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Yang, L.

Publications and source records attributed to Yang, L..

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Aqueous solution synthesis and photoluminescence properties of two-dimensional dendritic PbWO{sub 4} nanostructures

Graphical abstract: PbWO{sub 4} two-dimensional dendritic nanostructures (2DDNs) were prepared at room temperature through a facile aqueous solution route using only Pb(NO{sub 3}){sub 2} and Na{sub 2}WO{sub 4} as reaction reagents and distilled water as solvent. - Highlights: • Two-dimensional dendritic PbWO4 nanostructures were prepared through a facile aqueous solution route at room temperature. • A “two-step” growth mechanism was proposed for the formation of two-dimensional dendritic PbWO4 nanostructures. • The two-dimensional dendritic PbWO4 nanostructures exhibit good photoluminescence properties. - Abstract: PbWO{sub 4} two-dimensional dendritic nanostructures (2DDNs) were prepared at room temperature through a facile aqueous solution route. X-ray diffraction, scanning electron microscope, transmission electron microscope and X-ray energy dispersive spectrometer were used to characterize the obtained samples. The PbWO{sub 4} 2DDN was in one plane, with a nearly circular shape and sizes of ∼10 μm. The PbWO{sub 4} 2DDNs were composed of curved nanowires around 200 nm in diameters, which were connected together to form a network nanostructure. The effects of reaction conditions including the concentration of react reagents, the reaction temperature, and the reaction time were systematically investigated and a possible formation mechanism for the formation of 2DDNs was proposed. The optical properties, such as UV–vis spectra and photoluminescence spectra of PbWO{sub 4}, were studied. The advantages of this synthetic route include the first synthesis of PbWO{sub 4} 2DDNs, simple synthetic procedure, room reaction temperature, and high reproducibility of the process.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Dual effects of stochastic heating on electron injection in laser wakefield acceleration

Electron injection into the wakefield of an intense short laser pulse by a weaker laser pulse propagating in the opposite direction is reconsidered using two-dimensional (2D) particle-in-cell simulations as well as analytical modeling. It is found that for linearly polarized lasers the injection efficiency and the quality of the wakefield accelerated electrons increase with the intensity of the injection laser only up to a certain level, and then decreases. Theory and simulation tracking test electrons originally in the beat region of the two laser pulses show that the reduction of the injection efficiency at high injection-laser intensities is caused by stochastic overheating of the affected electrons.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

ATOMISTIC STUDIES OF GROWTH OF HELIUM BUBBLES IN a-FE

Experimental results and atomistic simulations demonstrate that nucleation and growth of He bubbles in a-Fe is will contribute to embrittlement and is significant material problem for development of fusion power. Understanding the nucleation growth of He bubbles in steels is one of the most important issues in nuclear fusion technology. In order to understand the formation and evolution of self-interstitials (SIAs) caused by He bubble growth under He-rich/vacancy-poor conditions, the clustering of He and growth of He bubbles in bulk Fe is currently being investigated by inserting He atoms one by one into one or two He clusters. We find that a 1/2 <111> dislocation loop is formed and eventually punched out by a single He cluster, but when two He clusters are present the configuration of the SIA loop formed depends on the distance between the two He clusters. A <100> cluster is created when the distance between the He clusters is less than about 6a0 and eventually grows into a <100>{100} dislocation loop.

Gao, Fei↗
DOE OSTI2014

A combined compensation method for the output voltage of an insulated core transformer power supply

An insulated core transformer (ICT) power supply is an ideal high-voltage generator for irradiation accelerators with energy lower than 3 MeV. However, there is a significant problem that the structure of the segmented cores leads to an increase in the leakage flux and voltage differences between rectifier disks. A high level of consistency in the output of the disks helps to achieve a compact structure by improving the utilization of both the rectifier components and the insulation distances, and consequently increase the output voltage of the power supply. The output voltages of the disks which are far away from the primary coils need to be improved to reduce their inhomogeneity. In this study, by investigating and comparing the existing compensation methods, a new combined compensation method is proposed, which increases the turns on the secondary coils and employs parallel capacitors to improve the consistency of the disks, while covering the entire operating range of the power supply. This method turns out to be both feasible and effective during the development of an ICT power supply. The non-uniformity of the output voltages of the disks is less than 3.5% from no-load to full-load, and the power supply reaches an output specification of 350 kV/60 mA.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

