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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Thermal spike effect in sputtering of porous germanium to form surface pattern by high energy heavy ions irradiation

Germanium exhibits a remarkable effect when subjected to high energy heavy ions irradiation. A synergic effect of high electronic energy loss (S{sub e} = 16.4 keV nm{sup −1}) and nuclear energy loss (S{sub n} = 0.1 keV nm{sup −1}) of 100 MeV Ag ions irradiation in Ge is presented. The results show that crystalline Ge is insensitive to the ionizing part of energy loss whereas thermal spike generated in the damaged Ge leads to the formation of porous structure. Further, an unusual high sputtering of the porous structure opens up the sub-surface voids to show the surface pattern. We explore the role of electron and phonon confinement to explain this effect.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Assessment of a Smoothed Particle Hydrodynamics Method for Thin Film on Textured Surfaces

A large number of previous studies suggest that the behavior of the near-wall liquid micro-layer plays a key role in boiling heat transfer and boiling crisis; see examples. The thin liquid layer interacts with heater surface and 'external' two-phase flow. The net effects of these interactions define the micro-hydrodynamics that leads to dryout. As a result, a good understanding of the thin-layer hydrodynamics is significant for the accurate prediction of CHF. Recently, with the advent of nanotechnology including micro-scale manufacturing, it becomes possible to perform high heat-flux boiling experiments with controlled surface conditions. Although many reports show rich observations about the effects of surface characteristics on CHF, physical mechanisms remain not fully understood. In order to have better understanding of the above phenomena, several computational models are developed, ranging from the lubrication theory to CFD methods. The former models are limited to one-dimensional formulation and unable to deal with the dry-out phenomena. It turns out that CFD methods have a greater potential for the mechanistic study of boiling. Towards the study objective, a particle-based CFD method called Smoothed Particle Hydrodynamics (SPH) is adopted. SPH is a Lagrangian particle method for solving systems of partial differential equations. Originally SPH is proposed for fluid dynamics in the context of astrophysical problems. Because mass and density are introduced during the particle approximation, SPH is also applied in fluid dynamic problems, where mass and density are important parameters to determine, without mass loss (a limitation of interface capturing schemes in mesh-based methods). Besides, geometrically complex and/or dynamic boundaries and interfaces can be handled without undue difficulty in SPH. Currently, most SPH simulations focus on large-scale scenarios (meter scale), like flooding and solitary wave. Also some works have been done with SPH in pore-scale. As for micro- or nano-scale simulation, people usually apply Dissipative Particle Dynamics (DPD) and Molecular Dynamics (MD) for particle-based simulation. Almost no work has been done on micro-scale with SPH, so assessments are needed to investigate the capability of SPH in application of micro-hydrodynamics. The Phenomena Identification and Ranking Table (PIRT) is applied to align application's technical requirements with associated physics and materials, models, simulation code capabilities and verification, validation and uncertainty quantification activities. The figures of merit are determined as: (1) Timing of micro-layer rewetting dry surface; (2) Effects of surface features. The corresponding key phenomena are determined as: (1) Hydrodynamics; (2) Interface Dynamics; (3) Energy; (4) Surface Effect. This study deals with isothermal scenario and no energy term is considered. Based on the current needs, a new SPH package, Micro-SPH, is compiled based on SPHysics with surface tension and wettability built in. Test cases are performed with Micro-SPH to assess the capability of SPH to each phenomenon identified. NEUTRINO with incompressible SPH solver is employed to investigate micro-fluid dynamics on a surface with uniformly distributed cylindrical pillars for application purposes. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2020

Dendrite-free Al recycling via electrodeposition using ionic liquid electrolytes: The effects of deposition temperature and cathode surface roughness

