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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Unipolar resistive switching in metal oxide/organic semiconductor non-volatile memories as a critical phenomenon

Diodes incorporating a bilayer of an organic semiconductor and a wide bandgap metal oxide can show unipolar, non-volatile memory behavior after electroforming. The prolonged bias voltage stress induces defects in the metal oxide with an areal density exceeding 10{sup 17 }m{sup −2}. We explain the electrical bistability by the coexistence of two thermodynamically stable phases at the interface between an organic semiconductor and metal oxide. One phase contains mainly ionized defects and has a low work function, while the other phase has mainly neutral defects and a high work function. In the diodes, domains of the phase with a low work function constitute current filaments. The phase composition and critical temperature are derived from a 2D Ising model as a function of chemical potential. The model predicts filamentary conduction exhibiting a negative differential resistance and nonvolatile memory behavior. The model is expected to be generally applicable to any bilayer system that shows unipolar resistive switching.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Effect of advanced nanowire-based targets in nanosecond laser-matter interaction (invited)

An experimental campaign aiming to investigate the effects of innovative nanostructured targets based on Ag nanowires on laser energy absorption in the ns time domain has been carried out at the Laser Energy for Nuclear Science laboratory of INFN-LNS in Catania. The tested targets were realized at INFN-Bologna by anodizing aluminium sheets in order to obtain layers of porous Al{sub 2}O{sub 3} of different thicknesses, on which nanowires of various metals are grown by electro-deposition with different heights. Targets were then irradiated by using a Nd:YAG laser at different pumping energies. Advanced diagnostic tools were used for characterizing the plasma plume and ion production. As compared with targets of pure Al, a huge enhancement (of almost two order of magnitude) of the X-ray flux emitted by the plasma has been observed when using the nanostructured targets, with a corresponding decrease of the “optical range” signal, pointing out that the energetic content of the laser produced plasma was remarkably increased. This analysis was furthermore confirmed from time-of-flight spectra.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Additive effects of electronic and nuclear energy loss in irradiation-induced amorphization of zircon

We used a combination of ion cascades and the unified thermal spike model to study the electronic effects from 800 keV Kr and Xe ion irradiation in zircon. We compared the damage production for four cases: (a) due to ion cascades alone, (b) due to ion cascades with the electronic energy loss activated as a friction term, (c) due to the thermal spike from the combined electronic and nuclear energy losses, and (d) due to ion cascades with electronic stopping and the electron-phonon interactions superimposed. As a result, we found that taking the electronic energy loss out as a friction term results in reduced damage, while the electronic electron-phonon interactions have additive impact on the final damage created per ion.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Tuning resistance states by thickness control in an electroforming-free nanometallic complementary resistance random access memory

Tuning low resistance state is crucial for resistance random access memory (RRAM) that aims to achieve optimal read margin and design flexibility. By back-to-back stacking two nanometallic bipolar RRAMs with different thickness into a complementary structure, we have found that its low resistance can be reliably tuned over several orders of magnitude. Such high tunability originates from the exponential thickness dependence of the high resistance state of nanometallic RRAM, in which electron wave localization in a random network gives rise to the unique scaling behavior. The complementary nanometallic RRAM provides electroforming-free, multi-resistance-state, sub-100 ns switching capability with advantageous characteristics for memory arrays.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Ferromagnetic resonance in low interacting permalloy nanowire arrays

Dipolar interactions on magnetic nanowire arrays have been investigated by various techniques. One of the most powerful techniques is the ferromagnetic resonance spectroscopy, because the resonance field depends directly on the anisotropy field strength and its frequency dependence. In order to evaluate the influence of magnetostatic dipolar interactions among ferromagnetic nanowire arrays, several densely packed hexagonal arrays of NiFe nanowires have been prepared by electrochemical deposition filling self-ordered nanopores of alumina membranes with different pore sizes but keeping the same interpore distance. Nanowires’ diameter was changed from 90 to 160 nm, while the lattice parameter was fixed to 300 nm, which was achieved by carefully reducing the pore diameter by means of Atomic Layer Deposition of conformal Al{sub 2}O{sub 3} layers on the nanoporous alumina templates. Field and frequency dependence of ferromagnetic resonance have been studied in order to obtain the dispersion diagram which gives information about anisotropy, damping factor, and gyromagnetic ratio. The relationship between resonance frequency and magnetic field can be explained by the roles played by the shape anisotropy and dipolar interactions among the ferromagnetic nanowires.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Engineering the switching dynamics of TiO{sub x}-based RRAM with Al doping

