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At least 1,801 records · Page 100
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Interaction of Black Phosphorus with Oxygen and Water

Black phosphorus (BP) has attracted significant interest as a monolayer or few-layer material with extraordinary electrical and optoelectronic properties. Chemical reactions with different ambient species, notably oxygen and water, are important as they govern key properties such as stability in air, electronic structure and charge transport, wetting by aqueous solutions, etc. Here, we report experiments combined with ab-initio calculations that address the effects of oxygen and water in contact with BP. Our results show that the reaction with oxygen is primarily responsible for changing properties of BP. Oxidation involving the dissociative chemisorption of O 2 causes the decomposition of BP and continuously lowers the conductance of BP field-effect transistors (FETs). In contrast, BP is stable in contact with deaerated (i.e., O 2 depleted) water and the carrier mobility in BP FETs gated by H 2 O increases significantly due to efficient dielectric screening of scattering centers by the high-k dielectric. Isotope labeling experiments, contact angle measurements and calculations show that the pristine BP surface is hydrophobic, but is turned progressively hydrophilic by oxidation. Lastly, our results open new avenues for exploring applications that require contact of BP with aqueous solutions including solution gating, electrochemistry, and solution-phase approaches for exfoliation, dispersion, and delivery of BP.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2022

Using the Black Carbon Particle Mixing State to Characterize the Lifecycle of Biomass Burning Aerosols

The lifecycle of black carbon (BC)-containing particles from biomass burns is examined using aircraft and surface observations of BC mixing state for plume ages from ~15 minutes to 10 days. Because BC is non-volatile and chemically inert, changes in the mixing state of BC-containing particles are driven solely by changes in particle coating, which is mainly secondary organic aerosol (SOA). The coating mass initially increases rapidly (k = 0.84 hr-1), then remains growth relatively constant for 1 to 2 days as plume dilution no longer supports further growth, then decreases slowly until only ~30 % of the maximum coating mass remains after 10 days, (kloss = 0.011 hr-1). The mass ratio of coating-to-core for a BC-containing particle with a 100 nm mass- equivalent diameter BC core reaches a maximum of ~20 after a few hours and drops to ~5 after 10 days of aging. The initial increase in coating mass can be used to determine SOA formation rates. The slow loss of coating material, not captured in global models, comprises the dominant fraction of the lifecycle of these particles. Coating-to-core mass ratios of BC particles in the stratosphere are much greater than those in the free troposphere indicating a different lifecycle.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Resonance-Enhanced Excitation of Interlayer Vibrations in Atomically Thin Black Phosphorus

The strength of interlayer coupling critically affects the physical properties of 2D materials such as black phosphorus (BP), where the electronic structure depends sensitively on layer thickness. Rigid-layer vibrations reflect directly the interlayer coupling strength in 2D van der Waals solids, but measurement of these characteristic frequencies is made difficult by sample instability and small Raman scattering cross sections in atomically thin elemental crystals. Here, we overcome these challenges in BP by performing resonance-enhanced low-frequency Raman scattering under an argon-protective environment. Interlayer breathing modes for atomically thin BP were previously unobservable under conventional (nonresonant) excitation but became strongly enhanced when the excitation energy matched the sub-band electronic transitions of few-layer BP, down to bilayer thicknesses. The measured out-of-plane interlayer force constant was found to be 10.1 × 10 19 N/m 3 in BP, which is comparable to graphene. Accurate characterization of the interlayer coupling strength lays the foundation for future exploration of BP twisted structures and heterostructures.

interlayer interaction↗
DOE OSTI2016

Nanostructured Black Phosphorus/Ketjenblack–Multiwalled Carbon Nanotubes Composite as High Performance Anode Material for Sodium-Ion Batteries

Sodium-ion batteries are promising alternatives to lithium-ion batteries for large-scale applications. However, the low capacity and poor rate capability of existing anodes for sodium-ion batteries are bottlenecks for future developments. Here, we report a high performance nanostructured anode material for sodium-ion batteries that is fabricated by high energy ball milling to form black phosphorus/Ketjenblack–multiwalled carbon nanotubes (BPC) composite. With this strategy, the BPC composite with a high phosphorus content (70 wt %) could deliver a very high initial Coulombic efficiency (>90%) and high specific capacity with excellent cyclability at high rate of charge/discharge (~1700 mAh g–1 after 100 cycles at 1.3 A g–1 based on the mass of P). In situ electrochemical impedance spectroscopy, synchrotron high energy X-ray diffraction, ex situ small/wide-angle X-ray scattering, high resolution transmission electronic microscopy, and nuclear magnetic resonance were further used to unravel its superior sodium storage performance. The scientific findings gained in this work are expected to serve as a guide for future design on high performance anode material for sodium-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2021

