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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Conductive paths through polycrystalline BaTiO{sub 3}: Scanning probe microscopy study

The microstructural features determining the leakage current through polycrystalline BaTiO{sub 3} films are investigated using Conductive Atomic Force Microscopy. Grain boundaries are found to be the dominant conductive paths compared to the conduction through the grains. Grain boundary currents are observed to reversibly rise with the increase of the applied DC voltages, indicating that the current is controlled by a field-activated charge transport process.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Mixed-flow design for microfluidic printing of two-component polymer semiconductor systems

The rational creation of two-component conjugated polymer systems with high levels of phase purity in each component is challenging but crucial for realizing printed soft-matter electronics. Here, we report a mixed-flow microfluidic printing (MFMP) approach for two-component π -polymer systems that significantly elevates phase purity in bulk-heterojunction solar cells and thin-film transistors. MFMP integrates laminar and extensional flows using a specially microstructured shear blade, designed with fluid flow simulation tools to tune the flow patterns and induce shear, stretch, and pushout effects. This optimizes polymer conformation and semiconducting blend order as assessed by atomic force microscopy (AFM), transmission electron microscopy (TEM), grazing incidence wide-angle X-ray scattering (GIWAXS), resonant soft X-ray scattering (R-SoXS), photovoltaic response, and field effect mobility. For printed all-polymer (poly[(5,6-difluoro-2-octyl-2H-benzotriazole-4,7-diyl)-2,5-thiophenediyl[4,8-bis[5-(2-hexyldecyl)-2-thienyl]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl]-2,5-thiophenediyl]) [J51]:(poly{[N,N′-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)}) [N2200]) solar cells, this approach enhances short-circuit currents and fill factors, with power conversion efficiency increasing from 5.20% for conventional blade coating to 7.80% for MFMP. Moreover, the performance of mixed polymer ambipolar [poly(3-hexylthiophene-2,5-diyl) (P3HT):N2200] and semiconducting:insulating polymer unipolar (N2200:polystyrene) transistors is similarly enhanced, underscoring versatility for two-component π -polymer systems. Mixed-flow designs offer modalities for achieving high-performance organic optoelectronics via innovative printing methodologies.

42 ENGINEERING↗
DOE OSTI2017

UV-assisted growth of transparent conducting layers based on zinc oxide

A comparative study of the microstructure and optical and electrical characteristics of gallium-doped ZnO films synthesized by magnetron sputtering with and without assistance to the growth process by UV radiation has been carried out. It was found that the UV assistance to the growth process of ZnO-based transparent conducting layers improves their electrical characteristics because of the formation of additional donor centers and the lower carrier scattering at grain boundaries, without any strong inf luence on the layer morphology and on the average optical transmittance in the visible spectral range.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1986

Process-induced defects in solar cell silicon

The microstructure of as-grown and processed, edge-defined film-fed grown, silicon ribbons was studied in order to identify the basic mechanisms responsible for the change of the as-grown defect structure during processing at elevated temperatures. The short heat treatment required to diffuse the p-n junction was sufficient to cause heterogeneous precipitation of impurity atoms, particularly transition metals. In addition, an elastic recovery of the ribbon occurred by dislocation glide, resulting in the formation of a polygonizationlike structure of subboundaries in the base. Mechanisms are suggested by which twin boundaries, acting as dislocation obstacles, can concentrate the relatively low average dislocation densities typical of edge-defined film-fed grown ribbons (10 to the 4th to 10 to the 8th/sq cm) to values which are sufficient to induce the formation of subgrainlike boundary structures.

