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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 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Tapered erbium-doped fibre laser system delivering 10 MW of peak power

We consider a fibre laser system generating ∼10-μJ, ∼500-fs pulses with a peak power of ∼10 MW at a repetition rate of 100 kHz and emission wavelength of 1.56 μm. The system is based on a master oscillator – power amplifier configuration. The amplifier ensures chirped-pulse amplification. The pulses are then compressed by a dispersive grating compressor. The output amplifier stage is based on a specially designed tapered large mode area erbium-doped fibre for suppressing nonlinear effects. The experimental data agree with numerical simulation results for the stretcher, amplifier and compressor. The stretcher and amplifier have been simulated using a generalised nonlinear Schrödinger equation. In addition, numerical simulation results suggest that optimising the stretcher and compressor will potentially allow the peak power of the system to be scaled up to ∼30 MW. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

High-Performance and Environmentally Stable Planar Heterojunction Perovskite Solar Cells Based on a Solution-Processed Copper-Doped Nickel Oxide Hole-Transporting Layer

An effective approach to significantly increase the electrical conductivity of a NiOx hole-transporting layer (HTL) to achieve high-efficiency planar heterojunction perovskite solar cells is demonstrated. Perovskite solar cells based on using Cu-doped NiOx HTL show a remarkably improved power conversion efficiency up to 15.40% due to the improved electrical conductivity and enhanced perovskite film quality. General applicability of Cu-doped NiOx to larger bandgap perovskites is also demonstrated in this study.

14 SOLAR ENERGY↗
DOE OSTI2021

Effects of Plasma Etching on Dopant Compensation between p- and n-Type Poly-Si Fingers in Passivated Interdigitated Back Contact Solar Cells

Efficiencies surpassing 26% have been achieved for single-junction Si solar cells based on the interdigitated back contact (IBC) architecture. However, the possibility of lateral shunting between the doped fingers has limited industrial adoption thus far. To avoid this possibility of shunt, complicated patterning techniques of the doped rear fingers have been developed, but spreading can still occur through multiple pathways during cell processing. Patterning can be simplified by using masked plasma-enhanced chemical vapor deposition (PECVD), but spreading during deposition will also lead to contamination of the isolation region between doped fingers. We significantly reduce the effect of this spreading through a short, gentle plasma etching step, which enables a trap-assisted compensation mechanism to take effect more easily than without the plasma etch. These two effects combined allow for the use of a simple patterning technique while still maintaining a highly resistive region between the doped fingers, and will reduce the complexity of IBC cell fabrication overall.

atom probe↗
DOE OSTI2017

Beating the thermodynamic limit with photo-activation of n-doping in organic semiconductors

Chemical doping of organic semiconductors using molecular dopants plays a key role in the fabrication of efficient organic electronic devices. While a variety of stable molecular p-dopants have been developed and successfully deployed in devices in the past decade, air-stable molecular n-dopants suitable for materials with low electron affinity are still elusive. In this work we demonstrate that photo-activation of a cleavable air-stable dimeric dopant can result in kinetically stable and efficient n-doping of host semiconductors, whose reduction potentials are beyond the thermodynamic reach of the dimer’s effective reducing strength. Electron-transport layers doped in this manner are used to fabricate high-efficiency organic light-emitting diodes. This strategy thus enables a new paradigm for using air-stable molecular dopants to improve conductivity in, and provide ohmic contacts to, organic semiconductors with very low electron affinity.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Proton damage in (Y,Lu,Gd) 3 (Al,Ga) 5 O 12 :Ce mixed garnet scintillators

