Search NASA⌕ Search

SEARCH · Search NASA

Results for “Band 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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

A Ringed Pole-on Outflow from DO Tauri Revealed by ALMA

We present new Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 observations including the CO(2−1) line and 1.3 mm continuum emission from the surroundings of the young stellar object DO Tauri. The ALMA CO molecular data show three different series of rings at different radial velocities. These rings have radii around 220 and 800 au. We make individual fits to the rings and note that their centers are aligned with DO Tauri and its optical high-velocity jet. In addition, we notice that the velocity of these structures increases with the separation from the young star. We discuss the data under the hypothesis that the rings represent velocity cuts through three outflowing shells that are possibly driven by a wide-angle wind, dragging the environment material along a direction close to the line of sight (i = 19°). We estimate the dynamical ages, the mass, the momentum, and the energy of each individual outflow shell and those of the whole outflow. The results are in agreement with those found in outflows from Class II sources. We make a rough estimate for the size of the jet/wind launching region, which needs to be of ≲15 au. We report the physical characteristics of DO Tauri’s disk continuum emission (almost face-on and with a projected major axis in the north–south direction) and its velocity gradient orientation (north–south), indicative of disk rotation for a 1–2 M {sub ⊙} central star. Finally, we show a Hubble Space Telescope [S ii] image of the optical jet and report a measurement of its orientation in the plane of the sky.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Enhanced charge carrier extraction and transport with interface modification for efficient tin-based perovskite solar cells

Interface modification improves charge carrier extraction in tin-based perovskite solar cells. Tin-based perovskites have become the most promising non-lead perovskites due to their ideal band gap and low toxicity. Although the open circuit voltage of tin-based perovskite solar cells (TPSCs) continues to approach the theoretical value, the short-circuit current is still far from the theoretical value. Here, we describe an interface modification method by regulating the property of hole transport layer, PEDOT:PSS, which improves the surface molecular morphology and the energy level alignment of PEDOT:PSS/perovskite interface. Advanced GIWAXS and IR s-SNOM characterization are conducted to achieve multi-dimensional characterization of nanoscale surface morphology and chemical distribution of PEDOT:PSS. With the multi-attribute optimization, charge carrier extraction and non-radiative recombination are also improved. The resultant TPSCs exhibit a higher power conversion efficiency of 13.32% in compared with the control device of 10.50%, accompanied with an increase in the short-circuit current from 18.10 to 20.50 mA cm −2 and FF from 68.23% to 76.43%. This work demonstrates a reliable strategy for improving charge carrier extraction and device performance for lead-free TPSCs.

Zhao, Zhenzhu↗
DOE OSTI2021

Tunable plasmon-enhanced second-order optical nonlinearity in transition metal dichalcogenide nanotriangles

The development of nanomaterials with a large nonlinear susceptibility is essential for nonlinear nanophotonics. Here we show that transition metal dichalcogenide (TMD) nanotriangles have a large effective second-order susceptibility [χ (2) ] at midinfrared to near-infrared frequencies owing to their broken centrosymmetry. χ (2) is calculated within the density-matrix formalism that accounts for dissipation and screening. χ (2) peaks in the vicinity of both two-photon resonances (specified by the geometry) and plasmon resonances (tunable via the carrier density). Aligning the resonances yields the values of χ (2) as high as 10 –6 m/V. These findings underscore the potential of TMD nanotriangles for nonlinear nanophotonics, particularly second-harmonic generation.

0-dimensional systems↗
DOE OSTI2020

A High Angular Resolution Survey of Massive Stars in Cygnus OB2: JHK Adaptive Optics Results from the Gemini Near-Infrared Imager

We present results of a high angular resolution survey of massive OB stars in the Cygnus OB2 association that we conducted with the Near-Infrared Imager camera and ALTAIR adaptive optics system of the Gemini North telescope. We observed 74 O- and early-B-type stars in Cyg OB2 in the JHK infrared bands in order to detect binary and multiple companions. The observations are sensitive to equal-brightness pairs at separations as small as [[Formula]], and progressively fainter companions are detectable out to △K=9 mag at a separation of 2″. This faint contrast limit due to read noise continues out to 10″ near the edge of the detector. We assigned a simple probability of chance alignment to each companion based upon its separation and magnitude difference from the central target star and upon areal star counts for the general star field of Cyg OB2. Companion stars with a field membership probability of less than 1% are assumed to be physical companions. This assessment indicates that 47% of the targets have at least one resolved companion that is probably gravitationally bound. Including known spectroscopic binaries, our sample includes 27 binary, 12 triple, and 9 systems with 4 or more components. These results confirm studies of high-mass stars in other environments that find that massive stars are born with a high-multiplicity fraction. The results are important for the placement of the stars in the Hertzsprung–Russell diagram, the interpretation of their spectroscopic analyses, and for future mass determinations through measurement of orbital motion.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

