CO Adsorbate Promotes Polaron Photoactivity on the Reduced Rutile TiO 2 (110) Surface
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SEARCH · Engineering Papers
Results for “photoactivity”
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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Few-fs resolution of a photoactive protein traversing a conical intersection
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Science & Technology - Other Topics↗
Dual-mode surface-enhanced Raman scattering sensors assembled from graphene plasmonic nanoresonator on photoactive SOI
The nanocavity construction of the 3D-graphene combines with the optical cavity system of the SOI to improve the interaction between the incident light and 3D-graphene. These properties enhance electronic interactions, thereon improving chemical/charge transfer effects in heterojunctions.
Zhang, Shan↗
Initial dynamic photoactive materials testing of an atmospheric chamber intended for radioactive and hazardous gases
Radioisotopes and hazardous gases can have undetermined environmental pathways. Researchers at Pacific Northwest National Laboratory constructed a chamber that complies with the requirements needed for an atmospheric reaction platform and the safety principles of interacting with hazardous dispersible sources to enable the environmental testing of these gases. Initial dynamic testing showed inter-chamber mixing completed from minutes to 1.5 hours. The photooxidation of butyl iodine showed the presence of signals from reaction products, and intermediaries for up to 50 hours. Current detection limits of the chamber and analytical collection and testing approach were shown to be in the single-digit parts per billion levels. In conclusion, the comparisons between the measured oxidation trends and literature show the utility of performing laboratory experiments to validate the results of modeling for larger-scale scenarios.
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Assemblies of Polyacrylonitrile-Derived Photoactive Polymers as Blue and Green Light Photo-Cocatalysts for Cu-Catalyzed ATRP in Water and Organic Solvents
Photoluminescent nanosized quasi-spherical polymeric assemblies prepared by the hydrothermal reaction of polyacrylonitrile (PAN), ht-PLP PAN , were demonstrated to have the ability to photo-induce atom transfer radical polymerization (ATRP) catalyzed by low, parts per million concentrations of Cu II complex with tris(2-pyridylmethyl)amine (TPMA). Such photo induced ATRP reactions of acrylate and methacrylate monomers were performed in water or organic solvents, using ht-PLP PAN as the photo-cocatalyst under blue or green light irradiation. Mechanistic studies indicate that ht-PLP PAN helps to sustain the polymerization by facilitating the activation of alkyl bromide species by two modes: 1) green or blue light-driven photoreduction of the Cu II catalyst to the activating Cu I form, and 2) direct activation of dormant alkyl bromide species which occurs only under blue light. The photoreduction of the Cu II complex by ht-PLP PAN was confirmed by linear sweep voltammetry performed under illumination. Analysis of the polymerization kinetics in aqueous media indicated even though Cu I complexes comprised only 1–1.4% of all Cu species at equilibrium, they exhibited high activation rate constant and activated the alkyl bromide initiators five to six orders of magnitude faster than ht-PLP PAN .
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Reducing power generated in the second photoact of photosynthesis.
Quantum yield of photoreduction intrinsically lower in Bishop Scenedesmus mutant than in wild- type algae photosynthesis
PHOTOREDUCTION↗
The reducing power generated in photoact I of photosynthesis.
Photoreduction of viologen dyes analyzed with chloroplasts, noting oxygen evolution and photophosphorylation efficiency, reduction potentials, etc
PHOTOSYNTHESIS↗
Photonic Diagnostic Technique For Thin Photoactive Films
Photonic diagnostic technique developed for use in noninvasive, rapid evaluation of thin paraelectric/ferroelectric films. Method proves useful in basic research, on-line monitoring for quality control at any stage of fabrication, and development of novel optoelectronic systems. Used to predict imprint-prone memory cells, and to study time evolution of defects in ferroelectric memories during processing. Plays vital role in enabling high-density ferroelectric memory manufacturing. One potential application lies in use of photoresponse for nondestructive readout of polarization memory states in high-density, high-speed memory devices. In another application, extension of basic concept of method makes possible to develop specially tailored ferrocapacitor to act as programmable detector, wherein remanent polarization used to modulate photoresponse. Large arrays of such detectors useful in optoelectronic processing, computing, and communication.
Thakoor, Sarita↗
Materials for controlling the epitaxial growth of photoactive layers in photovoltaic devices
There is disclosed ultrathin film material templating layers that force the morphology of subsequently grown electrically active thin films have been found to increase the performance of small molecule organic photovoltaic (OPV) cells. There is disclosed electron-transporting material, such as hexaazatriphenylene-hexacarbonitrile (HAT-CN) can be used as a templating material that forces donor materials, such as copper phthalocyanine (CuPc) to assume a vertical-standing morphology when deposited onto its surface on an electrode, such as an indium tin oxide (ITO) electrode. It has been shown that for a device with HAT-CN as the templating buffer layer, the fill factor and short circuit current of CuPc:C60 OPVs were both improved compared with cells lacking the HAT-CN template. This is explained by the reduction of the series resistance due to the improved crystallinity of CuPc grown onto the ITO surface.
