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At least 649 records · Page 36

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DOE OSTI2018

Ultrathin Visible-Light-Driven Mo Incorporating In 2 O 3 -ZnIn 2 Se 4 Z-Scheme Nanosheet Photocatalysts

Inspired by natural photosynthesis, the design of new Z-scheme photocatalytic systems is very promising for boosting the photocatalytic performance of H 2 production and CO 2 reduction, however, till now the direct synthesis of efficient Z-scheme photocatalysts remains a grand challenge. Herein, we demonstrate an interesting Z-scheme photocatalyst can be constructed by coupling In 2 O 3 and ZnIn 2 Se 4 semiconductors based on the theoretical calculations. Experimentally, we make a class of ultrathin In 2 O 3 -ZnIn 2 Se 4 (donated as In 2 O 3 -ZISe) spontaneous Z-scheme nanosheet photocatalysts for greatly enhancing the photocatalytic H 2 production. Furthermore, we incorporate Mo atoms to the Z-scheme In 2 O 3 -ZISe nanosheet photocatalyst by forming Mo-Se bond, confirmed by X-Ray photoelectron spectroscopy, in which the formed MoSe 2 works as co-catalyst of Z-scheme photocatalyst. As a consequence, such unique structure of In 2 O 3 -ZISe-Mo makes it exhibit 21.7 and 232.6 times higher photocatalytic H 2 evolution activity than those of In 2 O 3 -ZnIn 2 Se 4 nanosheet and In 2 O 3 nanosheets, respectively. And In 2 O 3 -ZISe-Mo is also very stable for photocatalytic H 2 production by showing almost no activity decay for 16 h test. Here, the ultraviolet-visible diffuse reflectance spectra, photoluminescence spectroscopy, transient photocurrent spectra and electrochemical impedance spectroscopy reveal that the enhanced photocatalytic performance of In 2 O 3 -ZISe-Mo is mainly attributed to its widened photoresponse range and effective carrier separation because of its special structure.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗

DOE OSTI2020

Design of 3D Oxide–Metal Hybrid Metamaterial for Tailorable Light–Matter Interactions in Visible and Near-Infrared Region

Dielectric–metallic hybrid metamaterials exhibit extraordinary optical properties due to the light–matter interactions at the dielectric–metallic interfaces. The ability in precision control of the light–matter interactions in nanoscale is key to tailor the optical properties of hybrid metamaterials. In this work, a complex 3D framework of multilayered self-assembled BaTiO 3 (BTO)-Au hybrid thin films is demonstrated with such precision control of the light–matter interaction in nanoscale. Here, unique “bamboo-like” Au nanostructures are formed via the bilayer and trilayer stacking of BTO-Au hybrid layers with interlayers of SrTiO 3 , CeO 2 , or MgO. Different film strain states introduced by the three interlayers result in variable diameter and density of Au nanopillars. Both simulated and experimental optical data demonstrate the localized surface plasmon resonance change and hyperbolic dispersion wavelength shift in visible to near-infrared because of the effective tuning of the Au nanopillar aspect ratio and free electron density. The highly tunable optical properties along with the ferroelectric behavior and thermal robustness of the 3D hybrid film enable it to be a great candidate for multifunctional applications. This study demonstrates a unique 3D approach for precision optical property tuning and combined functionalities in oxide–metal metamaterial systems toward future integrated photonic and electronic devices.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Mechanochemistry of Phosphorus and Arsenic Alloys for Visible and Infrared Photonics

Incorporating few‐layer 2D phosphorus–arsenic alloys (PAs) into optoelectronic devices requires a synthesis technique that allows control of the alloy composition while producing volumes of material suitable for application development such as photodetectors, solar cells, and lasers. With that goal in mind, high‐energy ball milling allows production of both orthorhombic (o‐PAs) and trigonal (t‐PAs) alloys by reacting red phosphorus and metallic arsenic powders. The synthesis follows a two‐step process in which arsenic rapidly reacts with red phosphorus to first produce t‐PAs followed by a slower phase transformation into o‐PAs; synthesis time and overall conversion rate are slightly enhanced by the presence of arsenic. Optical measurements on exfoliated alloys at the few‐layer atomic limit of the 2D PAs reveal emission spanning from the visible (≈1.9 eV) into the near‐infrared region, covering a broad application space. Rapid powder synthesis within a closed system for stochiometric control of the solid‐solution PAs alloys combined with solution‐based exfoliation opens up opportunities for a whole new class of optoelectronic devices based on PA nanomaterials.