New insights into backbending in the symmetry-adapted shell-model framework

Here we provide insights into the backbending phenomenon within the symmetry-adapted framework which naturally describes the intrinsic deformation of atomic nuclei. For 20 Ne, the canonical example of backbending in light nuclei, the ab initio symmetry-adapted no-core shell model shows that while the energy spectrum replicates the backbending from experimental energies under the rotor-model assumption, there is no change in the intrinsic deformation or intrinsic spin of the yrast band around the backbend. For the traditional example of 48 Cr, computed in the valence shell with empirical interactions, we confirm a high-spin nucleus that is effectively near-spherical, in agreement with previous models. However, we find that this spherical distribution results, on average, from an almost equal mixing of deformed prolate shapes with deformed oblate shapes. Microscopic calculations confirm the importance of spin alignment and configuration mixing, but surprisingly unveil no anomalous increase in moment of inertia. Furthermore, this finding opens the path toward further understanding the rotational behavior and moment of inertia of medium-mass nuclei.

20 ≤ A ≤ 38↗
DOE OSTI2026

Widespread windthrow in Southeast Asian tropical forests verified by satellite observations

Windthrow, defined as abrupt tree mortality caused by intense winds, is well documented in the Neotropics but remains largely unverified in Asian tropical forests. Using Landsat 8 imagery for the period 2020-2022 and established spectral (shortwave-infrared, near-infrared, and red band composites) and morphological criteria (fan-shaped geometry and sharp boundaries), this study verified the presence of windthrow across Sumatra, Borneo, and New Guinea and produced the first georeferenced inventory of 60 events in the region. Event sizes were right-skewed, with many small gaps and few large (>200 ha) disturbances. Orientations were anisotropic, with concentrations of windthrow events pointing west to northwest-to-north and eastward, both aligning with known pathways of organized convection in the Maritime Continent of Southeast Asia. Detection was conservatively biased low by cloud cover, long revisit intervals, and the exclusion of land-use areas. This study provides a verified baseline that enables reproducible mapping with higher resolution sensors and field observations to quantify windthrow frequency, severity, and ecological significance.

Asia’s tropical forests↗
DOE OSTI2025

Unraveling the Mechanism of Interfacial Charge Transfer and Photoresponsivity of WS 2 Quantum Dots/MoS 2 (0D–2D) Heterostructure-Based Transistors

To assess the efficacy of a mixed-dimensional van der Waals (vdW) heterostructure in modulating the optoelectronic responses of nanodevices, the charge transport properties of the transition-metal dichalcogenide (TMD)-based heterostructure comprising zero-dimensional (0D) WS 2 quantum dots (QDs) and two-dimensional (2D) MoS 2 flakes are critically analyzed. Herein, a facile strategy was materialized in developing an atomically thin phototransistor assembled from mechanically exfoliated MoS 2 and WS 2 QDs synthesized using a one-pot hydrothermal route. The amalgamated photodetectors exhibited a high responsivity of ∼8000 A/W at an incident power of 0.05 nW of white light, surpassing that of the pristine MoS 2 devices. Furthermore, the detectivity of pristine MoS 2 , which was on the order of 10 10 , increased to 10 12 Jones for the WS 2 QDs/MoS 2 heterostructure photodetector, outperforming other WS 2 -based materials. The quasiparticle band gap and density of states (DOS) are further analyzed to elucidate the photophysics of the WS 2 QD/MoS 2 hybrid assembly. The difference in the work function between MoS 2 and WS 2 QDs gives rise to an electric field across the 0D–2D interface, facilitating effective charge separation and migration and contributing to the enhancement of photoresponsivity. The analysis of optical responses using density functional theory (DFT) revealed stronger absorption and less reflection over a broader spectrum of wavelengths for the heterostructure compared to the pristine materials. The estimated optical conductivity aligns well with the experimentally predicted maximum photoresponsivity under visible light, which is attributed to the high absorbance of 2D MoS 2 . In conclusion, combining diverse spectroscopic and imaging techniques with quantum simulation provides insights that clarify the pertinence of 0D–2D TMDs in designing phototransistors.

