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.     

Interfacial Engineering in PtNiCo/NiCoS Nanowires for Enhanced Electrocatalysis and Electroanalysis

Searching for new anti-poisoning Pt-based catalysts with enhanced activity for alcohol oxidation is the key in direct alcohol fuel cells (DAFCs). However, in the traditional strategy for designing bimetallic or multimetallic alloy is still difficult to achieve a satisfactory heterogeneous electrocatalyst because the activity often depends on only the surface atoms. Herein, we fabricate the multicomponent active sites by creating a sulfide structure on 1D PtNiCo trimetallic nanowires (NWs), to give a PtNiCo/NiCoS interface NWs (IFNWs). Owing to the presence of sulfide interfaces, the PtNiCo/NiCoS IFNWs enable an impressive methanol/ethanol oxidation reaction (MOR/EOR) performance and excellent anti-CO poisoning tolerance. They have the MOR and EOR mass activities of 2.25 Amg^-1_Pt and 1.62 Amg^-1_Pt, around 1.26, 3.21 and 1.46, 2.96 times higher than those of PtNiCo NWs and commercial Pt/C, respectively. CO-stripping and XPS measurements further demonstrate that the new interfacial structure and optimal bonding of Pt−CO can result in accelerating the removal of surface adsorbed carbonaceous intermediates. Moreover, such a unique structure has also demonstrated a much-improved ability for the electrochemical detection of some important molecules (H₂O₂ and NH₂NH₂).     

Late‐Stage Peptide Diversification by Bioorthogonal Catalytic CH Arylation at 23 °C in H2O

The step‐economical late‐stage diversification of tryptophan‐containing peptides was accomplished through chemo‐ and site‐selective palladium‐catalyzed C?H arylation under exceedingly mild reaction conditions. Thus, the C?H functionalization occurred efficiently at 23 °C with a catalyst loading as low as 0.5 mol %, and/or in H₂O.     

Self-Assembly of Alkylammonium Chains on Montmorillonite: Effect of Interlayer Cations,CEC, and Chain Length

Recently, polymeric materials have been filled with synthetic or natural inorganic compounds in order to improve their properties. Especially, polymer clay nanocomposites have attracted both academic and industrial attention. Currently, the structure and physical phenomena of organoclays at molecular level are difficultly explained by existing experimental techniques. In this work, molecular dynamics (MD) simulation was executed using the CLAYFF and CHARMM force fields to evaluate the structural properties of organoclay such as basal spacing, interlayer density, energy and the arrangement of alkyl chains in the interlayer spacing. Our results are in good agreement with available experimental or other simulation data. The effects of interlayer cations (Na⁺, K⁺, Ca²⁺), the cation exchange capacity, and the alkyl chain length on the basal spacing and the structural properties are estimated. These simulations are expected to presage the microstructure of organo-montmorillonite and lead relevant engineering applications.     

On the normalized Laplacian of Möbius phenylene chain and its applications

Let denote a molecular graph of linear [n] phenylene with n hexagons and n squares, and let the Möbius phenylene chain be the graph obtained from the by identifying the opposite lateral edges in reversed way. Utilizing the decomposition theorem of the normalized Laplacian characteristic polynomial, we study the normalized Laplacian spectrum of , which consists of the eigenvalues of two symmetric matrices ℒ _R and ℒ _Q of order 3n. By investigating the relationship between the roots and coefficients of the characteristic polynomials of the two matrices above, we obtain an explicit closed-form formula of the multiplicative degree-Kirchhoff index as well as the number of spanning trees of . Furthermore, we determine the limited value for the quotient of the multiplicative degree-Kirchhoff index and the Gutman index of .     

紫外光固化阳离子复合胶粘剂的制备与表征

 以三芳基六氟磷酸硫鎓盐为引发剂,钛酸四异丙酯(TIP)为无机前驱体,3,4-环氧环己基甲基3,4-环氧环己基甲酸酯为单体,制备了含TiO2纳米结构的紫外光固化阳离子复合胶粘剂。通过原子力显微镜对复合胶粘剂形貌进行表征,研究了TIP含量对胶粘剂折射率和光透过率的影响。结果表明：TiO2无机相均匀地分散在胶粘剂的聚合物基体中,平均粒径约为20 nm;随着体系中TIP质量分数的变化,复合胶粘剂折射率为1.510 3~1.540 9可调;胶粘剂的光透过率随TIP质量分数增加略有减低,但当TIP含量高达40%时,光透过率维持在90%左右。     

Prandtl number effects in MRT lattice Boltzmann models for shocked and unshocked compressible fluids

This paper constructs a new multiple relaxation time lattice Boltzmann model which is not only for the shocked compressible fluids, but also for the unshocked compressible fluids. To make the model work for unshocked compressible fluids, a key step is to modify the collision operators of energy flux so that the viscous coefficient in momentum equation is consistent with that in energy equation even in the unshocked system. The unnecessity of the modification for systems under strong shock is analyzed. The model is validated by some well-known benchmark tests, including thermal Couette flow, Riemann problem. The first system is unshocked and the latter is shocked. In both systems, the Prandtl number effects are checked. Satisfying agreements are obtained between new model results and analytical ones.     

The Kirkendall Effect for Engineering Oxygen Vacancy of Hollow Co3O4 Nanoparticles toward High‐Performance Portable Zinc–Air Batteries

Structure and defect control are widely accepted effective strategies to manipulate the activity and stability of catalysts. On a freestanding hierarchically porous carbon microstructure, the tuning of oxygen vacancy in the embedded hollow cobaltosic oxide (Co₃O₄) nanoparticles is demonstrated through the regulation of nanoscale Kirkendall effect. Starting with the embedded cobalt nanoparticles, the concentration of oxygen‐vacancy defect can vary with the degree of Kirkendall oxidation, thus regulating the number of active sites and the catalytic performances. The optimized freestanding catalyst shows among the smallest reversible oxygen overpotential of 0.74 V for catalyzing oxygen reduction/evolution reactions in 0.1 m KOH. Moreover, the catalyst shows promise for substitution of noble metals to boost cathodic oxygen reactions in portable zinc–air batteries. This work provides a strategy to explore catalysts with controllable vacancy defects and desired nano‐/microstructures.