高电荷态离子与Si(110)晶面碰撞的沟道效应研究

不同电荷态低速离子(Arq+,Pbq+)轰击Si(110)晶面,测量不同入射角情况下的次级粒子的产额.通过比较溅射产额与入射角的关系,证实沟道效应的存在.高电荷态离子与Si相互作用产生的沟道效应说明溅射产额主要是由动能碰撞引起的.在小角入射条件下,高电荷态离子能够增大溅射产额.当高电荷态离子以40°—50°入射时,存在势能越高溅射产额越大的势能效应.

高电荷态离子~(207)Pb~(q+)(24≤q≤36)与Si(110)固体表面作用的电子发射研究

报道了利用兰州重离子加速器国家实验室ECR源引出的高电荷态离子207Pbq+(24≤q≤36)入射到Si(110)表面产生的电子发射的实验测量结果.结果表明,高电荷态离子与固体表面相互作用产生的电子发射产额Y与入射离子的电荷态q、入射角度ψ和入射能量E都有很强的关联.首次发现,电子发射产额Y与入射角度ψ间有接近1/tanψ的关系.理论分析认为,这些过程与基于经典过垒模型的势能电子发射过程密切相关.

高电荷态离子与Si(110)晶面碰撞的沟道效应研究

不同电荷态低速离子(Arq+，Pbq+)轰击Si(110)晶面，测量不同入射角情况下的次级粒子的产额. 通过比较溅射产额与入射角的关系，证实沟道效应的存在. 高电荷态离子与Si相互作用产生的沟道效应说明溅射产额主要是由动能碰撞引起的. 在小角入射条件下，高电荷态离子能够增大溅射产额. 当高电荷态离子以40°—50°入射时，存在势能越高溅射产额越大的势能效应.

Electron emission induced by the interaction of highly charged ions Pb-207(q+) (24 <= q <= 36) with solid surface of Si(110)

The electron emission induced by highly charged ions Pb-207(q+) (24 <= q <= 36) interacting with Si(110) surface is reported. The result shows that the electron emission yield Y has a strong dependence on the projectile charge state q, incidence angle psi and impact energy E. In fitting the experimental data we found a nearly 1/tan psi dependence of Y. Theoretical analysis shows that these processes are closely related to the process of potential electron emission based on the classical over-the-barrier model.

3T超导螺线管的研制

超导螺线管广泛应用于核磁共振仪、粒子探测器等设备。本文设计了中心场值为3T，中心附近Φ30mm区域内均匀度达到1×10-4的超导螺线管。磁体线圈采用多芯NbTi-Cu复合超导线绕制，并利用铁轭屏蔽漏场。磁体采用温孔冷铁轭、全浸泡冷却方式结构。同时，为了减少辐射漏热，采用液氮冷屏、真空多层绝热结构。 本文重点对带有冷铁轭的超导螺线管的磁场进行了优化设计。设计过程中结合了专业磁场计算软件OPERA和多种优化方法。线圈采用六次槽型结构，利用遗传算法和优选法优化线圈尺寸；铁轭采用正交试验设计优化尺寸。 利用有限元软件ANSYS对超导磁体进行电磁力分析，并且对降温后线圈、支撑筒和箍筒的热应力进行了模拟计算。估算了支撑系统的传导漏热、磁体的辐射漏热以及剩余气体漏热。详细介绍了超导磁体绕制工艺，超导磁体液氦杜瓦的加工工艺，并且对杜瓦的绝热工艺进行了介绍。最后介绍了超导螺线管的总体加工进展

Chemisorption and reaction characteristics of methyl radicals on Cu(110)