WS2 QDs/MoS2 heterostructure↗
DOE OSTI2024

Mapping domain structures near a grain boundary in a lead zirconate titanate ferroelectric film using X-ray nanodiffraction

The effect of an electric field on local domain structure near a 24° tilt grain boundary in a 200 nm-thick Pb(Zr 0.2 Ti 0.8 )O 3 bi-crystal ferroelectric film was probed using synchrotron nanodiffraction. The bi-crystal film was grown epitaxially on SrRuO 3 -coated (001) SrTiO 3 24° tilt bi-crystal substrates. From the nanodiffraction data, real-space maps of the ferroelectric domain structure around the grain boundary prior to and during application of a 200 kV cm −1 electric field were reconstructed. In the vicinity of the tilt grain boundary, the distributions of densities of c -type tetragonal domains with the c axis aligned with the film normal were calculated on the basis of diffracted intensity ratios of c - and a -type domains and reference powder diffraction data. Diffracted intensity was averaged along the grain boundary, and it was shown that the density of c -type tetragonal domains dropped to ∼50% of that of the bulk of the film over a range ±150 nm from the grain boundary. This work complements previous results acquired by band excitation piezoresponse force microscopy, suggesting that reduced nonlinear piezoelectric response around grain boundaries may be related to the change in domain structure, as well as to the possibility of increased pinning of domain wall motion. The implications of the results and analysis in terms of understanding the role of grain boundaries in affecting the nonlinear piezoelectric and dielectric responses of ferroelectric materials are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Layer Edge States Stabilized by Internal Electric Fields in Two-Dimensional Hybrid Perovskites

Two-dimensional (2D) organic-inorganic hybrid perovskites have been intensively explored in recent years due to their tunable band gaps and exciton binding energies and increased stability with respect to three-dimensional (3D) hybrid perovskites. Experimental observations suggest the existence of localized edge states in 2D hybrid perovskites which facilitate extremely efficient electron-hole dissociation and long carrier lifetimes, while multiple origins for their formation have been proposed. Using first-principles calculations, we demonstrate that layer edge states are stabilized by internal electric fields created by polarized molecular alignment of organic cations in 2D hybrid perovskites when they are two layers or thicker. Overall, our study gives a simple physical explanation of the edge state formation, and facilitating the design and manipulation of layer edge states for optoelectronic applications.

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

Scattering insights into shear-induced scission of rod-like micelles

Understanding the scission of rod-like micelles under mechanical forces is crucial for optimizing their stability and behavior in industrial applications. This study investigates how micelle length, flexibility, and external forces interact, offering insights into the design of micellar systems in processes influenced by mechanical stress. Although significant, direct experimental observations of flow-induced micellar scission using scattering techniques remain scarce. Small angle neutron scattering (SANS) is used to explore the shear response of aqueous cetyltrimethylammonium bromide (CTAB) solutions with sodium nitrate. Rheological tests show shear thinning with no shear banding, ensuring a uniform flow field for reliable interpretation of scattering data. As shear rate increases, the scattering spectra show angular distortion, which is analyzed using spherical harmonic decomposition to characterize flow-induced scission and micelle orientation under shear. Two analysis steps are used: a model-independent spectral eigendecomposition reveals a decrease in micellar length, while regression analysis quantifies the evolution of the length distribution and mean length with shear rate. Additionally, micelle alignment increases with shear, quantified by the orientational distribution function. In conclusion, these findings provide experimental evidence for flow-induced alignment and scission, offering a new framework for understanding shear-induced phenomena in micellar systems.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

A unique van Hove singularity in kagome superconductor CsV 3-x Ta x Sb 5 with enhanced superconductivity

Van Hove singularity (VHS) has been considered as a driving source for unconventional superconductivity. A VHS in two-dimensional (2D) materials consists of a saddle point connecting electron-like and hole-like bands. In a rare case, when a VHS appears at Fermi level, both electron-like and hole-like conduction can coexist, giving rise to an enhanced density of states as well as an attractive component of Coulomb interaction for unconventional electronic pairing. However, this van Hove scenario is often destroyed by an incorrect chemical potential or competing instabilities. Here, by using angle-resolved photoemission measurements, we report the observation of a VHS perfectly aligned with the Fermi level in a kagome superconductor CsV 3-x Ta x Sb 5 (x~ 0.4), in which a record-high superconducting transition temperature is achieved among all the current variants of AV 3 Sb 5 (A = Cs, Rb, K) at ambient pressure. Doping dependent measurements reveal the important role of van Hove scenario in boosting superconductivity, and spectroscopic-imaging scanning tunneling microscopy measurements indicate a distinct superconducting state in this system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

