Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “ORIENTATION”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Orientation transitions during the growth of imine covalent organic framework thin films

Oriented growth of thin films of covalent organic frameworks (COFs) has attracted significant interest as the anisotropically aligned channels provide ideal nanoscopic domains that can facilitate mass transport or charge percolation. Despite some experimental progress in achieving oriented COF thin films, little is known about the kinetics and thermodynamics associated with the orientation or control over the solution-based growth process. We performed a systematic study of the thin film growth of an imine-based COF as a function of concentration and growth time. Grazing incidence wide-angle X-ray scattering (GIWAXS) was used to reveal the orientation and evolution of crystallization within the thin films at sequential growth stages. Here, an unusual re-entrant transition from an oriented to disoriented to reoriented state was discovered, which correlates with the kinetics associated with independent surface- and solution-based nucleation and growth processes, as well as reorganization of disoriented COF crystallites.

36 MATERIALS SCIENCE↗
DOE OSTI2014

The influence of field-free orientation on the predissociation dynamics of the NaI molecule

The orientation and predissociation dynamics of the NaI molecule are studied by using a time-dependent wavepacket method. The NaI molecule is first pre-oriented by a single-cycle pulse (SCP) in terahertz (THz) region and then predissociated by a femtosecond pump pulse. The influence of the molecular field-free orientation on the predissociation dynamics is studied in detail. We calculate the radial and angular distributions, the molecular orientation degrees, and the time-dependent populations for both the ground and excited electronic states. It is found that the pre-orientation affects the angular distributions significantly, and that it has weak influence on the radial distributions. By varying the delay time between the THz SCP and the pump pulse, the angular distribution of the fragments from the predissociation can be manipulated.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2014

Determination of crystallographic orientation of lead-free piezoelectric (K,Na)NbO{sub 3} epitaxial thin films grown on SrTiO{sub 3} (100) surfaces

Crystallographic structure of sol-gel-processed lead-free (K,Na)NbO{sub 3} (KNN) epitaxial films on [100]-cut SrTiO{sub 3} single-crystalline substrates was investigated for a deeper understanding of its piezoelectric response. Lattice parameter measurement by high-resolution X-ray diffraction and transmission electron microscopy revealed that the orthorhombic KNN films on SrTiO{sub 3} (100) surfaces are [010] oriented (b-axis-oriented) rather than commonly identified c-axis orientation. Based on the crystallographic orientation and corresponding ferroelectric domain structure investigated by piezoresponse force microscopy, the superior piezoelectric property along b-axis of epitaxial KNN films than other orientations can be explained.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Theory of third-order spectroscopic methods to extract detailed molecular orientational dynamics for planar surfaces and other uniaxial systems

Functionalized organic monolayers deposited on planar two-dimensional surfaces are important systems for studying ultrafast orientational motions and structures of interfacial molecules. Several studies have successfully observed the orientational relaxation of functionalized monolayers by fluorescence depolarization experiments and recently by polarization-resolved heterodyne detected vibrational transient grating (HDTG) experiments. In this article we provide a model-independent theory to extract orientational correlation functions unique to interfacial molecules and other uniaxial systems based on polarization-resolved resonant third-order spectroscopies, such as pump-probe spectroscopy, HDTG spectroscopy, and fluorescence depolarization experiment. It will be shown (in the small beam-crossing angle limit) that five measurements are necessary to completely characterize the monolayer's motions: I{sub ∥}(t) and I{sub ⊥}(t) with the incident beams normal to the surface, I{sub ∥}(t) and I{sub ⊥}(t) with a non-zero incident angle, and a time averaged linear dichroism measurement. Once these measurements are performed, two orientational correlation functions corresponding to in-plane and out-of-plane motions are obtained. The procedure is applicable not only for monolayers on flat surfaces, but any samples with uniaxial symmetry such as uniaxial liquid crystals and aligned planar bilayers. The theory is valid regardless of the nature of the actual molecular motions on interface. We then apply the general results to wobbling-in-a-cone model, in which molecular motions are restricted to a limited range of angles. Within the context of the model, the cone angle, the tilt of the cone relative to the surface normal, and the orientational diffusion constant can be determined. The results are extended to describe analysis of experiments where the beams are not crossing in the small angle limit.

