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Luminescence Properties of Blue Light-emitting Diode Grown on Patterned Sapphire Substrate
Dang-Hui Wang,Tian-Han Xu,Lei Wang 한국광학회 2017 Current Optics and Photonics Vol.1 No.4
In this study, we present a detailed investigation of luminescence properties of a blue light-emittingdiode using InGaN/GaN (indium component is 17.43%) multiple quantum wells as the active region grownon patterned sapphire substrate by low-pressure metal-organic chemical vapor deposition (MOCVD). HighresolutionX-ray diffraction (HRXRD), atomic force microscopy (AFM), scanning electron microscopy(SEM), Raman scattering (RS) and photoluminescence (PL) measurements are employed to study the crystalquality, the threading dislocation density, surface morphology, residual strain existing in the active regionand optical properties. We conclude that the crystalline quality and surface morphology can be greatlyimproved, the red-shift of peak wavelength is eliminated and the superior blue light LED can be obtainedbecause the residual strain that existed in the active region can be relaxed when the LED is grown onpatterned sapphire substrate (PSS). We discuss the mechanisms of growing on PSS to enhance the superiorluminescence properties of blue light LED from the viewpoint of residual strain in the active region.
Xu Haiyu,Luo Kai,Dang Jianjun,Li Daijin,Huang Chuang 대한조선학회 2021 International Journal of Naval Architecture and Oc Vol.13 No.1
To investigate the supercavity geometry and gas flow structure for the supercavities with two closure types under the different flow conditions, an inhomogeneous multiphase model with the SST turbulence model was established, and validated by experimental results. The results show that two distinct regions exist inside the supercavity, which include the downstream flow region along the gas-water interface and the reverse flow region. For the twin-vortex supercavity, the internal gas leaks from the supercavity boundary by two paths: the supercavity surface and the two-vortex tubes. Increasing Froude number leads to more internal gas stripped from the supercavity surface. Two types of gas loss exist for the reentrant jet supercavity with high Froude number, one type is the steady process of gas loss, and the major gas-leaking path is the supercavity surface rather than supercavity closure region. The other type is the unsteady periodic ejection, and the gas cluster of periodic ejection is merely a small part of the gas stored inside the supercavity.
Dang Mengyue,Li Ying,Xu Chaoxiang,He Yulin,Yu Chunpeng,Liu Wenbo,Jin Hongming,Zhu Mingyuan,Zhang Jiujun,Li Wenxian 한국물리학회 2021 Current Applied Physics Vol.32 No.-
The electrochemical performances of LiNi0.5Co0.2Mn0.3O2 (NCM523) layered cathode material, such as poor rate capacity and cycling stability caused by undesirable intrinsic conductivity and low rate of lithium ion transportation, are not fairly good especially at elevated rate and cut-off voltage. To improve these properties, in this study, the co-coating layer of graphene and TiO2 was constructed on NCM523 surface. The graphene/TiO2 coating layer could effectively prevent hydrofluoric acid (HF) attacks, suppress the side reaction, accelerate the lithium ion diffusion and facilitate the electron migration. The enhancement of cycle performance and rate capacity was contributed to the uniform co-modified surface, interacting each other and thus exhibiting synergistic effects.
Sonochemical fabrication of Cu<sub>2</sub>OΓ/graphene nanohybrid with a hierarchical architecture
Xu, J.,Dang, D.K.,Chung, J.S.,Hur, S.H.,Choi, W.M.,Kim, E.J. Academic Press 2014 Journal of Solid State Chemistry Vol.220 No.-
A three-dimensional Cu<SUB>2</SUB>OΓ/graphene nanohybrid hierarchical sphere-like architecture has been successfully synthesized by a sonochemical method. The as-prepared nanocomposite has been characterized using various techniques including powder X-ray diffraction, scanning electron microscopy, field emission transmission electron microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy and Fourier transmission infrared spectrometry. Secondary big hierarchical Cu<SUB>2</SUB>OΓ spheres (diameter of ~200nm) consist of primary small Cu<SUB>2</SUB>OΓ spheres (diameter of 5-10nm), which are uniformly distributed on the graphene surface. In the primary small Cu<SUB>2</SUB>OΓ sphere, amorphous carbon is formed by the oxidation-reduction reaction between 1-aminopyrene and copper(II) acetate in the sonochemical process. Our facile sonochemical method may apply to the preparation of other metal oxide/graphene hierarchical nanohybrids.
Dang-Hui Wang,Sheng-Rui Xu,Jin-Cheng Zhang,Ke Chen,Zhi-Wei Bi,Lin-Xia Zhang,Fan-Na Meng,Shan Ai,Yue Hao 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.4
In this study, we report on the crystal quality of InGaN epifilms with different indium fractions grown at different growth temperatures on c-plane sapphire substrates with an AlN nucleation layer by using low-pressure metal-organic chemical-vapor deposition (MOCVD). High-resolution X-ray diffraction (HRXRD), atom force microscopy (AFM), photoluminescence (PL) and Raman scattering measurements were employed to study the crystal quality, optical properties and strain condition of InGaN epifilms with increasing indium fraction (from 4.36% to 15.36%). Results show that InGaN epitaxial layers can be realized with a higher indium fraction at a lower temperature by inserting an AlN nucleation layer between the sapphire substrate and the GaN buffer layer and that the obtained InGaN epifilms have an improved crystal quality and a lower threading dislocation density.
