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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

A-site- and/or B-site-modified PbZrTiO3 materials and (Pb, Sr, Ca, Ba, Mg) (Zr, Ti, Nb, Ta)O3 films having utility in ferroelectric random access memories and high performance thin film microactuators

A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite crystal material includes crystal lattice A-sites and B-sites at least one of which is modified by the presence of a substituent selected from the group consisting of (i) A-site substituents consisting of Sr, Ca, Ba and Mg, and (ii) B-site substituents selected from the group consisting of Nb and Ta. The perovskite crystal thin film material may be formed by liquid delivery MOCVD from metalorganic precursors of the metal components of the thin film, to form PZT and PSZT, and other piezoelectric and ferroelectric thin film materials. The thin films of the invention have utility in non-volatile ferroelectric memory devices (NV-FeRAMs), and in microelectromechanical systems (MEMS) as sensor and/or actuator elements, e.g., high speed digital system actuators requiring low input power levels.

Roeder, Jeffrey F.↗
NASA NTRS2004

A-SITE-AND/OR B-SITE-MODIFIED PBZRTIO3 MATERIALS AND (PB, SR, CA, BA, MG) (ZR, TI,NB, TA)O3 FILMS HAVING UTILITY IN FERROELECTRIC RANDOM ACCESS MEMORIES AND HIGH PERFORMANCE THIN FILM MICROACTUATORS

A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite crystal material includes crystal lattice A-sites and B-sites at least one of which is modified by the presence of a substituent selected from the group consisting of (i) A-site substituents consisting of Sr, Ca, Ba and Mg, and (ii) B-site substituents selected from the group consisting of Nb and Ta. The perovskite crystal thin film material may be formed by liquid delivery MOCVD from metalorganic precursors of the metal components of the thin film, to form PZT and PSZT, and other piezoelectric and ferroelectric thin film materials. The thin films of the invention have utility in non-volatile ferroelectric memory devices (NV-FeRAMs), and in microelectromechanical systems (MEMS) as sensor and/or actuator elements, e.g., high speed digital system actuators requiring low input power levels.

Roeder, Jeffrey F.↗
DOE OSTI2015

Methods for producing complex films, and films produced thereby

A method for producing a film, the method comprising melting a layer of precursor particles on a substrate until at least a portion of the melted particles are planarized and merged to produce the film. The invention is also directed to a method for producing a photovoltaic film, the method comprising depositing particles having a photovoltaic or other property onto a substrate, and affixing the particles to the substrate, wherein the particles may or may not be subsequently melted. Also described herein are films produced by these methods, methods for producing a patterned film on a substrate, and methods for producing a multilayer structure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Understanding Film Formation Morphology and Orientation in High Member 2D Ruddlesden-Popper Perovskites for High-Efficiency Solar Cells

We report that 2D Ruddlesden–Popper (RP) perovskites have recently emerged as promising candidates for hybrid perovskite photovoltaic cells, realizing power-conversion efficiencies (PCEs) of over 10% with technologically relevant stability. To achieve solar cell performance comparable to the state-of-the-art 3D perovskite cells, it is highly desirable to increase the conductivity and lower the optical bandgap for enhanced near-IR region absorption by increasing the perovskite slab thickness. Here, the use of the 2D higher member (n = 5) RP perovskite (n-butyl-NH 3 ) 2 (MeNH 3 ) 4 Pb 5 I 16 in depositing highly oriented thin films from dimethylformamide/dimethylsulfoxide mixtures using the hot-casting method is reported. In addition, they exhibit superior environmental stability over thin films of their 3D counterpart. These films are assembled into high-efficiency solar cells with an open-circuit voltage of ≈1 V and PCE of up to 10%. This is achieved by fine-tuning the solvent ratio, crystal growth orientation, and grain size in the thin films. Finally, the enhanced performance of the optimized devices is ascribed to the growth of micrometer-sized grains as opposed to more typically obtained nanometer grain size and highly crystalline, densely packed microstructures with the majority of the inorganic slabs preferentially aligned out of plane to the substrate, as confirmed by X-ray diffraction and grazing-incidence wide-angle X-ray scattering mapping.