Forrest, Stephen R.↗
High speed CMOS imager with motion artifact supression and anti-blooming
An image sensor includes pixels formed on a semiconductor substrate. Each pixel includes a photoactive region in the semiconductor substrate, a sense node, and a power supply node. A first electrode is disposed near a surface of the semiconductor substrate. A bias signal on the first electrode sets a potential in a region of the semiconductor substrate between the photoactive region and the sense node. A second electrode is disposed near the surface of the semiconductor substrate. A bias signal on the second electrode sets a potential in a region of the semiconductor substrate between the photoactive region and the power supply node. The image sensor includes a controller that causes bias signals to be provided to the electrodes so that photocharges generated in the photoactive region are accumulated in the photoactive region during a pixel integration period, the accumulated photocharges are transferred to the sense node during a charge transfer period, and photocharges generated in the photoactive region are transferred to the power supply node during a third period without passing through the sense node. The imager can operate at high shutter speeds with simultaneous integration of pixels in the array. High quality images can be produced free from motion artifacts. High quantum efficiency, good blooming control, low dark current, low noise and low image lag can be obtained.
Pain, Bedabrata↗
Image sensor with motion artifact supression and anti-blooming
An image sensor includes pixels formed on a semiconductor substrate. Each pixel includes a photoactive region in the semiconductor substrate, a sense node, and a power supply node. A first electrode is disposed near a surface of the semiconductor substrate. A bias signal on the first electrode sets a potential in a region of the semiconductor substrate between the photoactive region and the sense node. A second electrode is disposed near the surface of the semiconductor substrate. A bias signal on the second electrode sets a potential in a region of the semiconductor substrate between the photoactive region and the power supply node. The image sensor includes a controller that causes bias signals to be provided to the electrodes so that photocharges generated in the photoactive region are accumulated in the photoactive region during a pixel integration period, the accumulated photocharges are transferred to the sense node during a charge transfer period, and photocharges generated in the photoactive region are transferred to the power supply node during a third period without passing through the sense node. The imager can operate at high shutter speeds with simultaneous integration of pixels in the array. High quality images can be produced free from motion artifacts. High quantum efficiency, good blooming control, low dark current, low noise and low image lag can be obtained.
Pain, Bedabrata↗
Hybrid planar-mixed heterojunction for organic photovoltaics
Disclosed herein are organic photosensitive optoelectronic devices comprising two electrodes in superposed relation; a mixed photoactive layer located between the two electrodes, wherein the mixed photoactive layer comprises at least one donor material having a HOMO energy and at least one acceptor material having a LUMO energy, wherein the at least one donor material and the at least one acceptor material form a mixed donor-acceptor heterojunction; a photoactive layer adjacent to and interfacing with the mixed photoactive layer, wherein the photoactive layer comprises a material having a LUMO energy within 0.3 eV of the LUMO energy of the at least one acceptor material or a HOMO energy within 0.3 eV of the HOMO energy of the at least one donor material; and a buffer layer adjacent to and interfacing with the mixed photoactive layer.
Forrest, Stephen R.↗
Mechanically stacked tandem photovoltaic cells with intermediate optical filters
A method of fabricating a multi-junction photosensitive device is provided. The method may include fabricating at least two photoactive layers, wherein at least one photoactive layer is fabricated on a transparent substrate, and at least one photoactive layer is fabricated on a reflective substrate, patterning at least one optical filter layer on at least one photoactive layer fabricated on a transparent substrate, and bonding the at least two photoactive layers using cold weld or van der Waals bonding. A multi-junction photosensitive device is also provided. The device may have at least two photoactive layers, and at least one optical filter layer, wherein at least two layers are bonded using cold weld or van der Waals bonding. The optical filter layer may be a Distributed Bragg Reflector.
Forrest, Stephen R.↗
Development of a scalar-based geometric parameterization approach for the crystal structure landscape of dithienylethene-based crystalline solids
Dithienylethenes (DTEs) are a promising class of organic photoswitches that can be used to create crystalline solids with properties controlled by light. However, the ability of DTEs to adopt multiple conformations, only one of which is photoactive, complicates the rational design of these materials. Herein, the synthesis and structural characterization of 19 crystalline solids containing a single DTE molecule are described. A novel D – D analysis of the molecular geometries obtained from rotational potential energy surface calculations and the ensemble of experimental structures were used to construct a crystal landscape for DTE. Of the 19 crystal structures, 17 contained photoinactive DTE rotamers and only 2 were photoactive. These results highlight the challenges associated with the design of these materials. Overall, the D – D analysis described herein provides rapid, effective and intuitive means of linking the molecular structure to photoactivity that could be applied more broadly to afford a general strategy for producing photoactive diarylethene-based crystalline solids.
