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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Enhanced photosensitized degradation of rhodamine B on CdS/TiO{sub 2} nanocomposites under visible light irradiation

Graphical abstract: The photosensitized degradation of RhB was largely enhanced by the synergistic effect of the RhB and CdS/TiO{sub 2} nanocomposite. The composite of the two inorganic semiconductors with appropriate oxidation reduction energy levels enhanced the charge separation and extended the absorption response to visible region. - Highlights: • CdS/TiO{sub 2} nanocomposites were synthesized by a simple hydrothermal method. • Samples prepared at 200 °C, 12 h, CdS/TiO{sub 2} = 12% possessed the best activity. • The photosensitized degradation of RhB was largely enhanced by the composite. • The better activity was due to the synergistic effect of the RhB and CdS/TiO{sub 2}. - Abstract: Visible-light-driven photocatalysts, CdS/TiO{sub 2} nanocomposites were synthesized by a simple hydrothermal method. Their formation and structures were characterized by X-ray diffractometer, transmission electron microscopy, diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. Taking rhodamine B (RhB) as a model, their photocatalytic activities in aqueous phase under visible light irradiation (420 < λ < 800 nm) were tested. The results showed that the composite of CdS and TiO{sub 2} with appropriate oxidation reduction energy levels enhanced the charge separation and extended the absorption response into visible light region. Thus, the photosensitized degradation of RhB was largely enhanced. The degradation mechanism was explored concretely.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Combustion synthesis of CdS/reduced graphene oxide composites and their photocatalytic properties

Highlights: • CdS/reduced graphene oxide composites were prepared by a combustion method. • The phase changed from hexagonal to cubic phase by increasing the added amount of GO. • The composites showed excellent visible-light photocatalytic properties. • The plausible mechanism of photodegradation was discussed. - Abstract: CdS/reduced graphene oxide composites were synthesized by a simple one-pot combustion method using cadmium nitrate, thiourea and graphite as raw materials. The structure, morphologies, and photocatalytic properties of the as-prepared samples were studied by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, photoluminescence and ultraviolet–visible spectrophotometry. The results show that the structure of CdS in as-prepared samples changes from hexagonal to cubic phase by increasing the added amount of graphene oxide. During combustion reaction, graphene oxide was reduced to reduced graphene oxide. As-obtained CdS/reduced graphene oxide composites show high visible-light photoactivities, attributed to the minimized recombination of photoinduced electrons and holes and the high surface area of reduced graphene oxide sheets.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Thin films of copper antimony sulfide: A photovoltaic absorber material

Highlights: • CuSbS{sub 2} thin films were prepared by heating Sb{sub 2}S{sub 3}/Cu layers. • Analyzed the structure, composition, optical, and electrical properties. • PV structures: glass/SnO{sub 2}:F/n-CdS/p-CuSbS{sub 2}/C/Ag were formed at different conditions. • The PV parameters (J{sub sc}, V{sub oc}, and FF) were evaluated from the J–V characteristics. • J{sub sc}: 0.52–3.20 mA/cm{sup 2}, V{sub oc}:187–323 mV, FF: 0.27–0.48 were obtained. - Abstract: In this work, we report preparation and characterization of CuSbS{sub 2} thin films by heating glass/Sb{sub 2}S{sub 3}/Cu layers and their use as absorber material in photovoltaic structures: glass/SnO{sub 2}:F/n-CdS/p-CuSbS{sub 2}/C/Ag. The Sb{sub 2}S{sub 3} thin films of 600 nm were prepared by chemical bath deposition on which copper thin films of 50 nm were thermally evaporated, and the glass/Sb{sub 2}S{sub 3}/Cu multilayers were heated in vacuum at different temperatures. X-ray diffraction analysis showed the formation of orthorhombic CuSbS{sub 2} after heating the precursor layers. Studies on identification and chemical state of the elements were done using X-ray photoelectron spectroscopy. The optical band gap of the CuSbS{sub 2} thin films was 1.55 eV and the thin films were photoconductive. The photovoltaic parameters of the devices using CuSbS{sub 2} as absorber and CdS as window layer were evaluated from the J–V curves, yielding J{sub sc}, V{sub oc}, and FF values in the range of 0.52–3.20 mA/cm{sup 2}, 187–323 mV, and 0.27–0.48, respectively, under illumination of AM1.5 radiation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

