Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “alignment”

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 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Low-temperature growth of well-aligned ZnO nanorods/nanowires on flexible graphite sheet and their photoluminescence properties

Highlights: ► Well-aligned ZnO nanostructures were grown on flexible graphite sheets at 500–650 °C. ► ZnO nanostructures are formed via self-catalytic vapor–solid process assisted by immiscibility of ZnO with graphite. ► The ZnO nanostructures show intensive green emission. ► The photoluminescence property can be easily tuned by changing growth condition or annealing treatment. -- Abstract: We have grown large-scale well-aligned ZnO nanorods/nanowires on commercial flexible graphite sheet (FGS) at low temperature via chemical vapor deposition method. The products were characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The effects of the growth temperature and oxygen flow rate on the morphology of ZnO nanostructures have been investigated. The growth mechanism of ZnO is found to be a self-catalytic vapor–solid process assisted by the immiscibility of ZnO with graphite. The as-grown ZnO/FGS products show strong green emission and their photoluminescence properties can be tuned by changing growth condition or annealing treatment.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Synthesis of vertically aligned boron nitride nanosheets using CVD method

Highlights: ► The synthesized boron nitride nanosheets (BNNSs) are vertically aligned and very thin. ► No electrical field is applied in the CVD process. ► The thin BNNSs show a low turn-on field of 6.5 V μm{sup −1} and emit strong UV light. -- Abstract: Boron nitride nanosheets (BNNSs) protruding from boron nitride (BN) films were synthesized on silicon substrates by chemical vapor deposition technique from a gas mixture of BCl{sub 3}–NH{sub 3}–H{sub 2}–N{sub 2}. Parts of the as-grown nanosheets were vertically aligned on the BN films. The morphology and structure of the synthesized BNNSs were characterized by scanning electron microscopy, transmission electron microscopy, and Fourier transformation infrared spectroscopy. The chemical composition was studied by energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Cathodoluminescence spectra revealed that the product emitted strong UV light with a broad band ranging from 250 to 400 nm. Field-emission characteristic of the product shows a low turn-on field of 6.5 V μm{sup −1}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Drift Chamber Alignment using Cosmic Rays

The Collider Detector at Fermilab (CDF) is a general-purpose experimental apparatus with an inner tracking detector for measuring charged particles, surrounded by a calorimeter for measurements of electromagnetic and hadronic showers, and a muon detector system. We present a technique for, and results of, a precise relative alignment of the drift chamber wires of the CDF tracker. This alignment has been an important component of the track momentum calibration, which is the basis for the charged-lepton calibration for the measurement of the W boson mass at CDF.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Prolate-to-oblate transition and backbending along the yrast line induced by quasiparticle alignment

The yrast lines in Kr isotopes with N = 42, 44, and 46 are investigated in a beyond mean field framework with both prolate-oblate coexistence and quasiparticle alignment taken into account. Quasiparticle orbitals with high-j and low-Ω on the oblate side are shown to be responsible for the sharp backbending observed in 82Kr, by driving the yrast shape from prolate to oblate. This suggests that quasiparticle alignment may not be neglected in the investigation of the shape evolution along the yrast line.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Impact of globally spin-aligned vector mesons on the search for the chiral magnetic effect in heavy-ion collisions

In high-energy heavy-ion collisions, the chiral magnetic effect (CME) is predicted to arise from the interplay between the chirality imbalance of quarks in the nuclear medium and the intense magnetic field, and will cause a charge separation along the magnetic field direction. While the search for the CME is still ongoing in experiments at Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC), the CME-sensitive observables need to be scrutinized to exclude the non-CME contributions. In this work, we examine the influence of globally spin-aligned ρ mesons on the γ 112 correlator, the R Ψ 2 (ΔS) correlator, and the signed balance functions, via a toy model and a multiphase transport model (AMPT). The global spin alignment of vector mesons could originate from non-CME mechanisms in heavy-ion collisions, and is characterized by the 00-component of the spin density matrix, ρ 00 . Here, we find that the CME observables show similar dependence on ρ 00 , and could receive a positive (negative) contribution from ρ-decay pions, if the ρ 00 of ρ mesons is larger (smaller) than 1/3. Since pions are the most abundant particles in such collisions, the ρ 00 measurements for ρ mesons become crucial to the interpretation of the CME data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Band alignment of front contact layers for high-efficiency CdTe solar cells