Scintillators are vital components for nuclear instrumentation and its applications, including plasma diagnostics and imaging. As yields in controlled fusion experiments increase, the radiation tolerance of scintillator candidates for use in instrumentation is of particular importance. High radiation exposure can damage scintillating materials and alter the optical properties. The effects of radiation damage in Ce-doped mixed garnet ceramics over the compositional range (Y,Gd,Lu) 3 (Al,Ga) 5 O 12 are investigated using optical techniques. The samples were exposed to 200 keV protons to an accumulated fluence of 10 16 protons per square centimeter, then characterized using diffuse reflectance spectroscopy (DRS). DRS with visible light can assess the radiation tolerance of opaque poly-crystalline samples, which can be easily sintered from powders and thus offer distinct advantages in characterization compared to single crystals. Qualitative trends in induced absorption are presented as a function of composition, and the ideal cerium dopant concentration for Y 2 LuAl 5 O 12 is determined to be 0.60–0.75 mol.%.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

Comparison of carrier transport mechanism under UV/Vis illumination in an AZO photodetector and an AZO/p-Si heterojunction photodiode produced by spray pyrolysis

In this study, Aluminum doped Zinc Oxide (AZO) layer is deposited on p-type silicon (p-Si) by spray pyrolysis method to fabricate ultraviolet-visible (UV/Vis) photodetector as Al doping process can have positive effect on the photodetector performance. Morphology, crystalline structure, and Al concentration of AZO layer are investigated by SEM, XRD, and EDX. The goal of this study is to analyze the mechanism of carrier transport by means of current-voltage characteristics under UV/Vis illumination in two cases: (a) electrodes connected to the surface of AZO layer and (b) electrodes connected to cross section of heterojunction (AZO/p-Si). Measurements indicate that the AZO/p-Si photodiode exhibits a higher photocurrent and lower photoresponse time under visible illumination with respect to AZO photodetector; while under UV illumination, the above result is inversed. Besides, the internal junction field of AZO/p-Si heterojunction plays an important role on this mechanism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

N-Doping improves charge transport and morphology in the organic non-fullerene acceptor O-IDTBR

Molecular doping has been shown to improve the performance of various organic (opto)electronic devices. When compared to p-doped systems, research into n-doped organic small-molecules is relatively limited, primarily due to the lack of suitable dopants and the often encountered unfavourable microstructural effects. These factors have prevented the use of n-doping in a wider range of existing materials, such as non-fullerene acceptors (NFAs), that have already shown great promise for a range of (opto)electronic applications. Here, we show that several different molecular n-dopants, namely [1,2-b:2',1'-d]benzo[i][2.5]benzodiazocine potassium triflate adduct (DMBI-BDZC), tetra-n-butylammonium fluoride (TBAF) and 4-(2,3-dihydro-1,3-dimethyl-1H-benzimidazol-2-yl)-N,N-dimethylbenzenamine (N-DMBI), can be used to n-dope the molecular semiconductor O-IDTBR, a promising NFA, and increase the electron field-effect mobility to >1 cm 2 V -1 s -1 . By combining complementary experimental techniques with computer simulations of doping and charge carrier dynamics, we show that improved charge transport arises from synergistic effects of n-type doping and morphological changes. Specifically, a new, previously unreported dopant-induced packing orientation results in one of the highest electron mobility values reported to-date for an NFA molecule. Overall, this work highlights the importance of dopant–semiconductor interactions and their impact on morphology, showing that dopant-induced molecular packing motifs may be generic and a key element of the charge transport enhancement observed in doped organics.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Electrochemical removal of hydrogen atoms in Mg-doped GaN epitaxial layers

Hydrogen atoms inside of an Mg-doped GaN epitaxial layer were effectively removed by the electrochemical potentiostatic activation (EPA) method. The role of hydrogen was investigated in terms of the device performance of light-emitting diodes (LEDs). The effect of the main process parameters for EPA such as solution type, voltage, and time was studied and optimized for application to LED fabrication. In optimized conditions, the light output of 385-nm LEDs was improved by about 26% at 30 mA, which was caused by the reduction of the hydrogen concentration by ∼35%. Further removal of hydrogen seems to be involved in the breaking of Ga-H bonds that passivate the nitrogen vacancies. An EPA process with high voltage breaks not only Mg-H bonds that generate hole carriers but also Ga-H bonds that generate electron carriers, thus causing compensation that impedes the practical increase of hole concentration, regardless of the drastic removal of hydrogen atoms. A decrease in hydrogen concentration affects the current-voltage characteristics, reducing the reverse current by about one order and altering the forward current behavior in the low voltage region.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Andreev Reflection and Klein Tunneling in High-Temperature Superconductor-Graphene Junctions