Titanium oxide (TiO{sub x}) has attracted a lot of attention as an active material for resistive random access memory (RRAM), due to its versatility and variety of possible crystal phases. Although existing RRAM materials have demonstrated impressive characteristics, like ultra-fast switching and high cycling endurance, this technology still encounters challenges like low yields, large variability of switching characteristics, and ultimately device failure. Electroforming has been often considered responsible for introducing irreversible damage to devices, with high switching voltages contributing to device degradation. In this paper, we have employed Al doping for tuning the resistive switching characteristics of titanium oxide RRAM. The resistive switching threshold voltages of undoped and Al-doped TiO{sub x} thin films were first assessed by conductive atomic force microscopy. The thin films were then transferred in RRAM devices and tested with voltage pulse sweeping, demonstrating that the Al-doped devices could on average form at lower potentials compared to the undoped ones and could support both analog and binary switching at potentials as low as 0.9 V. This work demonstrates a potential pathway for implementing low-power RRAM systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Reactions at noble metal contacts with methylammonium lead triiodide perovskites: Role of underpotential deposition and electrochemistry

Chemical reactivity of halide perovskites coupled with a low energy of formation makes it a challenge to characterize material properties and achieve long-term device stability. In this study, we elucidate electrochemical reactions occurring at the methylammonium lead triiodide (MAPbI 3 )/Au interface. X-ray photoemission spectroscopy is used to identify a type of reduction/oxidation reaction termed underpotential deposition (UPD) involving lead, iodine, and hydrogen occurring at interfaces with noble metals. Changes in surface compositions and oxidation states suggest that UPD derived adsorbates at MAPbI 3 /Au interfaces lower the energy barrier for release of volatile HI and/or I 2 catalyzing degradation at exposed contacts. Additionally, comparison to PbI 2 /Au interfaces demonstrates that the presence of methylammonium/methylamine accelerates the formation of a Pb 0 adlayer on the Au. Reactions involving UPD Pb 0 can transform the typically anodic (hole collecting) Au to a cathode in a photovoltaic measurement. Cyclic voltammetry reveals electrochemical reaction peaks in indium tin oxide (ITO)/MAPbI 3 /Au devices occurring within voltage ranges commonly used for perovskite characterization. The electrochemical stability window of this device architecture is measured to be between -0.5 V and 0.9 V. Voltage induced interfacial reactions contribute to reversible electrochemical peaks, hysteresis, switchable perovskite diode polarity, and permanent degradation at larger voltages. These types of surface reactions alter the interface/interphase composition beyond ion accumulation, provide a source for the diffusion of defects, and contribute to electrode material dependent current-voltage hysteresis. Moreover, the results imply fundamental limitations to achieving high device stability with noble metals and/or methylammonium containing perovskites.

36 MATERIALS SCIENCE↗
DOE OSTI2017

CO 2 reduction to acetate in mixtures of ultrasmall (Cu) n ,(Ag) m bimetallic nanoparticles

Significance Efficient reduction of carbon dioxide to useful fuels and chemicals is an important research goal in artificial photosynthesis. Significant progress has been made for the C1 products, CO and HCOO − . We report here a procedure based on the use of ultrasmall, monodispersed Cu and Ag bimetallic nanoparticles on thin, electrochemically polymerized poly-Fe(vbpy) 3 (PF 6 ) 2 films. They reduce CO 2 to acetate at pH 7 in aqueous HCO 3 − solutions at relatively high efficiencies with significant rate enhancements with added benzotriazole. In the sequence of clusters, the most efficient results for acetate production were obtained in films of (Cu) 2 ,(Ag) 3 with a faradaic efficiency of 21.2% for acetate from CO 2 at −1.33 V vs. reversible hydrogen electrode in 0.5 M KHCO 3 with 8 ppm of added benzotriazole at 0 °C.

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

Samarium thin films molecular plated from N , N -dimethylformamide characterized by XPS

Characterization of samarium thin films molecular plated from N,N -dimethylformamide solutions onto stainless steel substrates, with either mirrorlike or brushed finishes, was carried out using a Thermo Scientific K-Alpha x-ray photoelectron spectrometer. Survey scans of the two specimens showed the presence of samarium, carbon, and oxygen with minor amounts of sodium. High-resolution spectra were then taken of the Sm 3 d , O 1 s , and C 1 s regions. Furthermore, the chemical compositions of the two samples were found to be very similar, with the key difference being the relative amounts of two carbon species. Spectra from the survey and narrow high-resolution scans of the Sm 3 d , O 1 s , and C 1 s regions are reported herein.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Synthesis and properties of Fe/Ni nanotubes

Fe/Ni nanotubes were formed in pores of polyethylenterephtalate-based template matrices by electrochemical deposition. The inner diameter, wall height, and thickness of the nanostructures, as well as the elemental and phase compositions, can be controlled by varying the deposition conditions. The volume deposition rate constants have been determined for each potential difference, due to which the nanostructure growth could be controlled. An X-ray diffraction analysis of the samples obtained at a potential difference of 1-1.6 V has revealed their composition to correspond to the substitutional solid solution, with an iron atom replaced by a nickel atom and dominance of the bcc a-Fe phase. The samples obtained at a potential difference of 1.8–2 V contain the bcc a-Fe phase and fcc Ni phase; the fcc phase dominates in the sample obtained at a potential difference of 2 V, which can be related to the high Ni content in nanotubes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Investigation of the influence of electron irradiation on the properties of cobalt nanotubes