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

Direct observation of binding stress-induced crystalline orientation change in piezoelectric plate sensors

We have examined the mechanism of the detection resonance frequency shift, Δf/f, of a 1370 μm long and 537 μm wide [Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}]{sub 0.65}[PbTiO{sub 3}]{sub 0.35} (PMN-PT) piezoelectric plate sensor (PEPS) made of a 8-μm thick PMN-PT freestanding film. The Δf/f of the PEPS was monitored in a three-step binding model detections of (1) binding of maleimide-activated biotin to the sulfhydryl on the PEPS surface followed by (2) binding of streptavidin to the bound biotin and (3) subsequent binding of biotinylated probe deoxyribonucleic acid to the bound streptavidin. We used a PMN-PT surrogate made of the same 8-μm thick PMN-PT freestanding film that the PEPS was made of but was about 1 cm in length and width to carry out crystalline orientation study using X-ray diffraction (XRD) scan around the (002)/(200) peaks after each of the binding steps. The result of the XRD studies indicated that each binding step caused the crystalline orientation of the PMN-PT thin layer to switch from the vertical (002) orientation to the horizontal (200) orientation, and most of the PEPS detection Δf/f was due to the change in the lateral Young's modulus of the PMN-PT thin layer as a result of the crystalline orientation change.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Synthesis mechanism and improved (100) oriented NaNbO{sub 3} templates by ultrasonication

The plate-like NaNbO{sub 3} (NN) templates with (100) preferential orientation was synthesized from bismuth layer structured ferroelectric Bi{sub 2.5}Na{sub 3.5}Nb{sub 5}O{sub 18} (BNN) precursor by topochemical microcrystal conversion (TMC) method. The large platelets of BNN were first obtained by molten salt synthesis at the 1125 °C with a salt-to oxide weight ratio 1.5: 1. The anisotropic NN templates were derived from BNN at the 975 °C with BNN/ Na{sub 2}CO{sub 3} molar ratio of 1:1.5. The NaNbO{sub 3} templates have an average length of ~ 10-14 µm. The NN templates retains their elemental constitutes of Na, Nb and O in stoichiometric proportion. The effect of ultrasonication on the orientation factor (F{sub h00}) of NN templates was understood by X-ray diffraction (XRD) and scanning electron microscopy (SEM) results. The degree of (100) orientation of as synthesized NN templates (~57%) was found to be increased (~89%) after ultrasonication. Moreover, the microstructure i.e. alignment / shape of as synthesized NN templates was changed from rectangular (110) orientation to square (100) orientation geometry after ultrasonication. Hence, ultrasonication is a cost effective approach to preparing the textured piezoelectric ceramics by the template grain growth technique using tape casting.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Orbital orientation mapping of V 2 O 5 thin films

We report the effects of growth methods on the orbital orientation in vanadium pentoxide (V 2 O 5 ) thin films, an important factor to consider when selecting growth techniques for highly selective catalysts and devices. Thermal evaporation and sol-gel methods were used to synthesize the V 2 O 5 films. The surface morphology, roughness, and orientation of the films were characterized by atomic force microscopy and x-ray diffraction. Surface electronic properties and oxidation states were assessed by x-ray photoemission spectroscopy. Polarized x-ray absorption spectroscopy demonstrated that the thermally evaporated film [which was in the (001) orientation] exhibited greater anisotropy than the (100) oriented sol-gel film. The observed increase in anisotropy agrees well with computational findings which revealed that more vanadyl bonds are present at the surface of the thermally evaporated film than at the surface of the sol-gel film. The same computational study also found that the orientation of these bonds is more parallel to the film surface in the thermally evaporated film than in the sol-gel film. Finally, the data suggest that the method of growth may be used as a controlled variable to select key film characteristics for potential applications.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Grain orientation effects on dynamic strength of FCC multicrystals at low shock pressures: a hydrodynamic instability study

Variability in local dynamic plasticity due to material anisotropy in polycrystalline metals is likely to be important on damage nucleation and growth at low pressures. Hydrodynamic instabilities could be used to study these plasticity effects by correlating measured changes in perturbation amplitudes at free surfaces to local plastic behaviour and grain orientation, but amplitude changes are typically too small to be measured reliably at low pressures using conventional diagnostics. Correlations between strength at low shock pressures and grain orientation were studied in copper (grain size ≈ 800 μm) using the Richtmyer–Meshkov instability with a square-wave surface perturbation (wavelength = 150 μm, amplitude = 5 μm), shocked at 2.7 GPa using symmetric plate impacts. A Plexiglas window was pressed against the peaks of the perturbation, keeping valleys as free surfaces. This produced perturbation amplitude changes much larger than those predicted without the window. Amplitude reductions from 64 to 88% were measured in recovered samples and grains oriented close to $\langle$0 0 1$\rangle$ parallel to the shock had the largest final amplitude, whereas grains with shocks directions close to $\langle$1 0 1$\rangle$ had the lowest. Finite element simulations were performed with elastic-perfectly plastic models to estimate yield strengths leading lead to those final amplitudes. Anisotropic elasticity and these yield strengths were used to calculate the resolved shear stresses at yielding for the two orientations. In conclusion, results are compared with reports on orientation dependence of dynamic yielding in Cu single crystals and the higher values obtained suggest that strength estimations via hydrodynamic instabilities are sensitive to strain hardening and strain rate effects.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Orientation-dependent stabilization of MgCr 2 O 4 spinel thin films