Scattering processes in quantum materials emerge as resonances in electronic transport, including confined modes, Andreev states, and Yu-Shiba-Rusinov states. However, in most instances, these resonances are driven by a single scattering mechanism. Here, in this paper, we show the appearance of resonances due to the combination of two simultaneous scattering mechanisms, one from superconductivity and the other from graphene p-n junctions. These resonances stem from Andreev reflection and Klein tunneling that occur at two different interfaces of a hole-doped region of graphene formed at the boundary with superconducting graphene due to proximity effects from Bi 2 Sr 2 Ca 1 Cu 2 O 8+δ . The resonances persist with gating from p + -p and p-n configurations. The suppression of the oscillation amplitude above the bias energy which is comparable to the induced superconducting gap indicates the contribution from Andreev reflection. Our experimental measurements are supported by quantum transport calculations in such interfaces, leading to analogous resonances. Our results put forward a hybrid scattering mechanism in graphene–high-temperature superconductor heterojunctions of potential impact for graphene-based Josephson junctions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Synthesis of Synergistic Nitrogen-Doped NiMoO 4 /Ni 3 N Heterostructure for Implementation of an Efficient Alkaline Electrocatalytic Hydrogen Evolution Reaction

Electrochemical water splitting is considered as an effective and promising method to produce the ideal hydrogen energy to solve the energy crisis and environmental pollution problems. In this paper, we successfully synthesized the N-doped NiMoO 4 /Ni 3 N heterostructure, which exhibited an efficient HER performance with a lower overpotential of 51 mV at 10 mA cm -2 and a lower Tafel slope value of 45.47 mV dec -1 compared with those of NiMoO 4 , N-doped NiMoO 4 , or Ni 3 N owing to the synergistic effect of N doping and construction of the superior heterostructure. When the N-doped NiMoO 4 /Ni 3 N heterostructure is used as a cathode and the well-recognized excellent OER material (NiFe-LDH) is used as an anode to construct the two-electrode electrolyzer, the system requires only 1.506 and 1.559 V to achieve the current densities of 10 and 20 mA cm -2 , respectively, which are lower than those of the commercial Pt/C//RuO 2 system (1.573 and 1.634 V, respectively) or many other reported systems. At the same time, this two-electrode system demonstrates excellent durability in electrocatalytic water splitting. This design method paved the way for the development of another electrocatalytic system.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Giant increase of critical current density and vortex pinning in Mn doped K{sub x}Fe{sub 2−y}Se{sub 2} single crystals

We report a comparative study of the critical current density (J{sub c}) and vortex pinning among pure and Mn doped K{sub x}Fe{sub 2−y}Se{sub 2} single crystals. It is found that the J{sub c} values can be greatly improved by Mn doping and post-quenching treatment when comparing to pristine pure sample. In contrast to pure samples, an anomalous second magnetization peak (SMP) effect is observed in both 1% and 2% Mn doped samples at T = 3 K for H∥ab but not for H∥c. Referring to Dew-Hughes and Kramer's model, we performed scaling analyses of the vortex pinning force density vs magnetic field in 1% Mn doped and quenched pristine crystals. The results show that the normal point defects are the dominant pinning sources, which probably originate from the variations of intercalated K atoms. We propose that the large nonsuperconducting K-Mn-Se inclusions may contribute to the partial normal surface pinning and give rise to the anomalous SMP effect for H∥ab in Mn doped crystals. These results may facilitate further understanding of the superconductivity and vortex pinning in intercalated iron-selenides superconductors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Bandgap engineering of Magnéli phase Ti{sub n}O{sub 2n−1}: Electron-hole self-compensation

