A Surface Femtosecond Two-Photon Photoemission Spectrometer for Excited Electron Dynamics and Time-Dependent Photochemical Kinetics

搭建了一套研究金属和金属氧化物表面的超快激发态电子动力学和光化学动力学的飞秒双光子光电子能谱仪. 该装置将半球形电子能量分析仪和成像技术相结合,同时测量光电子的能量和角度分布.通过Mach-Zehnder干涉仪测量时间分辨的双光子光电子能谱获得超快激发电子态的动力学信息. 这一功能在Cu(111)上得到了证实. 另外还发展了一个通过实时测量双光子光电子能谱来研究表面光化学的方法,并成功应用到CH₃CH₂OH/TiO₂(110)体系. 研究表明,只有将两种方法结合起来才能正确地研究光诱导的表面激发共振的动力学.     

薄膜介质层绕式Blumlein线理论与实验研究

对薄膜介质层绕式Blumlein线的特性参数进行了理论分析。采用Pspice软件对电路模型进行了计算,分析了开关电感、寄生电阻对负载输出波形的影响。结果表明:开关电感的存在使得负载波形前沿变缓,后延波形扭曲变差,寄生电阻会影响负载的电压输出效率。采用模拟软件对传输线中的电磁场分布进行了计算,结果表明薄电极边缘场畸变以及折叠弯曲部分的场变化是绝缘介质耐压必须考虑的因素。基于此理论分析,设计制作了一种新型薄膜介质Blumlein线,绝缘材料为聚酯薄膜,单层薄膜厚100μm,电极为厚50μm的铜皮,单元模块设计耐压50 kV。进行了三级模块串联叠加实验,充电25 kV,匹配负载输出60 kV,脉冲上升沿80 ns,脉冲宽度200 ns。     

Vertically Grown Few-Layer MoS2 Nanosheets on Hierarchical Carbon Nanocages for Pseudocapacitive Lithium Storage with Ultrahigh-Rate Capability and Long-Term Recyclability

Molybdenum disulfide (MoS₂) is an intensively studied anode material for lithium-ion batteries (LIBs) owing to its high theoretical capacity, but it is still confronted by severe challenges of unsatisfactory rate capability and cycle life. Herein, few-layer MoS₂ nanosheets, vertically grown on hierarchical carbon nanocages (hCNC) by a facile hydrothermal method, introduce pseudocapacitive lithium storage owing to the highly exposed MoS₂ basal planes, enhanced conductivity, and facilitated electrolyte access arising from good hybridization with hCNC. Thus, the optimized MoS₂/hCNC exhibits reversible capacities of 1670 mAh g⁻¹ at 0.1 A g⁻¹ after 50 cycles, 621 mAh g⁻¹ at 5.0 A g⁻¹ after 500 cycles, and 196 mAh g⁻¹ at 50 A g⁻¹ after 2500 cycles, which are among the best for MoS₂-based anode materials. The specific power and specific energy, which can reach 16.1 kW and 252.8 Wh after 3000 cycles, respectively, indicate great potential in high-power and long-life LIBs. These findings suggest a promising strategy for exploring advanced anode materials with high reversible capacity, high-rate capability, and long-term recyclability.     

Catalyst-controlled diastereoselective ring-opening formal [3+2]-cycloadditions of arylvinyl oxirane 2,2-diesters with cyclic N-sulfonyl imines

A diastereoselectivity-controllable formal [3+2]-cycloaddition of arylvinyl oxirane 2,2-diesters with cyclic N-sulfonyl imines is developed, affording the corresponding tricyclic oxazolidine derivatives in moderate to excellent yields with excellent diastereoselectivities in the presence of palladium(0) or scandium(III) triflate. This protocol allows selective synthesis of diastereomers of tricyclic oxazolidine derivatives under switchable and mild conditions. Further transformations of the obtained products were conducted by removing ester groups and arylvinyl moieties.     

Control the self-assembly of fluorenone-based polycatenars by tuning chain length

Using Suzuki coupling reactions as key steps, a series of fluorenone-based polycatenars, consisting of a central 2,7-diphenyl-9-fluorenone core connected with the 3,4,5-trialkoxybenzoate unit via –COO- linkage at each side have been synthesized. Upon elongation of the terminal alkyl chain, these compounds self-assembled into mesophase sequence of Col_hex/p6mm - Cub_I/$\mathit{Pm}\overline{3}n$ in solid states as well as organogels with interesting morphologies varied from 3D helical fibers to spherical structures in solvents.     

Electron transport of a quantum wire with spatially periodic spin–orbit coupling

Electron transport properties of an ideal one-dimensional (1D) quantum wire are studied including spatially periodic Rashba spin–orbit coupling (SOC) and Dresselhaus SOC. By comparing with the previous work [S.J. Gong, Z.Q. Yang, J. Phys. Condens. Matter 19 (2007) 446209], two transmission gaps appear in the transmission probability of electrons and their widths are also broadened dramatically. Moreover, it is found that their widths are sensitive not only to the strength of SOCs but also to the length ratio of SOCs segment and non-SOCs segment. In addition, a ‘circle-type’ transmission behavior has been found by tuning the strength of SOCs continuously. Our results may extend the previous work and provide an more effective method to manipulate the current in nanoelectric devices.     

Nondestructive rare earth element imaging of fish teeth from deep‐sea sediments

X‐ray fluorescence computed tomography is an emerging imaging modality that allows for the nondestructive reconstruction of the internal distribution of elements within a sample. The common use of X‐ray excitation energy (up to approximately 20 keV) has necessitated the use of l ‐shell fluorescence for heavy elements. In this study, based on high energy X‐ray at BL13W1 of the Shanghai Synchrotron Radiation Facility, we employed high‐energy excitation for tomographic imaging of the heavy metals (rare earth elements) in fish teeth from deep‐sea sediments on the micrometer scale using K‐shell X‐ray fluorescence. The virtual cross‐sectional distribution of La, Ce, Pm, Pr, Nd, and Sm were obtained, thereby providing a feasible approach for analyzing the enrichment mechanism of rare earth elements. Copyright © 2015 John Wiley & Sons, Ltd.