfer unit.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Effective Thermal Contact Resistance of Regularly Textured Bodies in the Presence of Intercontact Heat-Conducting Media and the Phenomenon of Thermal Rectification

We compute the effective thermal contact resistance of a pair of materials formed by AISI 304 stainless steel and 200 nickel alloy in the presence of a periodic array of gaps filled with a heat-conducting medium (argon, water, helium, oxygen, or air) on the interface of these materials. In the nondeformed state, the surface of AISI 304 stainless steel has a microtextured topography formed by regularly located grooves of identical shapes, while the surface of 200 nickel alloy is perfectly flat. We estimate the level of thermal rectification for structures of this kind for different values of the applied mechanical and thermal loads and the maximal height of the surface grooves.

42 ENGINEERING↗
DOE OSTI2020

Suppressing Molecular Charging, Nanochemistry, and Optical Rectification in the Tip-Enhanced Raman Geometry

Classical vs quantum plasmons are operative in tapping vs contact mode tip-enhanced Raman scattering (TERS) and lead to distinct observables. Under otherwise identical experimental conditions, we illustrate the concept through tapping and contact mode TERS mapping of chemically functionalized silver nanocubes. Whereas molecular charging, chemical transformations, and optical rectification are prominent observables in contact mode TERS, the same effects are suppressed using tapping mode feedback. In effect, this work demonstrates that nanoscale physical and chemical processes can be accessed/suppressed on-demand in the TERS geometry. Further, the advantages of tapping mode TERS are otherwise highlighted with the latter in mind.

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

Electron Spin Polarization and Rectification Driven by Chiral Perylene Diimide-Based Nanodonuts

The chirality-induced spin selectivity (CISS) effect allows thin-film layers of chiral conjugated molecules to function as spin filters at ambient temperature. Through solvent-modulated dropcasting of chiral l- and d-perylene diimide (PDI) monomeric building blocks, two types of aggregate morphologies, nanofibers and nanodonuts, may be realized. Spin-diode behavior is evidenced in the nanodonut structures. Stacked PDI units, which form the conjugated core of these nanostructures, dominate the nanodonut–Au electrode contact; in contrast, the AFM tip contacts largely the high-resistance solubilizing alkyl chains of the chiral monomers that form these nanodonuts. Current–voltage responses of the nanodonuts, measured by magnetic conductive AFM (mC-AFM), demonstrate substantial spin polarizations as well as spin current rectification ratios (>10) that exceed the magnitudes of those determined to date for other chiral nanoscale systems. Furthermore, these results underscore the potential for chiral nanostructures, featuring asymmetric molecular junctions, to enable CISS-based nanoscale spin current rectifiers.

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

Terahertz rectification in ring-shaped quantum barriers

Tunneling is the most fundamental quantum mechanical phenomenon with wide-ranging applications. Matter waves such as electrons in solids can tunnel through a one-dimensional potential barrier, e.g. an insulating layer sandwiched between conductors. A general approach to control tunneling currents is to apply voltage across the barrier. Here, we form closed loops of tunneling barriers exposed to external optical control to manipulate ultrafast tunneling electrons. Eddy currents induced by incoming electromagnetic pulses project upon the ring, spatiotemporally changing the local potential. The total tunneling current which is determined by the sum of contributions from all the parts along the perimeter is critically dependent upon the symmetry of the loop and the polarization of the incident fields, enabling full-wave rectification of terahertz pulses. By introducing global geometry and local operation to current-driven circuitry, our work provides a novel platform for ultrafast optoelectronics, macroscopic quantum phenomena, energy harvesting, and multi-functional quantum devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Rectification of nanopores in aprotic solvents – transport properties of nanopores with surface dipoles

Nanopores have become a model system to understand transport properties at the nanoscale. In this paper, we report experiments and modeling of ionic current in aprotic solvents with different dipole moments through conically shaped nanopores in a polycarbonate film and through glass nanopipettes. We focus on solutions of the salt LiClO4, which is of great importance in modeling lithium based batteries. Results presented suggest ion current rectification observed results from two effects: (i) adsorption of Li+ ions to the pore walls, and (ii) a finite dipole moment rendered by adsorbed solvent molecules. Properties of surfaces in various solvents were probed by means of scanning ion conductance microscopy, which confirmed existence of an effectively positive surface potential in aprotic solvents with high dipole moments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Note: Electrical detection and quantification of spin rectification effect enabled by shorted microstrip transmission line technique