3C-SiC nanocrystals/TiO{sub 2} nanotube heterostructures with enhanced photocatalytic performance

p-type ultrathin 3C-SiC nanocrystals are coated on heat-treated n-type TiO{sub 2} nanotube arrays formed by electrochemical etching of Ti sheets to produce heterostructured photocatalysts. Depending on the amounts of 3C-SiC nanocrystals on the TiO{sub 2} nanotubes, photocatalytic degradation of organic species can be enhanced. The intrinsic electric field induced by the heterojunction promotes separation of the photoexcited electrons-holes in both the TiO{sub 2} nanotubes and 3C-SiC nanocrystals. Hence, holes can more effectively travel to the surface of 3C-SiC nanocrystals and there are more electrons on the surface of TiO{sub 2} nanotubes consequently forming more {sup •}O{sub 2}{sup −} and {sup •}OH species to degrade organic molecules.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Correlations between 1/f noise and thermal treatment of Al-doped ZnO thin films deposited by direct current sputtering

Al-doped ZnO thin films (AZO) have been deposited on amorphous glass substrates by DC sputtering at different substrate temperatures T{sub s}. X-Ray diffraction results reveal that AZO thin films have a hexagonal wurtzite structure with (002) preferred orientation. (002) peaks indicate that the crystalline structure of the films is oriented with c-axis perpendicular to the substrate. Three-dimensional (3D) atomic force microscopy images of AZO thin films deposited on glass substrate at 200 °C, 300 °C, and 400 °C, respectively, shows the improvement of the crystallinity and the homogeneity of AZO thin films with T{sub s} which is in agreement with the noise measurements. The noise was characterized between 1 Hz and 100 kHz and we have obtained 1/f spectra. The noise is very sensitive to the crystal structure especially to the orientation of the crystallites which is perpendicular to the substrate and to the grain boundaries which generate a high current flow and a sharp increase in noise. Through time, R{sub sh} and [αμ]{sub eff} increase with the modification of the crystallinity of AZO thin films. Study of noise aging shows that the noise is more sensitive than resistivity for all AZO thin films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Improved measurement of the 2 ν β β half-life of 136 Xe with the EXO-200 detector

In this work, we report on an improved measurement of the 2 ν β β half-life of 136 Xe performed by EXO-200. The use of a large and homogeneous time-projection chamber allows for the precise estimate of the fiducial mass used for the measurement, resulting in a small systematic uncertainty. We also discuss in detail the data-analysis methods used for double- β decay searches with EXO-200, while emphasizing those directly related to the present measurement. The 136 Xe 2 ν β β half-life is found to be T 1 / 2 2 ν β β = 2.165 ± 0.016 ( stat ) ± 0.059 ( sys ) × 10 21 yr. Finally, this is the most precisely measured half-life of any 2 ν β β decay to date.

136Xe↗
DOE OSTI2014

Binding energetics of substitutional and interstitial helium and di-helium defects with grain boundary structure in α-Fe

The formation/binding energetics and length scales associated with the interaction between He atoms and grain boundaries in BCC α-Fe were explored. Ten different low Σ grain boundaries from the 〈100〉 and 〈110〉 symmetric tilt grain boundary systems were used. In this work, we then calculated formation/binding energies for 1–2 He atoms in the substitutional and interstitial sites (HeV, He{sub 2}V, HeInt, He{sub 2}Int) at all potential grain boundary sites within 15 Å of the boundary (52 826 simulations total). The present results provide detailed information about the interaction energies and length scales of 1–2 He atoms with grain boundaries for the structures examined. A number of interesting new findings emerge from the present study. For instance, the Σ3(112) twin boundary in BCC Fe possesses a much smaller binding energy than other boundaries, which corresponds in long time dynamics simulations to the ability of an interstitial He defect to break away from the boundary in simulations on the order of nanoseconds. Additionally, positive correlations between the calculated formation/binding energies of the He defects (R > 0.9) asserts that the local environment surrounding each site strongly influences the He defect energies and that highly accurate quantum mechanics calculations of lower order defects may be an adequate predictor of higher order defects. Various metrics to quantify or classify the local environment were compared with the He defect binding energies. The present work shows that the binding and formation energies for He defects are important for understanding the physics of He diffusion and trapping by grain boundaries, which can be important for modeling He interactions in polycrystalline steels.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