Atomic-Scale Investigation of Oxidation at the Black Phosphorus Surface

Black phosphorus (BP) exhibits extraordinary electronic properties that are desirable for a wide variety of electronic and optoelectronic applications. However, applications of BP are hindered by its rapid degradation in ambient conditions. Despite significant advances that have been made in understanding the degradation mechanism, no consensus has yet been reached on how BP oxidation occurs at the atomic scale as experimental studies have been mostly restricted to averaged effects of degradation over a micron- to millimeter-sized region. Here, BP oxidation is investigated using scanning tunneling microscopy/spectroscopy (STM/S). Introducing O 2 gas to the BP surface in ultrahigh vacuum at a pressure of 10 –5 mbar for 1 min creates two new types of defects on the surface. We identify these defects as dangling atomic oxygen and phosphorus multivacancies using density functional theory simulations. In addition to the structural changes to the surface, the electronic structure is also drastically altered by the introduction of oxygen. The 300 meV band gap of BP is lifted due to dosing. This change in the electronic structure is reversible through STM tip manipulation. As a result, these are the first experimental results showing the atomic-scale oxidation of BP, an important step toward understanding the degradation process

2D materials↗
DOE OSTI2026

Surfactant Effects on Carbon Black Slurries for Aqueous Flow-Electrode Applications

Aqueous carbon black (CB) slurries are promising for flow-electrode applications due to their low cost and high electrical conductivity. Here, in this study, we investigate the impact of introducing a nonionic surfactant (Tween 20) on the rheological and electrical properties of 5 wt % Vulcan XC72R CB slurries in a 50 mM NaCl aqueous solution. We observe a Tween 20 critical concentration around 1.2 wt % that triggers an abrupt transition from a conductive gel to a high-resistance Newtonian fluid. This sudden network collapse coincides with a 250-fold reduction in settled mass, a 1–2 order of magnitude drop in viscosity, and a nearly 100-fold decrease in slurry conductivity. Centrifuged pellet conductivity measurements support the conclusion that this performance loss is largely due to the destruction of the gel network, rather than increased particle-to-particle resistance. SEM imaging suggests that the network is built from large 10 to 50 μm agglomerates that are fully dissolved above the critical surfactant concentration. We found that subcritical surfactant addition improved slurry shelf stability over 90 days, but that electrochemical cell testing revealed progressive performance degradation during operation. These results highlight the need for strategies that maximize long-term electrical conductivity without compromising viscosity, sedimentation stability, or resistance to accumulation on internal surfaces.

Materials science↗
DOE OSTI2016

Proton Reduction Using a Hydrogenase-Modified Nanoporous Black Silicon Photoelectrode

Metalloenzymes featuring earth-abundant metal-based cores exhibit rates for catalytic processes such as hydrogen evolution comparable to those of noble metals. Realizing these superb catalytic properties in artificial systems is challenging owing to the difficulty of effectively interfacing metalloenzymes with an electrode surface in a manner that supports efficient charge-transfer. Here, we demonstrate that a nanoporous 'black' silicon (b-Si) photocathode provides a unique interface for binding an adsorbed [FeFe]-hydrogenase enzyme ([FeFe]-H2ase). The resulting [FeFe]-H2ase/b-Si photoelectrode displays a 280 mV more positive onset potential for hydrogen generation than bare b-Si without hydrogenase, similar to that observed for a b-Si/Pt photoelectrode at the same light intensity. Additionally, we show that this H2ase/b-Si electrode exhibits a turnover frequency of >/=1300 s-1 and a turnover number above 107 and sustains current densities of at least 1 mA/cm2 based on the actual surface area of the electrode (not the smaller projected geometric area), orders of magnitude greater than that observed for previous enzyme-catalyzed electrodes. While the long-term stability of hydrogenase on the b-Si surface remains too low for practical applications, this work extends the proof-of-concept that biologically derived metalloenzymes can be interfaced with inorganic substrates to support technologically relevant current densities.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Edge-Confined Excitons in Monolayer Black Phosphorus

