Growth,Cathodoluminescence and Field Emission of ZnS Tetrapod Tree‐like Heterostructures

We report the growth mechanism, cathodoluminescence and field emission of dual phase ZnS tetrapod tree‐like heterostructures. This novel heterostructures consist of two phases: zinc blende for the trunk and hexagonal wurtzite for the branch. Direct evidence is presented for the polarity induced growth of tetrapod ZnS trees through high‐resolution electron microscopy study, demonstrating that Zn‐terminated ZnS (111)/(0001) polar surface is chemically active and S‐terminated ( )/(000 ) polar surface is inert in the growth of tetrapod ZnS trees. Two strong UV emissions centered at 3.68 and 3.83 eV have been observed at room temperature, which are attributed to the bandgap emissions from the zinc blende trunk and hexagonal wurtzite branch, indicating that such structures can be used as unique electromechanical and optoelectronic components in potential light sources, laser and light emitting display devices. In addition, the low turn‐on field (2.66 Vµm⁻¹), high field‐enhancement factor (over 2600), large current density (over 30 mAcm⁻² at a macroscopic field of 4.33 Vµm⁻¹) and small fluctuation (∼1%) further indicate the availability of ZnS tetrapod tree‐like heterostructures for field emission panel display. This excellent field‐emission property is attributed to the specific crystallographic feature with high crystallinity and cone‐shape patterned branch with nanometer‐sized tips. Such a structure may optimize the FE properties and make a promising field emitter.     

Hole-enhanced electron injection from ZnO in inverted polymer light-emitting diodes

Metal oxides as ZnO provide an interesting alternative for conventional low work function metals as electron injection layer in organic light-emitting diodes (OLEDs). However, for most state-of-the-art OLED materials the high work function of ZnO leads to a large injection barrier for electrons. As a result the electron current in the OLED is largely limited by the contact, leading to a strong reduction of the conversion efficiency. Here we demonstrate that by depositing an amorphous ZnO layer as cathode in an inverted polymer LED, the electron injection can be strongly enhanced by electrical conditioning. For suited polymers comparable conversion efficiencies of the conventional and inverted PLEDs can be achieved.     

Multiscale penalized weighted least-squares sinogram restoration for low-dose x-ray computed tomography

In this paper, we propose a novel multiscale penalized weighted least-squares (PWLS) method for restoration of low-dose computed tomography (CT) sinogram. The method utilizes wavelet transform for the multiscale or multiresolution analysis on the sinogram. Specifically, the Mallat-Zhong's wavelet transform is applied to decompose the sinogram to different resolution levels. At each decomposed resolution level, a PWLS criterion is applied to restore the noise-contaminated wavelet coefficients, where the penalty is adaptive to each resolution scale and the weight is updated by an exponential relationship between the data variance and mean at each scale and location. The proposed PWLS method is based on the observations that 1) noise in the CT sinogram after logarithm transform and calibration can be modeled as signal-dependent variables and the sample variance depends on the sample mean by an exponential relationship; and 2) noise reduction can be more effective when it is adaptive to different resolution levels. The effectiveness of the proposed multiscale PWLS method is validated by both computer simulations and experimental studies. The gain by multiscale approach over single scale means is quantified by noise-resolution tradeoff measures.     

不同温度下半导体硅势垒的正向I-V特性曲线的汇聚特性

以正向电压为自变量,以正向电流的对数为应变量,以温度为参数得到的p-n结的I-V-(T)特性曲线在第一象限中近似汇聚于一点.汇聚点对应的电压近似等于半导体材料的禁带宽度.汇聚点可以用来获取任意温度下的I-V特性曲线.     

背入射Al0.42Ga0.58N/Al0.40Ga0.60N 异质结 p-i-n 太阳光盲紫外探测器成

在蓝宝石上用MOCVD生长的材料制备了背入射Al0.42Ga0.58N/Al0.40Ga0.60N 异质结 p-i-n 太阳光盲紫外探测器. 从器件的正向I-V特性曲线计算了理想因子n与串联电阻RS分别为3和93Ω. 器件在零偏压下275nm峰值波长处的外量子效率与探测率分别为9%和4.98e11cm·Hz1/2/W,分析表明Al0.42Ga0.58N窗口层在275nm波长处的透过率仅为15.7%,是器件外量子效率和探测率偏低的原因之一.     