14 SOLAR ENERGY↗
DOE OSTI2015

Tailoring the electronic transitions of NdNiO{sub 3} films through (111){sub pc} oriented interfaces

Bulk NdNiO{sub 3} and thin films grown along the pseudocubic (001){sub pc} axis display a 1st order metal to insulator transition (MIT) together with a Néel transition at T = 200 K. Here, we show that for NdNiO{sub 3} films deposited on (111){sub pc} NdGaO{sub 3}, the MIT occurs at T = 335 K and the Néel transition at T = 230 K. By comparing transport and magnetic properties of layers grown on substrates with different symmetries and lattice parameters, we demonstrate a particularly large tuning when the epitaxy is realized on (111){sub pc} surfaces. We attribute this effect to the specific lattice matching conditions imposed along this direction when using orthorhombic substrates.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Spontaneous lateral phase separation of AlInP during thin film growth and its effect on luminescence

The occurrence of spontaneous lateral phase separation during thin film growth of Al{sub x}In{sub 1−x}P by metal-organic chemical vapor deposition was investigated using a combination of transmission electron microscopy and atom probe tomography to obtain a quantitative view of this phenomenon. An anisotropic and coherent composition modulation was observed in the nearly lattice-matched films deposited below 750 °C with a quasi-linear amplification with thickness that was inversely proportional to the growth temperature. The periodicity of the modulation increased exponentially with the growth temperature. A comparison of photoluminescence from phase separated and homogenous direct band gap Al{sub x}In{sub 1−x}P deposited on metamorphic In{sub y}Ga{sub 1−y}As graded buffers showed a lowering of peak-emission energy in accordance with the atom probe compositional characterization without any degradation in luminous intensity. Additionally, indications of carrier trapping in the low band gap regions were observed even at room-temperature. While some of these results are in qualitative agreement with theoretical models of kinetic instability in unstrained alloy growth in the literature, significant discrepancies remain.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Ferromagnetic resonance of a YIG film in the low frequency regime

An improved method for characterizing the magnetic anisotropy of films with cubic symmetry is described and is applied to an yttrium iron garnet (111) film. Analysis of the ferromagnetic resonance (FMR) spectra performed both in-plane and out-of-plane from 0.7 to 8 GHz yielded the magnetic anisotropy constants as well as the saturation magnetization. The field at which FMR is observed turns out to be quite sensitive to anisotropy constants (by more than a factor ten) in the low frequency (<2 GHz) regime, and when the orientation of the magnetic field is nearly normal to the sample plane; the restoring force on the magnetization arising from the magnetocrystalline anisotropy fields is then comparable to that from the external field, thereby allowing the anisotropy constants to be determined with greater accuracy. In this region, unusual dynamical behaviors are observed such as multiple resonances and a switching of FMR resonance with only a 1° change in field orientation at 0.7 GHz.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Reversed Remanent Magnetic Configuration in Epitaxial La 1-xSrxMnO3 Films

The polar discontinuity which can occur at oxide interfaces can modify the properties of oxide thin films. In such a system, an unusual reversed orientation of the remanent magnetic state was observed recently for La{sub 0.7}Sr{sub 0.3}MnO{sub 3} on Nb-doped SrTiO{sub 3}(0 0 1) deposited via pulsed laser deposition (Lee et al 2010 Phys. Rev. Lett. 105 257204). Here, we report on a similar effect for La{sub 0.7}Sr{sub 0.3}MnO{sub 3} grown via molecular beam epitaxy, a deposition method with different growth kinetics, onto both Nb-doped and undoped SrTiO{sub 3} (STO) substrates. The reversed magnetic state occurred in both samples, while enriched Mn{sup 3+} regions (intermediate layer) are slightly different. Intriguingly, the onset of the reversed remanent state occurred at different temperatures: {approx}125 K for the Nb : STO substrate and {approx}240 K for the undoped STO substrate. Our results point to an additional mechanism for controlling the magnetism in mixed-valence oxide films.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Electrodeposition Process and Performance of CuIn(Se{sub x}S{sub 1−x}){sub 2} Film for Absorption Layer of Thin-Film Solar Cells

