Influence of disorder and deformation on the optical properties of two-dimensional photonic crystal waveguide

We investigate the effect of disorder and mechanical deformation on two- dimensional photonic crystal waveguide. The dispersion characteristics and transmittance of the waveguide are studied by using the finite element method. Results show that the geometric change of the dielectric material perpendicular to the light propagation direction has a larger influence on the waveguide characteristics than that parallel to the light propagation direction. Mechanical deformation has an obvious influence on the performance of the waveguide. In particular, longitudinal deformed structure exhibits distinct optical characteristics from the ideal one. Studies on this work will provide useful guideline to the fabrications and practical applications based on photonic crystal waveguides.     

Donor-bound electron states in a two-dimensional quantum ring under uniform magnetic field

The electron states in a two-dimensional GaAs/AlGaAs quantum ring are theoretically studied in effective mass approximation. On-centre donor impurity and uniform magnetic field perpendicular to the ring plane are taken into account. The energy spectrum with different angular momentum changes dramatically with the geometry of the ring. The donor impurity reduces the energies with an almost fixed value; however, the magnetic field alters energies in a more complex way. For example, energy levels under magnetic field will cross each other when increasing the inner radius and outer radius of the ring, leading to the fact that the arrangement of energy levels is distinct in certain geometry of the ring. Moreover, energy levels with negative angular momentum exhibit the non-monotonous dependence on the increasing magnetic field.     

基于Si-rich SiNx/N-rich SiNy多层膜结构电致发光特性研究

利用等离子体增强化学气相沉积法制备了富硅氮化硅/富氮氮化硅多层膜,并以此氮化硅基多层膜作为有源层构建电致发光器件,在室温下观察到了较强的电致可见发光.在此基础上,研究多层膜结构中作为势垒层的富氮氮化硅层对器件电致发光性质的影响,实验结果表明通过改变势垒层的Si/N组分,调制其势垒高度,器件的电致发光效率可得到显著地提高.     

2,4-二氟戊烷的构象与能量的理论研究

在MP2/6-311++G**和G3水平下,对2,4-二氟戊烷异构体的构象进行几何优化和能量计算.氟的强电负效应使构型发生偏转,同时导致了相隔超过3个键的原子间的电子相互作用.     

应变补偿层对量子点生长影响的理论研究

量子点的光学特性与量子点的大小均匀性、密度、内部应变以及隔离层的厚度等有密切关系.文中从理论角度定量研究了GaNXAs1-X应变补偿层对InAs/GaAs量子点生长质量的改善作用,分析了应变补偿层对隔离层厚度减小的作用.讨论了应变补偿层的补偿位置和补偿层N组分X对量子点生长时局部应变和体系应变的补偿作用.分析了应变补偿层对体系应变的减少作用,并计算了相邻层量子点的垂直对准概率.研究结果对实验中应变补偿的优化和高质量量子点阵列的生长实现提供了理论依据.     

Analysis of the impacts of mechanical errors on the RF performance of a single spoke cavity

Mechanical errors can not be avoided in fabrication. They will cause geometry errors and have impacts on the cavity performance. This paper systematically analyzes the impacts of mechanical errors on the RF performance of Peking University single spoke cavity. The various kinds of shape and size errors are considered, the influences on the resonation frequency and field flatness are studied by numerical simulation and the theoretical models are analyzed. The results show that the single spoke cavity is robust with respect to the mechanical tolerance. It also indicates the most essential factors for fabrication.     

Discrete Charge Storage Nonvolatile Memory Based on Si Nanocrystals with Nitridation Treatment

A nonvolatile memory device with nitrided Si nanocrystals embedded in a floating gate was fabricated. The uniform Si nanocrystals with high density （3× 10^11 cm^-2 ） were deposited on ultra-thin tunnel oxide layer （- 3 nm） and followed by a nitridation treatment in ammonia to form a thin silicon nitride layer on the surface of nanocrystals. A memory window of 2.4 V was obtained and it would be larger than 1.3 V after ten years from the extrapolated retention data. The results can be explained by the nitrogen passivation of the surface traps of Si nanoerystals, which slows the charge loss rate.     

Piezoelectric effects and electronic structures of InAs/GaAs quantum dots grown along (111) and (011) directions

Piezoelectric effects and electronic structures of InAs/GaAs quantum dots grown along (111) and (011) directions are investigated in this paper. The finite element method is used. Electronic energy levels are calculated by solving the three-dimensional effective mass Schr?dinger equation including a strain modified confinement potential and piezoelectric effects. The difference in electronic structure between quantum dots grown along the (111) direction and the (011) direction are compared. The cubic and truncated pyramidal shaped quantum dots are adopted.     

激光晶化形成纳米硅材料的场电子发射性质研究

利用KrF准分子激光退火超薄非晶硅膜,并结合热退火技术制备了单层纳米硅薄膜并研究了薄膜的场电子发射性质.在晶化形成的纳米硅薄膜中可以观测到稳定的场电子发射现象,其开启电场从原始淀积的非晶硅薄膜的17V/μm降低到8.5V/μm,而场发射电流密度可以达到0.1mA/cm².激光晶化后形成的纳米硅材料的场电子发射特性的改善可以从薄膜表面形貌的改变以及高密度纳米硅的形成所导致的内部电场增强作用来解释. 关键词： 纳米硅 场发射 激光晶化     

The First Nine-Cell TESLA Cavity Made in China

A totally home-made 9-cell TESLA type superconducting cavity is mane at Peking University. The cavity abrication is according to DESY specification. The cavity is made of high purity niobium from OTIC, Ningxia. The electron beam welding is carried out at Harbin Institute of Technology, Harbin. By the cooperation, the cavity is tested at Thomas Jefferson National Accelerator Facility, USA. The preliminary result shows the acceleration gradient Eacc is 23 MV/m without quench and has potential for improvement.