A Revisited Mechanism of the Graphite-to-Diamond Transition at High Temperature

The graphite-diamond transition, under high-pressure and high-temperature conditions, has been a central subject in physical science. However, its atomistic mechanism remains under debate. Employing large-scale molecular dynamics (MD) simulations, we report a mechanism whereby the diamond nuclei in the graphite matrix propagate in two preferred directions, among which the graphite [120] is about 2.5 times faster than [001]. Consequently, cubic diamond (CD) is the kinetically favorable product, while only a few hexagonal diamonds (HDs) can exist as the twins of CDs. The coherent interface of t-(100)gr//(11-1)cd + [010]gr//[1-10]cd observed in MD simulation was confirmed by our high-resolution transmission electron microscopy experiment. This proposed mechanism not only clarifies the role of HD in graphite-diamond transition but also yields atomistic insight into strengthening synthetic diamond via microstructure engineering.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The nanoscale distribution of copper and its influence on charge collection in CdTe solar cells

For decades, Cu has been the primary dopant in CdTe photovoltaic absorbers. Typically, Cu acceptor concentrations in these devices are on the order of 1 1014 cm-3, which has made it notoriously difficult to directly correlate nanoscale Cu distributions to the local charge transport properties of these devices. To measure and correlate these properties, measurement techniques require high sensitivity to elemental concentration, large penetration depth, and operando compatibility. Techniques such as secondary-ion mass spectroscopy and X-ray energy dispersive spectroscopy are widely adopted to measure Cu concentrations, but they are limited by penetration depth, sensitivity, or spatial resolution. Additionally, they lack the operando capabilities required to correlate one-to-one Cu concentrations to electrical performance. In this work, correlative X-ray microscopy is used to investigate the spatial distribution of Cu and its impact on charge collection through the depth and breadth of CdTe photovoltaic devices. Plan-view, nanoscale X-ray fluorescence maps clearly demonstrate the spatial segregation of copper around regions thought to be CdTe grain boundaries. Complementary cross-section imaging unveils the transition of the maximum charge-collection efficiency from the ZnTe-CdTe interface to the CdS-CdTe interface as a function of Cu incorporation. The copper concentration through the depth of the CdTe layer is characterized by slow and fast diffusion components, and cross-section charge-transport modeling shows that the experimentally obtained charge collection can be explained by the modeled acceptor distribution through the depth of the CdTe layer.

14 SOLAR ENERGY↗
DOE OSTI2018

Quantum-dot doped polymeric scintillation material for radiation detection

In this study, scintillation and luminescence enhancement were observed in a Quantum Dot-doped scintillating polymer, facilitating energy transfer with polymer medium and scintillating dye. 2,5-diphenyloxazole (PPO) and Cadmium Sulfide (CdS) Quantum Dots (QD) with 418 nm emission coated with oleic acid were dispersed in a polyvinyl toluene (PVT) matrix with transparency retained. Under UV excitation a sharp emission was detected at 426 nm from minimal QD loading with possible indication of QD energy transfer. Scintillation enhancement was observed with different radioactive sources in PVT-PPO/QD polymer with a photomultiplier detector setup. The response to gamma and beta radiation was investigated with differences in the energy spectrum and a count increase observed with increased QD loading.