In this report, the electrodeposition of Al from aluminum scrap alloys (A2020) on copper cathode substrates with varied surface roughness under different deposition temperatures was studied using low-temperature AlCl 3 -1-butyl-3-methyl-imidazolium chloride (BMIC) ionic liquid electrolytes. The bulk electrodeposition of Al was carried out under a voltage of 1.5 V at a stirring rate of 120 rpm using a fixed ionic liquid electrolyte concentration (molar ratio AlCl 3 : BMIC = 2:1). The effects of deposition temperature (range from 80 °C to 140 °C) and surface roughness of Cu cathode substrates (polished by 320, 600, 800, 1200 grits SiC sandpapers and mirror polishing process) on the morphology of deposited Al, current density, current efficiency and energy consumption, were investigated. The Al deposits were characterized using scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), profilometer, and electrochemical measurements for current density, current efficiency, and energy consumption. It is demonstrated that the deposition temperature and surface roughness of Cu electrodes play a critical role in the nucleation and growth of Al deposits. Higher deposition temperature promotes the diffusion and/or migration of Al 2 Cl 7 - ions and then enhances the current density and efficiency during the electrodeposition of Al. Smoother surface of Cu electrodes is preferred for the formation of dendrite-free Al deposits. Typically, on the mirror polished Cu electrode, no Al dendrite structure was observed, and only plate-like Al deposits were formed at the deposition temperature of 100 °C. Pure metallic Al was successfully deposited on Cu electrodes in AlCl 3 + BMIC ionic liquid electrolytes for all experiments with a current efficiency range from 72% to 99% and energy consumption of 4.6–6.3 kW h/kg Al.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Effect of Helium Flux on Near-surface Helium Accumulation in Plasma-Exposed Tungsten

We report results of object kinetic Monte Carlo (OKMC) simulations aimed at understanding the effect of helium flux on the near-surface helium accumulation in plasma-facing tungsten, which is initially defect-free and has a W(100) surface orientation. These OKMC simulations are performed at 933 K for fluxes ranging from 10 22 to 4 × 10 25 He/m 2 s, with 100 eV helium atoms impinging on a W(100) surface up to a maximum fluence of 4×10 19 He/m 2 . In the near-surface region, helium clusters interact elastically with the free surface. The interaction is attractive and results in the drift of mobile helium clusters towards the surface as well as increased trap mutation rates. The associated kinetics and energetics of the above-mentioned processes obtained from molecular dynamics simulations are also considered. The OKMC simulations indicate that as the flux decreases, the retention of implanted helium decreases, and its depth distribution shifts to deeper below the surface in initially pristine tungsten. Furthermore, the fraction of retained helium diffusing into the bulk increases as well, so much so that for 10 22 He/m 2 s, almost all of the retained helium diffused into the bulk with minimal/negligible near-surface helium accumulation. At a given flux, with increasing fluence, the fraction of retained helium initially decreases and then starts to increase after reaching a minimum. The occurrence of the retention minimum shifts to higher fluences as the flux decreases. Although the near-surface helium accumulation spreads deeper into the material with decreasing flux and increasing fluence, the spread appears to saturate at depths between 80 and 100 nm. Finally, we present a detailed analysis of the influence of helium flux on the size and depth distribution of total helium and helium bubbles.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Climate change penalty and benefit on surface ozone: a global perspective based on CMIP6 earth system models

Abstract This work presents an analysis of the effect of climate change on surface ozone discussing the related penalties and benefits around the globe from the global modelling perspective based on simulations with five CMIP6 (Coupled Model Intercomparison Project Phase 6) Earth System Models. As part of AerChemMIP (Aerosol Chemistry Model Intercomparison Project) all models conducted simulation experiments considering future climate (ssp370SST) and present-day climate (ssp370pdSST) under the same future emissions trajectory (SSP3-7.0). A multi-model global average climate change benefit on surface ozone of −0.96 ± 0.07 ppbv °C −1 is calculated which is mainly linked to the dominating role of enhanced ozone destruction with higher water vapour abundances under a warmer climate. Over regions remote from pollution sources, there is a robust decline in mean surface ozone concentration on an annual basis as well as for boreal winter and summer varying spatially from −0.2 to −2 ppbv °C −1 , with strongest decline over tropical oceanic regions. The implication is that over regions remote from pollution sources (except over the Arctic) there is a consistent climate change benefit for baseline ozone due to global warming. However, ozone increases over regions close to anthropogenic pollution sources or close to enhanced natural biogenic volatile organic compounds emission sources with a rate ranging regionally from 0.2 to 2 ppbv C −1 , implying a regional surface ozone penalty due to global warming. Overall, the future climate change enhances the efficiency of precursor emissions to generate surface ozone in polluted regions and thus the magnitude of this effect depends on the regional emission changes considered in this study within the SSP3_7.0 scenario. The comparison of the climate change impact effect on surface ozone versus the combined effect of climate and emission changes indicates the dominant role of precursor emission changes in projecting surface ozone concentrations under future climate change scenarios.