An electron-hole self-compensation effect is revealed and confirmed in nitrogen doped Magnéli phase Ti{sub n}O{sub 2n−1} (n = 7, 8, and 9) by using hybrid density functional theory calculations. We found that the self-compensation effect between the free electrons in Magnéli phase Ti{sub n}O{sub 2n−1} (n = 7, 8, and 9) and the holes induced by p-type nitrogen doping could not only prevent the recombination of photo-generated electron-hole pairs, but also lead to an effective bandgap reduction. This novel electron-hole self-compensation effect may provide a new approach for bandgap engineering of Magnéli phase metal suboxides.

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

Pushing Lithium–Sulfur Batteries towards Practical Working Conditions through a Cathode–Electrolyte Synergy

Abstract The commercialization of lithium–sulfur (Li−S) batteries is still hindered by the unsatisfactory cell performance under practical working conditions, which is mainly caused by the sluggish cathode redox kinetics, severe polysulfide shuttling, and poor Li stripping/plating reversibility. Herein, we report an effective strategy by combining Se‐doped S hosted in an ordered macroporous framework with a highly fluorinated ether (HFE)‐based electrolyte to simultaneously address the aforementioned issues in both cathode and anode. A reversible and stable high areal capacity of >5.4 mAh cm −2 with high Coulombic efficiency >99.2 % can be achieved under high areal Se/S loading (5.8 mg cm −2 ), while the underlying mechanism was further revealed through synchrotron X‐ray probes and Time‐of‐Flight Secondary Ion Mass Spectrometry (ToF‐SIMS). The practical application potential was further evaluated at low (0 °C) and high (55 °C) temperatures under high areal Se/S loading (>5.0 mg cm −2 ) and thin Li metal (40 μm).

Zhao, Chen↗
DOE OSTI2017

Quantification of Sheet Resistance in Boron-Diffused Silicon Using Micro-Photoluminescence Spectroscopy at Room Temperature

A micro-photoluminescence-based technique is presented, to quantify and map sheet resistances of boron-diffused layers in silicon solar cell precursors with micron-scale spatial resolution at room temperature. The technique utilizes bandgap narrowing effects in the heavily-doped layers, yielding a broader photoluminescence spectrum at the long-wavelength side compared to the spectrum emitted from lightly doped silicon. By choosing an appropriate spectral range as a metric to assess the doping density, the impacts of photon reabsorption on the analysis can be avoided; thus, an accurate characterization of the sheet resistance can be made. This metric is demonstrated to be better representative of the sheet resistance than the surface doping density or the total dopant concentration of the diffused layer. The technique is applied to quantify sheet resistances of 12-um-wide diffused fingers in interdigitated back-contact solar cell precursors and large diffused areas. The results are confirmed by both 4-point probe and time-of-flight secondary-ion mass spectrometry measurements. Lastly, the practical limitations associated with extending the proposed technique into an imaging mode are presented and explained.

14 SOLAR ENERGY↗
DOE OSTI2018

Effects of Microwave-Assisted Annealing on the Structure and Magnetic Properties of (Nd{sub 0.75}Pr{sub 0.25}){sub 9}Fe{sub 72}Ti{sub 1}Zr{sub 3}Mn{sub x} Mo{sub 4−x}B{sub 10.5}C{sub 0.5} Amorphous Ribbons

The amorphous as-spun ribbons with nominal composition (Nd{sub 0.75}Pr{sub 0.25}){sub 9}Fe{sub 72}Ti{sub 1}Zr{sub 3}Mn{sub x}Mo{sub 4−x}B{sub 10.5}C{sub 0.5}(x = 1, 2, 3) were annealed by microwave-assisted annealing. The effects of the Mn-doped alloys on glass-forming ability (GFA), crystallization, and magnetic properties of the Nd{sub 2}Fe{sub 14}B/α-Fe nanocomposite magnets were examined by thermal differential scanning calorimetry (DSC), X-ray diffraction (XRD), and vibrating sample magnetometry (VSM). An appropriate amount of Mn was beneficial to the optimization of the structure and magnetic properties. Compared with conventional annealing, the microwave-assisted annealing has contributed to the precipitation of hard magnetic phases and adjusted the proportion of hard and soft magnetic phases. The optimum magnetic properties with coercivity up to 805 kA/m were found for ribbons (with composition x = 1) annealed under the microwave power of 2000 W for 10 min.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Multiple temperature-induced magnetization reversals in SmCr{sub 1−x}Fe{sub x}O{sub 3} system