36 MATERIALS SCIENCE↗
DOE OSTI2016

High Resolution Dopant Profiles Revealed by Atom Probe Tomography and STEM-EBIC for CdTe Based Solar Cells

Segregated elements and their diffusion profiles within grain boundaries and interfaces resulting from post deposition heat treatments are revealed using atom probe tomography (APT), scanning transmission electron microscopy (STEM), and electron beam induced current (EBIC) techniques. The results demonstrate how these techniques complement each other to provide conclusive evidence for locations of space charge regions and mechanisms that create them at the nanoscale. Most importantly, a Cl dopant profile that extends ~5 nm into CdTe grains interfacing the CdS is shown using APT and STEM synergy, which has been shown to push the pn-junction into the CdTe layer indicative of a homojunction (revealed by STEM EBIC). In addition, Cu and Cl concentrations within grain boundaries within several nms and µms from the CdS/CdTe interface are compared, Na segregation of <0.1% is detected, and S variations of ~1–3% are witnessed between CdTe grains close to the CdS/CdTe interface. The segregation and diffusion of these elements directly impacts on the material properties, such as band gap energy and n/p type properties. Optimization of the interfacial and grain boundary doping will lead to higher efficiency solar cells.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Sesame: A 2-dimensional solar cell modeling tool

This work introduces a new software package “Sesame” for the numerical computation of classical semiconductor equations. It supports 1 and 2-dimensional systems and provides tools to easily implement extended defects such as grain boundaries or sample surfaces. Sesame is designed to facilitate fast exploration of the system parameter space and to visualize local charge transport properties. Sesame has been benchmarked against other software packages, and results for single crystal and polycrystalline CdS-CdTe heterojunctions are presented. Sesame is distributed as a Python package or as a standalone GUI application, and is available at https://pages.nist.gov/sesame/.

14 SOLAR ENERGY↗
DOE OSTI2020

Stable magnesium zinc oxide by reactive Co-Sputtering for CdTe-based solar cells

Magnesium zinc oxide (MZO) is a promising front contact material for CdTe solar cells. Due to its higher band gap than traditional CdS, MZO can reduce parasitic absorption to significantly increase short-circuit current density while also providing a benefit of conduction band offset tuning through Mg:Zn ratio optimization. MZO has been successfully implemented into CdTe devices, however its stability has been of concern. The MZO stability issue has been attributed to the presence of oxygen in the CdTe device processing ambient, leading to double-diode behavior (S-kink) in the current density-voltage curves. Here we report on MZO thin films deposited by reactive co-sputtering. The reactively co-sputtered MZO thin films have encouraging stability, show no significant variation in work function of the surface over a period of 6 months, as measured by Kelvin probe. Energy conversion efficiencies of around 16% have been achieved both with and without presence of oxygen in device processing ambients across multiple research facilities. Finally, these efficiencies should be possible to increase further by tuning of the thin film deposition and device processing parameters, especially through optimization of the back contact.

14 SOLAR ENERGY↗
DOE OSTI2020

Combining fast magic angle spinning dynamic nuclear polarization with indirect detection to further enhance the sensitivity of solid-state NMR spectroscopy

Dynamic nuclear polarization (DNP) and indirect detection are two commonly applied approaches for enhancing the sensitivity of solid-state NMR spectroscopy. However, their use in tandem has not yet been investigated. With the advent of low-temperature fast magic angle spinning (MAS) probes with 1.3-mm diameter rotors capable of MAS at 40 kHz it becomes feasible to combine these two techniques. In this study, we performed DNP-enhanced 2D indirectly detected heteronuclear correlation (idHETCOR) experiments on 13 C, 15 N, 113 Cd and 89 Y nuclei in functionalized mesoporous silica, CdS nanoparticles, and Y 2 O 3 nanoparticles. The sensitivity of the 2D idHETCOR experiments was compared with those of DNP-enhanced directly-detected 1D cross polarization (CP) and 2D HETCOR experiments performed with a standard 3.2-mm rotor. Due to low CP polarization transfer efficiencies and large proton linewidth, the sensitivity gains achieved by indirect detection alone were lower than in conventional (non-DNP) experiments. Nevertheless, despite the smaller sample volume the 2D idHETCOR experiments showed better absolute sensitivities than 2D HETCOR experiments for nuclei with the lowest gyromagnetic ratios. Finally, for 89 Y, 2D idHETCOR provided 8.2 times better sensitivity than the 1 D 89 Y-detected CP experiment performed with a 3.2-mm rotor.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Equine cytochrome P450 2B6 — Genomic identification, expression and functional characterization with ketamine