Zanis, Prodromos↗
DOE OSTI2018

Climate impact of a regional nuclear weapons exchange: An improved assessment based on detailed source calculations

In this paper, we present a multi-scale study examining the impact of a regional exchange of nuclear weapons on global climate. Our models investigate multiple phases of the effects of nuclear weapons usage, including growth and rise of the nuclear fireball, ignition and spread of the induced firestorm, and comprehensive Earth system modeling of the oceans, land, ice, and atmosphere. This study follows from the scenario originally envisioned by Robock et al. (2007a), based on the analysis of Toon et al. (2007), which assumes a regional exchange between India and Pakistan of fifty 15-kiloton weapons detonated by each side. We expand this scenario by modeling the processes that lead to production of black carbon, in order to refine the black carbon forcing estimates of these previous studies. When the Earth system model is initiated with 5 × 10 9 kg of black carbon in the upper troposphere (approximately 9 to 13 km), the impact on climate variables such as global temperature and precipitation in our simulations is similar to that predicted by previously published work. However, while our thorough simulations of the firestorm produce about 3.7 × 10 9 kg of black carbon, we find that the vast majority of the black carbon never reaches an altitude above weather systems (approximately 12 km). Therefore, our Earth system model simulations conducted with model-informed atmospheric distributions of black carbon produce significantly lower global climatic impacts than assessed in prior studies, as the carbon at lower altitudes is more quickly removed from the atmosphere. In addition, our model ensembles indicate that statistically significant effects on global surface temperatures are limited to the first 5 years and are much smaller in magnitude than those shown in earlier works. None of the simulations produced a nuclear winter effect. We find that the effects on global surface temperatures are not uniform and are concentrated primarily around the highest arctic latitudes, dramatically reducing the global impact on human health and agriculture compared with that reported by earlier studies. Lastly, our analysis demonstrates that the probability of significant global cooling from a limited exchange scenario as envisioned in the previous studies is highly unlikely, a conclusion supported by examination of natural analogs, such as large forest fires and volcanic eruptions.

58 GEOSCIENCES↗
DOE OSTI2020

Boosting electrosynthesis of ammonia on surface-engineered MXene Ti 3 C 2

Seeking a breakthrough in the development of efficient nitrogen fixation catalysts has become the frontier of energy and chemical conversion schemes. In this work, we report that the MXene Ti 3 C 2 can serve as a promising catalyst for the electrochemical N 2 reduction reaction (NRR) under ambient conditions. The electrocatalytic performance of Ti 3 C 2 can be further optimized through surface engineering. Specifically, Ti 3 C 2 with the increased surface hydroxyl moieties demonstrates enhanced production of NH 3 with a yield rate of 1.71 μg h -1 cm -2 , a Faradaic efficiency of 7.01% at -0.2 V vs. RHE at 20 °C and an even higher yield rate of 12.46 μg h -1 cm -2 together with a Faradaic efficiency of 9.03% at -0.2 V vs. RHE at 60 °C. The detailed electrochemical analysis suggests that the surface hydroxyl modification can effectively facilitate the electron transfer, surface adsorption and activation of dinitrogen. Our work sheds light on the development of efficient NRR catalysts based on earth-abundant elements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Performance analysis of photodetectors based on 2D materials and heterostructures