Quantum confinement of two-dimensional excitons in van der Waals materials via electrostatic trapping, lithographic patterning, Moiré potentials, and chemical implantation has enabled significant advances in tailoring light emission from nanostructures. While such approaches rely on complex preparation of materials, natural edges are a ubiquitous feature in layered materials and provide a different approach for investigating quantum-confined excitons. Here, we observe that certain edge sites of monolayer black phosphorus (BP) strongly localize the intrinsic quasi-one-dimensional excitons, yielding sharp spectral lines in photoluminescence, with nearly an order of magnitude line width reduction. Through structural characterization of BP edges using transmission electron microscopy and first-principles GW plus Bethe–Salpeter equation (GW-BSE) calculations of exemplary BP nanoribbons, we find that certain atomic reconstructions can strongly quantum-confine excitons resulting in distinct emission features, mediated by local strain and screening. Here we observe linearly polarized luminescence emission from edge reconstructions that preserve the mirror symmetry of the parent BP lattice, in agreement with calculations. Furthermore, we demonstrate efficient electrical switching of localized edge excitonic luminescence, whose sites act as excitonic transistors for emission. Localized emission from BP edges motivates exploration of nanoribbons and quantum dots as hosts for tunable narrowband light generation, with future potential to create atomic-like structures for quantum information processing applications as well as exploration of exotic phases that may reside in atomic edge structures.

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

Lattice Anisotropy-Driven Reduction of Phonon Velocities in Black Phosphorus

Phonon dynamics and transport determine how heat is utilized and dissipated in materials. In 2D systems for optoelectronics and thermoelectrics, the impact of nanoscale material structure on phonon propagation is central to controlling thermal conduction. Here, we directly observe in-plane coherent acoustic phonon propagation in black phosphorus (BP) using ultrafast electron microscopy. We identify a significant reduction of the group velocities in directions intermediate to the armchair and zigzag lattice directions. Using a machine learning-based model with an >8000 atom supercell, we find that this slowing results from the mixing of in-plane transverse and longitudinal acoustic phonons and is independent of broken symmetries of edge reconstructions. In conclusion, this work demonstrates how coherent phonon transport is sensitive to propagation direction in the lattice plane.

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

Controlled Sculpture of Black Phosphorus Nanoribbons

Black phosphorus (BP) is a highly anisotropic allotrope of phosphorus with high promise for fast functional electronics and optoelectronics. We demonstrate that high-resolution and controlled structural modification of few-layer BP along arbitrary crystal direction can be achieved with nanometer-scale precision on a few-minute timescales leading to the formation of sub-nm wide armchair and zigzag BP nanoribbons. The nanoribbons are assembled, along with nanopores and nanogaps, using a combination of mechanical-liquid exfoliation and in situ transmission electron microscope (TEM) and scanning TEM nanosculpting. Here we report time-dependent structural properties of the one-dimensional systems under electron irradiation and probe their oxidation properties with electron energy-loss spectroscopy (EELS). Finally, we demonstrate the use of STEM to controllably narrow and thin the nanoribbons until they break into nanogaps. The observations are rationalized using density functional theory for transition state calculations and electronic band-structure evolution for the various stages of the narrowing procedure. In particular, we predict that the sub- and few-nm wide BP nanoribbons realized experimentally possess clear one-dimensional quantum confinement, even when the systems are made up of a few layers. We find the demonstration of this procedure is key for the development of BP-based electronic, optoelectronic, thermoelectric, and other applications in reduced dimensions.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Anisotropic Electron–Phonon Interactions in Angle-Resolved Raman Study of Strained Black Phosphorus

Few-layer black phosphorus (BP) with an in-plane puckered crystalline structure has attracted intense interest for strain engineering due to both its significant anisotropy in mechanical and electrical properties and its high intrinsic strain limit. Here, we investigated the phonon response of few layer BP under uniaxial tensile strain (~7%) with in situ polarized Raman spectroscopy. Together with the first-principles density functional theory (DFT) analysis, the anisotropic Poisson’s ratio in few-layer BP was verified as one of the primary factors that caused the large discrepancy in the trend of reported Raman frequency shift for strained BP, armchair (AC) direction in particular. By carefully including and excluding the anisotropic Poisson’s ratio in the DFT emulations, we rebuilt both trends reported for Raman mode shifts. Furthermore, the angle-resolved Raman spectroscopy was conducted in situ under tensile strain for systematic investigation of the in-plane anisotropy of BP phonon response. The experimentally observed thickness and crystallographic orientation dependence is elaborated using DFT theory as having a strong correlation between the strain-perturbated electronic-band structure and the phonon vibration modes. Furthermore, this study provides insight, both experimentally and theoretically, for the complex electron–phonon interaction behavior in strained BP, which enables diverse possibilities for the strain engineering of electrical and optical properties in BP and similar two-dimensional nanomaterials.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Uptake Mechanism for Iodine Species to Black Carbon

