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At least 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Quantitative Mid-infrared Photoluminescence Characterization of Black Phosphorus–Arsenic Alloys

Black phosphorus (bP) is a promising material for mid-infrared (mid-IR) optoelectronic applications, exhibiting high performance light emission and detection. Alloying bP with arsenic extends its operation toward longer wavelengths from 3.7 μm (bP) to 5 μm (bP 3 As 7 ), which is of great practical interest. Quantitative optical characterizations are performed to establish black phosphorus-arsenic (bPAs) alloys optoelectronic quality. Anisotropic optical constants (refractive index, extinction coefficient, and absorption coefficient) of bPAs alloys from near-infrared to mid-IR (0.2-0.9 eV) are extracted with reflection measurements, which helps optical device design. Quantitative photoluminescence (PL) of bPAs alloys with different As concentrations are measured from room temperature to 77 K. PL quantum yield measurements reveal a 2 orders of magnitude decrease in radiative efficiency with increasing As concentration. An optical cavity is designed for bP 3 As 7 , which allows for up to an order of magnitude enhancement in the quantum yield due to the Purcell effect. In conclusion, our comprehensive optical characterization provides the foundation for high performance mid-IR optical device design using bPAs alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Mid-Wave Infrared Photoconductors Based on Black Phosphorus-Arsenic Alloys

Black phosphorus (b-P) and more recently black phosphorus-arsenic alloys (b-PAs) are candidate 2D materials for the detection of mid-wave and potentially long-wave infrared radiation. However, studies to date have utilized laser-based measurements to extract device performance and the responsivity of these detectors. As such, their performance under thermal radiation and spectral response has not been fully characterized. In this work, we perform a systematic investigation of gated-photoconductors based on b-PAs alloys as a function of thickness over the composition range of 0-91% As. Infrared transmission and reflection measurements are performed to determine the bandgap of the various compositions. The spectrally resolved photoresponse for various compositions in this material system is investigated to confirm absorption measurements, and we find that the cutoff wavelength can be tuned from 3.9 to 4.6 μm over the studied compositional range. In addition, we investigated the temperature-dependent photoresponse and performed calibrated responsivity measurements using blackbody flood illumination. Notably, we find that the specific detectivity (D*) can be optimized by adjusting the thickness of the b-P/b-PAs layer to maximize absorption and minimize dark current. We obtain a peak D* of 6 × 10 10 cm Hz 1/2 W -1 and 2.4 × 1010 cm Hz 1/2 W -1 for pure b-P and b-PAs (91% As), respectively, at room temperature, which is an order of magnitude higher than commercially available mid-wave infrared detectors operating at room temperature.

2D materials↗
DOE OSTI2019

Phonon-Mediated Ultrafast Hole Transfer from Photoexcited CdSe Quantum Dots to Black Dye

We have applied non-adiabatic molecular dynamics (NAMD) and Fewest Switching surface hopping (FSSH) method to simulate the energy dissipation and charge transfer processes in the CdSe quantum dot (QD) functionalized by the Black dye. Our calculations reveal ultrafast hole transfer from the photoexcited QD to the dye, despite a significant energy splitting between QD’s and dye’s occupied states. The mechanism of such ultrafast QD-to-dye hole transfer is rationalized by strong non-adiabatic couplings between the delocalized surface orbitals of the QD and the high-frequency vibrations of isothiocyanate ligands of the Black dye. Here, this mechanism is also confirmed by a very rapid lose of coherency of the excitation due to strong electronic couplings with vibrational modes of the dye.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Unusual Seismic Signals in the Sevier Desert, Utah Possibly Related to the Black Rock Volcanic Field

Abstract On September 12, 2018 and April 14, 2019 shallow (<2.5 km from the surface, <1 km relative to sea level) earthquakes ( M w 4.0 and 4.1, respectively) struck a relatively aseismic area in south‐central Utah, within the Black Rock Desert volcanic field. Seismic waveforms are dominated by long‐period energy, no clear direct S‐wave arrivals, and signal durations of ∼100 s. Using co‐seismic interferograms, we detect clear and distinguishable surface deformation confirming the shallowness of the two mainshocks, while full moment tensor solutions rule out an isotropic source, such as an explosion or collapse. For the April 2019 sequence, we build an earthquake catalog using a dense temporary geophone array. The enhanced earthquake catalog shows a rapidly decaying aftershock sequence, with 85% of aftershocks occurring during the first three hours. Combining these observations, we argue that these earthquake sequences are related to the Black Rock Desert volcanic field.