The unprecedented demand for sophisticated, self-powered, compact, ultrafast, cost-effective, and broadband light sensors for a myriad of applications has spurred a lot of research, precipitating in a slew of studies over the last decade. Apart from the photosensing ability of an active element in the light sensor, the device architecture is crucial in terms of photoinduced charge carrier generation and separation. Since the inception of graphene and the subsequent research growth in the atomically thin 2D materials, researchers have developed and adapted different families of 2D materials and device architectures, including single element 2D, 0D/2D, 2D/2D, 1D/2D stacked structures, and so on. Here this review discusses the recent reports on the light-sensing properties of various 2D materials, their heterostructures, and characteristics applicable to the ultraviolet-near infrared (UV-NIR), short-wave IR (SWIR), mid-wave IR (MWIR), long-wave IR (LWIR), and terahertz (THz) spectral ranges. It highlights the novelty of the burgeoning field, the heightened activity at the boundaries of engineering and materials science, particularly in the generation of charge carriers, their separation, and extraction, and the increased understanding of the underpinning science through modern experimental approaches. Devices based on the simultaneous effects of the pyro-phototronic effect (PPE) and the localized surface plasmon resonance (LSPR) effect, the photothermoelectric effect (PTE)-assisted photodetectors (PDs), waveguide-integrated silicon-2D PDs, metal-2D-metal PDs, and organic material PDs are examined rigorously. Theoretical treatment utilizing various computational approaches to investigate 2D materials and heterostructures for photodetection applications is also briefly discussed. At the end, current challenges and solutions to enhance the figures of merit of photodetectors are proposed.

2D transition metal chalcogenides↗
DOE OSTI2022

Spatiotemporal Modeling of Real World Backsheets Field Survey Data: Hierarchical (Multilevel) Generalized Additive Models: Preprint

Assessing photovoltaic module backsheet durability is critical to increasing module lifetime. Lab based accelerating testing has recently failed to predict large scale failures of widely adopted polymeric materials. Field surveyed data is critical to assess the performance of component lifetime. Using a documented field survey protocol, 13 field surveys where conducted. Each measurement is encoded with it's spatial location in respect to the other modules. By combining field survey data on degradation predictors with real time satellite weather data, data-driven predictive models of backsheet degradation were trained. LOESS models were constructed to investigate the spatial dependence of measurements. It was found that micro-climatic effects like treelines, ground surface changes, and elevation changes effected the magnitude and variance of the measurements. A GAM model was created to predict the value of degradation based on measured predictors. The model includes variables on the climate of the system and the location of each measurement in the PV mounting structure. The model performed well with an adj:R2 of 0:95 for yellowness index prediction. The model was cross-validated using k-folds.

backsheet↗
DOE OSTI2019

Surface Solar Irradiance in Continental Shallow Cumulus Fields: Observations and Large-Eddy Simulation

This study examines shallow cumulus cloud fields and their surface shortwave radiative effects using large-eddy simulation (LES) along with observations across multiple days at the Atmospheric Radiation Measurement Southern Great Plains atmospheric observatory. Pronounced differences are found between probability density functions (PDFs) of downwelling surface solar irradiance derived from observations and LES one-dimensional (1D) online radiation calculations. The shape of the observed PDF is bimodal, which is only reproduced by offline three-dimensional (3D) radiative transfer calculations, demonstrating PDF bimodality as a 3D radiative signature of continental shallow cumuli. Local differences between 3D and 1D radiative transfer calculations of downwelling surface solar irradiance are, on average, larger than 150 W m -2 on one afternoon. The differences are substantially reduced when spatially averaged over the LES domain and temporally averaged over the diurnal cycle, but systematic 3D biases ranging from 2 to 8 W m -2 persist across different days. Covariations between the domain-averaged surface irradiance, framed as a surface cloud radiative effect, and the simulated cloud fraction are found to follow a consistent diurnal relationship, often exhibiting hysteresis. In contrast, observations show highly variable behavior. By subsampling the LES domain, it is shown that this is due to the limited sampling density of inherently 3D observations. These findings help to define observational requirements for detecting such relationships, provide valuable insight for evaluating weather and climate models against surface observations as they push to ever higher resolutions, and have important implications for future assessments of solar renewable energy potential.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Distinct roles of land cover in regulating spatial variabilities of temperature responses to radiative effects of aerosols and clouds