Ketamine is an anesthetic and analgesic regularly used in veterinary patients. As ketamine is almost always administered in combination with other drugs, interactions between ketamine and other drugs bear the risk of either adverse effects or diminished efficacy. Since cytochrome P450 enzymes (CYPs) play a pivotal role in the phase I metabolism of the majority of all marketed drugs, drug–drug interactions often occur at the active site of these enzymes. CYPs have been thoroughly examined in humans and laboratory animals, but little is known about equine CYPs. The characterization of equine CYPs is essential for a better understanding of drug metabolism in horses. We report annotation, cloning and heterologous expression of the equine CYP2B6 in V79 Chinese hamster fibroblasts. After computational annotation of all CYP2B genes, the coding sequence (CDS) of equine CYP2B6 was amplified by RT-PCR from horse liver total RNA and revealed an amino acid sequence identity of 77% and a similarity of 93.7% to its human ortholog. A non-synonymous variant c.226G>A in exon 2 of the equine CYP2B6 was detected in 97 horses. The mutant A-allele showed an allele frequency of 82%. Two further variants in exon 3 were detected in one and two horses of this group, respectively. Transfected V79 cells were incubated with racemic ketamine and norketamine as probe substrates to determine metabolic activity. The recombinant equine CYP2B6 N-demethylated ketamine to norketamine and produced metabolites of norketamine, such as hydroxylated norketamines and 5,6-dehydronorketamine. V{sub max} for S-/and R-norketamine formation was 0.49 and 0.45 nmol/h/mg cellular protein and K{sub m} was 3.41 and 2.66 μM, respectively. The N-demethylation of S-/R-ketamine was inhibited concentration-dependently with clopidogrel showing an IC{sub 50} of 5.63 and 6.26 μM, respectively. The functional importance of the recorded genetic variants remains to be explored. Equine CYP2B6 was determined to be a CYP enzyme involved in ketamine and norketamine metabolism, thus confirming results from inhibition studies with horse liver microsomes. Clopidogrel seems to be a feasible inhibitor for equine CYP2B6. The specificity still needs to be established with other single equine CYPs. Heterologous expression of single equine CYP enzymes opens new possibilities to substantially improve the understanding of drug metabolism and drug interactions in horses. -- Highlights: ► We annotate, express and functionally characterize equine CYP2B6. ► 3 genetic variants within this gene are described. ► Equine CYP2B6 N-demethylates ketamine and metabolizes norketamine. ► Equine CYP2B6 can be inhibited by clopidogrel.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Buffer/absorber interface recombination reduction and improvement of back-contact barrier height in CdTe solar cells

Electronic properties of a CdTe solar cell are reported using temperature-dependent capacitance spectroscopy and current-voltage characteristics, the latter in dark and illuminated conditions. The baseline solar cell material stack investigated is comprised of soda-lime-glass/SnO 2 :F/SnO 2 /CdS:O-buffer/CdTe-absorber/Cu/Au. Properties are compared with CdTe solar cells in which the back surface was hydroiodic acid etched, before the back-contact formation, and a CdTe device in which Mg-doped ZnO (MZO) replaces buffer layer CdS. Reduced back-contact barrier height and grain boundary barrier height are observed in the HI treated CdTe cell. As a result, improved device performance in the MZO-based CdTe device is attributed to reduced emitter/absorber interface recombination when using the MZO window layer.