AB 2 O 4 normal spinels with a magnetic B site can host a variety of magnetic and orbital frustrations leading to spin-liquid phases and field-induced phase transitions. Here, we report the epitaxial growth of (111)-oriented MgCr 2 O 4 thin films. By characterizing the structural and electronic properties of films grown along the (001) and (111) directions, the influence of growth orientation has been studied. Despite distinctly different growth modes observed during deposition, the comprehensive characterization reveals no measurable disorder in the cation distribution nor multivalency issue for Cr ions in either orientation. Contrary to a naive expectation, the (111) stabilized films exhibit a smoother surface and a higher degree of crystallinity than (001)-oriented films. The preference in growth orientation is explained within the framework of heteroepitaxial stabilization in connection to a significantly lower (111) surface energy. Furthermore, these findings open broad opportunities in the fabrication of two-dimensional kagome-triangular heterostructures with emergent magnetic behavior inaccessible in bulk crystals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Hamiltonians and order parameters for crystals of orientable molecules

Many modern functional materials exhibit microscopic degrees of freedom that are difficult to describe mathematically or do not conform to conventional models in solid state physics. In this paper, we consider crystals containing orientable molecular species, which encompass the class of promising photovoltaic materials CH 3 NH 3 PbX 3 . Abstracting these materials as crystals of orientable rigid rotors, we develop an effective Hamiltonian that expresses the crystal potential energy in terms of collective orientations of interacting rigid rotors. The approach is motivated by the cluster expansion framework from alloy theory and is appropriate for describing both chiral and achiral molecules. This framework utilizes a quaternion parametrization of molecular orientation and makes full use of the symmetry both of the rotors and of the crystal in order to constrain the functional form of the final Hamiltonian expression. The resulting Hamiltonian is compact, systematically improvable, and is suitable for Monte Carlo or molecular dynamics simulation. We apply this formalism to CH 3 NH 3 PbI 3 and report symmetry-adapted basis functions that can be used to construct order parameters or Hamiltonians that describe orientational correlation of methylammonium ions in hybrid organic-inorganic halide perovskite materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Enhanced interfacial ferromagnetism and exchange bias in (111)-oriented LaNiO 3 / CaMnO 3 superlattices

Emergent properties of complex oxide interfaces are based on interface reconstruction that is driven by mismatch of electronic bands, valence states, interaction lengths, and even crystal symmetry of the interface. In particular, emergent ferromagnetism at the interface of two materials that do not exhibit ferro- or ferrimagnetism in the bulk has been stabilized as a result of competing exchange interactions. When LaNiO 3 and CaMnO 3 , which are a paramagnetic metal and antiferromagnetic insulator in the bulk, respectively, are brought together, ferromagnetism emerges at the interface. Here we show that in (111)-oriented LaNiO 3 / CaMnO 3 (LNO/CMO) superlattices, Ni 2+ -Mn 4+ superexchange interactions due to polar mismatch at the LNO/CMO interfaces are responsible for the emergent ferromagnetism. Compared to (001)-oriented LNO/CMO superlattices, (111)-oriented LNO/CMO superlattices exhibit enhanced interfacial ferromagnetism with a T C > 200 K, greater than the bulk antiferromagnetic transition temperature of CaMnO 3 and a saturated magnetic moment enhanced by up to a factor of 3. Furthermore, we observe exchange bias in (111)-oriented superlattices. The strong exchange interactions along the (111) interface, manifest in the enhanced T c and exchange bias, make this class of CMO-based materials with (111)-oriented interfaces good candidates for low-dimensional spin-polarized materials in spintronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Experimental study of multiple-orientation muon tomography with image optimization in sparse data environments

