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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 1,801 records · Page 100
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Anatase TiO 2 Surface Hydration: Infrared Vibrational Assignment and Facet-Specific Stability

Anatase TiO 2 nanoparticles support a subtle diversity of surface aqua and hydroxy coordination environments that are characteristic of distinct facets and defect sites. The disparate properties and stability of each molecularly or dissociatively absorbed water environment may provide unique reactivity for facet- and site-selective atomic layer deposition (ALD). Here we probe the temperature-dependent and facet-specific stretching frequency and stability of surface hydroxyls on faceted anatase TiO 2 nanoparticles via in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Well-defined truncated octahedra, disks, and rods fabricated through hydrothermal synthesis present dominant (101), (001), and (010) facets, respectively. The selective dehydration of discrete local coordination environments as a function of temperature provides a potential pathway to site-selective and facet-selective ALD on metal oxide nanomaterials.

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

Metal-induced crystallization of amorphous zinc tin oxide semiconductors for high mobility thin-film transistors

Transition tantalum induced crystallization of amorphous zinc tin oxide (a-ZTO) was observed at low temperature annealing of 300 °C. Thin-film transistors (TFTs) with an a-ZTO channel layer exhibited a reasonable field-effect mobility of 12.4 cm{sup 2}/V s, subthreshold swing (SS) of 0.39 V/decade, threshold voltage (V{sub TH}) of 1.5 V, and I{sub ON/OFF} ratio of ∼10{sup 7}. A significant improvement in the field-effect mobility (up to ∼33.5 cm{sup 2}/V s) was achieved for crystallized ZTO TFTs: this improvement was accomplished without compromising the SS, V{sub TH}, or I{sub ON/OFF} ratio due to the presence of a highly ordered microstructure.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Identification of Pigments in Colored Layers of a Painting by Raman Spectroscopy

Using the method of Raman spectroscopy the pigment composition is investigated of, and the brushwork technique used in, the original layer of a 19th century painting is established. It is an overdoor worked, presumably, by Antoine Jean-Etienne Faivre. It is established that the artist used the following pigments: cinnabar and dyes on the basis of goethite and hematite (for red, yellow–orange, and brown shades), ultramarine and Prussian blue (for blue shades), and Emerald green and a mixture of blue and yellow shades (to obtain a green color). It is determined that white lead was used a primer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Structural enhancement of ZnO on SiO{sub 2} for photonic applications

Multi-layer thin films are often the basis of photonic devices. Zinc oxide (ZnO) with its excellent optoelectronic properties can serve as a high quality emitter in structures like microdisks or photonic crystals. Here, we present a detailed study on the enhancement of the structural properties of low-temperature MBE grown ZnO on silica (SiO{sub 2}). By thermal annealing a grain coalescence of the initially polycrystalline layer leads to an enhancement of the electronic structure, indicated by a blue shift of the photoluminescence (PL) signal maximum. Oxygen atmosphere during the annealing process prevents the creation of intrinsic defects by out-diffusion. Pre-annealing deposited SiO{sub 2} capping layers instead obstruct the recrystallization and lead to less intense emission. While thin capping layers partially detach from the ZnO film at high temperatures and cause higher surface roughness and the weakest emission, thicker layers remain smoother and exhibit a significantly stronger photoluminescence.

36 MATERIALS SCIENCE↗
DOE OSTI2015

State diagram of an orthogonal spin transfer spin valve device

We present the switching characteristics of a spin-transfer device that incorporates a perpendicularly magnetized spin-polarizing layer with an in-plane magnetized free and fixed magnetic layer, known as an orthogonal spin transfer spin valve device. This device shows clear switching between parallel (P) and antiparallel (AP) resistance states and the reverse transition (AP → P) for both current polarities. Further, hysteretic transitions are shown to occur into a state with a resistance intermediate between that of the P and AP states, again for both current polarities. These unusual spin-transfer switching characteristics can be explained within a simple macrospin model that incorporates thermal fluctuations and considers a spin-polarized current that is tilted with respect to the free layer's plane, due to the presence of the spin-transfer torque from the polarizing layer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Distribution of pairing functions in superconducting spin valve SF1F2