Mesimeri, Maria↗
DOE OSTI2020

Optical follow-up of the neutron star–black hole mergers S200105ae and S200115j

LIGO and Virgo’s third observing run revealed the first neutron star–black hole (NSBH) merger candidates in gravitational waves. These events are predicted to synthesize r-process elements creating optical/near-infrared ‘kilonova’ emission. The joint gravitational wave and electromagnetic detection of an NSBH merger could be used to constrain the equation of state of dense nuclear matter, and independently measure the local expansion rate of the Universe. Here, we present the optical follow-up and analysis of two of the only three high-significance NSBH merger candidates detected to date, S200105ae and S200115j, with the Zwicky Transient Facility. The Zwicky Transient Facility observed ~48% of S200105ae and ~22% of S200115j’s localization probabilities, with observations sensitive to kilonovae brighter than –17.5 mag fading at 0.5 mag d –1 in the g- and r-bands; extensive searches and systematic follow-up of candidates did not yield a viable counterpart. We present state-of-the-art kilonova models tailored to NSBH systems that place constraints on the ejecta properties of these NSBH mergers. Here, we show that with observed depths of apparent magnitude ~22 mag, attainable in metre-class, wide-field-of-view survey instruments, strong constraints on ejecta mass are possible, with the potential to rule out low mass ratios, high black hole spins and large neutron star radii.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Revealing the semiconductor–catalyst interface in buried platinum black silicon photocathodes

Nanoporous 'black' silicon semiconductors interfaced with buried platinum nanoparticle catalysts have exhibited stable activity for photoelectrochemical hydrogen evolution even after months of exposure to ambient conditions. The mechanism behind this stability has not been explained in detail, but is thought to involve a Pt/Si interface free from SiOx layer that would adversely affect interfacial charge transfer kinetics. In this paper, we resolve the chemical composition and structure of buried Pt/Si interfaces in black silicon photocathodes from a micron to sub-nanometer level using aberration corrected analytical scanning transmission electron microscopy. Through a controlled electrodeposition of copper on samples aged for one month in ambient conditions, we demonstrate that the main active catalytic sites are the buried Pt nanoparticles located below the 400-800 nm thick nanoporous SiOx layer. Though hydrogen production performance degrades over 100 h under photoelectrochemical operating conditions, this burying strategy preserves an atomically clean catalyst/Si interface free of oxide or other phases under air exposure and provides an example of a potential method for stabilizing silicon photoelectrodes from oxidative degradation in photoelectrochemical applications.

14 SOLAR ENERGY↗
DOE OSTI2025

SANE: strategic autonomous non-smooth exploration for multiple optima discovery in multi-modal and non-differentiable black-box functions

Both computational and experimental material discovery bring forth the challenge of exploring multidimensional and multimodal parameter spaces, such as phase diagrams of Hamiltonians with multiple interactions, composition spaces of combinatorial libraries, material structure image spaces, and molecular embedding spaces. Often these systems are black-boxes and time-consuming to evaluate, which resulted in strong interest towards active learning methods such as Bayesian optimization (BO). However, these systems are often noisy which make the black box function severely multi-modal and non-differentiable, where a vanilla BO can get overly focused near a single or faux optimum, deviating from the broader goal of scientific discovery. To address these limitations, here we developed Strategic Autonomous Non-Smooth Exploration (SANE) to facilitate an intelligent Bayesian optimized navigation with a proposed cost-driven probabilistic acquisition function to find multiple global and local optimal regions, avoiding the tendency to becoming trapped in a single optimum. To distinguish between a true and false optimal region due to noisy experimental measurements, a human (domain) knowledge driven dynamic surrogate gate is integrated with SANE. We implemented the gate-SANE into pre-acquired piezoresponse spectroscopy data of a ferroelectric combinatorial library with high noise levels in specific regions, and piezoresponse force microscopy (PFM) hyperspectral data. SANE demonstrated better performance than classical BO to facilitate the exploration of multiple optimal regions and thereby prioritized learning with higher coverage of scientific values in autonomous experiments. Our work showcases the potential application of this method to real-world experiments, where such combined strategic and human intervening approaches can be critical to unlocking new discoveries in autonomous research.