Gleichmann, R.↗
DOE OSTI2022

Effect of Applied Stress on the Selective Oxidation of Alloy 600 Exposed to PWR Primary Water and Rhines Pack Environments

A mechanistic understanding of corrosion and oxidation processes is crucial to ensure long-term resistance to stress corrosion cracking of Ni-base structural alloys in pressurized water reactor (PWR) primary and secondary systems. Aqueous corrosion of Ni-base alloys under PWR primary water conditions was previously compared to gaseous oxidation with comparable oxygen potentials. However, those studies considered only stress-free conditions, which removes a critical parameter for understanding stress corrosion behaviors. A significant knowledge gap exists for the role of applied stresses on selective internal oxidation in gaseous environments. A micro-4-point-bend jig was designed to facilitate stress in a Rhines Pack set-up. Selective oxidation at different stress and strain conditions was investigated in a series of Rhines Pack experiments for Alloy 600. Focused ion beam milling enabled the extraction of site-specific specimens containing selected high-energy grain boundaries from tensile and compressive stress regions. Analytical transmission electron microscopy was employed to analyze the microstructure and chemical composition of the resulting oxides. Protective surface oxide films and selective intergranular oxides were observed at different conditions. The implications of these fundamental differences are discussed relative to intergranular attack and stress corrosion cracking mechanisms in PWR primary water.

stress, 4-point-bend, selective oxidation, Alloy 6↗
DOE OSTI2015

Coupling In Situ TEM and Ex Situ Analysis to Understand Heterogeneous Sodiation of Antimony

Here, we employed an in situ electrochemical cell in the transmission electron microscope (TEM) together with ex situ time-of-flight, secondary-ion mass spectrometry (TOF-SIMS) depth profiling, and FIB–helium ion scanning microscope (HIM) imaging to detail the structural and compositional changes associated with Na/Na+ charging/discharging of 50 and 100 nm thin films of Sb. TOF-SIMS on a partially sodiated 100 nm Sb film gives a Na signal that progressively decreases toward the current collector, indicating that sodiation does not proceed uniformly. This heterogeneity will lead to local volumetric expansion gradients that would in turn serve as a major source of intrinsic stress in the microstructure. In situ TEM shows time-dependent buckling and localized separation of the sodiated films from their TiN-Ge nanowire support, which is a mechanism of stress-relaxation. Localized horizontal fracture does not occur directly at the interface, but rather at a short distance away within the bulk of the Sb. HIM images of FIB cross sections taken from sodiated half-cells, electrically disconnected, and aged at room temperature, demonstrate nonuniform film swelling and the onset of analogous through-bulk separation. TOF-SIMS highlights time-dependent segregation of Na within the structure, both to the film-current collector interface and to the film surface where a solid electrolyte interphase (SEI) exists, agreeing with the electrochemical impedance results that show time-dependent increase of the films’ charge transfer resistance. We propose that Na segregation serves as a secondary source of stress relief, which occurs over somewhat longer time scales.

25 ENERGY STORAGE↗
DOE OSTI2015

Large-area SiC membrane produced by plasma enhanced chemical vapor deposition at relatively high temperature

Advances in the growth of silicon carbide (SiC) thin films with outstanding thermal and mechanical properties have received considerable attention. However, the fabrication of large-area free-standing SiC membrane still remains a challenge. Here, the authors report a plasma enhanced chemical vapor deposition process at a relatively high temperature to improve the free-standing SiC membrane area. A systematic study on the microstructural, mechanical, and optical properties of hydrogenated polycrystalline silicon carbide (poly-SiC{sub x}:H) thin films deposited at 600 °C with different annealing temperatures has been performed. In the as-deposited state, SiC{sub x}:H thin films show a polycrystalline structure. The crystallinity degree can be further improved with the increase of the postdeposition annealing temperature. The resulting process produced free-standing 2-μm-thick SiC membranes up to 70 mm in diameter with root mean square roughness of 3.384 nm and optical transparency of about 70% at 632.8 nm wavelength. The large-area SiC membranes made out of poly-SiC{sub x}:H thin films deposited at a relatively high temperature can be beneficial for a wide variety of applications, such as x-ray diffractive optical elements, optical and mechanical filtering, lithography mask, lightweight space telescopes, etc.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Novel phase of carbon, ferromagnetism, and conversion into diamond