Pedersen, Samuel V.↗

DOE OSTI2015

High-Performance Semitransparent Perovskite Solar Cells with 10% Power Conversion Efficiency and 25% Average Visible Transmittance Based on Transparent CuSCN as the Hole-Transporting Material

High-performance planar heterojunction perovskite (CH3NH3PbI3) solar cell (PVSC) is demonstrated by utilizing CuSCN as a hole-transporting layer. Efficient hole-transport and hole-extraction at the CuSCN/CH3NH3PbI3 interface facilitate the PVSCs to reach 16% power conversion efficiency (PCE). In addition, excellent transparency of CuSCN enables high-performance semitransparent PVSC (10% PCE and 25% average visible transmittance) to be realized.

14 SOLAR ENERGY↗

DOE OSTI2015

Visible‐Light‐Triggered Molecular Photoswitch Based on Reversible E / Z Isomerization of a 1,2‐Dicyanoethene Derivative

Abstract A designed bis(dithienyl) dicyanoethene‐based, strictly E / Z photoswitch (4TCE) operates through state‐selective ( E and Z isomer) photoactivation with visible light. The E and Z isomers of 4TCE exhibit remarkably different spectroscopic characteristics, including a large separation (70 nm) in their absorption maxima ( λ max ) and a 2.5‐fold increase in molar extinction coefficient from cis to trans . The energetically stable trans form can be completely converted to the cis form within minutes when exposed to white light, whereas the reverse isomerization occurs readily upon irradiation by blue light ( λ <480 nm) or completely by thermal conversion at elevated temperatures. These features together with excellent thermal stability and photostability of both isomers make this new E / Z photoswitch a promising building block for photoswitchable materials that operate without the need for UV light.

Guo, Xin↗

DOE OSTI2018

Pressure‐Tuneable Visible‐Range Band Gap in the Ionic Spinel Tin Nitride

Abstract The application of pressure allows systematic tuning of the charge density of a material cleanly, that is, without changes to the chemical composition via dopants, and exploratory high‐pressure experiments can inform the design of bulk syntheses of materials that benefit from their properties under compression. The electronic and structural response of semiconducting tin nitride Sn 3 N 4 under compression is now reported. A continuous opening of the optical band gap was observed from 1.3 eV to 3.0 eV over a range of 100 GPa, a 540 nm blue‐shift spanning the entire visible spectrum. The pressure‐mediated band gap opening is general to this material across numerous high‐density polymorphs, implicating the predominant ionic bonding in the material as the cause. The rate of decompression to ambient conditions permits access to recoverable metastable states with varying band gaps energies, opening the possibility of pressure‐tuneable electronic properties for future applications.

Kearney, John S. C.↗

DOE OSTI2015

Visible‐Light‐Triggered Molecular Photoswitch Based on Reversible E / Z Isomerization of a 1,2‐Dicyanoethene Derivative

Guo, Xin↗

DOE OSTI2025

Host Cavities Enhance the Photocatalytic Conversion of α‐Terpinene to Ascaridole Under Visible‐Light Irradiation

BODIPY-functionalized host molecules have been used as effective visible-light photosensitizers in the conversion of α-terpinene to ascaridole in the presence of molecular oxygen. Host-guest interactions enhance the effective local concentration of the substrate and singlet oxygen generated by the photosensitizing host. This results in up to a 28-fold increase in the rate of conversion depending on the host employed. A tetramethyl BODIPY analogue, in which guest access to the host cavity is blocked, was also employed to confirm that the cavities do indeed enhance substrate turnover. Whilst the latter photocatalyst is more efficient due to the suppression of nonradiative relaxation pathways associated with rotation of the meso-phenyl substituent, the rate enhancement induced by host-guest binding is not present. Combined, this provides insight for the future design of enhanced systems.

Main, Mawgan U↗

DOE OSTI2016

Hierarchically Superstructured Metal Sulfides: Facile Perturbation-Assisted Nanofusion Synthesis and Visible Light Photocatalytic Characterizations

A novel and simple perturbation-assisted nanofusion (PNF) synthetic strategy was developed for the fabrication of stable hierarchically superstructured metal sulfides. This promising approach, based on a kinetically controlled precipitation to simultaneously condense and re-dissolve polymorphic nanocrystallites, provides the resultant samples with a unique mesoporous framework. This PNF approach is environmentally friendly, produces gram-scale products in a matter of hours, and is complimentary to traditional hard or soft templating methods for the construction of mesoporous metal sulfides. PNF derived hierarchical porous CdS exhibited a vastly improved photocatalytic performance over its commercial bulk counterpart under visible light irradiation, demonstrating the advantage of the porous morphology for photocatalysis resulting from the enlarged surface area and the easy accessibility of the mesopores.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2016