We describe a shorted microstrip method for the sensitive quantification of Spin Rectification Effect (SRE). SRE for a Permalloy (Ni{sub 80}Fe{sub 20}) thin film strip sputtered onto SiO{sub 2} substrate is demonstrated. Our method obviates the need for simultaneous lithographic patterning of the sample and transmission line, therefore greatly simplifying the SRE measurement process. Such a shorted microstrip method can allow different contributions to SRE (anisotropic magnetoresistance, Hall effect, and anomalous Hall effect) to be simultaneously determined. Furthermore, SRE signals from unpatterned 50 nm thick Permalloy films of area dimensions 5 mm × 10 mm can even be detected.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Non-radiative relaxation and rectification behavior of metal/semiconductor tetrapod heterostructures

The metal-semiconductor hetero-structures have recently emerged as functional materials for their potential applications in the areas of photonic, optoelectronic, and other fields. Here, we discuss the structural characterization of Au/CdSe tetrapod hetero-structures by using high-resolution transmission electron microscope, high angle annular dark field-scanning transmission electron microscopic, and X-ray diffraction. The blue shifting of the plasmonic band and red shifting of the excitonic band suggest a strong surface plasmon-exciton interaction between Au and CdSe in Au/CdSe tetrapod heterostructure. A significant photoluminescence quenching (83.4%) of CdSe nanorod (NR) is observed in the presence of Au nanoparticle in Au/CdSe tetrapod heterostructure. The radiative and nonradiative decay rates of CdSe nanorods are found to be modified in Au/CdSe tetrapod structures and the nonradiative rate changes from 1.91 × 10{sup 7} s{sup −1} to 9.33 × 10{sup 9} s{sup −1} for CdSe NR to Au/CdSe tetrapod structure, respectively. Current-voltage characteristics of Au/CdSe heterostructure exhibit the rectification property with a threshold voltage of about 0.85 V and the rectifying ratio is 140 which can open up avenues for developing challenging devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Terahertz field enhancement via coherent superposition of the pulse sequences after a single optical-rectification crystal

Terahertz electromagnetic pulses are frequently generated by optical rectification of femtosecond laser pulses. In many cases, the efficiency of this process is known to saturate with increasing intensity of the generation beam because of two-photon absorption. Here, we demonstrate two routes to reduce this effect in ZnTe(110) crystals and enhance efficiency, namely, by (i) recycling the generation pulses and by (ii) splitting each generation pulse into two pulses before pumping the crystal. In both methods, the second pulse arrives ∼1 ns after the first one, sufficiently long for optically generated carriers to relax. Enhancement is achieved by coherently superimposing the two resulting terahertz fields.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Electric field controlled reversible magnetic anisotropy switching studied by spin rectification

In this letter, spin rectification was used to study the electric field controlled dynamic magnetic properties of the multiferroic composite which is a Co stripe with induced in-plane anisotropy deposited onto a Pb(Mg{sub 1∕3}Nb{sub 2∕3})O{sub 3}-PbTiO{sub 3} substrate. Due to the coupling between piezoelectric and magnetoelastic effects, a reversible in-plane anisotropy switching has been realized by varying the history of the applied electric field. This merit results from the electric hysteresis of the polarization in the nonlinear piezoelectric regime, which has been proved by a butterfly type electric field dependence of the in-plane anisotropy field. Moreover, the electric field dependent effective demagnetization field and linewidth have been observed at the same time.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Rectification properties of n-type nanocrystalline diamond heterojunctions to p-type silicon carbide at high temperatures

Highly rectifying heterojunctions of n-type nanocrystalline diamond (NCD) films to p-type 4H-SiC substrates are fabricated to develop p-n junction diodes operable at high temperatures. In reverse bias condition, a potential barrier for holes at the interface prevents the injection of reverse leakage current from the NCD into the SiC and achieves the high rectification ratios of the order of 10{sup 7} at room temperature and 10{sup 4} even at 570 K. The mechanism of the forward current injection is described with the upward shift of the defect energy levels in the NCD to the conduction band of the SiC by forward biasing. The forward current shows different behavior from typical SiC Schottky diodes at high temperatures.

36 MATERIALS SCIENCE↗