电磁波在大气层人造等离子体中的衰减特性

利用洛沦兹模型来研究大气层人造非均匀等离子体的电磁响应特性,讨论了电磁波频率、等离子体密度及电子碰撞频率对电磁波衰减特性的影响.结果表明,电磁波在长波长区域及等离子体密度大时,其能量衰减越快.当等离子体密度高时,电子温度越低,大气层高度越高,电磁波的能量衰减越快. 关键词： 电磁波 大气等离子体 能量衰减     

有机薄膜光盘的微区结构

通过光学显微镜（ＯＭ）扫描电镜（ＳＥＭ）和扫描隧道显微镜（ＳＴＭ）观察了光记录有机薄膜的微区结构，从微区结构的形貌可以看出光记录后酞菁薄膜上产生了鼓泡，通过这些观察方法的比较发现扫描隧道显微镜可以提供更加详细，精确的三维参数，薄膜的微区结构研究对于分析光盘的性能，了解记录机理具有重要意义。     

Fabrication of silicon nanowires

2 at 750 °C and 850 °C. The oxide and interface morphology are characterized by cross-sectional scanning electron microscope images. It is found that the oxidized nanowire following oxidation at 750 °C still keeps its pentagon shape even if it has been oxidized for 19 h. However, the oxidized samples at 850 °C become circular in shape. The oxidation-temperature dependence of the sample shapes is discussed. Our results should be useful in generating silicon nanowires coated with SiO₂ in microelectronic technology with careful selection of the SiO₂ growth temperatures. Received: 26 September 1997/Accepted: 8 December 1997     

Gas source MBE grown wavelength extended 2.2 and 2.5 μm InGaAs PIN photodetectors

Using homo-junction structure and relative thin linear graded In_xGa_1−xAs as the buffer layer, extended wavelength InGaAs PIN photodetectors with cut-off wavelength of 2.2 and 2.5 μm at room temperature have been grown by using GSMBE, and their performance over a wide temperature range have been extensively investigated. For those 2.2 or 2.5 μm detectors with 100 μm diameter, the typical dark current (V_R = 10 mV) and R₀A are 57 nA/10.3 Ω cm² or 67 nA/12.7 Ω cm² at 290 K, and 84 pA/4.70 kΩ cm² or 161 pA/3.12 kΩ cm² at 210 K respectively. The thermal activation energies of the dark current are 0.447 eV or 0.404 eV for 2.2 or 2.5 μm detectors respectively.     

二维正方格子磁性光子晶体的带隙结构

采用平面波展开的方法计算了正方格子二维磁性光子晶体(MPC)的光子带隙结构.散射子的形状分别为：长方形，正方形，六角形和圆形.通过调节磁导率，填充率和散射子的旋转角度，找到了MPC各种结构的最大的绝对带隙宽高比ω_R.研究发现：随着磁导率的增加，MPC绝对带隙中心频率ω_g单调减小，绝对带隙宽度Δω和其宽高比ω_R可能不同时达到最大值.而随着填充率或者散射子旋转角的增加，基本不改变ω_g的大小，各种结构的Δω和ω_R同时达到最大值. 关键词： 磁性光子晶体 光子带隙结构     

二维正方格子磁性光子晶体的界面传导模

采用平面波展开加超元胞方法计算了二维正方格子磁性光子晶体的光子带隙结构，其中散射子的形状分别为长方形，正方形，六角形和圆形.结果表明绝对带隙宽度和其宽高比远大于同种结构的非磁性光子晶体.在此基础上，构成了混合型异质结，并计算了相应的传导模，发现了理想的界面传导模，而且当磁性散射子为长方形、圆形、六角形散射子时产生传导模都不需要晶格畸变，这也是磁性光子晶体异质结所具备的优点. 关键词： 光子晶体 光子带隙结构 传导模     

Synthesis of AN-g-casein copolymer in concentrated aqueous solution of sodium thiocyanate and AN-g-casein fiber's structure and property

The main products of graft copolymerization of acrylonitrile (AN) onto casein in concentrated aqueous solution of sodium thiocyanate in homogeneous phase were characterized as a graft copolymer (AN-g-casein) by Fourier transform infrared. The effects of the monomer concentration, initiator concentration, reaction temperature and reaction time on copolymerization were investigated. The result of WAXD showed that the major part of casein in graft copolymer is amorphous. The SDSC determination showed that the lateral order of PAN, the side chain of copolymer, decreases and the lateral order distribution becomes wider with the increase of the casein component in copolymer. It revealed that the two systems of AN-g-casein copolymer are incompatible by an investigation of DMTA, SEM. The two systems of AN-g-casein exist in separating phases, but tie up each other. So the phenomena of characteristic boundary relaxation occur.Direct spinning of graft copolymer in concentrated aqueous solution of sodium thiocyanate in homogeneous phase was successfully carried out. The skin-core layer structure of AN-g-casein fiber cross-section was observed by scanning electron microscope (SEM). In the core layer, the dimension of phase domain of casein is about from 20 to 60 nm. When the fiber was drawn into broken, microfibrillation occurs, the fiber skin layer is compact, and its broken section is flat. Many long and thin casein strips are formed in the surface of the fiber, respective crystalline grade of two components is scarcely effected by the change of the content of casein. AN-g-casein fibers have good hygroscopicity and dyeability, and more, they can be dyed by acidic dyestuff and cationic dyestuff. AN-g-casein fiber still has good mechanical properties, so AN-g-casein fiber is a new type modified “silk-like” fiber for wide application.     

Nd:YAG纳米粉体的制备和光谱性质

采用共沉淀方法，以碳酸氢铵（NthHC03）为沉淀剂制备得到Nd：YAG前驱物，将其在不同的温度下煅烧并采用红外光谱（FT-IR）、X射线衍射（XRD）、透射电镜（TEM）、荧光光谱分析等技术对样品进行了表征。在900～1000℃下煅烧前驱物，出现YAP和YAM中间相并对共沉淀法中间相出现的原因进行了分析；获得纯YAG晶相的煅烧温度为1100℃，晶粒粒度分布约为40～80nm，具有良好的分散性。光谱研究表明Nd：YAG纳米粉体的发光性能良好，其红外光谱及荧光光谱与单晶无明显的差异。