We report the discovery of a new phase of carbon (referred to as Q-carbon) and address fundamental issues related to direct conversion of carbon into diamond at ambient temperatures and pressures in air without any need for catalyst and presence of hydrogen. The Q-carbon is formed as result of quenching from super undercooled state by using high-power nanosecond laser pulses. We discuss the equilibrium phase diagram (P vs. T) of carbon and show that by rapid quenching kinetics can shift thermodynamic graphite/diamond/liquid carbon triple point from 5000 K/12 GPa to super undercooled carbon at atmospheric pressure in air. It is shown that nanosecond laser heating of diamond-like amorphous carbon on sapphire, glass, and polymer substrates can be confined to melt carbon in a super undercooled state. By quenching the carbon from the super undercooled state, we have created a new state of carbon (Q-carbon) from which nanodiamond, microdiamond, microneedles, and single-crystal thin films are formed depending upon the nucleation and growth times allowed for diamond formation. The Q-carbon quenched from liquid is a new state of solid carbon with a higher mass density than amorphous carbon and a mixture of mostly fourfold sp{sup 3} (75%–85%) with the rest being threefold sp{sup 2} bonded carbon (with distinct entropy). It is expected to have new and improved mechanical hardness, electrical conductivity, chemical, and physical properties, including room-temperature ferromagnetism (RTFM) and enhanced field emission. Here we present interesting results on RTFM, enhanced electrical conductivity and surface potential of Q-carbon to emphasize its unique properties. The Q-carbon exhibits robust bulk ferromagnetism with estimated Curie temperature of about 500 K and saturation magnetization value of 20 emu g{sup −1}. From the Q-carbon, diamond phase is nucleated and a variety of micro- and nanostructures and large-area single-crystal diamond sheets are grown by allowing growth times as needed. Subsequent laser pulses can be used to grow nanodiamond into microdiamond and nucleate other nanostructures of diamond on the top of existing microdiamond and create novel nanostructured materials. The microstructural details provide insights into the mechanism of formation of nanodiamond, microdiamond, nanoneedles, microneedles, and single-crystal thin films. This process allows carbon-to-diamond conversion and formation of useful nanostructures and microstructures at ambient temperatures in air at atmospheric pressure on practical and heat-sensitive substrates in a controlled way without need for any catalysts and hydrogen to stabilize sp{sup 3} bonding for diamond formation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Synthesis of Lanthanum Tungsten Oxynitride Perovskite Thin Films

Ternary metal-oxide material systems commonly crystallize in the perovskite crystal structure, which is utilized in numerous electronic applications. In contrast to oxides, there are no known nitride perovskites, likely due to the competition with oxidation, which makes the formation of pure nitride materials difficult and synthesis of oxynitride materials more common. While deposition of oxynitride perovskite thin films is important for many electronic applications, it is difficult to control oxygen and nitrogen stoichiometry. Lanthanum tungsten oxynitride (LaWN3-..delta..O..delta..) thin films with varying La:W ratio are synthesized by combinatorial sputtering and characterized for their chemical composition, crystal structure, and microstructure. A three-step synthesis method, which involves co-sputtering, capping layer deposition, and rapid thermal annealing, is established for producing crystalline thin films while minimizing the oxygen content. Elemental depth profiling results show that the cation-stoichiometric films contain approximately one oxygen for every five nitrogen (..delta.. = 0.5). Synchrotron-based diffraction indicates a tetragonal perovskite crystal structure. These results are discussed in terms of the perovskite tolerance factors, octahedral tilting, and bond valence. Overall, this synthesis and characterization is expected to pave the way toward future thin film property measurements of lanthanum tungsten oxynitrides and eventual synthesis of oxygen-free nitride perovskites.