Titania Composites with 2 D Transition Metal Carbides as Photocatalysts for Hydrogen Production under Visible-Light Irradiation

In the MXenes family of two-dimensional transition-metal carbides there were successful demonstrations of co-catalysts with rutile TiO 2 for visible-light-induced solar hydrogen production from water splitting. The physicochemical properties of Ti 3 C 2 T x MXene coupled with TiO 2 were investigated by a variety of characterization techniques. The effect of the Ti 3 C 2 T x loading on the photocatalytic performance of the TiO 2 /Ti 3 C 2 T x composites was elucidated. Moreover, with an optimized Ti 3 C 2 T x content of 5 wt %, the TiO 2 /Ti 3 C 2 T x composite shows a 400 % enhancement in the photocatalytic hydrogen evolution reaction compared with that of pure rutile TiO 2 . We also expanded our exploration to other MXenes (Nb 2 CT x and Ti 2 CT x ) as co-catalysts coupled with TiO 2 , and these materials also exhibited enhanced hydrogen production. These results manifest the generality of MXenes as effective co-catalysts for solar hydrogen production.

36 MATERIALS SCIENCE↗

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 OSTI2021

Crystal structures of inhibitor complexes of M‐PMV protease with visible flap loops

Abstract Mason‐Pfizer monkey virus protease (PR) was crystallized in complex with two pepstatin‐based inhibitors in P 1 space group. In both crystal structures, the extended flap loops that lock the inhibitor/substrate over the active site, are visible in the electron density either completely or with only small gaps, providing the first observation of the conformation of the flap loops in dimeric complex form of this retropepsin. The H‐bond network in the active site (with D26N mutation) differs from that reported for the P 2 1 crystal structures and is similar to a rarely occurring system in HIV‐1 PR.

Wosicki, Stanislaw↗

DOE OSTI2023

Discovering Reactant Supply Pathways at Electrode/PEM Reaction Interfaces Via a Tailored Interface-Visible Characterization Cell

In situ and micro-scale visualization of electrochemical reactions and multiphase transports on the interface of porous transport electrode (PTE) materials and solid polymer electrolyte (SPE) has been one of the greatest challenges for electrochemical energy conversion devices, such as proton exchange membrane electrolyzer cells (PEMECs), CO 2 reduction electrolyzers, PEM fuel cells, etc. Here, an interface-visible characterization cell (IV-CC) is developed to in situ visualize micro-scaled and rapid electrochemical reactions and transports in PTE/SPE interfaces. Taking the PEMEC of a green hydrogen generator as a study case, the unanticipated local gas blockage, micro water droplets, and their evolution processes are successfully visualized on PTE/PEM interfaces in a practical PEMEC device, indicating the existence of unconventional reactant supply pathways in PEMs. Further comprehensive results reveal that PEM water supplies to reaction interfaces are significantly impacted with current densities. Here these results provide critical insights about the reaction interface optimization and mass transport enhancement in various electrochemical energy conversion devices.

30 DIRECT ENERGY CONVERSION↗

DOE OSTI2017

New physics in the visible final states of B → D(*) τν

We derive compact expressions for the helicity amplitudes of the many-body B → D (*) (→ DY)τ(→ Xν)ν decays, specifically for X = ℓν or π and Y = π or γ. We include contributions from all ten possible new physics four-Fermi operators with arbitrary couplings. Our results capture interference effects in the full phase space of the visible τ and D * decay products which are missed in analyses that treat the τ or D * or both as stable. The τ interference effects are sizable, formally of order m τ /m B for the standard model, and may be of order unity in the presence of new physics. Treating interference correctly is essential when considering kinematic distributions of the τ or D * decay products, and when including experimentally unavoidable phase space cuts. Our amplitude-level results also allow for efficient exploration of new physics effects in the fully differential phase space, by enabling experiments to perform such studies on fully simulated Monte Carlo datasets via efficient event reweighing. As an example, we explore a class of new physics interactions that can fit the observed R(D (*) ) ratios, and show that analyses including more differential kinematic information can provide greater discriminating power for new physics, than single kinematic variables alone.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2024