Biswas, Arpan [University of Tennessee, Knoxville,↗
DOE OSTI2026

Ionic liquid-enhanced recycling of lithium-ion battery black mass via heavy liquid centrifugal separation

Direct recycling of lithium-ion batteries (LIBs) is of great significance to supply chain security and environmental protection by restoring spent battery materials to their original purpose without destroying their chemical structure. One of the key processes for direct recycling is to separate valuable anode and cathode active materials from black mass. This study evaluates ionic liquid-enhanced Heavy Liquid Centrifugal Separation (HLCS) as an efficient method for separating LIB black mass into its constituent anode and cathode materials. The optimized HLCS process achieved a separation efficiency of over 95%, yielding a graphite-rich upper layer and an NMC-rich lower layer. Characterization by thermogravimetric analysis (TGA), X-ray diffraction (XRD), and inductively coupled plasma-optical emission spectroscopy (ICP-OES) confirmed the purity and structural integrity of the recovered fractions. The addition of N-methyl-2-pyrrolidone and ionic liquid 1-ethyl-3-methylimidazolium bromide decoupled entangled particles, while subsequent treatment of the anode layer with 1-(2,3-dihydroxypropyl)-3-methylimidazolium chloride further enhanced separation purity. The recycled graphite exhibited comparable battery performance to pristine graphite. These results demonstrate HLCS as a promising LIB recycling strategy, advancing sustainable battery manufacturing.

Adigun, Babafemi [Univ. of Tennessee, Knoxville, T↗
DOE OSTI2011

Luminescence of black silicon fabricated by high-repetition rate femtosecond laser pulses

We studied the photoluminescence (PL) from black silicon that was fabricated using an 800 nm, 250 kHz femtosecond laser in air. By changing the scan velocity and the fluence of the femtosecond laser, the formation of the PL band between the orange (600 nm) and red bands (near 680 nm) could be controlled. The red band PL from the photoinduced microstructures on the black silicon was observed even without annealing due to the thermal accumulation of high-repetition rate femtosecond laser pulses. The orange band PL was easily quenched under 532 nm cw laser irradiation, whereas the red band PL was more stable; this can be attributed to ''defect luminescence'' and ''quantum confinement'', respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2013

A normal-incidence PtSi photoemissive detector with black silicon light-trapping

A normal-incidence light-trapping scheme relying on black silicon surface nanostructures for Si-based photoemissive detectors, operating in the IR spectral range, is proposed. An absorptance enhancement by a factor of 2–3 is demonstrated for technologically most relevant, ultrathin (2 nm–3 nm) PtSi rear layers on Si. It is shown that this increase can be translated into an equivalent increase in responsivity because of the absorption limitation of detector performance. Pd{sub 2}Si/p-Si detectors with black silicon are suggested as promising candidates for room temperature detection in the third optical window with an expected external quantum efficiency in the range of 9%–14%.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Effect of stacking order on device performance of bilayer black phosphorene-field-effect transistor

We investigate the effect of stacking order of bilayer black phosphorene on the device properties of p-MOSFET and n-MOSFET. Two layers of black phosphorus are stacked in three different orders and are used as channel material in both n-MOSFET and p-MOSFET devices. The effects of different stacking orders on electron and hole effective masses and output characteristics of MOSFETs, such as ON currents, ON/OFF ratio, and transconductance are analyzed. Our results show that about 1.37 times and 1.49 times increase in ON current is possible along armchair and zigzag directions, respectively, 55.11% variation in transconductance is possible along armchair direction, by changing stacking orders (AA, AB, and AC) and about 8 times increase in ON current is achievable by changing channel orientation (armchair or zigzag) in p-MOSFET. About 14.8 mV/V drain induced barrier lowering is observed for both p-MOSFET and n-MOSFET, which signifies good immunity to short channel effects.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Effective photoconductivity of exfoliated black phosphorus for optoelectronic switching under 1.55 μm optical excitation