The distribution of the spin-singlet component, the short-range spin-triplet component with zero projection, and the long-range spin-triplet component with projection ±1 of the superconducting pairing function has been obtained for different regimes of switching of a spin valve with a three-layer heterostructure (superconductor/ferromagnet/ferromagnet). The distribution of the components is discussed as the main reason for the behavior of the superconducting transition temperature as a function of the angle between the magnetic moments of the ferromagnetic layers in these regimes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Dynamic Strength of a Titanium Alloy with an Electron-Beam-Modified Surface

Data are presented of plane-wave experiments aimed at determining the dynamic strength of 3M titanium alloy with a surface processed by a microsecond electron beam. It has been found that the dynamic strength of processed specimens is higher than that of unprocessed specimens. Metallographic examination of test specimens has revealed spallation macrofracture inside the unprocessed specimens and spallation microfracture at the interface between the hardened layer and the substrate in the beam-processed specimens.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Particle-in-cell modeling of electron beam generated plasma

Plasmas generated using energetic electron beams are well known for their low electron temperature (T e ) and plasma potential, which makes them attractive for atomic-precision plasma processing applications such as atomic layer etch and deposition. A 2-dimensional particle-in-cell model for an electron beam-generated plasma in argon confined by a constant applied magnetic field is described here in this article. Plasma production primarily occurs in the path of the beam electrons in the center of the chamber. The resulting plasma spreads out in the chamber through non-ambipolar diffusion with a short-circuiting effect allowing unequal electron and ion fluxes to different regions of the bounding conductive chamber walls. The cross-field transport of the electrons (and thus the steady-state characteristics of the plasma) are strongly impacted by the magnetic field. T e is anisotropic in the electron beam region, but low and isotropic away from the plasma production zone. The plasma density increases and the plasma becomes more confined near the region of production when the magnetic field strengthens. The magnetic field reduces both electron physical and energy transport perpendicular to the magnetic field. T e is uniform along the magnetic field lines and slowly decreases perpendicular to it. Electrons are less energetic in the sheath regions where the sheath electric field repels and confines the low-energy electrons from the bulk plasma. Even though electron and ion densities are similar in the bulk plasma due to quasi-neutrality, electron and ion fluxes on the grounded chamber walls are unequal at most locations. Electron confinement by the magnetic field weakens with increasing pressure, and the plasma spread out farther from the electron beam region.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Visualization of Chiral Electronic Structure and Anomalous Optical Response in a Material with Chiral Charge Density Waves

Chiral materials have attracted significant research interests as they exhibit intriguing physical properties, such as chiral optical response, spin-momentum locking, and chiral induced spin selectivity. Recently, layered transition metal dichalcogenide 1T–TaS 2 has been found to host a chiral charge density wave (CDW) order. Nevertheless, the physical consequences of the chiral order, for example, in electronic structures and the optical properties, are yet to be explored. Here, we report the spectroscopic visualization of an emergent chiral electronic band structure in the CDW phase, characterized by windmill-shaped Fermi surfaces. Further, we uncover a remarkable chirality-dependent circularly polarized Raman response due to the salient in-plane chiral symmetry of CDW, although the ordinary circular dichroism vanishes. Chiral Fermi surfaces and anomalous Raman responses coincide with the CDW transition, proving their lattice origin. Our Letter paves a path to manipulate the chiral electronic and optical properties in two-dimensional materials and explore applications in polarization optics and spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Titanium doped kagome superconductor CsV 3–x Ti x Sb 5 and two distinct phases