Natural organic matter (NOM) plays an important role in determining the fate and transport of iodine species such as iodide (I-) and iodate (IO3-) in groundwater system. Although NOM exists as diverse forms in environments, prior iodine studies have mainly focused on uptake processes of iodide and iodate to humic materials. This study was conducted to determine the iodide and iodate uptake potential for a particulate NOM (i.e., black carbon [BC]). A laboratory-produced BC and commercial humic acid were used for batch experiments to compare their iodine uptake properties. The BC exhibited >100 times greater uptake capability for iodide than iodate at low pH~3, while iodide uptake was negligible for the humic acid. The uptake properties of both solids strongly depend on the initial iodine aqueous concentrations. After uptake reaction of iodide to the BC, X-ray Absorption Fine Structure spectroscopy results indicated that the iodide was converted to electrophilic species, and iodine was covalently bound to carbon atom in polycyclic aromatic hydrocarbons present in the BC. The computed distribution coefficients (i.e., Kd values) suggest that the BC materials retard significantly the transport of iodide at low pH in environmental systems containing even a small amount of BC.

black carbon↗
DOE OSTI2019

Direct Observation of Symmetry-Dependent Electron–Phonon Coupling in Black Phosphorus

Electron–phonon coupling in two-dimensional nanomaterials plays a fundamental role in determining their physical properties. Such interplay is particularly intriguing in semiconducting black phosphorus (BP) due to the highly anisotropic nature of its electronic structure and phonon dispersions. Here we report the direct observation of symmetry-dependent electron–phonon coupling in BP by performing the polarization-selective resonance Raman measurement in the visible and ultraviolet regimes, focusing on the out-of-plane A g 1 and in-plane A g 2 phonon modes. Their intrinsic resonance Raman excitation profiles (REPs) were extracted and quantitatively compared. The in-plane A g 2 mode exhibits remarkably strong resonance enhancement across the excitation wavelengths when the excitation polarization is parallel to the armchair (A g 2 //AC) direction. In contrast, a dramatically weak resonance effect was observed for the same mode with the polarization parallel to zigzag (A g 2 //ZZ) direction and for the out-of-plane A g 1 mode (A g 1 //AC and A g 1 //ZZ). Analysis on quantum perturbation theory and first-principles calculations on the anisotropic electron distributions in BP demonstrated that electron–phonon coupling considering the symmetry of the involved excited states and phonon vibration patterns is responsible for this phenomenon. Further analysis of the polarization-dependent REPs for A g phonons allows us to resolve the existing controversies on the physical origin of Raman anomaly in BP and its dependence on excitation energy, sample thickness, phonon modes, and crystalline orientation. Finally, our study gives deep insights into the underlying interplay between electrons and phonons in BP and paves the way for manipulating the electron–phonon coupling in anisotropic nanomaterials for future device applications.

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

Impacts of Aerosol Dry Deposition on Black Carbon Spatial Distributions and Radiative Effects in the Community Atmosphere Model CAM5

Dry deposition is a vital process affecting the lifetime and spatial distributions of atmospheric aerosols. Black carbon (BC) plays an important role in the Earth’s climate. To explore the sensitivity of modeled BC spatial distributions to particle dry deposition treatments, the scheme of Petroff & Zhang (2010) (PZ10) is implemented into the Community Atmospheric Model version 5 (CAM5), and model simulations using PZ10 are compared with the one using the default scheme of Zhang et al. (2001) (Z01). The PZ10 scheme suggests much lower dry deposition velocities than Z01 for fine particles in Aitken, primary carbon, and accumulation modes, resulting in 73.0% lower of global mean BC dry deposition fluxes and 23.2% higher of global mean BC column burdens. CAM5 with PZ10 increases modeled BC concentrations at all altitudes and latitudes compared to Z01, which improves the agreement with observations of BC profiles in the lower troposphere in the Arctic. It also helps the simulation of surface BC concentrations in high-latitudes remote regions and its seasonality in the Arctic. Yet, PZ10 slightly exacerbates the overestimation of modeled BC concentrations in the middle and upper troposphere, which might be due to model uncertainties in other aerosol physical and chemical processes. The global annual mean radiative effects due to aerosol-radiation interactions (REari) and aerosol-cloud interactions (REaci) of BC from the CAM5 experiment using Z01 are 0.61±0.007 and -0.11±0.02 W m -2 , respectively, compared to slightly larger REari (0.75±0.01 W m -2 ) and REaci (-0.14±0.02 W m -2 ) from CAM5 using PZ10.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Black Carbon Amplifies Haze Over the North China Plain by Weakening the East Asian Winter Monsoon