CuIn(Se{sub x}S{sub 1−x}){sub 2} thin film is prepared by the electrodeposition method for the absorption layer of the solar cell. The CuIn(Se{sub x}S{sub 1−x}){sub 2} films are characterized by cyclic voltammetry measurement for the reduction of copper, indium, selenium and sulfur in selenium and sulfur in aqueous solutions with sodium citrate and without sodium citrate. In the four cases, the defined reduction process for every single element is obtained and it is observed that sodium citrate changes the reduction potentials. A linear relationship between the current density of the reduction peak and (scan rate v){sup 1/2} for copper and indium is achieved, indicating that the process is diffusion controlled. The diffusion coefficients of copper and indium ions are calculated. The diffusional coefficient D value of copper is higher than that of indium, and this is the reason why the deposition rate of copper is higher. When four elements are co-deposited in the aqueous solution with sodium citrate, the quaternary compound of CuIn(Se{sub x}S{sub 1−x}){sub 2} is deposited together with Cu{sub 3}Se{sub 2} impure phases after annealing, as found by XRD spectra. Morphology is observed by SEM and AFM. The chemical state of the films components is analyzed by XPS. The UV-Visible spectrophotometer and electrochemistry workstation are employed to measure the photoelectric properties. The results show that the smooth, uniform and compact CuIn(Se{sub x}S{sub 1−x}){sub 2} film is a semiconductor with a band gap of 1.49 eV and a photovoltaic conversion efficiency of 0.45%.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Sol–gel preparation of well-adhered films and long range ordered inverse opal films of BaTiO{sub 3} and Bi{sub 2}Ti{sub 2}O{sub 7}

Highlights: • Highly adaptable sols are presented for processing of the electroceramic materials BaTiO{sub 3} and Bi{sub 2}Ti{sub 2}O{sub 7}. • High quality thin films are produced by dip coating with good phase control. • Infiltration of cross-linked polystyrene templates led to high quality inverse opals. - Abstract: Barium and bismuth titanate thin films and well-ordered inverse opal films are produced by dip coating from sols containing titanium alkoxides with acetic acid, acetylacetone, methoxyethanol and water. The inverse opal preparations used crosslinked polystyrene opal templates. Heat treatment in air produced tetragonal BaTiO{sub 3} or mixtures of the hexagonal and tetragonal phases, or phase pure Bi{sub 2}Ti{sub 2}O{sub 7}. Good quality films were obtained with a thickness of 5 μm from a single dipping, and the thickness could be increased by dipping multiple times. Inverse opals were well ordered and exhibited opalescence and photonic stop band effects.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Ferroelastic Hysteresis in Thin Films of Methylammonium Lead Iodide

Mechanical strain can modify the structural and electronic properties of methylammonium lead iodide MAPbI 3 . The consequences of ferroelastic hysteresis, which involves the retention of structural memory upon cycles of deformation, are reported for polycrystalline thin films of MAPbI 3 . Repeatedly bent films were examined using grazing incidence wide-angle X-ray scattering (GIWAXS) to quantitatively characterize the strains and proportions of twin domains. Approximate locations for the coercive stress and saturation on the ferroelastic stress–strain curve are identified, and changes to the stress–strain curve with cyclic strain are characterized. Notably, an external stress source, such as thermal stress from the substrate or a roll-to-roll printing setup, must apply at least |50| MPa to modify the proportions of different twins. The presence of specific twin domains is found to correlate to previously reported strain and defect heterogeneity in MAPbI 3 films. Domains from differently strained twin sets interact with each other. Long-term stability testing reveals that the domain walls are highly immobile over extended periods. Nucleation of new domain walls occurs for specific mechanical strains and correlates closely with degradation. Furthermore, these results help to explain the behavior of ion migration, degradation rate, and photoluminescence in thin films under compressive and tensile strain.

Defects↗
DOE OSTI2016

Increased Optoelectronic Quality and Uniformity of Hydrogenated p-InP Thin Films

The thin-film vapor-liquid-solid (TF-VLS) growth technique presents a promising route for high quality, scalable, and cost-effective InP thin films for optoelectronic devices. Toward this goal, careful optimization of material properties and device performance is of utmost interest. Here, we show that exposure of polycrystalline Zn-doped TF-VLS InP to a hydrogen plasma (in the following referred to as hydrogenation) results in improved optoelectronic quality as well as lateral optoelectronic uniformity. A combination of low temperature photoluminescence and transient photocurrent spectroscopy was used to analyze the energy position and relative density of defect states before and after hydrogenation. Notably, hydrogenation reduces the relative intragap defect density by 1 order of magnitude. As a metric to monitor lateral optoelectronic uniformity of polycrystalline TF-VLS InP, photoluminescence and electron beam induced current mapping reveal homogenization of the grain versus grain boundary upon hydrogenation. At the device level, we measured more than 260 TF-VLS InP solar cells before and after hydrogenation to verify the improved optoelectronic properties. Hydrogenation increased the average open-circuit voltage (VOC) of individual TF-VLS InP solar cells by up to 130 mV and reduced the variance in VOC for the analyzed devices.

