把DAC的输出从单端模式转换到差分模式的电路

高速DAC,比如模拟器件(AnalogDevices)公司的AD9776/78/79TxDAC系列,能提供差分输出,但对于低端交流电应用或高精度电平设置应用,配备差分转换电路的单端电流输出DAC提供了一种新颖的方法来生成差分波形控制功能。图1中的基本电路组合了电流输出DAC(即IC1,如8位AD5424D A C)和一个单端至差分运算放大级IC2、IC3A、IC3B——来产生要求的输出。对于双电源应用,可选择DAC的单极工作模式来达到DAC的最优性能。DAC利用单一运算放大器提供了双象限倍增或单极输出电压摆动。DAC的输出需要缓冲器,这是因为对施加到DAC输入端的代…     

单光子态的产生与测量

报道了通过自发参量下转换产生单光子态的实验研究,使用中心波长425 nm的飞秒脉冲泵浦Ⅰ类非共线相位匹配的BBO晶体,在实验上得到单光子计数率为2.978×10-4,并分析了实验中的相关问题.     

固态金属中声子热传递的分子动力学模拟研究

固态金属中的热传递是声子和自由电子共同作用的结果。自由电子引起的热导率可以通过电导率,利用Wiedemann-Franz定律得到,声子引起的热导率目前仍然不能进行实验测量,只能借助其他方法来研究。本文采用非平衡分子动力学(NEMD)方法,用镶嵌原子方法(EAM)势能模型,模拟计算了不同厚度(1.760-10.56nm)金属镍薄膜中由于声子-声子作用引起的热导率。然后根据纳米厚度金属薄膜的热导率借助关联式推到宏观尺度下由于声子-声子作用引起的热导率。结果表明,对于纳米厚度金属薄膜,由于声子-声子作用引起的热导率比块体金属镍的热导率小一个数量级;薄膜厚度越小,声子-声子作用引起的热导率越小;对于块体金属镍,由于声子-声子作用引起的热导率约占其总热导率的33.0%左右。     

Recombination Efficiency in Double-Layer Organic Light-Emitting Devices

We analyse the influence of properties of organic/organic interface (OOI) on the characteristics of recombination efficiency of organic double-layer light-emitting diodes. Based on the disordered hopping theory model, spatial and energetic disorder of hopping states are also discussed for the case of space charge limited currents in hole transmitting layers but injection-limited currents in electron transporting layers. The results show that the recombination efficiency increases firstly and then decreases for different OOI parameters, and there is a maximum value changed with different spatial disorder parameters and energetic disorder scale. Different spatial disorder parameters make carrier mobilities change greatly, and the energetic disorder scale causes various localized state densities. Our calculated results are qualitatively in agreement with the experimental data.     

Nano-tribological study on a super-hydrophobic film formed on rough aluminium substrates

A novel super-hydrophobic stearic acid (STA) film with a water contact angle of 166^o was prepared by chemical adsorption on aluminum wafer coated with polyethyleneimine (PEI) film. The micro-tribological behavior of the super-hydrophobic STA monolayer was compared with that of the polished and PEI-coated Al surfaces. The effect of relative humidity on the adhesion and friction was investigated as well. It was found that the STA monolayer showed decreased friction, while the adhesive force was greatly decreased by increasing the surface roughness of the Al wafer to reduce the contact area between the atomic force microscope (AFM) tip and the sample surface to be tested. Thus the friction and adhesion of the Al wafer was effectively decreased by generating the STA monolayer, which indicated that it could be feasible and rational to prepare a surface with good adhesion resistance and lubricity by properly controlling the surface morphology and the chemical composition. Both the adhesion and friction decreased as the relative humidity was lowered from 65% to 10%, though the decrease extent became insignificant for the STA monolayer. The project supported by the National Natural Science Foundation of China (50375151, 50323007, 10225209) and the Chinese Academy of Sciences (KJCX-SW-L2)     

记录媒体用薄膜材料及相关靶材的技术和发展

 信息化时代随着计算机技术的普及来到我们面前,其突出表现是信息总量和信息交换的剧增,因此,发展海量存储技术日趋重要。随着信息及计算机技术的不断发展,对其作为主要工具的记录媒体的需求越来越大,要求越来越高。记录媒体中大多数磁盘、磁光盘、光盘是以相关靶材磁控溅射而成的,因此,为满足信息记录媒体的高密度化、小型化和低价格化,需要对其相关靶材的成分、制造工艺、性能和溅射工艺做进一步研究。目前,随着新材料的开发和记录媒体的发展,磁光盘、光盘用靶材市场在不断增长。尤其近几年CD、VCD、DVD市场的迅速扩大,其相关靶材的前景也日益被看好。     

Multiple Scattering Effects of Ag Particles in Random Ag-SiN Film

A layer of 40nm-thick Ag-SiN film with Ag nano-particles embedded and distributed randomly in the SiN thin film were deposited by the method of radiant-frequency magnetron sputtering. Specimens orderly comprising a random Ag-SiN film and an optical phase change recording layer were exposed to a focused laser beam with wavelength of 69Ohm. It is shown that, with a random Ag-SiN layer deposited above the recording layer. Calculation by the finite difference time domain method of a 4Ohm-thick SiN film under a Gaussian beam irradiation has been carried out to simulate the near-field distribution in the film, which showed a huge local near-field intensity enhancement of about 200 times if small Ag particles with diameter of 6 nm were modelled inthe SiN film in the central region of the in cident laser spot.     

Nanoporous Structure in Low-Dielectric Films with Positronium Annihilation Lifetime Spectroscopy

We investigate nano-porous structures in thin low-dielectric films, i.e. the pore sizes, distributions, and interconnectivity, by using depth profiled positronium annihilation lifetime spectroscopy (PALS). It is found that PALS has good sensitivity to probe both interconnected and closed pores in the range from 0.3nm to 3Onto, even in the film buried beneath a diffusion barrier. A series of low dielectric constant films of organosilicon-silsequioxane with different weight percentages of porogen have been comparatively investigated. The PALS technique can be used to distinguish the open porosity from the closed one, to determine the pore size, and to detect the percolation threshold with the increasing porosity that represents the transition from closed pores to interconnected pores.Furthermore, the pore percolation length can be derived.