We present a microwave photoconductive switch based on exfoliated black phosphorus and strongly responding to a 1.55 μm optical excitation. According to its number of atomic layers, exfoliated black phosphorus presents unique properties for optoelectronic applications, like a tunable direct bandgap from 0.3 eV to 2 eV, strong mobilities, and strong conductivities. The switch shows a maximum ON/OFF ratio of 17 dB at 1 GHz, and 2.2 dB at 20 GHz under 1.55-μm laser excitation at 50 mW, never achieved with bidimensional materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Noble metal free photocatalytic H 2 generation on black TiO 2 : On the influence of crystal facets vs. crystal damage

In this study, we investigate noble metal free photocatalytic water splitting on natural anatase single crystal facets and on wafer slices of the [001] plane before and after these surfaces have been modified by high pressure hydrogenation and hydrogen ion-implantation. Here, we find that on the natural, intact low index planes, photocatalytic H 2 evolution (in the absence of a noble metal co-catalyst) can only be achieved when the hydrogenation treatment is accompanied by the introduction of crystal damage, such as simple scratching and miscut in the crystal, or by implantation damage. X-ray reflectivity, Raman, and optical reflection measurements show that plain hydrogenation leads to a ≈ 1 nm thick black titania surface layer without activity, while a colorless, density modified, and ≈7 nm thick layer with broken crystal symmetry is present on the ion implanted surface. These results demonstrate that (i) the H-treatment of an intact anatase surface needs to be combined with defect formation for catalytic activation and (ii) activation does not necessarily coincide with the presence of black color.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Estimating mass-absorption cross-section of ambient black carbon aerosols: theoretical, empirical, and machine learning models

The mass-absorption cross-section of black carbon (MAC BC ) is an essential parameter to link the atmospheric concentration of black carbon (BC) with its radiative forcing. When a direct calculation of MAC BC based on observations of aerosol light absorption and BC mass concentration is impossible, we rely on modeling and simulations to estimate MAC BC , but currently, there is no consensus model that can be relied on for accurate predictions across all atmospheric environments when BC particles have different coating thicknesses. Here, we applied five MAC BC prediction models (including three light scattering theories, an empirical model based on observations of particle mass concentrations, and a machine learning model developed in our previous work) to aerosols from three Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) field campaigns. While many studies have found that increasing the complexity of the models helps to constrain biases of the estimated MAC BC , our effort is to evaluate the models based on the criteria of simplicity and accuracy. We find that our machine learning model (support vector machine for regression, SVM) generally performs well across all DOE ARM field campaign data, while the accuracy of core-shell Mie theory depends on the bias correction algorithm applied to filter-based light absorption data. Generally, the empirical model for internally-mixed particles that we considered tends to over-predict MAC BC , while Mie theory for externally-mixed particles tends to under-predict MAC BC . An examination of the influence of coating material on BC cores suggests that the performance of our current SVM model is degraded when the BC is thickly-coated (e.g., it has undergone aging and mixing with other materials in the atmosphere).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2012

