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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.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Photooxidative decomposition and defluorination of perfluorooctanoic acid (PFOA) using an innovative technology of UV–vis/Zn x Cu 1-x Fe 2 O 4 /oxalic acid

Per- and polyfluoroalkyl substances (PFAS) are a large group of perfluorinated organic molecules that have been in use since the 1940s for industrial, commercial, and consumer applications. PFAS are a growing concern because some of them have shown persistent, bioaccumulative and toxic effects. In this work, we demonstrate an innovative technology of UV–vis/Zn x Cu 1-x Fe 2 O 4 /oxalic acid for the degradation of perfluorooctanoic acid (PFOA) in water. The magnetically retrievable nanocrystalline heterogeneous ferrite catalysts, Zn x Cu 1-x Fe 2 O 4 were synthesized using a sol-gel auto-combustion process followed by calcination at 400 °C. The combination of Zn x Cu 1-x Fe 2 O 4 and oxalic acid generate reactive species under UV light irradiation. These reactive species are then shown to be capable of the photodegradation of PFOA. The degree of degradation is tracked by identifying transformation products using liquid chromatography coupled with quadrupole time-of-flight mass spectroscopy (LC-QTOF-MS).

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

UV-Vis spectrophotometric determination of rare earth elements (REE) speciation at near-neutral to alkaline pH. Part II: hydrolysis of Er from 25 to 75 °C

Aqueous speciation of rare earth elements (REE) controls their mobilization, fractionation, and enrichment in the natural waters. Geochemical modeling of their speciation is key to improve our understanding of the formation of economic mineral deposits, for developing mineral separation and mine tailing recovery technologies, and for characterizing the geochemistry of thermal water. However, our ability to predict the fate of REE in a wide pH and temperature range is limited by the scarcity of thermodynamic data for the REE hydroxyl complexes. In part I of this study (H. J. Han and A. P. Gysi, Dalton Trans., 2024, 53, 13129–13141), the optical properties of m-cresol purple (mCP) were determined using UV-Vis spectrophotometry between 25 and 75 °C in order to develop a method for deriving the hydrolysis constants of erbium (Er). Here, UV-Vis spectrophotometry experiments were conducted as a function of temperature between 35 and 75 °C to determine the hydrolysis of Er in near-neutral to alkaline solutions using mCP as an in situ pH color indicator. Here, the experiments were conducted with Er concentrations from 0 to ~0.253 mmol kg –1 in low ionic strength solutions (≤0.001 mol kg –1 ).

58 GEOSCIENCES↗
DOE OSTI2025

High-Intensity UV Exposure for the Rapid Screening of Silicon Photovoltaic Architectures

Advanced Si photovoltaic architectures incorporate different materials and processing pathways that influence degradation modes. Ultraviolet-induced degradation (UVID) is an understudied degradation mode for advanced cell architectures and is of increasing concern to industry due to growing adoption of UV-transparent encapsulation and bifacial technologies. In order to adopt new and evolving technologies confidently, novel component materials and processing techniques must be evaluated and designed for long-term stability, in addition to the conventional design focus on efficiency. In this work, a study protocol framework is presented for the rapid screening of unencapsulated devices against UVID. Unencapsulated passivated emitter rear contact (PERC) and tunnel oxide passivated contact (TOPCon) devices were aged under different UV irradiance intensities and measured via conventional nondestructive electrical characterization methods to assess performance degradation. Based on the results, protocol efficacy and recommendations for further study are discussed. As a result, this work is part of a broader effort to develop rapid screening processes that cut across architectures and exposure conditions to aid module manufacturers in vetting new materials choices for long-term stability.

Accelerated exposure↗
DOE OSTI2022

UV Degradation in Backsheets: A Ray-Tracing Irradiance Simulation Approach

Around 90% of current photovoltaic (PV) modules are less than ten years old. New PV technologies and materials are deployed without documented durability and performance histories. Accelerated testing attempts to capture degradation modes but can produce false results with such rapid deployment of new materials. Current testing assumes UV dosage on the rear of a module to be 10% of that incident on the front. We present a method to quantify degradation on PV backsheets in the field. We aim to evaluate if current acceleration factors for UV damage in chambers are properly estimating degradation for different PV site installations. The method leverages bifacial_radiance to ray-trace and evaluate irradiance on the front and the rear of the modules. Then an equation to estimate the relative degradation is proposed.

accelerated testing↗
DOE OSTI2025

Characterization of PuO 2 With Visible and UV Raman Spectroscopy: Discrimination Between the Bulk, Surface, and an Intermediate Disordered Layer