14 SOLAR ENERGY↗
DOE OSTI2021

Bulk and Short-Circuit Anion Diffusion in Epitaxial Fe 2 O 3 Films Quantified Using Buried Isotopic Tracer Layers

Self-diffusion is a fundamental physical process that, in solid materials, is intimately correlated with both microstructure and functional properties. In this work, a universal approach is presented to precisely characterize self-diffusion in ionic solids by isotopically enriching anions and/or cations at specific locations within an epitaxial film stack, and characterize their redistribution at high spatial resolution with atom probe tomography. Nanoscale anion diffusivity is quantified in epitaxial α-Fe 2 O 3 thin films deposited by molecular beam epitaxy with a thin (10 nm) buried layer highly enriched in 18 O. The isotopic sensitivity of the atom probe allows precise measurement of 18 O distribution across the sharp interfaces between this layer and the surrounding Fe 2 O 3 after annealing. Short-circuit anion diffusion through 1D and 2D structural defects in Fe 2 O 3 are also directly visualized in 3D. This versatile approach to study precisely tailored thin film samples at high spatial and mass fidelity will facilitate a deeper understanding of atomic-scale diffusion phenomena.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Chapter 15: Summary and Outlook

In the various chapters of this book, numerous characterization techniques are presented that can be applied to thin-film solar cells to determine (micro)structural, compositional, electrical, and optoelectronic properties. What has yet to be more fully elucidated is to what extent these characterization techniques can be combined, in a correlative way, to enhance the information gathered on materials and devices. Indeed, it is valuable to consider combining techniques to verify the relevance of the measured materials properties or to obtain them on different length scales-to compare surface with bulk properties, or to correlate structure and composition of materials with electrical and optoelectronic properties.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2013

Multilevel and long retentive resistive switching in low temperature nanostructured Cu/SiO{sub x}-W-SiO{sub x}/Pt

Amorphous SiO{sub x}-based memory films are fabricated at room temperature, and study on their resistive switching characteristics and improvement approaches is performed. Multilevel resistive states with large ratio 1: ∼10{sup 2}: 3 × 10{sup 5} and long retention exceeding 2 × 10{sup 6} s at ambient temperature and humidity are observed in Cu/SiO{sub x} (9 nm)-W (∼2 nm)-SiO{sub x} (9 nm)/Pt ultrathin stack. Nonvolatile switching is consistently realized in microscopy. Based on investigations of microscopic conduction and microstructure, tungsten incorporation with copper as relay bridges for conducting filaments is proposed to attribute to the performance improvement and the multilevel switching mechanism.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Tuning the ferromagnetic-antiferromagnetic interfaces of granular Co-CoO exchange bias systems by annealing

The low-temperature magnetic behavior of granular Co-CoO exchange bias systems, prepared by oxygen ion implantation in Co thin films and subsequent annealing, is addressed. The thermal activation effects lead to an O migration which results in virtually pure Co areas embedded in a structurally relaxed and nearly stoichiometric CoO phase. This yields decreased training and exchange bias shifts, while the blocking temperature significantly increases, coming close to the Néel temperature of bulk CoO for samples implanted to a fluence above 1 × 10{sup 17} ions/cm{sup 2} (15% O). The dependence of the exchange bias shift on the pristine O-implanted content is analogous to that of the antiferromagnetic thickness in most ferromagnetic/antiferromagnetic systems (i.e., an increase in the exchange bias shift up to a maximum followed by a decrease until a steady state is reached), suggesting that, after annealing, the enriched Co areas might be rather similar in size for samples implanted above 1 × 10{sup 17} ions/cm{sup 2}, whereas the corresponding CoO counterparts become enlarged with pristine O content (i.e., effect of the antiferromagnet size). This study demonstrates that the magnetic properties of granular Co-CoO systems can be tailored by controllably modifying the local microstructure through annealing treatments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