The vanadium-based kagome superconductor CsV 3 Sb 5 has attracted tremendous attention due to its unexcepted anomalous Hall effect (AHE), charge density waves (CDWs), nematicity, and a pseudogap pair density wave (PDW) coexisting with unconventional strong-coupling superconductivity. The origins of CDWs, unconventional superconductivity, and their correlation with different electronic states in this kagome system are of great significance, but so far, are still under debate. Chemical doping in the kagome layer provides one of the most direct ways to reveal the intrinsic physics, but remains unexplored. Here, we report, for the first time, the synthesis of Ti-substituted CsV 3 Sb 5 single crystals and its rich phase diagram mapping the evolution of intertwining electronic states. The Ti atoms directly substitute for V in the kagome layers. CsV 3–x Ti x Sb 5 shows two distinct superconductivity phases upon substitution. The Ti slightly-substituted phase displays an unconventional V-shaped superconductivity gap, coexisting with weakening CDW, PDW, AHE, and nematicity. The Ti highly-substituted phase has a U-shaped superconductivity gap concomitant with a short-range rotation symmetry breaking CDW, while long-range CDW, twofold symmetry of in-plane resistivity, AHE, and PDW are absent. Furthermore, we also demonstrate the chemical substitution of V atoms with other elements such as Cr and Nb, showing a different modulation on the superconductivity phases and CDWs. These findings open up a way to synthesise a new family of doped CsV 3 Sb 5 materials, and further represent a new platform for tuning the different correlated electronic states and superconducting pairing in kagome superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Ferroelectricity in Atomic Layer Deposited Wurtzite Zinc Magnesium Oxide Zn 1– x Mg x O

Conformal deposition of wurtzite ferroelectrics, which is needed for their use in scaled nonvolatile memories, is challenging using current physical vapor deposition techniques. To overcome the conformality barrier, this work demonstrates ferroelectricity in wurtzite Zn 1− x Mg x O thin films prepared by plasma-enhanced atomic layer deposition, which is a non-line-of-sight deposition method. Films ranging in composition from x = 0.00 to x = 0.58 are predominantly wurtzite phase and exhibit a (0001)-texture. Increasing the magnesium content decreases the c/a ratio, increases the optical bandgap energy, increases the piezoelectric response, and enables polarization reversal. Clear polarization switching is demonstrated in 50 nm thick Zn 1− x Mg x O films by piezoresponse force microscopy in compositions containing x = 0.46 and x = 0.58.

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

Atomic Layer Deposition of Ruthenium Films Using Ruthenium Diketonates and O 2 , H 2 , or N 2 O: The Role of Ruthenium Etching

In this work, the evolution of the surface during the steps that comprise the atomic layer deposition (ALD) of ruthenium films on a nickel substrate using tris(2,2,6,6-tetramethyl-3,5-heptanedionato)ruthenium(III) (Ru(tmhd) 3 ) and molecular oxygen was characterized using a combination of X-ray photoelectron (XPS) and reflection–absorption infrared (RAIRS) spectroscopies. The uptake of the Ru metalorganic precursor was determined to be activated, involving the average loss of two out of the three ligands (and the retention of the third, in molecular form, at the surface–vacuum interface), and self-limited, as required in ALD. The reaction of the resulting layer from that first half of the ALD cycle with O 2 proved to be more complex: in addition to the desired removal of the carbon-containing material, the Ni substrate becomes oxidized, and some Ru is etched away in the form of the volatile RuO 4 gas. By testing different combinations of exposures and temperatures it was determined that Ru film growth was possible, but tuning and optimizing the ALD or atomic layer etching (ALE) process conditions for maximum film growth or removal rate per cycle proved difficult. Replacing O 2 with H 2 was shown not to be viable either, as such an agent can reduce the nickel oxide formed after O 2 treatments (in fact, Ru(tmhd) 3 can do this as well) but not remove the carbonaceous material deposited on the surface by the Ru precursor. The use of N 2 O, on the other hand, showed much promise, being capable of removing most of the surface carbon without affecting the Ru film or the Ni substrate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Strain Engineering of Adsorbate Self-Assembly on Graphene for Band Gap Tuning

Recent interest in functionalized graphene has been motivated by the prospect of creating a two-dimensional semiconductor with a tunable band gap. Various approaches to band gap engineering have been made over the last decade, one of which is chemical functionalization. In this work, a predictive physical model of the self-assembly of halogenated carbene layers on graphene is suggested. Self-assembly of the adsorbed layer is found to be governed by a combination of the curvature of the graphene sheet, local distortions, as introduced by molecular adsorption, and short-range intermolecular repulsion. The thermodynamics of bidental covalent molecular adsorption and the resultant electronic structure are computed using density functional theory. It is predicted that a direct band gap is opened that is tunable by varying coverages and is dependent on the ripple amplitude. This provides a mechanism for the controlled engineering of graphene’s electronic structure and thus its use in semiconductor technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Binding of Cholera Toxin B-Subunit to a Ganglioside GM1-Functionalized PEG-Tethered Lipid Membrane