ECCI analysis of shear accommodations at grain boundaries in commercially pure alpha titanium

This study uses a novel approach that couples electron channeling contrast imaging (ECCI) with controlled removal of surface material to investigate the slip system/grain boundary interactions by assessing the geometry of slip planes and grain boundaries as a function of depth. The comparison of spacing, relative distributions, and correlations of slip bands across grain boundaries reveals surface biasing on the slip band behavior in the grain boundary region. Furthermore, using analysis of the compatibility factor m’, the Schmid factor of each slip system, and the angles θ between slip planes, a more comprehensive understanding of the details of the mechanisms of strain transfer and heterogeneous deformation is developed. In general, the misalignment of primary slip systems on the grain boundary planes necessitates the activation of secondary accommodating slip systems close to the grain boundary area that are better aligned (higher m’ and lower θ) with respect to the incoming slip system across the grain boundary. Such systems have the same Burgers vector as the primary slip systems within the respective grains, but are typically on low mobility slip planes.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Printed Microwave Connector

This paper describes the development of a printed, planar microwave connector operating from 1-7 GHz. The connector, which is based on a Grounded Coplanar Waveguide (GCPW) transmission line structure, is fabricated using 3D-printed thermoplastic material (PEEK) and conductive nanoparticle silver ink. Electromagnetic models were established to provide guidance on design tradeoffs and their impact on microwave performance. New mechanical designs were also developed to provide accurate alignment and robust connection of the two halves of the planar connector structure. Initial connector prototypes were fabricated to validate the new planar design using conventional double-sided copper laminates (Isola MT40). The designs were then implemented in an all-printed version of the connector. Electromagnetic models of the printed connectors were developed using the measured dielectric properties of printed PEEK. The insertion loss of the printed connectors was measured to be less than 1.7dB across the band.

Microwave Connector, printed electronics, additive↗
DOE OSTI2021

A 1D Lyman-alpha profile camera for plasma edge neutral studies on the DIII-D tokamak

A one dimensional, absolutely calibrated pinhole camera system was installed on the DIII-D tokamak to measure edge Lyman-alpha (Ly-α) emission from hydrogen isotopes, which can be used to infer neutral density and ionization rate profiles. The system is composed of two cameras, each providing a toroidal fan of 20 lines of sight, viewing the plasma edge on the inboard and outboard side of DIII-D. The cameras’ views lie in a horizontal plane 77 cm below the midplane. At its tangency radius, each channel provides a radial resolution of ~2 cm full width at half maximum (FWHM) with a total coverage of 22 cm. Each camera consists of a rectangular pinhole, Ly-α reflective mirror, narrow-band Ly-α transmission filter, and a 20 channel AXUV photodetector. The combined mirror and transmission filter have a FWHM of 5 nm, centered near the Ly-α wavelength of 121.6nm and is capable of rejecting significant, parasitic carbon-III (C-III) emission from intrinsic plasma impurities. To provide a high spatial resolution measurement in a compact footprint, the camera utilizes advanced engineering and manufacturing techniques including 3D printing, high stability mirror mounts, and a novel alignment procedure. Absolutely calibrated, spatially resolved Ly-α brightness measurements utilize a bright, isolated line with low parasitic surface reflections and enable quantitative comparison to modeling to study divertor neutral leakage, main chamber fueling, and radial particle transport.

Ionization Rate↗
DOE OSTI2021

Interstellar Extinction, Polarization, and Grain Alignment in the Sh 2-185 (IC 59 and IC 63) Region

Optical and infrared continuum polarization from the interstellar medium is driven by radiative processes aligning the grains with the magnetic field. While a quantitative, predictive theory of radiative alignment torques (RATs) exists and has been extensively tested, several parameters of the theory remain to be fully constrained. In a recent paper, Medan & Andersson showed that the polarization efficiency (and therefore grain alignment efficiency) at different locations in the wall of the Local Bubble (LB) could be modeled as proportional to the integrated light intensity from the surrounding stars and OB associations. Here we probe that relationship at high radiation field intensities by studying the extinction and polarization in the two reflection nebulae IC 59 and IC 63 in the Sh 2-185 H ii region, illuminated by the B0 IV star γ Cassiopeia. We combine archival visual polarimetry with new seven-band photometry in the Vilnius system, to derive the polarization efficiency from the material. We find that the same linear relationship seen in the LB wall also applies to the Sh 2-185 region, strengthening the conclusion from the earlier study.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

