不同形状的光斑触发砷化镓光导开关

为研究使用不同形状光斑触发光导开关对光电导特性的影响,研制了12 mm间隙的半绝缘砷化镓光导开关,在不同的偏置电压下,使用波长为1 064 nm的不同能量的激光触发光导开关并进行了光电导测试。使用了不同形状的光斑(包括面状、线状和点状光斑)触发光导开关并进行了光电导特性的比较,讨论了触发光参数对光导开关特性的影响。对处于开关电极间不同位置的线状光斑触发特性进行了比较,结果显示,本征光电导和非本征光电导情况下光斑位置对光电流的影响正好相反。     

硅衬底上纳米晶金刚石生长

研究了蚀刻气体对生长在硅衬底上纳米晶金刚石合成的影响.合成方法为热丝化学气相沉积法,衬底温度为550 oC,反应压力为4 kPa. 其中甲烷和氢气分别作为源气体和稀释气体. 氮气、氢气和氨气用作蚀刻气体. 结果表明,仅氢气作为蚀刻气体可获得最佳工艺条件.     

Effects of N2 addition on nanocrystalline diamond films by HFCVD in Ar/CH4 gas mixture

Nanocrystalline diamond (NCD) films were grown on silicon substrates by hot filament chemical vapor deposition in Ar/N₂/CH₄ gas mixtures. The effects of seeding process prior to deposition, the total gas pressure, and concentration of nitrogen on the grain size, morphology and bonding nature in HFCVD technique were investigated. The results indicated that a low total gas pressure is favorable for nanosized diamond crystallites. Films micrograph obtained from scanning electron microscopy showed diamond nanograins elongated with the addition of nitrogen in the plasma. Crystal structure investigations were carried out by X-ray diffraction measurements for deposited films. An increase in the size of crystallite is also observed from XRD measurements in NCD film when nitrogen was added in plasma. From Raman spectra, it was observed that the relative intensity of G peak increases indicating more graphite content after nitrogen added in the plasma. The effects of the nitrogen incorporation in nanocrystalline films in HFCVD are discussed.     

A fast luminosity monitor for BEPCⅡ

The fast luminosity monitor counting the γ photons above a given energy threshold emitted from radiative Bhabha scattering has been operated in the BEPC Ⅱ to measure the relative luminosity bunch by bunch for the first time and used successfully in beam tuning of BEPC Ⅱ. In the relative mode the monitor is able to deliver the relative luminosities with an accuracy of 0.8 %. By steering the electron beam while observing the counting rate changes of the monitor the horizontal and vertical sizes of the bunch spots can be estimated as： Sxe＋ =Sxe =0.356 mm, Sye＋ =Sye- =0.011 mm.     

Effect of progressive annealing on Silicon Nanostructures grown by Hot Wire Chemical Vapor Deposition

In this work, the evolution of Silicon Nanostructures with progressive annealing has been studied. Hot Wire CVD (HWCVD) process was used to deposit a Si_xN_y/a-Si structure on an n-type 〈100〉$〈100〉$ Silicon substrate with the Nitride acting as the buffer layer. The depositions were carried out at a low substrate temperature (250 °C) which is precisely why HWCVD was chosen over other processes for this work. The as-deposited sample was then annealed at 800 °C and 900 °C respectively. AFM studies revealed promising results hinting at the presence of Silicon Nanostructures. With progressive annealing the Nanostructures began to evolve, eventually turning into sharp Nanopillars upon annealing at 900 °C. In this paper, a growth model has been proposed which attempts to validate the experimental results. Though a lot of work is currently underway in this field, study of Silicon Nanostructures grown by HWCVD technique is relatively new.     

Surface characterization and growth mechanism of laminated Ti3SiC2 crystals fabricated by hot isostatic pressing

Laminated Ti₃SiC₂ crystals were prepared by hot isostatic pressing from Ti, Si, C and Al powders with NaCl additive in argon at 1350 °C. The morphology and microstructure of Ti₃SiC₂ crystals were investigated by means of XRD, SEM, and TEM. The high symmetry and crystalline was revealed by high resolution transmission electronic microscope (HRTEM) and selected area electron diffraction (SAED). The growth mechanism of Ti₃SiC₂ crystals controlled by two-dimensional nucleation was put forward. The growth pattern of layered steps implies that the growth of the (0 0 2) face should undergo two steps, the intermittent two-dimensional nucleation and the continuous lateral spreading of layers on growth faces.     

The 60° or 180° twinned Bi-doped PbTe film studied by EBSD

The Bi-doped PbTe film was grown on Si(1 1 1) substrate by using hot wall epitaxy (HWE) technique. The film was characterized by means of scanning electron microscopy, micro-area X-ray diffraction and electron backscatter diffraction (EBSD). The results indicate that the film is dominated by 〈1 1 1〉 orientation. The film consists of two twinned domains, rotated 60° or 180° around the normal to the film surface. It is speculated that the twinned PbTe film results from the deviated triangular grains. The ratio between the grains with two different orientations will decrease with the increase of the film thickness.     

雾玻璃上的彩色环

向一个冷玻璃上哈气,在玻璃表面会形成水雾.透过起雾的玻璃去观察白光光源,会看到有多层彩色环(内层蓝色,外层红色),并且在中央会出现白色亮斑.利用散射光干涉的模型解释了彩色圆环的成因.     

激光能量叠加过程中对准精度对焦斑的影响

利用多光束激光输出耦合叠加是一种提高激光器输出功率的有效方法。采用两束矩形激光对准系统,分析两光束不同对准情况下的焦斑特性。完全对准的情况下,两束光的远场焦斑重合在一起,焦斑能量是两光束能量之和。在实际光束对准系统中,讨论了三种常见的对准误差,并比较了这些误差对焦斑特性的影响。利用ZEMAX软件对设计系统进行了模拟分析,并进行了实验验证。结果表明,元件的位置误差会使远场焦斑能量集中度降低,焦斑半径增大。     

液体冷媒融霜系统回液时间的实验研究

对液体冷媒融霜系统的回液时间进行实验研究。在保温体温度-15℃工况下分别对回液时间7s、27s、25s、30s、40s、50s进行实验,记录并分析被融霜蒸发器融霜前和回液时间内压缩机吸气口的温度和压力变化,相机拍摄制冷压缩机吸气口和机身的结霜状况。实验表明:回液时间7s时,压缩机吸气过潮,回液时间在27s左右可以避免压缩机吸气过潮,确保系统安全正常的运行,大于27s被融霜蒸发器恢复制冷时间过长将影响库房温度的稳定并降低制冷系统的效率。