铌对钨中氦行为影响的第一性原理研究

采用第一性原理计算方法系统研究了合金化元素铌(Nb)对钨(W)中氦(He)溶解和扩散行为的影响.研究发现,Nb的存在显著降低了He在W中的溶解能,Nb可以作为W中He捕陷中心,在最稳定位置处Nb对He的捕陷能达到0.37 eV.通过电荷分析发现,这主要是因为Nb的存在引起了W中电荷密度的重新分布.而He在W中的扩散能垒将随着He—Nb间距离的缩小逐渐降低,这从动力学上表明He被Nb捕陷是可行的.因此,Nb的存在将有利于W中He的聚集成泡.     

Absolute frequency measurement of rubidium 5S-7S two-photon transitions with a femtosecond laser comb

The absolute frequencies of rubidium 5S-7S two-photon transitions at 760 nm are measured to an accuracy of 20 kHz with an optical frequency comb based on a mode-locked femtosecond Ti:sapphire laser. The rubidium 5S-7S two-photon transitions are potential candidates for frequency standards and serve as important optical frequency standards for telecommunication applications. The accuracy of the hyperfine constant of the 7S1/2 state is improved by a factor of 5 in comparison with previous results.     

薄膜法布里-珀罗滤光片中反射高斯光束分裂现象

提出了一种模拟薄膜法布里-珀罗滤光片中反射光束分裂现象的方法.根据反射率曲线，简单解释了产生这个现象的原因.实验上制备了薄膜法布里-珀罗滤光片，观察和测量了反射光束分裂的现象，理论计算基本与实验结果符合. 关键词： 薄膜 法布里-珀罗 光束分裂     

Spin-polarized current through a lateral double quantum dot with spin–orbit interaction

We study the spin-polarized current through a vertical double quantum dot scheme. Both the Rashba spin–orbit (RSO) interaction inside one of the quantum dots and the strong intradot Coulomb interactions on the two dots are taken into account by using the second-quantized form of the Hamiltonian. Due to the existence of the RSO interaction, spin-up and spin-down electrons couple to the external leads with different strengths, and then a spin polarized current can be driven out of the middle lead by controlling a set of structure parameters and the external bias voltage. Moreover, by properly adjusting the dot levels and the external bias voltages, a pure spin current with no accompanying charge current can be generated in the weak coupling regime. We show that the difference between the intradot Coulomb interactions strongly influences the spin-polarized currents flowing through the middle lead and is undesirable in the generation of the net spin current. Based on the RSO interaction, the structure we propose can efficiently polarize the electron spin without the usage of any magnetic field or ferromagnetic material. This device can be used as a spin-battery and is realizable using the present available technologies.     

Gain Measurement and Anomalous Decrease of Peak Gain at Long Wavelength for InAs/GaAs Quantum-Dot Lasers

Mode gain spectrum is measured by the Fourier series expansion method for InAs/GaAs quantum-dot （QD） lasers with seven stacks of QDs at different injection currents. Gain spectra with distinctive peaks are observed at the short and long wavelengths of about 1210nm and 1300nm. For a QD laser with the cavity length of 1060μm, the peak gain of the long wavelength first increases slowly or even decreases with the injection current as the peak gain of the short wavelength increases quickly, and finally increases quickly before approaching the saturated values as the injection current further increases.     

Improved Faddeev-Jackiw quantization of the electromagnetic field and Lagrange multiplier fields

We use the improved Faddeev-Jackiw quantization method to quantize the electromagnetic field and its Lagrange multiplier fields. The method's comparison with the usual Faddeev-Jackiw method and the Dirac method is given. We show that this method is equivalent to the Dirac method and also retains all the merits of the usual Faddeev-Jackiw method. Moreover, it is simpler than the usual one if one needs to obtain new secondary constraints. Therefore, the improved Faddeev-Jackiw method is essential. Meanwhile, we find the new meaning of the Lagrange multipliers and explain the Faddeev-Jackiw generalized brackets concerning the Lagrange multipliers.     

ICP-AES测定向日葵花盘中13种金属元素

向日葵花盘经湿法消解,采用ICP-AES对其中钾、钙、钠、钡、铝、铬、铜、镁、铁、锰、镍、锶、锌13种元素进行测定.对光谱仪的工作条件及分析谱线等测定条件进行了选择,并进行了方法的回收率及精密度试验,其回收率在95％-122％之间.     

改性ZSM-5分子筛催化合成乙酸戊酯

以ZSM-5为原料,采用浸渍法将其交换成HZSM-5,以HZSM-5为催化剂,对以冰乙酸和正戊醇为原料合成乙酸戊酯的反应条件进行了研究。研究表明,以1.0m ol/L硫酸浸渍后的ZSM-5催化活性最高,当醇酸摩尔比为1.1∶1,催化剂用量为0.4g,反应时间为90m in,反应温度为125—135℃,酯化率可达82.5%。     

热丝化学气相沉积技术低温制备多晶硅薄膜的结构与光电特性

以金属W和Ta为热丝，采用热丝化学气相沉积 ，在250℃玻璃衬底上沉积多晶硅薄膜.研究了热丝温度、沉积气压、热丝与衬底间距等沉积参数对硅薄膜结构和光电特性的影响，在优化条件下获得晶态比X_c＞90%，暗电导率σ_d=10^-7—10-6Ω ^-1cm^-1，激活能E_a=0.5eV，光能隙E_opt≤1.3 eV的多晶硅薄膜. 关键词： 多晶硅薄膜 热丝化学气相沉积 光电特性     

纳米隧道结的量子电容现象

利用STM针尖和二维Au纳米团簇构造的双隧道结，通过对单电子隧穿谱的测量，研究了纳米隧道结的电容随隧道结宽度的变化，发现电容随结宽度的变化偏离了经典电容的行为，为纳米隧道结的量子电容效应提供了实验证据。