Raman spectroscopy is an ideal tool in the characterization of materials including PuO 2 . The wavelength-dependent absorptivity of the material defines the light penetration depth and the relative Raman scattering contribution from the bulk and the surface. Here, the surface contribution to the total Raman scattering was investigated for PuO 2 calcined at various temperatures and recorded with laser wavelengths of 355, 325, and 244 nm. These experiments provided the first glimpse of the wavelength-dependent disappearance and emergence of new phonons and electronic bands from the PuO 2 surface layers. The first indication of the wavelength transition in the Raman spectra was the loss of the 2LO2 (overtone, ~1155 cm -1 ) band and the weakening intensity of the Г 1 → Γ 5 electronic band (~2135 cm -1 ) with the 355-nm excitation laser. The Γ 5 electronic band was barely visible with the 244-nm excitation. The electronic band located at ~1050 cm -1 , corresponding to the Г 1 → Γ 4 electronic transition was observed to dramatically increase in intensity while the Г 1 → Γ 3 electronic band (2640 cm -1 ) sharpened as the UV wavelength was increased in energy from the near- to deep-UV (355–325–244 nm). The FWHM of the T 2g band was found to vary with calcination temperature (450°C and 900°C) with the 325-nm laser and the 244-nm laser. The T 2g band attributes, the strong emergence of the Г 1 → Γ 4 electronic band, and the disappearance of the 2LO2 overtone acquired with the 244-nm excitation for the different calcination temperatures suggest a shallow penetration depth.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

IR dynamics from UV divergences: UV/IR mixing, NCFT, and the hierarchy problem

The persistence of the hierarchy problem points to a violation of effective field theory expectations. A compelling possibility is that this results from a physical breakdown of EFT, which may arise from correlations between ultraviolet (UV) and infrared (IR) physics. To this end, we study noncommutative field theory (NCFT) as a toy model of UV/IR mixing which generates an emergent infrared scale from ultraviolet dynamics. We explore the range of such theories where ultraviolet divergences are transmogrified into infrared scales, focusing particularly on the properties of Yukawa theory, where we identify a new infrared pole accessible in the s-channel of the Lorentzian theory. We further investigate the interplay between UV-finiteness and UV/IR mixing by studying properties of the softly-broken noncommutative Wess-Zumino model as soft terms are varied relative to the cutoff. While the Lorentz violation inherent to noncommutative theories may limit their direct application to the hierarchy problem, these toy models provide general lessons to guide the realization of UV/IR mixing in more realistic theories.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Leptonic scalars and collider signatures in a UV-complete model

We study the non-standard interactions of neutrinos with light leptonic scalars ( ϕ ) in a global ( B – L )-conserved ultraviolet (UV)-complete model. The model utilizes Type-II seesaw motivated neutrino interactions with an SU(2) L -triplet scalar, along with an additional singlet in the scalar sector. This UV-completion leads to an enriched spectrum and consequently new observable signatures. We examine the low-energy lepton flavor violation constraints, as well as the perturbativity and unitarity constraints on the model parameters. Then we lay out a search strategy for the unique signature of the model resulting from the leptonic scalars at the hadron colliders via the processes H ±± → W ± W ± ϕ and H ± → W ± ϕ for both small and large leptonic Yukawa coupling cases. We find that via these associated production processes at the HL-LHC, the prospects of doubly-charged scalar H ±± can reach up to 800 (500) GeV and 1.1 (0.8) TeV at the 2 σ (5 σ ) significance for small and large Yukawa couplings, respectively. A future 100 TeV hadron collider will further increase the mass reaches up to 3.8 (2.6) TeV and 4 (2.7) TeV, at the 2 σ (5 σ ) significance, respectively. We also demonstrate that the mass of ϕ can be determined at about 10% accuracy at the LHC for the large Yukawa coupling case even though it escapes as missing energy from the detectors.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

The UV fate of anomalous U(1)s and the Swampland

Massive U(1) gauge theories featuring parametrically light vectors are suspected to belong in the Swampland of consistent EFTs that cannot be embedded into a theory of quantum gravity. We study four-dimensional, chiral U(1) gauge theories that appear anomalous over a range of energies up to the scale of anomaly-cancelling massive chiral fermions. We show that such theories must be UV-completed at a finite cutoff below which a radial mode must appear, and cannot be decoupled — a Stückelberg limit does not exist. When the infrared fermion spectrum contains a mixed U(1)-gravitational anomaly, this class of theories provides a toy model of a boundary into the Swampland, for sufficiently small values of the vector mass. In this context, we show that the limit of a parametrically light vector comes at the cost of a quantum gravity scale that lies parametrically below MP1, and our result provides field theoretic evidence for the existence of a Swampland of EFTs that is disconnected from the subset of theories compatible with a gravitational UV-completion. Moreover, when the low energy theory also contains a U(1) 3 anomaly, the Weak Gravity Conjecture scale makes an appearance in the form of a quantum gravity cutoff for values of the gauge coupling above a certain critical size.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Holographic entanglement from the UV to the IR

