单晶硅晶格间距的测量技术进展及应用

单晶硅晶格间距是许多重要物理常数测量的基础。本文介绍了硅晶格间距测量技术的发展历程,包括X射线干涉仪直接测量和晶格比较仪间接测量两种方法,以及影响测量结果不确定度的关键因素。得益于晶格间距测量的进展,在纳米尺度,硅晶格间距被国际计量局(BIPM)批准成为新的米定义复现形式。最后介绍了硅晶格在计量学中的应用,以及基于硅晶格实现纳米几何量测量的溯源体系的研究趋势。     

磁性量子元胞自动机功能阵列的实验研究

采用电子束光刻、热蒸镀和剥离工艺在室温下制备了多组磁性量子元胞自动机器件功能阵列. 实验研究了曝光剂量和曝光时间对三个不同间距参数磁性量子元胞自动机阵列图案的影响, 发现100 pA电子束束流和0.38 μs曝光时间可获得理想的阵列图案. 对制备的反相器阵列结构进行了磁力显微测试, 结果显示了正确的逻辑功能, 成功实现了不同间距参数功能阵列的实验制备. 此外, 实验还发现纳磁体阵列制备中容易出现缺陷, 模拟结果表明丢失纳磁体缺陷导致了信号传递反相.     

新型宽温区高热稳定性微波功率SiGe 异质结双极晶体管

宽温区大电流下的热不稳定性严重制约着功率SiGe 异质结双极晶体管 (HBT) 在射频和微波电路中的应用.为改善器件的热不稳定性, 本文利用SILVACO TCAD建立的多指功率SiGe HBT模型, 分析了器件纵向结构中基区Ge组分分布对微波功率SiGe HBT电学特性和热学特性的影响. 研究表明, 对于基区Ge组分为阶梯分布的HBT, 由于Ge组分缓变引入了少子加速电场, 使它与均匀基区Ge组分HBT相比, 具有更高的特征频率f_T, 且电流增益β和f_T随温度变化变弱, 这有利于防止器件在宽温区工作时电学特性的漂移.同时, 器件整体温度有所降低, 但器件各指温度分布均匀性较差.考虑多指HBT各发射极指散热能力存在差异, 在器件纵向结构设计为基区Ge组分阶梯分布的同时, 对其横向版图进行发射极指间距渐变结构设计, 用于改善器件各指温度分布的均匀性, 进而提高HBT的热稳定性.结果表明, 与基区Ge组分为均匀分布的等发射极指间距结构HBT相比, 新器件各指温度分布均匀性明显改善, f_T保持了较高的值, 且β和f_T 随温度变化不敏感, 热不稳定性得到显著改善, 显示了新器件在宽温区大电流下工作的优越性. 关键词： SiGe 异质结双极晶体管 Ge组分分布 发射极指间距渐变技术 热稳定性     

极紫外平场光栅光谱仪的研制和性能测试

研制了一台高分辨率极紫外光谱仪,用于磁约束等离子体诊断。采用一块具有平场特性的全息球面变线距光栅作为分光元件,光栅公称线密度为1 200 lines·mm-1,掠入射角为3°。一台可深度制冷、背照式面阵CCD作为光谱探测器,用机械快门控制曝光时间。通过CCD在光谱聚焦面的移动,可以记录的光谱范围为5～50 nm。用Penning放电光源测试了光谱仪的性能; 利用光源的标准谱线,进行了波长标定,波长精度为0.003 nm,并计算出系统各参数的实际值;当入缝宽度设置为30 μm时,在20 nm附近,光谱分辨率达0.015 nm,达到设计指标。     

Efficient modification with flexible spacing coating for in situ reversible assembly of semirigid macroscopic objects through hierarchical metal coordination

Macroscopic supramolecular assembly plays a key role to bridge the fundamental researches on molecular recognition to the potential applications as supramolecular materials. However, the challenge remains to promote the research from soft hydrogel system to semirigid objects or building blocks. Herein, the concept of flexible spacing coating was employed to modify the model polydimethylsiloxane building blocks, and reversible macroscopic assembly was successfully realized through introducing highly directional, dynamic, and reversible coordinate interactions as driving forces. The driving force for the macroscopic assembly was confirmed by introducing highly competitive ethylene diamine tetra acetic acid solution as an orthodox system to disassemble the assembled blocks. Moreover, the coordinate interaction was further understood through unique in situ measurements of binding forces between building blocks during assembly process. This work of macroscopic supramolecular assembly provides an in situ visible platform, which is significant to clarify the highly fascinating and facile coordinate interactions on the macroscopic assembly behavior.     

关于自由射流计算的两点考虑

本文用Multi-Block算法和标准的κ-ε模型计算轴对称自由射流,计算中发现:(1)不同的纵向网格宽度比(疏密度比)会导致不同的扩张速率的计算结果。(2)在相同的网格疏密度比下,由于不同喷管长度L带来的射流上游进口的湍流结构的变化与下游射流扩张速率有清晰的关联。     

A Coverage Model for Improving Public Transit System Accessibility and Expanding Access

Accessible and efficient service are vital features of well-utilized public transit systems. Modeling approaches to support the evaluation of transit operations for management and planning are essential for continued improvement. A hybrid coverage model is developed in this paper for simultaneously expanding service access and increasing accessibility. This paper discusses the use and integration of this model in a geographic information system environment for strategic planning. Analysis is presented for public transit service in Brisbane, Australia. The structured model provides flexibility in developing viable policies for addressing system improvements and service expansion, all of which are likely to promote increased utilization of public transit.     

Quantum chaos and fluctuation properties of regular and irregular spectra

Fluctuation properties of the regular and irregular energy levels for the Hénon-Heiles Hamiltonian are examined. The spacing distributions and the calculated values of the Δ₃-statistic show that there is no difference in the short range correlation properties of these spectra. Remarkably, the Δ₃ values agree with the results of random matrix theory. on leave of absence from P.R.L., Ahmedabad     

The energy level spacing for two harmonic oscillators with golden mean ratio of frequencies

Berry and Tabor discussed, among other things, a beautiful problem about the energy level spacing distribution for a system of two harmonic oscillators. They gave some interesting theoretical arguments which show that there is no level clustering for generic harmonic oscillators, and various numerical experiments were exposed and discussed. But the main question they posed about the existence of the limit distribution of the level spacing remained open. The present paper discusses this question in the case when the ratio of the frequencies is the golden mean =(5–1)/2. The approach enables one to study the generic case of the frequency ratio as well, which is done elsewhere.     

Temperature‐dependent location of a weakly segregated block copolymer in binary blends of block copolymers

The phase behaviors of binary blends of poly(styrene‐b‐butadiene) block copolymers were investigated by a small‐angle X‐ray scattering technique. The blends were composed of weakly segregated one in a random micellar phase and the other in a cylindrical phase with similar molecular weights and complementary volume fractions. Morphologies, domain spacings, and order–disorder transition temperatures of the blends indicated that the junctions of the constituent block copolymers share the interface at low temperatures. The domain spacing decreased as temperature increased in a blend with a small amount of the weakly segregated block copolymer. In the cases of the blends with a large amount of the weakly segregated constituent, domain spacing increased with increasing temperature. These results implied that some of the weakly segregated block copolymer moved from the interface to one microdomain at higher temperatures. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 470–476