红外LED用掺硅HB-GaAs单晶纵向载流子浓度分布研究

GaAs单晶作为一种重要的LED衬底材料在光电器件中应用十分广泛,但载流子浓度(C.C.)分布不均、杂质浓度过高等缺陷会严重影响相关器件的性能.为制备纵向载流子浓度分布均匀的掺硅HB-GaAs单晶,本文探讨了单晶生长过程中熔区长度对纵向载流子浓度分布的影响.以高纯GaAs多晶为原料,设定不同的拉晶温度曲线,采用窄熔区技术进行晶体生长研究,最终生长出C.C.值分布更均匀、位错密度低(EPD≤10 000 cm-2)的<111>向N型掺硅GaAs单晶.利用辉光放电质谱法(GDMS)和范德堡法霍尔效应测试对晶体进行了表征,单晶纯度达到5N且无硼杂质沾污.     

Excellent UV-absorbing cotton fabric with high durability and hydrophobicity based on surface-initiated ATRP of polymerizable organic UV-absorber

Cellulose - Ultraviolet (UV) protective cotton fabric is a convenient and reliable way to protect human body from sunlight. Herein, a polymerizable UV-absorber,...     

一种改进的用于Adams预估-校正算法的步长控制方法

1 引 言 对于一阶常微分方程 y'=f(t,y).(1) 的数值解法,目前常用的主要有两类方法:单步法和线性多步法(Linear Multistep Methods,LMM).     

Properties of ZnO thin films grown on Si substrates by photo-assisted MOCVD

ZnO thin films were grown on (1 0 0) p-Si substrates by Photo-assisted Metal Organic Chemical Vapor Deposition (PA-MOCVD) using diethylzinc (DEZn) and O₂ as source materials and tungsten-halogen lamp as a light source. The effects of tungsten-halogen lamp irradiation on the surface morphology, structural and optical properties of the deposited ZnO films have been investigated by means of atomic force microscope (AFM), X-ray diffraction and photoluminescence (PL) spectra measurements. Compared with the samples without irradiation, the several characteristics of ZnO films with irradiation are improved, including an improvement in the crystallinity of c-axis orientation, an increase in the grain size and an improvement in optical quality of ZnO films. These results indicated that light irradiation played an important role in the growth of ZnO films by PA-MOCVD.     

Proline-based reduced dipeptides as recyclable and highly enantioselective organocatalysts for asymmetric Michael addition

A series of novel proline-based reduced dipeptides was developed and evaluated for a direct Michael addition of ketones and aldehydes to nitroalkenes. Excellent yields (up to 95%), diastereoselectivities (up to 98% dr) and enantioselectivities (up to 98% ee) were achieved in the presence of 5 mol% catalyst without any additional additives at room temperature.     

Suppression of elliptic flow in a minimally viscous quark–gluon plasma

We compute the time evolution of elliptic flow in non-central relativistic heavy-ion collisions, using a (2+1$2+1$)-dimensional code with longitudinal boost-invariance to simulate viscous fluid dynamics in the causal Israel–Stewart formulation. We show that even “minimal” shear viscosity η/s=?/(4π)$\eta /s=?/(4\pi )$ leads to a large reduction of elliptic flow compared to ideal fluid dynamics, raising questions about the interpretation of recent experimental data from the Relativistic Heavy Ion Collider.     

Chiral pyrrolidine quaternary derivatives as organocatalysts for asymmetric Michael additions

A series of chiral pyrrolidine quaternary derivatives were designed and synthesized. It was found that these derivatives are highly efficient organocatalysts for the asymmetric Michael addition reactions of aldehydes and ketones to nitroolefins with high yields (up to 96%), high enantioselectivities (up to 99% ee), and high diastereoselectivities (up to 97:3 dr). Furthermore, catalyst 7a could be recycled without remarkable loss of catalytic activity and stereoselectivity.     

A time-dependent perturbation solution from a steady state for Marangoni problem

In this article, based on the T-weakly continuous theory, we prove the existence of global weak solution of the 2D incompressible Marangoni problem, which is modelled by the Boussinesq equations omitting effect of buoyancy. Moreover, we show that such weak solution is unique, and which is a time-dependent perturbation solution from a steady state.     

Crosslinked polyacrylonitrile precursor for S@pPAN composite cathode materials for rechargeable lithium batteries

S@pPAN has become promising cathode materials in rechargeable batteries due to its high compressed density,low E/S ratio,no polysulfide dissolution,no self-discharge,and stable cycling.However,it is a big challenge to enhance its sulfur content which determines its practical specific capacity.Herein,we prepare crosslinked PAN as precursor,leading to effective enhancement of sulfur content up to 55 wt%and a reversible specific capacity of 838 mAh g _composites^-1 at 0.2C.Because of the microporous structure and high specific area,crosslinked PAN provides more space to accommodate sulfur molecule and improve the interfacial reaction of S@pPAN as well.This work provides a promising direction to design S@pPAN for lithium sulfur batteries with high energy density.     

Efficient adsorption of U(VI) using in low-level radioactive wastewater containing organic matter by amino groups modified polyacrylonitrile fibers

Journal of Radioanalytical and Nuclear Chemistry - A kind of amino groups modified polyacrylonitrile fibers (PAN-A) was prepared to extract uranium from organic-containing low-level radioactive...