Black carbon (BC) has previously been found to intensify haze in China by stabilizing the planetary boundary layer. With ocean, sea ice, and cloud feedbacks included in a global aerosol-climate model, we show here that BC emitted from the North China Plain can be transported to the oceans, which in turn changes cloud structure and land-sea thermal contrast. As a result, East Asian winter monsoon wind speeds decrease over the North China Plain. This decrease causes air stagnation that can further intensify haze. Our results suggest that in addition to the local BC-induced interactions between aerosol and the planetary boundary layer, BC can also amplify haze in the North China Plain by weakening East Asian winter monsoon through ocean, sea ice, and cloud feedbacks. It implies that reducing BC emissions could have significant indirect benefits for air quality in the North China Plain.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Constraining Aging Processes of Black Carbon in the Community Atmosphere Model Using Environmental Chamber Measurements

Abstract The direct radiative forcing of black carbon aerosol (BC) on the Earth system remains unsettled, largely due to the uncertainty with physical properties of BC throughout their lifecycle. Here we show that ambient chamber measurements of BC properties provide a novel constraint on the crude BC aging representation in climate models. Observational evidence for significant absorption enhancement of BC can be reproduced when the aging processes in the four‐mode version of the Modal Aerosol Module (MAM4) aerosol scheme in the Community Atmosphere Model version 5 are calibrated by the recent in situ chamber measurements. An observation‐based scaling method is developed in the aging timescale calculation to alleviate the influence of biases in the simulated model chemical composition. Model sensitivity simulations suggest that the different monolayer settings in the BC aging parameterization of MAM4 can cause as large as 26% and 24% differences in BC burden and radiative forcing, respectively. We also find that an increase in coating materials (e.g., sulfate and secondary organic aerosols) reduces BC lifetime by increasing the hygroscopicity of the mixture but enhances its absorption, resulting in a net increase in BC direct radiative forcing. Our results suggest that accurate simulations of BC aging processes as well as other aerosol species are equally important in reducing the uncertainty of BC forcing estimation.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Mie scattering captures observed optical properties of ambient biomass burning plumes assuming uniform black, brown, and organic carbon mixtures

We use a simple model of a spherical biomass burning aerosol particle containing an internal mixture of black carbon (BC) and organic carbon (OC) with an effective refractive index calculated as a volume fraction weighted mean of refractive indices. Brown carbon (BrC) is considered to be an OC with an imaginary part of refractive index at the blue end of the solar spectrum higher (in absolute value) than at the red end. Mie scattering formalism is employed to calculate Absorption Ångström Exponent (AAE) as a function of single scattering albedo (SSA) for a set of BC refractive indices, BC volume fraction, and a set of effective refractive indices of BC and BrC mixture. Ambient plumes are characterized by their mean SSA at 405 nm wavelength and two–wavelength (405 nm and 781 nm) AAE values. Comparing observed and model calculated AAE and SSA values identifies the BC refractive index and its volume fraction, and an effective refractive index of the BC and BrC mixture. From these values the imaginary part of BrC refractive index is calculated. For observed southwestern ambient fires the imaginary part of BrC refractive index ≤0.016. In contrast, fires in the Amazon and from Africa are dominated by BC. Here, we also use the Mie scattering model to establish the upper limit on AAE of BC (AAE≤1.4), and the upper limit of the BC and OC mixture (AAE≤1.7). Any AAE(405/781)>1.7 requires the presence of BrC. We derive several relationships between AAE, SSA, BC fractions, and imaginary part of BrC refractive index of ambient fires.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

A Strong Anthropogenic Black Carbon Forcing Constrained by Pollution Trends Over China

Estimates of the effective radiative forcing from aerosol-radiation interaction (ERF ari ) of anthropogenic Black Carbon (BC) have been disputable and require better constraints. Here we find a substantial decline in atmospheric absorption of −5.79Wm −2 decade −1 over eastern central China (ECC) responding to recent anthropogenic BC emission reductions. By combining the observational finding with advances from Coupled Model Intercomparison Project phase6 (CMIP6), we identify an emergent constraint on the ERF ari of anthropogenic BC. We show that across CMIP6 models the simulated trends correlate well with simulated annual mean shortwave atmospheric absorption by anthropogenic BC over China. Making use of this emergent relationship allows us to constrain the aerosol absorption optical depth of anthropogenic BC and further provide a constrained range of 2.4–3.0 Wm −2 for its top-of-atmosphere ERF ari over China, higher than existing estimates. Furthermore, our work supports a strong warming effect of BC over China, and highlights the need to improve BC simulations over source regions.

CMIP6 models↗

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