Due to the high penetrating power of cosmic-ray muons, they can be used to probe very thick and dense objects. As muons are charged particles, they can be tracked by ionization detectors, determining the position and direction of the muons. With detectors on either side of an object to measure particle direction change, scattering information within the object can be found. This can be used to produce a scattering-intensity image within the object related to density and atomic number. Such imaging is typically performed with a single detector-object orientation, taking advantage of the more intense downward flux of muons, producing planar imaging with some depth-of-field information in the third dimension. Several simulation studies were published with multiorientation tomography, which can form a three-dimensional representation faster than a single-orientation view. In this study, experimental muon-scatter-based tomography was performed using a concrete filled steel drum with several different metal wedges inside, with the drum between detector planes. Data were collected from different detector-object orientations by rotating the steel drum. The data collected from each orientation were combined using two different tomographic methods. A traditional inverse Radon transform approach used for computed tomography and a combination of multiple depth-of-field reconstructions were applied to the data. As cosmic-ray muon flux imaging is rate limited, the imaging techniques were compared for sparse data. Using the combined depth-of-field reconstruction technique, fewer detector-object orientations were needed to reconstruct images that could be used to differentiate the metal wedges.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

End-to-end orientation estimation from 2D cryo-EM1images

Cryo-electron microscopy (cryo-EM) is a Nobel Prize-winning technique for deter-mining high-resolution 3D structures of biological macromolecules. A 3D structure is reconstructed from hundreds of thousands of noisy 2D projection images. However, existing 3D reconstruction methods are still time-consuming, and one of the major computational bottlenecks is to recover the unknown orientation of the particle in16each 2D image. The dominant methods typically exploit expensive global search on each image to estimate the missing orientations. Here, a novel end-to-end supervised learning method is introduced to directly recover the missing orientations from 2D cryo-EM images. A neural network is used to approximate the mapping from images to orientations. Furthermore, a robust loss function is proposed for optimizing the parameters of the network, which can handle both asymmetric and symmetric 3D structures. Experiments on synthetic datasets with various symmetry types confirm that the neural network is capable of recovering orientations from 2D cryo-EM images, and the results on one real cryo-EM dataset further demonstrate its potential in more challenging imaging conditions.

3D reconstruction↗
DOE OSTI2022

(110)-Oriented GaAs Devices and Spalling as a Platform for Low-Cost III-V Photovoltaics

Here, we demonstrate the growth of GaAs solar cells by hydride vapor phase epitaxy (HVPE) on epi-ready and previously spalled (110) GaAs wafers as an advance towards a potentially low-cost (110)-based device platform. Controlled spalling offers a fracture-based path to substrate cost amortization, enabling device exfoliation and substrate reuse, but the faceted surface generated during the spalling of (100)-oriented GaAs presents hurdles to direct regrowth of subsequent devices. Spalling of (110) substrates instead eliminates faceting by aligning the substrate surface with the predominant crystal cleavage plane. III-V epitaxy of solar cells is significantly less developed on (110)-oriented substrates, however. Here, we develop (110)-based GaAs solar cells grown by HVPE on epi-ready substrates, demonstrating equal performance to devices grown on the more standard (100) orientation. We also characterize the surface of spalled, (110)-oriented substrates, revealing flat terraces separated by steps with sub-micron-scale height on average. Finally, we present an initial device grown on a previously spalled surface without additional surface re-preparation with nearly 16% efficiency under a simulated AM1.5G spectrum. Together, these results provide preliminary evidence of a potentially low-cost path to enable terrestrial III-V photovoltaics via the (110) substrate orientation.

14 SOLAR ENERGY↗
DOE OSTI2016

SU-G-IeP1-08: MR Geometric Distortion Dependency On Imaging Sequence, Acquisition Orientation and Receiver Bandwidth of a Dedicated 1.5T MR-Simulator

Purpose: To investigate the 3D geometric distortion of four potential MR sequences for radiotheraptic applications, and its dependency on sequence-type, acquisition-orientation and receiver-bandwidth from a dedicated 1.5T 700mm-wide bore MR-simulator (Magnetom-Aera, Sienmens Healthcare, Erlangen, Germany), using a large customized geometric accuracy phantom. Methods: This work studied 3D gradient-echo (VIBE) and spin-echo (SPACE) sequences for anatomical imaging; a specific ultra-short-TE sequence (PETRA) potentially for bone imaging and MR-based dosimetry; and a motion-insensitive sequence (BLADE) for dynamic applications like 4D-MRI. Integrated geometric-correction was employed, three orthogonal acquisition-orientations and up to three receiver-bandwidths were used, yielding 27 acquisitions for testing (Table 1a).A customized geometric accuracy phantom (polyurethane, MR/CT invisible, W×L×H:55×55×32.5cm3) was constructed and filled with 3892 spherical markers (6mm diameter, MR/CT visible) arranged on a 25mm-interval 3D isotropic-grid (Fig.1). The marker positions in MR images were quantitatively calculated and compared against those in the CT-reference using customized MatLab scripts. Results: The average distortion within various diameter-of-spherical-volumes (DSVs) and the usable DSVs under various distortion limits were measured (Tables 1b-c). It was observed that distortions fluctuated when sequence-type, acquisition-orientation or receiver-bandwidth changed (e.g. within 300mm-DSV, the lowest/highest average distortions of VIBE were 0.40mm/0.59mm, a 47.5% difference). According to AAPM-TG66 (<1mm distortion, left-most column of Table 1c), PETRA (Largest-DSV:253.9mm) has the potential on brain treatment, while BLADE (Largest-DSV:207.2mm) may need improvement for thoracic/abdominal applications. The results of VIBE (Largest-DSVs:294.3mm, the best among tested acquisitions) and SPACE (Largest-DSVs:267.7mm) suggests their potentials on head and neck applications. These Largest-DSVs were attained on different acquisition-orientations and receiver-bandwidths. Conclusion: Geometric distortion was shown to be dependent on sequence-type, acquisition-orientation and receiver-bandwidth. In the experiment, no configuration in any one of these factors could consistently reduce distortion while the others were varying. The distortion analysis result is a valuable guideline for sequence selection and optimization for MR-aided radiotherapy applications.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Oriented chiral water wires in artificial transmembrane channels