14 SOLAR ENERGY↗
DOE OSTI2013

Controlling electron beam-induced structure modifications and cation exchange in cadmium sulfide–copper sulfide heterostructured nanorods

The atomic structure and interfaces of CdS/Cu 2 S heterostructured nanorods are explored with the aberration-corrected TEAM 0.5 electron microscope operated at 80 kV and 300 kV applying in-line holography and complementary techniques. Cu 2 S exhibits a low-chalcocite structure in pristine CdS/Cu 2 S nanorods. Under electron beam irradiation the Cu 2 S phase transforms into a high-chalcocite phase while the CdS phase maintains its wurtzite structure. Time-resolved experiments reveal that Cu + -Cd 2+ cation exchange at the CdS/Cu 2 S interfaces is stimulated by the electron beam and proceeds within an undisturbed and coherent sulfur sub-lattice. A variation of the electron beam current provides an efficient way to control and exploit such irreversible solid-state chemical processes that provide unique information about system dynamics at the atomic scale. Particularly, we show that the electron beam-induced copper-cadmium exchange is site specific and anisotropic. A resulting displacement of the CdS/Cu 2 S interfaces caused by beam-induced cation interdiffusion equals within a factor of 3-10 previously reported Cu diffusion length measurements in heterostructured CdS/Cu 2 S thin film solar cells with an activation energy of 0.96 eV.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Pre-steady-state kinetics of nanocrystal:molybdenum nitrogenase biohybrids reveals hole-scavenging efficiency is critical to N 2 reduction

Molybdenum (Mo) nitrogenase is a two-component enzyme complex that catalyzes the reduction of dinitrogen to ammonia and protons to hydrogen gas. We have shown that electrons for dinitrogen reduction can be delivered photochemically to the catalytic MoFe protein component by cadmium sulfide (CdS) nanocrystals. In this study, we used electron paramagnetic resonance spectroscopy to measure the transient populations of catalytic intermediates. We fit the populations with a pre-steady-state kinetic model, which allowed us to distinguish between productive and non-productive reaction pathways and extract the rate constants for the reaction. Our results demonstrated that the rate of catalytic electron delivery into MoFe protein increased with the concentration of the sacrificial electron donor. This enabled electron delivery to exceed the rate of hydride protonation, a relaxation pathway that competes with N 2 binding. Thus, managing the balance between electron transfer and hole transfer reactions is required to achieve a kinetic regime that favors N 2 reduction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Shape Control of Colloidal Semiconductor Nanocrystals through Thermodynamically Driven Aggregative Growth

The optoelectronic properties of colloidal semiconductor nanocrystals (NCs) can be manipulated by changing their geometric shapes. The precise synthetic control over particle morphologies, however, has remained elusive. Conventional growth techniques rely on the kinetic assembly of atomic units, where supersaturation and precipitation processes can lead to a broad distribution of particle shapes. In this paper, we demonstrate that replacing atomic precursors with small-size nanocrystals as building blocks for larger colloids offers an easier, more predictive control over nanoparticle shape evolution. The reported growth strategy is illustrated via shape-selective syntheses of CdSe and CdS NC cubes, spheres, rods, as well as unprecedented “donut” and ring-like structures. Growth of desired particle morphologies was achieved by choosing an appropriate reaction solvent that minimizes the surface free energy through a unique shape formation. This so-called "aggregative growth mechanism" is explained using a thermodynamic model for interacting viscous colloids. We expect that this novel growth strategy will offer a viable platform for shape–selective synthesis of many inorganic colloids, providing pathways to optimizable optoelectronic materials.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Selective Sorbent Design: CaS Aerogel for Rapid Remediation of Aqueous Pb (II)