Resistive oxide materials play an important role in the front contact of CdTe solar cells. The high-resistance transparent (HRT) or “buffer” layer has been used extensively in CdTe thin-film photovoltaics to enable a reduction in CdS thickness while maintaining near-maximum device voltage and fill factor. SnO 2 - and ZnO-based alloys were tested as HRT layers on a fluorine-doped tin oxide transparent conducting oxide. SnO 2 -based alloy HRT layers were deposited via atmospheric pressure chemical vapor deposition (APCVD). Alloying ZnO with MgO to create MgxZn 1–x O (MZO) via radio-frequency sputter deposition was explored as a way to reduce the electron affinity of ZnO HRT layers. Additionally, to fully understand the behavior of these materials, many devices were fabricated with either no CdS layer, a sublimated CdS layer, or a sputtered, oxygenated CdS layer. MZO layers resulted in high open-circuit voltage and device efficiency even with the complete elimination of the CdS layer. In both HRT systems, controlling electron affinity to optimize front contact band alignment is an important consideration. Band measurements using photoelectron spectroscopy and synchrotron techniques correlate band alignment measurements with efficiency parameters in the design of HRT and CdS layers.

14 SOLAR ENERGY↗
DOE OSTI2022

Energy alignment manipulation at the C 60 /TiO 2 (110) interface using a blanket molecular dipole approach

In this work, modifying the energy alignment between the frontier levels of a chromophore and the band edges of a semiconductor substrate using a “blanket layer” of molecular dipoles is explored. The electronic structure, measured with ultraviolet and x-ray photoemission spectroscopy, of C 60 deposited directly onto the TiO 2 (110) surface is compared with that of C 60 deposited onto the surface covered by a blanket layer of the custom-designed helical peptide Z-(Aib) 6 -Ipa, which has a large dipole moment of 18.6 D oriented along its molecular axis and pointing toward the substrate. The C 60 HOMO level is shifted 600 meV to deeper binding energy in the presence of the blanket layer, in good agreement with what is expected from a simple parallel plate capacitor model. These results demonstrate a simple and versatile strategy for controlling energy level alignment at organic/inorganic interfaces.

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

High-Performance Capacitive Deionization via Manganese Oxide-Coated, Vertically Aligned Carbon Nanotubes

Discovering electrode materials with exceptional capacitance, an indicator of the ability of a material to hold charge, is critical for developing capacitive deionization devices for water desalination. Maganese oxides (MnOx) have shown promise as capacitive electrode materials, but they exhibit a tradeoff where higher loading of the active MnOx comes at a cost of lower conductivity. To address this challenge and achieve high salt adsorption, we fabricated electrodes comprising vertically aligned core-shell nanostructures using atomic layer deposition (ALD) to coat thin films of MnOx onto vertically aligned carbon nanotubes (VACNTs). The inherently hierarchical, anisotropic, three-dimensional macroporous structure of VACNTs and the tunable coating, a hallmark of ALD, enabled co-optimization of the hybrid material’s specific capacitance with respect to mass and geometric area. The specific capacitance was optimized in this study to 215 ± 7 F/g and 1.1 ± 0.1 F/cm 2 in 1 M NaCl electrolyte at 5 mV/s scan rate, respectively. This material exhibited remarkable sodium ion adsorption capacity of 489 ± 25 μmol Na /g material (two-fold higher than pristine VACNTs) at a functioning voltage of 1.2 V, which may ultimately enable expanded desalination applications of capacitive deionization.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Role of Polycyclic Aromatic Alkylammonium Cations in Tuning the Electronic Properties and Band Alignment of Two-Dimensional Hybrid Perovskite Semiconductors