ORBITAL-PHASE-DEPENDENT {gamma}-RAY EMISSIONS FROM THE BLACK WIDOW PULSAR

We report on evidence for orbital phase dependence of the {gamma}-ray emission from the PSR B1957+20 black widow system using data from the Fermi Large Area Telescope. We divide an orbital cycle into two regions: one containing the inferior conjunction and the other containing the rest of the orbital cycle. We show that the observed spectra for the different orbital regions are fitted by different functional forms. The spectrum of the orbital region containing the inferior conjunction can be described by a power law with an exponential cutoff (PLE) model, which also gives the best-fit model for the orbital phase without the inferior conjunction, plus an extra component above {approx}2.7 GeV. The emission above 3 GeV in this region is detected with a {approx}7{sigma} confidence level. The {gamma}-ray data above {approx}2.7 GeV are observed to be modulated at the orbital period at the {approx}2.3{sigma} level. We anticipate that the PLE component dominant below {approx}2.7 GeV originates from the pulsar magnetosphere. We also show that inverse Compton scattering of the thermal radiation of the companion star off a ''cold'' ultrarelativistic pulsar wind can explain the extra component above {approx}2.7 GeV. The black widow pulsar PSR B1957+20 may be a member of a new class of object, in the sense that the system is showing {gamma}-ray emission with both magnetospheric and pulsar wind origins.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Radio timing and optical photometry of the black widow system PSR J1518+0204C in the globular cluster M5

We report on the determination of astrometric, spin, and orbital parameters for PSR J1518+0204C, a 'black widow' binary millisecond pulsar in the globular cluster (GC) M5. The accurate position and orbital parameters obtained from radio timing allowed us to search for the optical companion. By using WFC3/Hubble Space Telescope images, we identified a very faint variable star (m{sub F390W} ≳ 24.8, m{sub F606W} ≳ 24.3, m{sub F814W} ≳ 23.1) located at only 0.''25 from the pulsar's timing position. Due to its strong variability, this star is visible only in a subsample of images. However, the light curve obtained folding the available data with the orbital parameters of the pulsar shows a maximum at the pulsar inferior conjunction and a possible minimum at the pulsar superior conjunction. Furthermore, the shape of the optical modulation indicates a heating process possibly due to the pulsar wind. This is the first identification of an optical companion to a black widow pulsar in the dense stellar environment of a GC.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Multi-wavelength observations of the black widow pulsar 2FGL J2339.6-0532 with OISTER and Suzaku

Multi-wavelength observations of the black widow binary system 2FGL J2339.6-0532 are reported. The Fermi gamma-ray source 2FGL J2339.6-0532 was recently categorized as a black widow in which a recycled millisecond pulsar (MSP) is evaporating the companion star with its powerful pulsar wind. Our optical observations show clear sinusoidal light curves due to the asymmetric temperature distribution of the companion star. Assuming a simple geometry, we constrained the range of the inclination angle of the binary system to 52{sup ∘}<i<59{sup ∘}, which enables us to discuss the interaction between the pulsar wind and the companion in detail. The X-ray spectrum consists of two components: a soft, steady component that seems to originate from the surface of the MSP, and a hard, variable component from the wind-termination shock near the companion star. The measured X-ray luminosity is comparable to the bolometric luminosity of the companion, meaning that the heating efficiency is less than 0.5. In the companion orbit, 10{sup 11} cm from the pulsar, the pulsar wind is already in the particle-dominant stage with a magnetization parameter of σ<0.1. In addition, we precisely investigated the time variations of the X-ray periodograms and detected a weakening of the orbital modulation. The observed phenomenon may be related to unstable pulsar wind activity or weak mass accretion, both of which can result in the temporal extinction of the radio pulse.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Radio timing and optical photometry of the black widow system PSR J1953+1846A in the globular cluster M71

We report on the determination of the astrometric, spin, and orbital parameters for PSR J1953+1846 A, a “black widow” binary millisecond pulsar in the globular cluster M71. By using the accurate position and orbital parameters obtained from radio timing, we identified the optical companion in Advanced Camera for Surveys/Hubble Space Telescope images. It turns out to be a faint (m{sub F606W}≳24, m{sub F814W}≳23) and variable star located at only ∼0.″06 from the pulsar timing position. The light curve shows a maximum at the pulsar inferior conjunction and a minimum at the pulsar superior conjunction, thus confirming the association with the system. The shape of the optical modulation suggests that the companion star is heated, likely by the pulsar wind. The comparison with the X-ray light curve possibly suggests the presence of an intra-binary shock due to the interaction between the pulsar wind and the material released by the companion. This is the second identification (after COM-M5C) of an optical companion to a black widow pulsar in a globular cluster. Interestingly, the two companions show a similar light curve and share the same position in the color–magnitude diagram.

79 ASTRONOMY AND ASTROPHYSICS↗