In AdS/CFT, observables on the boundary are invariant under renormalization group (RG) flow in the bulk. In this paper, we study holographic entanglement entropy under bulk RG flow and find that it is indeed invariant. We focus on tree-level RG flow, where massive fields in a UV theory are integrated out to give the IR theory. We explicitly show that in several simple examples, holographic entanglement entropy calculated in the UV theory agrees with that calculated in the IR theory. Moreover, we give an argument for this agreement to hold for general tree-level RG flow. Along the way, we generalize the replica method of calculating holographic entanglement entropy to bulk theories that include matter fields with nonzero spin.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Observation of Long-Lived UV-Induced Fluorescence from Environmental Materials Using the HVeV Detector as Developed for SuperCDMS

Here, we describe recent experiments using a SuperCDMS HVeV single-charge sensitive detector illuminated with an ultraviolet LED (275 nm) and a monochromatic laser(650 nm) using a dual fiber optic system installed in a small dilution refrigerator at Stanford University. We observed a population of fluorescence background events after UV exposure but not after exposure to the laser source. The fluorescence was likely due to scattered UV photons absorbed outside the detector. We discuss the possibility of fluorescence being a contributor to the low energy excess background observed in above-ground Dark Matter experiments.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Zero-biased and visible-blind UV photodetectors based on nitrogen-doped ultrananocrystalline diamond nanowires

Taking advantage of the superflat surface of ultrananocrystalline diamond (UNCD), highly precise UNCD nanowire (NW) arrays were fabricated to develop high-performance UV photodetectors. The large surface-to-volume ratio of a nanowire significantly increases the number of surface trap states, and the reduced dimensionality effectively confines the active area of the charge carrier and shortens the transit time, which results in an enhanced photoconductivity and response speed. Here, in this paper, the zero-biased UV photodetectors based on nitrogen-incorporated ultrananocrystalline diamond nanowire arrays have been demonstrated and characterized. The estimated responsivity was 2.0 A/W for 350 nm incident light when the device operated at room temperature. The UVA and UVB photocurrent signals from this visible blind photodetector were well defined with a rise and decay time of less than 1 s.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Preliminary Studies of UV Photolysis of Gas-phase CH3I in Air: Time-resolved Infrared Identification of Methanol and Formaldehyde Products

Halogen-bearing compounds are known to photolyze under UV radiation; analysis of degradation products is of interest for both safety and environmental considerations. Time-resolved infrared spectroscopy was used in the laboratory to study the UV-photolysis of methyl iodide. Photolysis products methanol (CH3OH) and formaldehyde (HCHO) were clearly identified in a time-resolved manner. Preliminary kinetic models predict the formation of both CH3OH and HCHO.

Hughey, Kendall D.↗
DOE OSTI2020

Localized UV emitters on the surface of β-Ga 2 O 3

Abstract Monoclinic gallium oxide (β-Ga 2 O 3 ) is attracting intense focus as a material for power electronics, thanks to its ultra-wide bandgap (4.5–4.8 eV) and ability to be easily doped n -type. Because the holes self-trap, the band-edge luminescence is weak; hence, β-Ga 2 O 3 has not been regarded as a promising material for light emission. In this work, optical and structural imaging methods revealed the presence of localized surface defects that emit in the near-UV (3.27 eV, 380 nm) when excited by sub-bandgap light. The PL emission of these centers is extremely bright—50 times brighter than that of single-crystal ZnO, a direct-gap semiconductor that has been touted as an active material for UV devices.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Surmounting the interband threshold limit by the hot electron excitation of multi-metallic plasmonic AgAuCu NPs for UV photodetector application

We report multi-metallic alloy NPs composed of various elemental compositions can surmount the interband threshold limit of mono-metallic NPs and thus can offer a promising route to boost up the performance limit of conventional ultraviolet photodetectors (PDs). In this work, a hybrid UV-PD configuration has been demonstrated by combining the multi-metallic plasmonic alloy NPs of AgCu, AuCu, and AgAuCu on a GaN photoactive layer in order to exploit the improved photo carrier injection by the strong hot electrons and LSPR. Among various devices, the tri-metallic AgAuCu NP PD demonstrates the highest performance with a remarkably high photocurrent of 1.47 x 10 -2 A at 1 V with fast rise (T r ) and fall (T f ) times of 170 and 700 ms with a very stable current. This leads to the superior figure-of-merit parameters of the PD with a photoresponsivity of 4.3 x 10 6 mA W-1, detectivity of 3.52 x 10 12 Jones and EQE of 1.39 x 10 6 %, which is ~16 times higher than the bare GaN PD. This ranks the AgAuCu PD as one of the best GaN based UV photodetectors. The photocurrent enhancement and excellent figure-of-merit can be attributed to the significantly increased photo carrier injection by the efficient hot electron generation via the LSPR and improved interfacial barrier characteristics by the tri-metallic elemental synergy.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Carbazole-substituted benzobisoxazoles: near-UV fluorescent emitters and ambipolar hosts for organic light-emitting diodes