Two-dimensional hybrid organic–inorganic perovskites (HOIPs) have recently drawn intense attention as potential photovoltaic materials. However, n = 1 two-dimensional (2D) HOIPs face the challenge of low conductivity between the inorganic layers, leading to unsatisfactory device performance. Interestingly, 2D HOIPs employing π-conjugated molecules as organic moieties show energy and charge transfers between organic and inorganic layers, indicating potentially efficient carrier transport for photovoltaic applications. Nevertheless, the development of 2D HOIP-based solar cells especially utilizing polycyclic aromatic alkylammonium as cations is in its infancy. Herein, we investigated the electronic structure and band alignment of a series of n = 1 2D Ruddlesden–Popper (RP) phase HOIPs containing different polycyclic aromatic groups and alkyl chains, based on density functional theory calculations. We find that the polycyclic aromatic group plays an important role in controlling the functionality of 2D HOIPs by directly modifying band-edge states, and the band alignment at the organic–inorganic interface can be designed to promote either exciton trapping or dissociation for light-emitting or photovoltaic applications, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Electronic Structure and Band Alignment at the NiO and SrTiO 3 p–n Heterojunctions

Understanding the energetics at the interface including the alignment of valence and conduction bands, built-in potentials, and ionic and electronic reconstructions, is an important challenge in designing oxide interfaces that have controllable multi-functionalities for novel (opto-)electronic devices. In this work, we report detailed investigations on the hetero-interface of wide bandgap p-type NiO and n-type SrTiO3 (STO). We show that despite a large lattice mismatch (~7%) and dissimilar crystal structure, high-quality NiO and Li doped NiO (LNO) thin films can be epitaxially grown on STO(001) substrates through a domain matching epitaxy (DME) mechanism. X-ray photoelectron spectroscopy (XPS) studies indicate that NiO/STO heterojunctions form a type II “staggered” band alignment. In addition, a large built-in potential of up to 0.97 eV was observed at the interface of LNO and Nb doped STO (NbSTO). The LNO/NbSTO p-n heterojunctions exhibit a large rectification ratio of 2×103, but also a large ideality factor of 4.3. The NiO/STO p-n heterojunctions have important implication for applications in photocatalysis and photodetector as the interface provides favourable energetics for facile separation and transport of photogenerated electrons and holes.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Orientational Distribution Function of Aligned Elongated Molecules and Particulates Determined from Their Scattering Signature

In this paper, we present a strategy for quantitatively evaluating the field-induced alignment of nonspherical particles using small-angle scattering techniques. The orientational distribution function (ODF) is determined from the anisotropic scattering intensity via the scheme of real spherical harmonic expansion. Our developed approach is simple and analytical and does not require a presumptive hypothesis of the ODF as an input in data analysis. A model study of aligned rigid rods demonstrates the validity of this proposed approach to facilitate the quantitative structural characterization of materials with preferred orientational states.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Aligning the Induced Anisotropy of Isotropic Nanoparticles with Liquid Crystals

Thermotropic liquid crystals (LCs) present opportunities for synergistic interactions with ligand-functionalized nanoparticles (NPs). Understanding the dynamics and structures of ligand-coated NPs in an anisotropic LC environment allows for better design and control of versatile LC-NP hybrid materials. Here, simulations and experiments yield direct evidence that cyanobiphenyl LCs induce anisotropy in the biphenylalkyl ligand shells of spherical NPs. The ellipsoidal NP aligns with the LC director. Magnetic fields can dictate the directional ordering of mesogens and consequently allow control of the orientation of the nonmagnetic NPs. Further, controlling the alignment and deformation advances the design and engineering of these hybrid nanomaterials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Highly Conjugated Porphyrin Arrays Enable Optical Resolution of Ferromagnetic and Antiferromagnetic Aligned States of the Triplet Exciton and an Incorporated Stable Radical