Dang-Hui Wang,Tian-Han Xu 한국광학회 2016 Current Optics and Photonics Vol.20 No.1
In this study, we have investigated a high-temperature AlN nucleation layer and AlGaN epilayers onc-plane sapphire substrate by low-pressure metal-organic chemical vapor deposition (LP-MOCVD). Highresolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), scanning electron microscope(SEM) and Raman scattering measurements have been exploited to study the crystal quality, surfacemorphology, and residual strain of the HT-AlN nucleation layer. These analyses reveal that the insertionof an LT-AlN nucleation layer can improve the crystal quality, smooth the surface morphology of theHT-AlN nucleation layer and further reduce the threading dislocation density of AlGaN epifilms. Themechanism of inserting an LT-AlN nucleation layer to enhance the optical properties of HT-AlN nucleationlayer and AlGaN epifilm are discussed from the viewpoint of driving force of reaction in this paper.
Long, Dang Xuan,Xu, Yong,Wei, Huai-xin,Liu, Chuan,Noh, Yong-Young The Royal Society of Chemistry 2015 Physical chemistry chemical physics Vol.17 No.31
<P>A simply and facilely synthesized MoO<SUB>3</SUB> solution was developed to fabricate charge injection layers for improving the charge-injection properties in p-type organic field-effect transistors (OFETs). By dissolving MoO<SUB>3</SUB> powder in ammonium (NH<SUB>3</SUB>) solvent under an air atmosphere, an intermediate ammonium molybdate ((NH<SUB>4</SUB>)<SUB>2</SUB>MoO<SUB>4</SUB>) precursor is made stable, transparent and spin-coated to form the MoO<SUB>3</SUB> interfacial layers, the thickness and morphology of which can be well-controlled. When the MoO<SUB>3</SUB> layer was applied to OFETs with a cost-effective molybdenum (Mo) electrode, the field-effect mobility (<I>μ</I><SUB>FET</SUB>) was significantly improved to 0.17 or 1.85 cm<SUP>2</SUP> V<SUP>−1</SUP>s<SUP>−1</SUP> for polymer semiconductors, regioregular poly(3-hexylthiophene) (P3HT) or 3,6-bis-(5bromo-thiophen-2-yl)-<I>N</I>,<I>N</I>′-bis(2-octyl-1-dodecyl)-1,4-dioxo-pyrrolo[3,4-<I>c</I>]pyrrole (DPPT-TT), respectively. Device analysis indicates that the MoO<SUB>3</SUB>-deposited Mo contact exhibits a contact resistance <I>R</I><SUB>C</SUB> of 1.2 MΩ cm comparable to that in a device with the noble Au electrode. Kelvin-probe measurements show that the work function of the Mo electrode did not exhibit a dependence on the thickness of MoO<SUB>3</SUB> film. Instead, ultraviolet photoemission spectroscopy results show that a doping effect is probably induced by casting the MoO<SUB>3</SUB> layer on the P3HT semiconductor, which leads to the improved hole injection.</P> <P>Graphic Abstract</P><P>A simply synthesized MoO<SUB>3</SUB> is used as charge injection layers for printed p-type organic field-effect transistors (OFETs). <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5cp03369a'> </P>
Wei Bangzheng,Zhou Rui,Xu Dang,Chen Ruizhi,Yu Xinxi,Chen Pengqi,Cheng Jigui 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.12
The thermal stress between W plasma-facing material (PFM) and Cu heat sink in fusion reactors can be significantly reduced by using a WeCu functionally graded material (WeCu FGM) interlayer. However, there is still considerable stress at the joining interface between W and WeCu FGM in the W/WeCu FGM/Cu portions. In this work, we fabricate W skeletons with continuous gradients in porosity by a modified sedimentation method. Sintering densification behavior and pore characteristics of the sedimented W skeletons at different sintering temperatures were investigated. After Cu infiltration, the final WeCu FGM was obtained. The results indicate that the pore size and porosity in the W skeleton decrease gradually with the increase of sintering temperature, but the increase of skeleton sintering temperature does not reduce the gradient range of composition distribution of the final prepared WeCu FGM. And WeCu FGM with composition distribution from pure W to W-20.5wt.% Cu layer across the section was successfully obtained. The thickness of the pure W layer is about one-fifth of the whole sample thickness. In addition, the prepared WeCu FGM has a relative density of 94.5 % and thermal conductivity of 185 W/ (m K). The WeCu FGM prepared in this work may provide a good solution to alleviate the thermal stress between W PFM and Cu heat sink in the fusion reactors.