A multi-state magnetic memory dependent on the permeability of Metglas

A three-state magnetic memory was developed based on differences in the magnetic permeability of a soft ferromagnetic media, Metglas 2826MB (Fe{sub 40}Ni{sub 38}Mo{sub 4}B{sub 18}). By heating bits of a 250 nm thick Metglas film with 70–100 mW of laser power, we were able to tune the local microstructure, and hence, the permeability. Ternary memory states were created by using lower laser power to enhance the initial permeability through localized atomic rearrangement and higher power to reduce the permeability through crystallization. The permeability of the bits was read by detecting variations in an external 32 Oe probe field within 10 μm of the media via a magnetic tunnel junction read head. Compared to data based on remanent magnetization, these multi-permeability bits have enhanced insensitivity to unexpected field and temperature changes. We found that data was not corrupted after exposure to fields of 1 T or temperatures of 423 K, indicating the effectiveness of this multi-state approach for safely storing large amounts of data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Thin-Film Three-Layer Fe/Poly(diphenylene phthalide)/Fe Systems: Structural Properties and Behavior in Magnetic Fields

The structural and magnetic properties of thin-film Fe/poly(diphenylene phthalide) (PDP)/Fe systems are studied, along with the behavior of these systems in magnetic fields. The mean surface roughness of the studied samples is around 5–8 nm, and local near-surface magnetic properties show variation within 10%. The samples are characterized by two-step hysteresis loops, the step size depending on the thickness of the polymer layer and the difference in the thickness between the magnetic layers. The results are explained by the effects the exchange interaction between the magnetic layers, mediated by the PDP interlayer, has on the behavior of our samples in a magnetic field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Emergent and robust ferromagnetic-insulating state in highly strained ferroelastic LaCoO 3 thin films

Transition metal oxides are promising candidates for the next generation of spintronic devices due to their fascinating properties that can be effectively engineered by strain, defects, and microstructure. An excellent example can be found in ferroelastic LaCoO 3 with paramagnetism in bulk. In contrast, unexpected ferromagnetism is observed in tensile-strained LaCoO 3 films, however, its origin remains controversial. Here we simultaneously reveal the formation of ordered oxygen vacancies and previously unreported long-range suppression of CoO 6 octahedral rotations throughout LaCoO 3 films. Supported by density functional theory calculations, we find that the strong modification of Co 3d-O 2p hybridization associated with the increase of both Co-O-Co bond angle and Co-O bond length weakens the crystal-field splitting and facilitates an ordered high-spin state of Co ions, inducing an emergent ferromagnetic-insulating state. Our work provides unique insights into underlying mechanisms driving the ferromagnetic-insulating state in tensile-strained ferroelastic LaCoO 3 films while suggesting potential applications toward low-power spintronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Light Extraction System for OLED (LESO)

The DOE Office of Energy Efficiency and Renewable Energy is funding development of Solid-State Lighting (SSL) to replace incandescent and fluorescent technologies. A more aggressive innovation schedule could achieve site electricity consumption reductions from current projections of 40% to 60% by the year 2030 when compared to the no-LED scenario in the United States. These increased reductions would total an increase in savings of 395 TWh of energy. Based on preliminary data showing improvements of 2x in extraction efficiency with diffuser films, we will optimize surface relief structures to maximize the light extraction efficiency of OLED devices and test the optimized structures in prototype samples. To address the DOE desire for rapid SSL acceptance, Luminit, LLC, proposes to develop a new Light Extraction System for OLED (LESO) implemented in an ultraviolet (UV)-curable HRI polymer. The LESO uses optimized surface relief structures in high-index and low-index interfaces, which will significantly increase light extraction from the OLEDs. The LESO will significantly reduce environmental pollution compared to incandescent, compact fluorescent (CFL), and LED lamps. It will do so at a low price compared to other technologies, and with extremely high quality lighting (nearly perfect color matching, for example). Through LESO adoption, both CO 2 and other pollutants will be reduced by hundreds of megatons annually.

47 OTHER INSTRUMENTATION↗