Well-defined photogenerated molecular spin systems have potential utility in spintronics and quantum information science (QIS). Because molecular magnetic, optical, and electronic properties can be controlled by design, diverse spin systems can be prepared at modest temperatures. Photogenerated molecular spin systems often involve states prepared from the interaction of excitons and charges. Resolving the nature of electron spin alignment in photogenerated spin states described by the coupling of a triplet exciton and a stable radical commonly relies on EPR spectroscopy. Here, we describe ethyne-bridged (porphinato)metal ( PM n ) oligomers that incorporate a macrocycle-bound Cu(II) radical center. Upon photoexcitation of such PM n arrays, a singdoublet ( 2 S 1 ) state is formed; ultrafast internal conversion (IC) then produces a tripdoublet ( 2 T 1 ) state, which undergoes intersystem crossing (ISC) to produce a tripquartet ( 4 T 1 ) state, before relaxation to the ground state ( 2 S 0 ). These highly conjugated Cu(II) radical-containing PMn arrays enable direct observation of copper porphyrin 2 T 1 → 4 T 1 ISC dynamics from the biexponential decay of the near-infrared (NIR) 2,4 T 1 → 2,4 T n transient absorption manifold. Multireference n-electron valence perturbation theory (NEVPT2) computations illuminate how PM n electronic structure controls the relaxation dynamics of these long-lived (>10 ns) electronically excited multiplet states. These studies show that highly conjugated and polarizable porphyrin arrays incorporating stable spin centers provide rare π-delocalized systems where the ferromagnetic and antiferromagnetic alignment between a triplet exciton and a stable radical are both spectrally resolved and addressable using transient optical spectroscopy at wavelengths exceeding 1 μm, providing new opportunities to QIS.

14 SOLAR ENERGY↗
DOE OSTI2026

A Vibrational Probe of Electrical Doping in N2200 and Fermi-Level Alignment at Polymer Cathode/Metal Cocatalyst/Electrolyte Junctions

Hybrid (photo)­cathodes consisting of conjugated polymer and hydrogen evolution reaction (HER) cocatalysts are an emerging platform for low-cost solar fuel generation. Poly­{[N,N′-bis­(2-octyldodecyl)-naphthalene-1,4,5,8-bis­(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)}, known as P­(NDI2OD-T2) or N2200, is a promising electron accepting material for bulk heterojunction photocathodes. Unlike inorganic (photo)­electrodes, much less is known about the energetic alignment of conjugated polymer electrode/metal/electrolyte junctions. Here, in this work, we investigate the electrical doping behavior in an N2200 cathode and its Fermi-level alignment with gold nanoparticles, which is used here as a model for the hydrogen evolution metal cocatalyst. Through UV/visible, Raman, and attenuated total-reflectance infrared spectroelectrochemistry, we observe the impact of electrical doping on the vibrational frequencies of neutral, anion, and dianion species in N2200, which suggests that electron density changes within the corresponding naphthalene-diimide (NDI) units. Upon one-electron reduction, the $C=O$ stretching frequency of the NDI anion unit (polaron) shows a red shift by ∼ 68 cm –1 . Additionally, the $C=O$ stretching frequency of neutral units in the doped N2200 shows a minor red shift of ∼ 5 cm –1 , suggesting charge transfer from neighboring polaron units. Surface-enhanced Raman spectroscopy measurements of a gold nanoparticle-functionalized N2200 electrode revealed that the Au Fermi level only shifts with that of N2200 upon polaron formation; thus, the formal potential of polymer polaron formation determines the behavior of the catalyst Fermi level, which we posit will modulate reaction capability. This mechanistic study provides a new approach for understanding the nanometer-scale energetics at the conjugated polymer/cocatalyst junction and provides critical insights for the future design of HER (photo)­cathodes.