Graphical abstract: - Highlights: • Multiple temperature-induced magnetization reversals were observed in x = 0.1. • Coexistence of normal and inverse magnetocaloric effects was observed. • A reasonable model was proposed to explain the magnetization reversals. - Abstract: The structural and magnetic properties of the SmCr{sub 1−x}Fe{sub x}O{sub 3} (0 ≤ x ≤ 0.5) system have been investigated. Multiple temperature-induced magnetization reversals were observed in x = 0.1. The high-temperature magnetization reversal is due to the special spin structure, in which the net canted moment of the Cr-rich regions and the net moment of the Fe–Cr ordered regions orient in opposite direction; while the low temperature one can be ascribed to the spin reorientation. The sample with x = 0.5 exhibits the highest compensation temperature. Coexistence of normal and inverse magnetocaloric effects was observed in all doped samples. Potential applications in magnetic refrigeration based constant temperature bath near room temperature (∼286 K) have been demonstrated.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Chemical pressure effects on structural, dielectric and magnetic properties of solid solutions Mn{sub 3−x}Co{sub x}TeO{sub 6}

Highlights: • Mn{sub 3}TeO{sub 6} and Co{sub 3}TeO{sub 6} are antiferromagnets with corundum related structures. • The structural and magnetic properties of Mn{sub 3−x}Co{sub x}TeO{sub 6} ceramics were investigated. • All compounds adopt the trigonal structure of Mn{sub 3}TeO{sub 6} up to at least x = 2.4. • The antiferromagnetic transition temperature monotonously increases with x. • NPD data evidences the magnetic structure of the Mn{sub 3−x}Co{sub x}TeO{sub 6} ceramics. - Abstract: The effects of Co{sup 2+} doping on the structural, magnetic and dielectric properties of the multiferroic frustrated antiferromagnet Mn{sub 3}TeO{sub 6} have been investigated. Ceramic samples of the solid solution series Mn{sub 3−x}Co{sub x}TeO{sub 6} were prepared by a solid-state reaction route. X-ray and neutron powder diffraction and electron microscopy techniques were combined with calorimetric, dielectric and magnetic measurements to investigate the dependence of the crystal structure and physical properties on temperature and composition. It is shown that the compounds with x ≤ 2.4 adopt the trigonal corundum-related structure of pure Mn{sub 3}TeO{sub 6} (space group R3{sup ¯}) in the temperature range 5–295 K and that the lattice parameters a and c and the unit-cell volume V decrease linearly with increasing Co{sup 2+} concentration. The low-temperature magnetic susceptibility and heat capacity data evidence the antiferromagnetic ordering of all samples. The Neel temperature linearly increases with Co{sup 2+} concentration x. Curie–Weiss fits of the high temperature susceptibility indicate that the magnetic frustration decreases with x. The derived magnetic structure of Mn{sub 3}TeO{sub 6} can be described as an incommensurately modulated magnetic spin state with k = [0, 0, k{sub z}] and an elliptical spin-spiral order of spins within the chains of MnO{sub 6} octahedra. With increasing Co{sup 2+} concentration the propagation vector k{sub z} changes from 0.453 (x = 0) to 0.516 (x = 2.4). The magnetic anisotropy changes as well, leading to a reorientation of the spiral-basal plane. A possible coexistence of long-range order of electrical dipoles and magnetic moments in Mn{sub 3−x}Co{sub x}TeO{sub 6} is discussed.

36 MATERIALS SCIENCE↗