The design of organic light emitting diode (OLED) materials with the potential for exhibiting thermally-activated delayed fluorescence (TADF) is reported. Using computational methods (DFT/TD-DFT) as a guiding tool, six materials with a benzobisoxazole (BBO) core and donor–acceptor–donor architectures were designed by changing the conjugation position of carbazole-substituted phenyl substituents and the type of BBO isomer (cis- vs. trans-). Experimental steady-state and transient absorption spectroscopic techniques were utilized to probe the TADF activity of these molecules. Each material was then used in host–guest OLED devices as either near-UV dopants or host with low singlet-triplet energy differences. The electroluminescent properties show that when used as dopants these materials provide near-UV emission (CIE y < 0.06 and CIE x = 0.16), whereas when used as hosts, these materials show reduced operating voltages and increased performance efficiencies when compared to commercial materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The Chandra view of the relation between X-ray and UV emission in quasars

Here, we present a study of the relation between X-rays and ultraviolet emission in quasars for a sample of broad-line, radio-quiet objects obtained from the cross-match of the Sloan Digital Sky Survey DR14 with the latest Chandra Source Catalog 2.0 (2332 quasars) and the Chandra COSMOS Legacy survey (273 quasars). The non-linear relation between the ultraviolet (at 2500 Å, L UV ) and the X-ray (at 2 keV, L X ) emission in quasars has been proved to be characterised by a smaller intrinsic dispersion than the observed one, as long as a homogeneous selection, aimed at preventing the inclusion of contaminants in the sample, is fulfilled. By leveraging on the low background of Chandra, we performed a complete spectral analysis of all the data available for the SDSS-CSC2.0 quasar sample (i.e. 3430 X-ray observations), with the main goal of reducing the uncertainties on the source properties (e.g. flux, spectral slope). We analysed whether any evolution of the L X – L UV relation exists by dividing the sample in narrow redshift intervals across the redshift range spanned by our sample, z ≃ 0.5–4. We find that the slope of the relation does not evolve with redshift and it is consistent with the literature value of 0.6 over the explored redshift range, implying that the mechanism underlying the coupling of the accretion disc and hot corona is the same at the different cosmic epochs. We also find that the dispersion decreases when examining the highest redshifts, where only pointed observations are available. These results further confirm that quasars are ‘standardisable candles’, that is we can reliably measure cosmological distances at high redshifts where very few cosmological probes are available.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

The R-Process Alliance: Hunting for gold in the near-UV spectrum of 2MASS J05383296–5904280

Over the past few years, the R-Process Alliance (RPA) has successfully carried out a search for stars that are highly enhanced in elements produced via the rapid neutron-capture (r-) process. In particular, the RPA has identified a number of relatively bright, highly r-process-enhanced (r-II) stars, suitable for observations with the Hubble Space Telescope (HST), facilitating abundance derivation of elements such as gold (Au) and cadmium (Cd). This paper presents the detailed abundances derived for the metal-poor ([Fe/H] = −2.55) highly r-process-enhanced ([Eu/Fe] = +1.29) r-II star 2MASS J05383296–5904280. One-dimensional local thermodynamic equilibrium (LTE) elemental abundances were derived via equivalent width and spectral synthesis using high-resolution high signal-to-noise near-UV HST/STIS and optical Magellan/MIKE spectra. Abundances were determined for 43 elements, including 26 neutron-capture elements. In particular, abundances of the rarely studied elements Nb, Mo, Cd, Lu, Os, Pt, and Au are derived from the HST spectrum. These results, combined with RPA near-UV observations of two additional r-II stars, increase the number of Cd abundances derived for r-process-enriched stars from seven to ten and Au abundances from four to seven. A large star-to-star scatter is detected for both of these elements, highlighting the need for more detections enabling further investigations, specifically into possible non-LTE effects.

chemically peculiar stars↗
DOE OSTI2020

Excited state dynamics of cis , cis -1,3-cyclooctadiene: UV pump VUV probe time-resolved photoelectron spectroscopy

We present UV pump, vacuum ultraviolet probe time-resolved photoelectron spectroscopy measurements of the excited state dynamics of cis,cis-1,3-cyclooctadiene. A 4.75 eV deep UV pump pulse launches a vibrational wave packet on the first electronically excited state, and the ensuing dynamics are probed via ionization using a 7.92 eV probe pulse. The experimental results indicate that the wave packet undergoes rapid internal conversion to the ground state in under 100 fs. Comparing the measurements with electronic structure and trajectory surface hopping calculations, we are able to interpret the features in the measured photoelectron spectra in terms of ionization to several states of the molecular cation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