charge transfer↗
DOE OSTI2018

Intersubband plasmons in the quantum limit in gated and aligned carbon nanotubes

Confined electrons collectively oscillate in response to light, resulting in a plasmon resonance whose frequency is determined by the electron density and the size and shape of the confinement structure. Plasmons in metallic particles typically occur in the classical regime where the characteristic quantum level spacing is negligibly small compared to the plasma frequency. In doped semiconductor quantum wells, quantum plasmon excitations can be observed, where the quantization energy exceeds the plasma frequency. Such intersubband plasmons occur in the mid- and far-infrared ranges and exhibit a variety of dynamic manybody effects. Here, we report the observation of intersubband plasmons in carbon nanotubes, where both the quantization and plasma frequencies are larger than those of typical quantum wells by three orders of magnitude. As a result, we observed a pronounced absorption peak in the near-infrared. Specifically, we observed the near-infrared plasmon peak in gated films of aligned single-wall carbon nanotubes only for probe light polarized perpendicular to the nanotube axis and only when carriers are present either in the conduction or valence band. Both the intensity and frequency of the peak were found to increase with the carrier density, consistent with the plasmonic nature of the resonance. With this being said, our observation of gate-controlled quantum plasmons in aligned carbon nanotubes will not only pave the way for the development of carbon-based near-infrared optoelectronic devices but also allow us to study the collective dynamic response of interacting electrons in one dimension.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Femtosecond X-ray coherent diffraction of aligned amyloid fibrils on low background graphene

Here we present a new approach to diffraction imaging of amyloid fibrils, combining a free-standing graphene support and single nanofocused X-ray pulses of femtosecond duration from an X-ray free-electron laser. Due to the very low background scattering from the graphene support and mutual alignment of filaments, diffraction from tobacco mosaic virus (TMV) filaments and amyloid protofibrils is obtained to 2.7 Å and 2.4 Å resolution in single diffraction patterns, respectively. Some TMV diffraction patterns exhibit asymmetry that indicates the presence of a limited number of axial rotations in the XFEL focus. Signal-to-noise levels from individual diffraction patterns are enhanced using computational alignment and merging, giving patterns that are superior to those obtainable from synchrotron radiation sources. In conclusion, we anticipate that our approach will be a starting point for further investigations into unsolved structures of filaments and other weakly scattering objects.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

Retrieving transient conformational molecular structure information from inner-shell photoionization of laser-aligned molecules

We discuss a scheme to retrieve transient conformational molecular structure information using photoelectron angular distributions (PADs) that have averaged over partial alignments of isolated molecules. The photoelectron is pulled out from a localized inner-shell molecular orbital by an X-ray photon. We show that a transient change in the atomic positions from their equilibrium will lead to a sensitive change in the alignment-averaged PADs, which can be measured and used to retrieve the former. Exploiting the experimental convenience of changing the photon polarization direction, we show that it is advantageous to use PADs obtained from multiple photon polarization directions. Lastly, a simple single-scattering model is proposed and benchmarked to describe the photoionization process and to do the retrieval using a multiple-parameter fitting method.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

In situ synthesis and macroscale alignment of CsPbBr 3 perovskite nanorods in a polymer matrix

Here, we report an in situ catalyst-free strategy to synthesize inorganic CsPbBr 3 perovskite nanorods in a polymer matrix (NRs-PM) with good dimensional control, outstanding optical properties and ultrahigh environmental stability. Polarization photoluminescence (PL) imaging with high spatial resolution was carried out for the first time on single nanorod (NR) and shows a relatively high local polarization ratio (~0.4) consistent with theoretical predictions based on a dielectric contrast model. We further demonstrate that macroscale alignment of the CsPbBr 3 nanorods can be achieved through mechanically stretching the NRs-PM films at elevated temperature, without deteriorating the optical quality of the NRs. In conclusion, a polarization ratio of 0.23 is observed for these aligned NRs-PM films, suggesting their potential as polarized down-converters to increase the light efficiency in liquid crystal display (LCD) backlights.

36 MATERIALS SCIENCE↗