Cobalt nanotubes have been synthesized by electrochemical deposition in pores of ion track membranes. The structures obtained have been studied by scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction analysis, and gas permeability method. The influence of electron irradiation on the cobalt nanotube structure has been investigated. It is shown that an increase in the irradiation dose leads to the transformation of the sample crystal structure. This fact can be explained by the simultaneous reduction of the β-Co metastable phase and relaxation of the microstress formed by the fcc phase in the lattice. The degree of sample texturing along the [100] direction increases under electron irradiation. The dependences of the resistive and magnetic properties of cobalt nanotubes on the irradiation dose have been analyzed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Study of the Reactivity of Ni Nanotubes in Media with Different рН

Nickel nanotubes have been synthesized by electrochemical deposition, and their reactivity in aggressive media has been investigated. Kinetic curves of the variation in the atomic ratio between Ni and O in the nanotube crystal structure as a function of the medium acidity are built.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Degradation of the electrical characteristics of MOS structures with erbium, gadolinium, and dysprosium oxides under the effect of an electric field

The degradation of the characteristics of silicon metal-oxide-semiconductor (MOS) structures with oxides of rare-earth elements under the effect of electric fields with intensities of 0.1–4 MV/cm during the course of electroforming is studied. A specific feature of electroforming consists in the possibility of multiple switching of the structures from the insulating state to the low-resistivity one and back. The temporal characteristics of the degradation of MOS structures during the course of electroforming are exponential. The current-voltage characteristics follow the power law in the range of 0.2–3 V; the effect of an electric field brings about a variation in the distribution of the energy density of traps responsible for currents limited by space charge. It is established that multiple cycles of electroforming lead to an increase in the density of surface states at the Si-oxide interface and to a variation in the energy position of the trap levels, which affects the charge state of the traps.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Influence of the Surface Layer on the Electrochemical Deposition of Metals and Semiconductors into Mesoporous Silicon

The influence of the surface layer on the process of the electrochemical deposition of metals and semiconductors into porous silicon is studied. It is shown that the surface layer differs in structure and electrical characteristics from the host porous silicon bulk. It is established that a decrease in the conductivity of silicon crystallites that form the surface layer of porous silicon has a positive effect on the process of the filling of porous silicon with metals and semiconductors. This is demonstrated by the example of nickel and zinc oxide. The effect can be used for the formation of nanocomposite materials on the basis of porous silicon and nanostructures with a high aspect ratio.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of the Silicon Dioxide Layer Thickness on Electroforming in Open TiN–SiO{sub 2}–W Sandwiches

Based on experimental data for electroforming in open TiN–SiO{sub 2}–W sandwich structures (the end face of d = 10–30-nm-thick SiO{sub 2} films exposed to vacuum served as an insulating trench), it has been shown that the voltage at which conducive particles (CPs) arise (i.e., the electroforming onset voltage) changes insignificantly with decreasing thickness d. The electroforming process is initiated by a voltage with a threshold near 8.5 V, rather than by electric field strength. This value far exceeds the CP formation voltage threshold when already formed structures switch over (3–4 V). This points to the existence of two nonthermal mechanisms that activate CP formation under electron impact. In the case of electroforming, this is dissociative attachment of an electron, which causes an oxygen atom to escape into vacuum and, hence, an increase in the silicon atom concentration on the surface of the insulating trench. In the case of switching, this is a change in the molecular state of oxygen (or hydrogen) on the surface.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Mechanisms of Current Transport and Resistive Switching in Capacitors with Yttria-Stabilized Hafnia Layers

The peculiarities of resistive switching in capacitors with yttria-stabilized hafnia layers were studied. The characteristics of current transport in the initial state and after electroforming and resistive switching at different temperatures were examined. The parameters of a small-signal equivalent circuit of a capacitor were determined for switching into low- and high-resistance states. These parameters suggest that the resistance of filaments changes after each successive switching. This provides an opportunity to use such measurements to determine the nature of resistive switching and verify the reproducibility of its parameters. The contribution of electron traps to switching was revealed. Ion migration polarization was observed at temperatures above 500 K, and the activation energy of ion migration and the ion concentration were determined. The effect of resistive switching under the influence of temperature was observed and interpreted for the first time.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Solvation Structure and Electrochemical Properties of a New Weakly Coordinating Aluminate Salt as a Nonaqueous Electrolyte for Zinc Batteries

In continuation of our interest in developing multivalent electrolytes for energy storage, we report a new zinc salt with a weakly coordinating anion, tetrakis(perfluoro-tert-butoxy) aluminate (TPFA), as a stable electrolyte for nonaqueous systems. We examined the electrochemical and structural properties of this nonaqueous electrolyte in various solvents. ZnTPFA 2 supports highly reversible Zn deposition and stripping behavior in acetonitrile and ethereal solvents, with up to 91% Coulombic efficiency. A variety of analytical techniques were used to identify the local coordination structure around Zn 2+ in both the crystal phase and the solution phase, providing clear evidence of solvent coordination around the cation.

25 ENERGY STORAGE↗