Surface temperature responses to radiative perturbations due to aerosols and clouds are complicated by the land surface properties. To disentangle these complexities, this study, from a terrestrial surface energy budget perspective, isolates the underlying biophysical processes from the instantaneous radiative effects of aerosols and clouds on surface temperature using the National Center for Atmospheric Research Community Earth System Model version 1.2.1. It is found that in comparison with the global heterogeneous distributions of instantaneous radiative perturbations at the surface induced by aerosols and clouds, the spatial variations of the corresponding surface temperature responses to aerosol direct radiative effects (DRE) during the daytime and cloud radiative effects (CRE) during the nighttime are amplified. It is because of the consistent global distribution of the local surface climate sensitivity (a function of land cover properties such as surface roughness and Bowen ratio) with those of daytime DRE and nighttime CRE. By applying identical anthropogenic aerosol and precursor emissions over eight major past, present and projected future anthropogenic aerosol emitting regions (i.e. Brazil, China, East Africa, India, Indonesia, South Africa, United States and Western Europe), surface temperature responses to aerosol radiative cooling in the daytime and cloud radiative warming in the nighttime over these regions positively regulated by local surface climate sensitivities are prominent.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Effects of Zr Ion Implantation on Surface Mechanical Properties and Corrosion Resistance of Pure Magnesium

Zirconium (Zr) was implanted into pure Mg by metal vapor vacuum arc (MEVVA) at the dose of 2 × 10{sup 16} ions/cm{sup 2} at room temperature. The surface characteristics of Zr-implanted Mg were analyzed by the Stopping and Range of Ions in Matter software (SRIM) and x-ray photoelectron spectroscopy (XPS), the surface nanohardness and tribological behavior were measured through nanoindentation and a friction-abrasion testing machine, and the corrosion resistance of Zr-implanted Mg was evaluated by electrochemical measurement and immersion test in simulated body fluid (SBF). The results demonstrated that a gradient modified layer composed of MgO, Mg(OH){sub 2}, ZrO{sub 2} and Zr was formed on the near surface of pure Mg and the nanohardness of pure Mg was improved by 48%. Furthermore, the Zr-implanted Mg exhibited a more positive corrosion potential of − 1.43 V (versus SCE) and a lower corrosion current density of 19.9 μA/cm{sup 2}, and localized corrosion was effectively retarded during 24 h immersion in SBF, suggesting that the corrosion resistance of pure Mg was remarkably improved after Zr ion implantation. The mechanisms of surface strengthening and improved corrosion resistance were also discussed in this paper.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Different Forms of Application of a Laser Surface Treatment on Fatigue Crack Growth of an AA6013-T4 Aluminum Alloy

This work analyzes the effect of surface-localized laser heating treatment on the fatigue crack growth (FCG) rate on region II of the sigmoidal da/dN × ΔK curve of an aerospace-grade AA6013-T4 aluminum alloy sheet with 1.3 mm thickness. The influence on microstructure changes is also evaluated. Aiming to improve the FCG resistance without changing the mechanical behavior of the alloy, a Yb:fiber laser beam is defocused to generate a laser spot diameter of 2 mm, using 200 W power and a laser speed of 2 mm/s. Two laser lines are applied over fatigue C(T) specimens in two different forms: on only one and on both lateral specimen surfaces. Guinier–Preston zones, dispersoids and coarse constituent particles are found on the base material. On the heat-treated material, the same precipitates and also β′ and Q′ precipitates are found. These microstructural variations due to the laser thermal cycle, together with the presence of induced compressive residual stresses, improved the fatigue behavior of the material. The FCG retardation is optimized when two laser lines were applied on both lateral surfaces of the specimen.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Large-Scale Molecular Dynamics Simulation Studies on Deformation of Ni Nanowires: Surface Profile, Defects and Stacking Fault Width Analysis

