BEPCⅡ高频系统的建造

北京正负电子对撞机二期(BEPCⅡ)的高频系统已于2006年11月投入运行,它包括了3个子系统:超导腔、发射机和低电平控制系统.与以前的高频系统相比,工作频率由200MHz变为499.8MHz,超导腔取代了常温腔.在过去一年的运行中,高频系统表现良好,达到了设计指标.     

掺P25水热法制备纳晶多孔TiO2薄膜电极

以水热法为基础,向其溶胶中掺入适量的P25(二氧化钛粉体),来制备纳晶TiO₂胶体,以纳晶TiO₂为电子传输体组装染料敏化太阳能电池.通过XRD、SEM、UV-vis和电池的光电性能测试,来分析掺入P25对染料敏化太阳能电池性能的影响.结果表明,加入适量P25([P25]/[Ti]=0.2)后,染料敏化太阳能电池性能达到最佳值,在100 mW/cm²光照条件下,光电转换效率达到5.4%.     

纳米多晶NiTi形状记忆合金超弹性的晶粒取向依赖性相场研究

本文基于Ginzburg-Landau理论,建立了一个反映纳米多晶NiTi形状记忆合金取向依赖性的二维多晶相场模型,研究了晶粒取向对其超弹性性能的影响。结果表明,纳米多晶NiTi形状记忆合金的超弹性行为依赖于晶粒取向分布,即：多晶模型中在所研究的参数变化范围内,晶粒取向分布范围越广、晶粒间取向差越大（无明显织构）,超弹性性能越差;而晶粒取向分布范围越窄、晶粒间取向差越小（织构越强）,超弹性性能越好。该晶粒取向依赖性可解释为：由于晶粒取向的不同,马氏体相变过程中相邻晶粒间的变形不匹配程度不同,因此,多晶模型中在所研究的参数变化范围内,晶粒间取向差异越大,晶界处的变形失配越严重,由此而产生的局部内应力将阻碍其附近马氏体相变的扩展,进而导致纳米多晶NiTi形状记忆合金超弹性性能下降。     

Novel Boron Nitride Polymorphs with Graphite-Diamond Hybrid Structure

Both boron nitride（BN） and carbon（C） have sp, s^p2 and sp³ hybridization modes, thus resulting in a variety of BN and C polymorphs with similar structures, such as hexagonal BN（h BN） and graphite, cubic BN（c BN）and diamond. Here, five types of BN polymorph structures are proposed theoretically, inspired by the graphitediamond hybrid structures discovered in a recent experiment. These BN polymorphs with graphite-diamond hybrid structures possess excellent mechanical propertie...     

Configurational entropy-induced phase transition in spinel LiMn2O4

The spinel-type LiMn$_{2}$O$_{4}$ is a promising candidate as cathode material for rechargeable Li-ion batteries due to its good thermal stability and safety. Experimentally, it is observed that in this compound there occur the structural phase transitions from cubic ($Fd\bar{3}m)$ to tetragonal ($I4_{1}/{amd}$) phase at slightly below room temperature. To understand the phase transition mechanism, we compare the Gibbs free energy between cubic phase and tetragonal phase by including the configurational entropy. Our results show that the configurational entropy contributes substantially to the stability of the cubic phase at room temperature due to the disordered Mn$^{3+}$/Mn$^{4+}$ distribution as well as the orientation of the Jahn-Teller elongation of the Mn$^{3+}$O$_{6}$ octahedron in the the spinel phase. Meanwhile, the phase transition temperature is predicted to be 267.8 K, which is comparable to the experimentally observed temperature. These results serve as a good complement to the experimental study, and are beneficial to the improving of the electrochemical performance of LiMn$_{2}$O$_{4}$ cathode.     

325 MHz低β半波长谐振腔设计

对质子加速器中半波长谐振腔（HWR）型的设计进行了研究,完成一种新型HWR超导腔的初步设计。通过对超导腔设计方法及设计原则的研究,结合相关半波长谐振腔的研究现状,充分利用电磁设计软件的功能,对325 MHz低大孔径的半波长谐振腔进行了设计研究。在建模中,针对腔体的不同部位进行比较分析,优化模型形状;在计算中,采用新型有限元网格,使计算快速而结果稳定;在后处理中,使用参数扫描,实现了腔形参数优化;在腔形分析中,计算了二次电子倍增效应,验证了腔体形状的可行性。通过此设计过程,使所设计的新型为0.12的HWR腔具有较好的电磁参数,满足质子加速器的要求,并可应用到实际工程中。     

超声强化合成MgFe2O4纳米颗粒及其机理研究

用超声水解方法制备MgO纳米颗粒,用化学沉淀法制备α-Fe₂O₃纳米颗粒,将MgO/α-Fe₂O₃混合体常温下超声活化2h,400℃固相合成制备出MgFe₂O₄纳米颗粒.通过X射线衍射和透射电子显微镜测试产品的化学成分、晶体结构和形貌尺寸,分析声化学反应机理及其影响因素.研究结果表明:所制备的MgFe₂O₄为尖晶石铁氧体,颗粒尺寸分布在20-30nm之间,粒度分布均匀;超声空化效应提高了化学反应活性、增加反应物的比表面积和反应物之间的接触面积,促进固相合成反应速度,降低反应温度,实现了一般条件下难以完成的化学反应.     

二维GaAs 基光子晶体微腔的制作与光谱特性分析

研究了以InAs量子点为有源区的二维GaAs基光子晶体微腔的设计与制作,测试并分析了室温下微腔的光谱特性.观察到了波长约为1137 nm,谱线半高宽度约为1 nm的尖锐低阶谐振模式发光峰.我们比较了不同刻蚀条件下光子晶体微腔的发光谱线,结果表明空气孔洞截面的垂直度是影响光子晶体微腔发光特性的重要因素之一.通过调节干法刻蚀工艺,改变空气孔半径与晶格常数的比率,可以在较大范围内调节谐振模式发光峰位置,达到谐振模式与量子点发光峰调谐的目的.     

Physics of electron and lithium-ion transport in electrode materials for Li-ion batteries

The physics of ionic and electrical conduction at electrode materials of lithium-ion batteries(LIBs) are briefly summarized here, besides, we review the current research on ionic and electrical conduction in electrode material incorporating experimental and simulation studies. Commercial LIBs have been widely used in portable electronic devices and are now developed for large-scale applications in hybrid electric vehicles(HEV) and stationary distributed power stations. However,due to the physical limits of the materials, the overall performance of today's LIBs does not meet all the requirements for future applications, and the transport problem has been one of the main barriers to further improvement. The electron and Li-ion transport behaviors are important in determining the rate capacity of LIBs.     

用ARUPS研究在Cs/Ru(1010)面上的CO分子轨道对称性

用同步辐射角分辨紫外光电子能谱对CO与Cs在Ru(1010)面上共吸附的研究结果表明,由于Cs的强烈影响,CO的分子轨道重新排列.对应清洁表面上CO分子的(5σ+1π)轨道的7.5eV谱峰分裂成两个,分别处于6.3和7.8eV,6.3eV谱峰关于一个垂直于Ru(1010)面而平行于〈0001〉晶向的镜象面反对称性. 关键词：