Heavy metals are a persistent environmental problem due to their high toxicity, even at very low concentrations (parts per billion, ppb). The removal of such diluted heavy metals is challenging because of the competition the counterions (Ca 2+ , Na + , Mg 2+ , etc.) present in natural water bodies. The design of sorbents capable of removing ions below the action limit (15 ppb for Pb 2+ ) requires a strong driving force for selective uptake and rapid removal. In this work, we report the synthesis of porous CaS aerogels (surface area = 143.6 m 2 /g) by oxidative assembly of CaS nanoparticles and describe their use in selective Pb 2+ ion remediation from water. Despite the presence of amorphous CaCO 3 (up to 50 wt %) in the gel network, the gels demonstrated a capacity of 17.1 mmol Pb/g aerogel (3543 mg/g), and this could be augmented to 22.5 mmol Pb/g aerogel (4593 mg/g) by modifying the synthesis to reduce CaCO 3 content to ca. 15 wt %. Moreover, the selectivity of CaS aerogels toward Pb 2+ ions is high, as evidenced by little-to-no change in the distribution constant (K d ∼ 10 4 ) in the presence of competing ions (1 M) such as Na + , Mg 2+ , and Ca 2+ . During remediation with low concentrations (100 ppb) of Pb 2+ with CaS aerogels, the level of Pb 2+ dropped to 5.4 ppb (below the 15 ppb EPA limit) within 1 h with a 95.4% removal efficiency. In contrast to the CO 2 supercritically dried aerogels, lower surface area ambient dried gels (xerogels) only remove 40% of the lead ions from a 100 ppb solution, saturating within 1 h. The efficiency and rapidity of selective Pb 2+ uptake using CdS aerogels arise from a combination of a strong thermodynamic driving force for cation exchange (K eq = 2.5 × 10 27 ) and chemisorption along with favorable kinetics associated with the high surface area porous architecture. These results show that formation of high surface area metal chalcogenide aerogels by oxidative assembly to form nanocrystalline architectures, as previously demonstrated for II−VI and IV−VI semiconductors, can be extended to the more highly ionic alkaline earth sulfides.

Aerogels↗
DOE OSTI2016

Effects of thermochemical treatment on CuSbS 2 photovoltaic absorber quality and solar cell reproducibility

CuSbS 2 is a promising nontoxic and earth-abundant photovoltaic absorber that is chemically simpler than the widely studied Cu 2 ZnSnS 4 . However, CuSbS 2 photovoltaic (PV) devices currently have relatively low efficiency and poor reproducibility, often due to suboptimal material quality and insufficient optoelectronic properties. To address these issues, here we develop a thermochemical treatment (TT) for CuSbS 2 thin films, which consists of annealing in Sb 2 S 3 vapor followed by a selective KOH surface chemical etch. The annealed CuSbS 2 films show improved structural quality and optoelectronic properties, such as stronger band-edge photoluminescence and longer photoexcited carrier lifetime. These improvements also lead to more reproducible CuSbS 2 PV devices, with performance currently limited by a large cliff-type interface band offset with CdS contact. Altogether, these results point to the potential avenues to further increase the performance of CuSbS 2 thin film solar cell, and the findings can be transferred to other thin film photovoltaic technologies.

14 SOLAR ENERGY↗
DOE OSTI2019

Thermodynamics of Dual Doping in Quantum Dots

Dual doping is a powerful way to tailor the properties of semiconductor quantum dots (QDs) arising out of host–dopant and dopant–dopant interactions. Nevertheless, it has seldom been explored due to a variety of thermodynamic challenges, such as the differential bonding strength and diffusion constant within the host matrix that integrates with the host in dissimilar ways. This work discusses the challenges involved in administering them within the constraints of one host under similar conditions of temperature, time, and chemical parameters such as solubility and reactivity using CoPt-doped CdS QDs as a model system. In addition, the various forces in play, such as Kirkendall diffusion, solid- and liquid-state diffusion, hard acid soft base interaction with the host, and the effect of lattice strain due to lattice mismatch, are studied to understand the feasibility of the core to doped transformation. Furthermore, these findings suggest a potential approach for manipulating the properties of semiconductors by dual doping engineering.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