Aquaporins (AQPs) feature highly selective water transport through cell membranes, where the dipolar orientation of structured water wires spanning the AQP pore is of considerable importance for the selective translocation of water over ions. We recently discovered that water permeability through artificial water channels formed by stacked imidazole I-quartet superstructures increases when the channel water molecules are highly organized. Correlating water structure with molecular transport is essential for understanding the underlying mechanisms of (fast) water translocation and channel selectivity. Chirality adds another factor enabling unique dipolar oriented water structures. We show that water molecules exhibit a dipolar oriented wire structure within chiral I-quartet water channels both in the solid state and embedded in supported lipid bilayer membranes (SLBs). X-ray single-crystal structures show that crystallographic water wires exhibit dipolar orientation, which is unique for chiral I-quartets. The integration of I-quartets into SLBs was monitored with a quartz crystal microbalance with dissipation, quantizing the amount of channel water molecules. Nonlinear sum-frequency generation vibrational spectroscopy demonstrates the first experimental observation of dipolar oriented water structures within artificial water channels inserted in bilayer membranes. Confirmation of the ordered confined water is obtained via molecular simulations, which provide quantitative measures of hydrogen bond strength, connectivity, and the stability of their dipolar alignment in a membrane environment. Together, uncovering the interplay between the dipolar aligned water structure and water transport through the self-assembled I-quartets is critical to understanding the behavior of natural membrane channels and will accelerate the systematic discovery for developing artificial water channels for water desalting.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Method to measure orientation of discontinuous fiber embedded in the polymer matrix from computerized tomography scan data

Usage of discontinuous glass fibers in injection and compression molded resin components is rapidly increasing to improve their mechanical properties. Since added fiber contributes to more strength along the fiber direction compared to transverse direction, the mechanical properties of such components strongly depend on the fiber orientation. Thus it is important to estimate the fiber orientation distribution in such materials. Here, we are presenting recently developed method to estimate fiber orientation from 3D image of fibers generated using micro CT scan. Typically the 3D images from CT scan are very large and it becomes difficult to separate each fiber and extract end point information. In this paper a novel method to address this challenge is presented. The micro-CT images were broken into finite volume, reducing data size, and then each fiber was reduced to its own center line, further reducing the data size, using Mimics Innovation Suite (Materialise NV). These 3D centerlines were then used to quantify the 2nd order orientation tensor. Our results from the proposed method are compared with the measurements using well established industry standard approach called method of ellipses for validation. The key challenges in estimating the fiber orientation are identified and future improvements are proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Surface orientation ambiguity for single molecules at dielectric interfaces

Fluorescent molecules emit light in a dipole radiation pattern that can be used to infer their orientation through defocused fluorescence microscopy. Proper measurement of the orientation requires mathematical modeling of the radiation pattern expected for a dipole in the geometry of interest and subsequent comparison against experimental data. We point out an ambiguity in common calculations of these patterns that appears to compromise orientation measurements for molecules that are especially near dielectric surfaces. This results in a rotation of the measured emission dipole toward the surface for near-interface molecules, which can be mistaken for a preferentially horizontal orientation among the emitters. The proper treatment for on-surface emitters requires consideration of finite-sized current elements between two dielectric media, and we show that the theoretical ambiguity can be lifted via finite-element modeling. A prescription is provided for correcting measured orientations at arbitrary interfaces.

Dey, E. [University of Texas, Arlington, TX (Unite↗