Methyl radicals are generated by pyrolysis of azomethane, and the condition for achieving neat adsorption on Cu(110) is described for studying their chemisorption and reaction characteristics. The radical-surface system is examined by X-ray photoemission spectroscopy, ultraviolet photoemission spectroscopy, temperature-programmed desorption, low-energy electron diffraction (LEED), and high-resolution electron energy loss spectroscopy under ultrahigh vacuum conditions. It is observed that a small fraction of impinging CH3 radicals decompose into methylene possibly on surface defect sites. This type of CH2 radical has no apparent effect on CH3(ads) surface chemistry initiated by dehydrogenation to form active CH2(ads) followed by chain reactions to yield high-mass alkyl products. All thermal desorption products, such as H-2, CH4, C2H4, C2H6, and C3H6, are detected with a single desorption peak near 475 K. The product yields increase with surface coverage until saturation corresponding to 0.50 monolayer of CH3(ads). The mass distribution is, however, invariant with initial CH3(ads) coverage, and all desorbed species exhibit first-order reaction kinetics. LEED measurement reveals a c(2 x 2) adsorbate structure independent of the amount of gaseous exposure. This strongly suggests that the radicals aggregate into close-packed two-dimensional islands at any exposure. The islanding behavior can be correlated with the reaction kinetics and is deemed to be essential for the chain propagation reactions. Some relevant aspects of the CH3/Cu(111) system are also presented. The new results are compared with those of prior studies employing methyl halides as radical sources. Major differences are found in the product distribution and desorption kinetics, and these are attributed to the influence of surface halogen atoms present in those earlier investigations.

On the propagation rate of the chemical waves observed during the course of CO oxidation on a Ag/Pt(110) composite surface

We have analyzed the propagation rate of the chemical waves observed during the course of CO oxidation on a Ag/Pt(I 10) composite surface that were reported in our previous papers [Surf Interface Anal. 2001, 32, 179; J. Phys. Chem. B 2002, 106, 5645]. In all cases, the propagation rate v can be adequately fitted as v = v(0) + D-0/d, in which v(0) and D-0 are constants, and d is the distance between the reaction front of the chemical wave and the boundary from which the chemical wave originates. We propose that the surface species responsible for the formation of the chemical wave comes from two paths: the adsorption of molecules in the gas phase on the surface and the migration from the adjacent surface with different catalytic activity. v(0) corresponds to the contribution from the surface species due to the adsorption, and D-0/d to that of the surface species that migrates from the adjacent surface. The rate equation clearly suggests that the observed chemical wave results from the coupling between adjacent surfaces with different catalytic activities during the course of heterogeneous catalysis. These results, together with our previous reports, provide a good fundamental understanding of spillover, an important phenomenon in heterogeneous catalysis.

Synthesis, structure, and optical properties of a contorted (110)-oriented layered hybrid perovskite: C3H11SN3PbBr4

The < 110 >-oriented perovskite is very rare in the hybrid perovskites family. In this work, an unusual layered < 110 >-oriented hybrid perovskite, which is stabilized by a special organic ligand, 2-(aminoethyl)isothiourea, has been obtained. This ligand combines a primary amine and a formamidine on the two ends of one molecule. Introduction of the special ligand brings about contorted inorganic sheets in the hybrid perovskite structure. The optical properties of the new < 110 >-oriented perovskite were studied.

Novel < 110 >-oriented organic-inorganic perovskite compound stabilized by N-(3-aminopropyl) imidazole with improved optical properties

In the organic-inorganic perovskites family, the < 100 >-oriented type has been extensively investigated as a result of its unique magnetic, optical, and electrical properties, and only one type of < 110 >-oriented hybrid perovskite stabilized by methylammonium and iodoformamidinium cations or the latter themselves has been known so far. In this paper, another novel < 110 >-oriented organic-inorganic perovskite (C6H13N3)-PbBr4 (compound 1) has been prepared by reacting N-(3-aminopropyl)imidazole (API) with PbBr2 in hydrobromic acid. The crystal structure is determined, which indicates that the perovskite is stabilized by API. The introduction of the optically active organic ligand API into the hybrid perovskite results in a red shift and a great enhancement of photoluminescence in the perovskite with respect to organic ligand API itself. These results have been explained according to calculation based on density-functional theory. Moreover, the excellent film processing ability for the perovskite (C6H13N3)PbBr4 together with the improved optical properties makes it have potential application in optoelectronic devices.