微细问距COF连接研究

微细间距柔性(线路)板上芯片COF是解决移动显示模块轻薄短小化的重要方法之一.使用四点法测试接触电阻以及拉力和两组可靠性(加速湿度实验和热冲击实验)的测试比较,研究了30靘间距的倒装芯片采用金-锡共晶、金-金NCF、金-金共金3种连接方式的COF工艺.实验表明使用金-金NCF工艺的产品在经过504 h的可靠性测试后,依旧保持小于5∩的接触电阻,可靠性高,同时通过比较工艺流程,金-金NCF工艺变动成本低,只需通过对现有的,基于各向异性导电膜工艺的生产设备稍加变动,即可形成生产力.加速了企业微细间距COF技术转型并进入批量生产的过程.     

基于支持向量机的中文模糊本体映射

Taking into account that fuzzy ontology mapping has wide application and cannot be dealt with in many fields at present, a Chinese fuzzy ontology model and a method for Chinese fuzzy ontology mapping are proposed. The mapping discovery between two ontologies is achieved by computing the similarity between the concepts of two ontologies. Every concept consists of four features of concept name, property, instance and structure. First, the algorithms of calculating four individual similarities corresponding to the four features are given. Secondly, the similarity vectors consisting of four weighted individual similarities are built, and the weights are the linear function of harmony and reliability. The similarity vector is used to represent the similarity relation between two concepts which belong to different fuzzy ontolgoies. Lastly, Support Vector Machine (SVM) is used to get the mapping concept pairs by the similarity vectors. Experiment results are satisfactory.     

Improving the performance of polymer solar cells by altering polymer side chains and optimizing film morphologies

Two donor–acceptor (D–A) type conjugated polymers using dodecyl- and ethylhexyl-thiophene substituted benzo[1,2-b:4,5-b′]dithiophene (BDT-DDT and BDT-EHT, respectively) as donors and n-alkylthieno[3,4-c]pyrrole-4,6-dione (TPD) as acceptor were synthesized and characterized. The thiophene substituted BDT unit was recognized as a two-dimensional (2D) π-extended segment with high carrier mobility and TPD unit was a relatively strong electron-drawing acceptor, which could lead to deep-lying highest occupied molecular orbital (HOMO) levels of the polymers. The optical properties, electrochemical behavior, and charge carrier properties of the polymers were compared in parallel. The results indicated that ethylhexyl-substitution could optimize the polymer structures and properties. The bulk-heterojunction polymer solar cells (PSCs) based on the two polymers were fabricated and characterized. The devices based on ethylhexyl-substituted polymer showed better performance than that of dodecyl-substituted one. Further analysis proved that the improvement was mainly ascribed to the formation of well-defined nanostructures by using branched ethylhexyl side chains, which facilitated charge separation and transport in the bicontinous active layer. This study suggests that obtaining appropriate film morphology and phase separation by altering alkyl side chains is extraordinary important for high performance PSCs based on D–A type polymers.     

一种应用于MCA中的高速高精度峰值保持器PKD01

高性能峰值保持在核脉冲信号处理过程中具有重要的意义。结合实际x射线探测器输出脉冲特点,利用了一种运用跨导型运算放大器PKD01峰值保持芯片,该芯片具有通频带宽、响应速度快、峰值保持精度高、线性好等一系列优点,经过实际测量,可以准确的对脉冲信号进行峰值保持。     

基于低压高精度运放的带隙基准电压源设计

基于传统带隙基准源的电路结构,采用电平移位的折叠共源共栅输入级和甲乙类互补推挽共源输出级改进了其运算放大器的性能,并结合一阶温度补偿、电流负反馈技术设计了一款低温度系数、高电源电压抑制比(PSRR)的低压基准电压源。利用华润上华公司的CSMC 0.35μm标准CMOS工艺对电路进行了Hspice仿真,该带隙基准源电路的电源工作范围为1.5～2.3 V,输出基准电压为(600±0.2)mV;工作温度为10～130℃,输出电压仅变化8μV,温度系数为1.86×10-6/℃,低频时PSRR为-72 dB。实际流片进行测试,结果表明达到了预期结果。