We report large-scale molecular dynamics simulation deformation studies of Ni nanowire (NW) of size 100 Å (x) × 1000 Å (y) × 100 Å (z) comprising of 925,965 atoms. Surface and internal defects are introduced to study their effect on the surface profile, strength, fracture behavior and deformation mechanisms. Tensile tests have been carried out at a temperature of 10 K and at a strain rate of 10{sup 8} s{sup −1}. Periodic boundary condition is applied along the loading direction (y). Peak strength of 23 GPa is observed in the perfect NW, and the strength decreases with defects. The surface profiles of the deformed NWs show intrusion and extrusion regions corresponding to slip steps with wider valleys in the defect NWs. Several intrinsic and extrinsic parallel stacking faults (SFs) are generated after yielding by slip occurring on {111} planes. The calculated SF widths are in the range of 0.85-2.57 nm in the perfect NW. The dislocations are mainly Shockley partial dislocations of type 1/6 〈112〉, and Schmid’s factor (m) obtained is 0.471. Twinning dislocation of types 1/9 〈221〉 and 1/18 〈172〉 is also observed in the SFs. The density of Shockley partial dislocations is observed to be the maximum in all the NWs.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Leaching Model of Radionuclides in Metal-Organic Framework Particles

Metal-organic frameworks (MOFs) have been used to sequester radionuclides and seal them inside of porous scaffolds using postsynthetic modification procedures. Experiments show that certain Zr-MOF with different capping linkers significantly affects the radionuclide release kinetics. In this work, we developed a leaching model of radionuclides in Zr-MOF particles. The model assumes that uranyl species occupy two energetically favored sites: the metal node and the MOF pores. For a given overall concentration of uranyl species, the partitions of uranyl species at the metal nodes and within the pores are determined by their chemical potentials. The model also considers the effect of particle surface and concentration on chemical potentials and diffusivity. The effects of spatial and structural dependent chemical potentials and diffusivity as well as particle sizes on leaching kinetics are investigated with the model. Predicted and measured uranyl leaching kinetics in Zr-MOF particles under batch experiments are compared. The results demonstrate the model’s capability for exploring the mechanisms of leaching and provide guidance for material design.

Metal-Organic Framework, Diffusion, uranyl, Leachi↗
DOE OSTI2016

Technical Note: An investigation of polarity effects for wide-angle free-air chambers

Purpose: Wide-angle free-air chambers (WAFACs) are used as primary standard measurement devices for establishing the air-kerma strength of low-energy, low-dose rate brachytherapy seeds. The National Research Council of Canada (NRC) is commissioning a primary standard wide-angle free-air chamber (NRC WAFAC) to serve the calibration needs of Canadian clients. The University of Wisconsin has developed a similar variable-aperture free-air chamber (UW VAFAC) to be used as a research tool. As part of the NRC commissioning, measurements were carried out for both polarities of the applied bias voltage and the resulting effects were observed to be very large. Similar effects were identified with the UW VAFAC. The authors describe the measurements carried out to determine the underlying causes of the polarity effect and the approach used to eliminate it. Methods: The NRC WAFAC is based on the WAFAC design developed at the National Institute of Standards and Technology in the USA. Charge measurements for {sup 125}I and {sup 241}Am sources were carried out for both negative and positive polarities on the NRC WAFAC and UW VAFAC. Two aperture sizes were also investigated with the UW VAFAC. In addition, measurements on the NRC WAFAC were carried out with a small bias between the collecting electrode and the shield foil at the downstream end of the chamber. To mitigate all of the polarity effects, the downstream surface of the collecting electrode was covered with a thin layer of graphite on both the NRC and UW chambers. Results: Both chamber designs showed a difference of more than 30 % between the charge collected with positive and negative bias voltages for the smallest electrode separation. It was shown for the NRC WAFAC that charge could be collected in the small gap downstream of the collecting volume by applying a voltage between the shield foil and the collecting electrode, even though an insulating foil (Mylar or polyimide film) separated the conducting surface from the small gap region. The unwanted additional current was shown to be proportional to the size of the aperture for the UW VAFAC. The extra ionization produced in the small gap region was eliminated for both chambers by covering the insulating side of the collecting electrode with a grounded conducting layer. Conclusions: The small gap region downstream of the collecting electrode in the NRC WAFAC and UW VAFAC can serve as an unwanted source of ion current. It is concluded that a residual electric field in the small gap region may lead to ion transport and to charge being trapped on the surface of the foil. The foil then acts as a capacitor with an equal charge, but of opposite sign, being attracted to the conducting surface. Covering the back of the collecting electrode surface with a grounded conducting layer eliminated the polarity effect.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2018