A 1D Lyman-alpha Profile Camera for Plasma Edge Neutral Studies on the DIII-D Tokamak

A one dimensional, absolutely calibrated pinhole camera system was installed on the DIII-D tokamak to measure edge Lyman-alpha (Ly-a) emission from hydrogenic isotopes which can be used to infer neutral density and ionization rate proles. The system is composed of two cameras, each providing a toroidal fan of twenty lines of sight, viewing the plasma edge on the inboard and outboard side of DIII-D. The cameras' views lie in a horizontal plane 77 cm below the midplane. At its tangency radius, each channel provides a radial resolution of approximately 2 cm full width at half maximum (FWHM) with a total coverage of 22 cm. Each camera consists of a rectangular pinhole, Ly-a reflective mirror, narrow-band Ly-a transmission fiter, and a 20 channel AXUV photodetector. The combined mirror and transmission fiter have a FWHM of 5 nm, centered near the Ly-a wavelength of 121.6 nm and is capable of rejecting significant, parasitic carbon-III (C-III) emission from intrinsic plasma impurities. To provide a high spatial resolution measurement in a compact footprint, the camera utilizes advanced engineering and manufacturing techniques including 3D printing, high stability mirror mounts, and a novel alignment procedure. Absolutely calibrated, spatially resolved Ly-a brightness measurements utilize a bright, isolated line with low parasitic surface reflections and enable quantitative comparison to modeling to study divertor neutral leakage, main chamber fueling and radial particle transport.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Solution processed high aspect ratio ultra-long vertically well-aligned ZnO nano scintillators for potential X-ray imaging applications

We report the photon (PL), electron (CL) and X-ray (XEL) induced luminescence characteristics of high aspect ratio ultra-long (~ 50 µm) ZnO nanorods (NRs) and discuss the potential for fast X-ray detection based on the consistent and efficient visible emission (~ 580 nm) from ZnO NRs. Nanostructured ZnO scintillators were rearranged to form a vertically well-aligned NR design in order to help light absorption and coupling resulting in luminescent and fast scintillation properties. The design of the nanorod array combines the key advantages of a low-cost growth technique together with environmentally friendly and widely available materials. A low temperature hydrothermal method was adopted to grow ZnO NRs in one cycle growth and their structural, optical and X-ray scintillation properties were investigated. The relatively short (~ 10 µm) ZnO NRs emitting in the near-band-edge region were found to be almost insensitive to X-rays. On the other hand, the higher XEL response of long ZnO NRs, which is a key parameter for evaluation of materials to be used as scintillators for high quality X-ray detection and imaging, along with a decay time response in the order of ns confirmed promising scintillation properties for fast and high-resolution X-ray detector applications.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

Influence of Surface Ligands on Energetics at FASnI 3 /C 60 Interfaces and Their Impact on Photovoltaic Performance

Interfacial chemistry and energetics significantly impact the performance of photovoltaic devices. In the case of Pb-containing organic metal halide perovskites, photoelectron spectroscopy has been used to determine the energetic alignment of frontier electronic energy levels at various interfaces present in the photovoltaic device. For the Sn-containing analogues, which are less toxic, no such measurements have been made. Through a combination of ultraviolet, inverse, and X-ray photoelectron spectroscopy (UPS, IPES, and XPS, respectively) measurements taken at varying thickness increments during stepwise deposition of C 60 on FASnI 3 , we present the first direct measurements of the frontier electronic energy levels across the FASnI 3 /C 60 interface. The results show band bending in both materials and transport gap widening in FASnI 3 at the interface with C 60 . The XPS results show that iodide diffuses into C 60 and results in n-doping of C 60 . This iodide diffusion out of FASnI 3 impacts the valence and conduction band energies of FASnI 3 more than the core levels, with the core level shifts displaying a different trend than the valence and conduction bands. Surface treatment of FASnI 3 with carboxylic acids and bulky ammonium substituted surface ligands results in slight alterations in the interfacial energetics, and all surface ligands result in similar or improved PV performance relative to the untreated devices. Finally, the greatest PV stability results from treatment with a fluorinated carboxylic acid derivative; however, iodide diffusion is still observed to occur with this surface ligand.

interfacial energetics↗