Semi-visible jets + X: illuminating dark showers with radiation

We investigate the potential to search for semi-visible jets (SVJs) at the Large Hadron Collider (LHC) using initial-state radiation (ISR). Both photon ISR and jet ISR channels are considered, using a benchmark signal model with the decay of a leptophobic Z$^{′}$ mediator forming two SVJs. We compare and extend several techniques to decompose the missing transverse momentum into per-jet contributions, in order to reconstruct the mediator mass and to define a new observable measuring the fraction of invisible dark hadrons. The presence of ISR facilitates the identification of the SVJs, and the resulting boost improves the resolution of the observables, especially for models with high invisible fractions. We combine the two observables to propose a complete search strategy and discuss an extension of the strategy to probe the whole model parameter space.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

Clinical Outcome of the Visible Coil During Endoscopy After Transcatheter Arterial Embolization for Gastrointestinal Bleeding

Purpose: This study was designed to evaluate the clinical outcome of the visible coil during endoscopy after transcatheter arterial embolization (TAE) for gastrointestinal bleeding. Methods: We retrospectively reviewed the medical records of 1415 patients who underwent TAE for gastrointestinal bleeding between 2001 and 2017. Among these 1415 patients, 70 underwent TAE using coils and consecutive follow-up endoscopy. Finally, 11 patients with an extravascular coil seen on follow-up endoscopic examination were included in this study. We evaluated the underlying cause of the gastrointestinal bleeding, the technical and clinical success rates, the type of extravascular coil after TAE, and the clinical outcomes of the extravascular coil seen on follow-up endoscopic examination. Results: Of the 11 patients, the most common underlying cause of gastrointestinal bleeding was a duodenal ulcer (n = 7). On angiography, the bleeding artery was most commonly found in the gastroduodenal artery (n = 6). The technical success and clinical success rates of TAE were 100% and 90.9%, respectively. The type of extravascular coil found on endoscopic examination was classified by submucosal migration (n = 6) and protrusion (n = 5). On second-look endoscopic evaluation, 10 of 11 (90.9%) patients showed healing ulceration. On the final-look endoscopic evaluation, healing ulceration without further bleeding was seen in one (9.1%) patient and scar formation was seen in ten (90.9%) patients. Conclusions: Extravascular coil after TAE for gastrointestinal bleeding is rare, and the most common underlying cause is duodenal ulcer bleeding. The extravascular coils eventually show a healing process with adequate treatment of underlying bowel pathologies.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2017

Partial Least Squares Regression Calibration of an Ultraviolet-Visible Spectrophotometer for Measurements of Chemical Oxygen Demand in Dye Wastewater

Wastewater from the dye industry is typically analyzed using a standard method for measurement of chemical oxygen demand (COD) or by a single-wavelength spectroscopic method. To overcome the disadvantages of these methods, ultraviolet-visible (UV-Vis) spectroscopy was combined with principal component regression (PCR) and partial least squares regression (PLSR) in this study. Unlike the standard method, this method does not require digestion of the samples for preparation. Experiments showed that the PLSR model offered high prediction performance for COD, with a mean relative error of about 5% for two dyes. This error is similar to that obtained with the standard method. In this study, the precision of the PLSR model decreased with the number of dye compounds present. It is likely that multiple models will be required in reality, and the complexity of a COD monitoring system would be greatly reduced if the PLSR model is used because it can include several dyes. UV-Vis spectroscopy with PLSR successfully enhanced the performance of COD prediction for dye wastewater and showed good potential for application in on-line water quality monitoring.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Effect of Heat Treatment on Madagascar Dravite Tourmaline: UV-Visible and Diffuse Reflectance Infrared Spectroscopic Characterization

The color change and chemical behavior of Madagascar dravite when subjected to heating in air atmosphere were studied by energy-dispersive X-ray fluorescence spectrometry, UV-visible (UV-vis) spectroscopy and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Heat treatment was performed with temperatures of 500, 600, and 700°C for 2 h. Colors and color differences were measured and evaluated using CIELAB color measurement. The origin of color and its change after treatment are assessed via UV-vis spectra. The diffuse reflectance infrared spectra of the dravites revealed major absorption bands of OH, BO{sub 3}, Si{sub 6}O{sub 18}, and R–OH (where R = Fe, Mg). The variation of infrared spectra with increasing temperature indicates the deformation of R–OH bonds in an octahedron and, further, the deformation of BO{sub 3} and Si{sub 6}O{sub 18}. The results of color change may be utilized to enhance the color or clarity in dravite tourmaline and for generating satisfactory color.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