Highly efficient degradation of phenol over a Pd-BiOBr Mott–Schottky plasmonic photocatalyst

Highlights: • Pd cubes were successfully prepared and electrostatically assembled with BiOBr. • A Mott–Schottky junction may be formed between Pd and BiOBr. • Pd nanoparticles may be activated, due to SPR effect. • Pd modified BiOBr exhibited excellent activity in photocatalytic removal of phenol. - Abstract: Surface plasmonic resonance effect has been widely applied to improve oxidation activity of a photocatalyst under visible light irradiation. Palladium particles were successfully prepared, and electrostatically assembled with BiOBr in this work. Due to the differences in work function between palladium and BiOBr, a Mott–Schottky junction may be established. This junction is in favor of the separation of photogenerated charge carriers. Also, Pd particles on the surface may absorb visible-light photons and produce extra electrons to participate in the photocatalysis. The great improvement in the photocatalytic oxidation of phenol confirms the synergetic effect (SPR and Mott–Schottky junction). This work may serve as a solid evidence to confirm that surface-loaded palladium particles are capable of improving photocatalytic activity, and that electrostatic assembly may be an effective approach to load metal particles onto a surface.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

High-Resolution Near-Surface Imaging at the Basin Scale Using Dark Fiber and Distributed Acoustic Sensing: Toward Site Effect Estimation in Urban Environments

Near-surface seismic structure, particularly the shear wave velocity (V s ), can strongly affect local site response, and should be accurately estimated for ground motion prediction during seismic hazard assessment. The Imperial Valley (California), occupying the southern end of the Salton Trough, is a seismically active basin with thick surficial lacustrine sedimentary deposits. In this study, we utilize ambient noise records and local earthquake events for high-resolution near-surface characterization and site effect estimation with an unlit fiber-optic telecommunication infrastructure (dark fiber) in Imperial Valley by using the distributed acoustic sensing (DAS) technique. We apply ambient noise interferometry to retrieve coherent surface waves from DAS records, and evaluate performances of three different surface wave methods on DAS ambient noise dispersion imaging. We develop a quality control workflow to improve the dispersion measurement of noisy portions of the DAS data set by using a data selection strategy. Using the joint inversion of both the fundamental mode and higher overtones of Rayleigh waves, a high resolution two-dimensional (2D) V s structure down to 70 m depth is obtained. We successfully achieve an improved V s 30 (the time-averaged shear-wave velocity in the top 30 m) model with higher spatial-resolution and reliability compared to the existing community model for the area. We also explore the potential for utilizing DAS earthquake events for site amplification estimation. The preliminary results reveal a clear anti-correlation between the approximated site response and the V s 30 profile. In conclusion, our results indicate the potential utility of DAS deployed on dark fiber for near-surface characterization in appropriate contexts.

58 GEOSCIENCES↗