14 SOLAR ENERGY↗
DOE OSTI2021

Preparation of Ultrathin Gold Films with Subatomic Surface Roughness

Nanoscale device fabrication requires control over film growth at the atomic scale. Growth conditions must be tuned in consideration of interface parameters like chemical bonding, surface free energy, and lattice matching. In metals, electronic properties may also be utilized for control of physical parameters. Quantum size effects can induce metals to spontaneously form specific shapes and sizes according to their electronic structure. Unfortunately, such electronic growth is generally known only for a few systems and is typically only stable under cryogenic conditions. In this work, we explore a recently discovered class of electronic growth systems in which metal films are grown upon the relatively inert surfaces of van der Waals crystals. In this class of materials, the electronic growth is highly stable at room temperature and actually requires higher temperature annealing to achieve proper equilibrium. We work with the Au/MoS 2 system, which shows excellent stability and can readily form discrete and atomically flat nanostructures. Here, we show how the electronic growth modes facilitate the formation of atomically flat films with nanometer scale thickness. Here, the surface roughness of these films was found to be less than a single atom over several square microns, creating nearly perfect surfaces for studies of self-assembled monolayers or other applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Homoepitaxy of Crystalline Rubrene Thin Films

The smooth surface of crystalline rubrene films formed through an abrupt heating process provides a valuable platform to study organic homoepitaxy. By varying growth rate and substrate temperature, we are able to manipulate the onset of a transition from layer-by-layer to island growth modes, while the crystalline thin films maintain a remarkably smooth surface (less than 2.3 nm root-mean-square roughness) even with thick (80 nm) adlayers. We also uncover evidence of point and line defect formation in these films, indicating that homoepitaxy under our conditions is not at equilibrium or strain-free. Point defects that are resolved as screw dislocations can be eliminated under closer-to-equilibrium conditions, whereas we are not able to eliminate the formation of line defects within our experimental constraints at adlayer thicknesses above ~25 nm. We are, however, able to eliminate these line defects by growing on a bulk single crystal of rubrene, indicating that the line defects are a result of strain built into the thin film template. We utilize electron backscatter diffraction, which is a first for organics, to investigate the origin of these line defects and find that they preferentially occur parallel to the (002) plane, which is in agreement with expectations based on calculated surface energies of various rubrene crystal facets. By combining the benefits of crystallinity, low surface roughness, and thickness-tunability, this system provides an important study of attributes valuable to high-performance organic electronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Coupled Lattice Polarization and Ferromagnetism in Multiferroic NiTiO 3 Thin Films

Polarization-induced weak ferromagnetism (WFM) was demonstrated a few years back in LiNbO3-type compounds, MTiO3 (M = Fe, Mn, Ni). Although the coexistence of ferroelectric polarization and ferromagnetism has been demonstrated in this rare multiferroic family before, first in bulk FeTiO3, then in thin-film NiTiO3, the coupling of the two order parameters has not been confirmed Here, we report the stabilization of polar, ferromagnetic NiTiO3 by oxide epitaxy on a LiNbO3 substrate utilizing tensile strain and demonstrate the theoretically predicted coupling between its polarization and ferromagnetism by X-ray magnetic circular dichroism under applied fields. The experimentally observed direction of ferroic ordering in the film is supported by simulations using the phase-field approach. Our work validates symmetry-based criteria and first-principles calculations of the coexistence of ferroelectricity and WFM in MTiO3 transition metal titanates crystallizing in the LiNbO3 structure. It also demonstrates the applicability of epitaxial strain as a viable alternative to high-pressure crystal growth to stabilize metastable materials and a valuable tuning parameter to simultaneously control two ferroic order parameters to create a multiferroic. Multiferroic NiTiO3 has potential applications in spintronics where ferroic switching is used, such as new four-stage memories and electromagnetic switches.

36 MATERIALS SCIENCE↗