We report neutron reflectometry (NR) studies of polyethylene glycol (PEG)-tethered model lipid membranes at the solid–liquid interface and of cholera toxin’s B-subunit (CTxB) binding to tethered membranes containing ganglioside GM1 receptors. First, tethered polymer brushes were formed by grafting silane-functionalized PEG lipopolymers to quartz from solution. Subsequent deposition of lipids by Langmuir–Blodgett/Langmuir–Schaefer (LB/LS) resulted in a tethered bilayer structure separated from the solid support by a hydrated PEG layer. NR revealed that the tethers formed a highly hydrated polymer brush, uniformly separating the bilayer from the underlying solid substrate. Further, the lipid bilayer did not significantly perturb the brush’s conformation relative to a free brush. Biological functionality of the tethered bilayers was verified by interacting CTxB, with ganglioside GM1 receptors incorporated into the bilayer. The surface coverage of CTxB bound to the lipid membrane, θ CTB = 0.58 ± 0.08, was consistent with the coverage predicted for random sequential absorption, and toxin binding did not impact the membrane conformation.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Uniform Doping of Metal Oxide Nanowires Using Solid State Diffusion

The synthesis of one-dimensional nanostructures with specific properties is often hindered by difficulty in tuning the material composition without sacrificing morphology and material quality. In this work, we present a simple solid state diffusion method utilizing atomic layer deposition to controllably alter the composition of metal oxide nanowires. This compositional control allows for modification of the optical, electronic, and electrochemical properties of the semiconductor nanowires. Using this method and a novel process for manganese oxide atomic layer deposition, we produced manganese-doped rutile TiO2 nanowires and investigated their structural and photoelectrochemical properties. A homogeneous incorporation of the Mn dopant into the rutile lattice was observed, and the local chemical environment of the Mn was determined using X-ray absorption spectroscopy. The doping process resulted in a tunable enhancement in the electrocatalytic activity for water oxidation, demonstrating that this simple and general method can be used to control the properties of one-dimensional nanostructures for use in a variety of applications including solar-to-fuel generation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Understanding the Mechanism of Electronic Defect Suppression Enabled by Nonidealities in Atomic Layer Deposition

Silicon germanium (SiGe) is a multifunctional material considered for quantum computing, neuromorphic devices, and CMOS transistors. However, implementation of SiGe in nanoscale electronic devices necessitates suppression of surface states dominating the electronic properties. The absence of a stable and passive surface oxide for SiGe results in the formation of charge traps at the SiGe-oxide interface induced by GeOx. In an ideal ALD process in which oxide is grown layer by layer, the GeO x formation should be prevented with selective surface oxidation (i.e., formation of an SiO x interface) by controlling the oxidant dose in the first few ALD cycles of the oxide deposition on SiGe. However, in a real ALD process, the interface evolves during the entire ALD oxide deposition due to diffusion of reactant species through the gate oxide. In this work, this diffusion process in nonideal ALD is investigated and exploited: the diffusion through the oxide during ALD is utilized to passivate the interfacial defects by employing ozone as a secondary oxidant. Periodic ozone exposure during gate oxide ALD on SiGe is shown to reduce the integrated trap density (D it ) across the band gap by nearly 1 order of magnitude in Al 2 O 3 (<6 × 10 10 cm -2 ) and in HfO 2 (<3.9 × 10 11 cm -2 ) by forming a SiO x -rich interface on SiGe. Depletion of Ge from the interfacial layer (IL) by enhancement of volatile GeO x formation and consequent desorption from the SiGe with ozone insertion during the ALD growth process is confirmed by electron energy loss spectroscopy (STEM-EELS) and hypothesized to be the mechanism for reduction of the interfacial defects. In this work, the nanoscale mechanism for defect suppression at the SiGe-oxide interface is demonstrated, which is engineering of diffusion species in the ALD process due to facile diffusion of reactant species in nonideal ALD.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

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