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Structural and photoelectrochemical properties in the thin film system Cu–Fe–V–O and its ternary subsystems Fe–V–O and Cu–V–O
Thin-film material libraries in the ternary and quaternary metal oxide systems Fe–V–O, Cu–V–O, and Cu–Fe–V–O were synthesized using combinatorial reactive co-sputtering with subsequent annealing in air. Their compositional, structural, and functional properties were assessed using high-throughput characterization methods. Prior to the investigation of the quaternary system Cu–Fe–V–O, the compositions (Fe 61 V 39 )O x and (Cu 52 V 48 )O x with promising photoactivity were identified from their ternary subsystems Fe–V–O and Cu–V–O, respectively. Two Cu–Fe–V–O material libraries with (Cu 29-72 Fe 4-27 V 22-57 )O x and (Cu 11-55 Fe 27-73 V 12-34 )O x composition spread were investigated. Seven mixed ternary and quaternary phase regions were identified: I (α-Cu 3 FeV 6 O 26 /FeVO 4 ), II (Cu 5 V 2 O 10 /FeVO 4 /α-Cu 3 Fe 4 V 6 O 26 ), III (Cu 5 V 2 O 10 ), IV (Cu 5 V 2 O 10 /FeVO 4 , V (FeVO 4 /γ-Cu 2 V 2 O 7 /α-Cu 3 Fe 4 V 6 O 26 ), VI (β-Cu 2 V 2 O 7 /α-Cu 3 Fe 4 V 6 O 26 /FeVO 4 ), and VII (β-Cu 3 Fe 4 V 6 O 26 /FeVO 4 ). Furthermore, in the investigated composition range, two photoactive regions, (Cu 53 Fe 7 V 40 )O x and (Cu 45 Fe 21 V 34 )O x , were identified, exhibiting 103 μ A/cm 2 and 108 μ A/cm 2 photocurrent density for the oxygen evolution reaction at 1.63 V vs reversible hydrogen electrode, respectively. The highest photoactive region (Cu 45 Fe 21 V 34 )O x comprises the dominant α-Cu 3 Fe 4 V 6 O 24 phase and minor FeVO 4 phase. This photoactive region corresponds to having an indirect bandgap of 1.87 eV and a direct bandgap of 2.58 eV with an incident photon-to-current efficiency of 30% at a wavelength of 310 nm.
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Improving Thermal and Photostability of Polymer Solar Cells by Robust Interface Engineering
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Su, Li-Yun↗
Evaluation of Nanostructured β-Mn 2 V 2 O 7 Thin Films as Photoanodes for Photoelectrochemical Water Oxidation
β-Mn 2 V 2 O 7 (β-MVO) was recently reported to be a promising candidate for photoelectrochemical (PEC) water splitting, with a suitable band gap and band edge positions and reasonable stability and photoactivity in preliminary tests in alkaline solution. Here, we present an in-depth evaluation of the PEC performance and stability of phase-pure nanostructured β-Mn 2 V 2 O 7 films made by calcination of a spin-cast molecular ink. We show that β-Mn 2 V 2 O 7 dissolves in pure water, corrodes in aqueous electrolytes at pH 7 and 9, and converts to amorphous manganese (hydr)oxides within minutes at pH 13. Our β-Mn 2 V 2 O 7 films yielded only miniscule photocurrents (~uA cm -2 ) for the oxidation of iodide, sulfite, or water and the reduction of iodate or water in borate- and phosphate-buffered electrolytes at pH 7 and 9, the oxidation of [Fe(CN) 6 ] 4- or water at pH 13, and the oxidation of bromide in acetonitrile, regardless of film calcination temperature and time, film thickness, and illumination geometry. Minimal photoactivity was observed even in electrolytes in which film degradation was insignificant over the duration of the PEC tests. Ultrafast transient absorption spectroscopy shows that the poor photoactivity is likely the result of fast hole trapping and recombination at the MVO surface that leaves few free charge carriers beyond the picosecond time scale. Given its poor charge transport/extraction and chemical stability, native nanostructured β-Mn 2 V 2 O 7 is ineffective for solar water splitting and future research on this material should focus on the development of superior syntheses and film morphologies, MVO alloys, heterostructures, and surface coatings to alleviate recombination and boost operational stability. This work underscores the importance of careful follow-up studies of materials identified as "hits" in combinatorial materials discovery campaigns.
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Octupole moment driven free charge generation in partially chlorinated subphthalocyanine for planar heterojunction organic photodetectors
In this study, high-performance organic photodetectors are presented which utilize a pristine chlorinated subphthalocyanine photoactive layer. Optical and optoelectronic analyses indicate that the device photocurrent is primarily generated through direct charge generation within the chlorinated subphthalocyanine layer, rather than exciton separation at layer interfaces. Molecular modelling suggests that this direct charge generation is facilitated by chlorinated subphthalocyanine high octupole moment (-80 DÅ 2 ), which generates a 200 meV shift in molecular energetics. Increasing the thickness of chlorinated subphthalocyanine leads to faster response time, correlated with a decrease in trap density. Notably, photodetectors with a 50 nm thick chlorinated subphthalocyanine photoactive layer exhibit detectivities approaching 10 13 Jones, with a dark current below 10 -7 A cm -2 up to -5 V. Based on these findings, we conclude that high octupole moment molecular semiconductors are promising materials for high-performance organic photodetectors employing single-component photoactive layer.
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