A fully three-dimensional atomistic quantum mechanical study on random dopant-induced effects in 25-nm MOSFETs

A fully 3-D atomistic quantum mechanical simulation is presented to study the random dopant-induced effects in nanometer metal-oxide-semiconductor field-effect transistors. The empirical pseudopotential is used to represent the single particle Hamiltonian, and the linear combination of bulk band method is used to solve the million atom Schrodinger equation. The gate threshold fluctuation and lowering due to the discrete dopant configurations are studied. It is found that quantum mechanical effects increase the threshold fluctuation while decreasing the threshold lowering. The increase of threshold fluctuation is in agreement with the researchers' early study based on an approximated density gradient approach. However, the decrease in threshold lowering is in contrast with the density gradient calculations.

Annealing study of carrier concentration in gradient-doped GaAs/GaAlAs epilayers grown by molecular beam epitaxy

We measured the carrier concentration distribution of gradient-doped GaAs/GqAlAs epilayers grown by molecular beam epitaxy before and after annealing at 600 degrees C, using electrochemical capacitance voltage profiling, to investigate the internal variation of transmission-mode GaAs photocathodes arising from the annealing process. The results show that the carrier concentration increased after annealing. As a result, the total band-bending energy in the gradient-doped GaAs emission layer increased by 25.24% after annealing, which improves the pbotoexcited electron movement toward the surface. On the other hand, the annealing process resulted in a worse carrier concentration discrepancy between the GaAs and the GaAlAs, which causes a lower back interface potential barrier, decreasing the amount of high-energy photoelectrons. (C) 2009 Optical Society of America

SiGe/Si resonant-cavity-enhanced photodetectors for 1.3 mu m operation fabricated using wafer bonding techniques

A SiGe/Si multiple-quantum-well resonant-cavity-enhanced (RCE) photodetector for 1.3 mum operation was fabricated using bonding reflector process. A full width at half maximum (FWHM) of 6 nm and a quantum efficiency of 4.2% at 1314 nm were obtained. Compared to our previously reported SiGe RCE photodetectors fabricated on separation-by-implanted-oxygen wafer, the mirrors in the device can be more easily fabricated and the device can be further optimized. The FWHM is expected to be less than 1 nm and the detector is fit for density wavelength division multiplexing applications. (C) 2002 American Institute of Physics.

Broadband terahertz time-domain spectroscopy of drugs-of-abuse and the use of principal component analysis

EPSRC, the European Community IST FP6 Integrated, etc

线性低密度聚乙烯的官能化及其结构和性能研究

本文利用辐照产生的过氧化物作为引发剂，以丙烯酸（AA）、甲基丙烯酸环氧丙酯（GMA）和马来酸酐（MAH）为接枝单体，研制了官能化线性低密度聚乙烯（LLDPE）。利用红外光谱（FT－IR）对接枝物进行了表征。线性低密度聚乙烯接枝丙烯酸在 1712 cm~(-1) 处的羰基吸收峰；线性低密度聚乙烯接枝甲基丙烯酸环氧丙酯在 1720 cm~(-1)和840、910cm~(-1) 处的羰基与环氧吸收峰；线性低密度聚乙烯接枝马来酸酐在 1788和 1712cm~(-1)处的酸酐和羰基吸收峰均证明单体已经接枝到线性低密度聚乙烯分子链上。采用化学滴定法测定了官能化线性低密度聚乙烯的接枝率，并提出了其接枝反应的机理。系统研究了单体浓度、预辐照剂量、反应时间、反应温度等对接枝率和熔体流动速率的影响。研究结果表明，在一定工艺条件下，可以得到高接枝率，无凝胶的官能化线性低密度聚乙烯。通过以接枝单体特征基团的吸收峰（AA 1712 cm~(-1)、GMA 1720 cm~(-1)）与内标峰（1738 cm~(-1)）的强度比为纵坐标，以化学滴定法测得的相应单体接枝率为横坐标，得到了用红外光谱法测定接枝率的标准曲线。利用它可以方便、快速、准确地得到某一未知官能化产物的接枝率。用DSC研究了LLDPE及LLDPE-g-AA的热学性能。发现LLDPE-g-AA的ΔH_m下降，结晶温度升高大约4 ℃。这是由于在非极性的线性低密度聚乙烯分了链中引入了极性基团，使聚乙烯分子链的规整性下降，结晶缺陷增多，晶体的完善下降，从而使接枝物的ΔH_m下降，结晶度变小。等温结晶的结果表明，接枝物结晶速率大于纯 LLDPE的结晶速率，并且随接枝率的增加结晶速率加快。说明接枝到 LLDPE 分了链上的AA分子起到了成核剂的作用，从而使接枝物结晶速度加快。利用SEM观察LLDPE-g-AA 的球晶大小，发现 LLDPE-g-AA 的球晶尺寸明显减小，这进一步证实了前面的结论。测定了极性液体在不同接枝率的 LLDPE-g-AA 膜表面的接触角。发现随着接枝率的增加，接触角显著下降。采用 Zisman 作图法和接触角与表面张力的相关关系式得到了不同接枝率LLDPE-g-AA 的临界表面张力。并利用测接触角的方法计算了 LLDPE/LLDPE-g-AA 共混物的表面能。结果表明，共混物表面能随LLDPE-g-AA含量的增加而增加。用毛细管流变仪研究了官能化线性低密度聚乙烯的流变性能。结果表明，在剪切应力大于2.5×10~4 Pa时，其表现粘度比纯 LLDPE的小，流动性明显提高，加工成型性能得到了改善，且其表观粘度随AA含量的增加而减小，这说明接枝到 LLDPE分子链上的 AA 分子起到了内润滑剂的作用。官能化线性低密度聚乙烯的力学性能测试结果表明，其拉伸强度、模量和断裂伸长率没有显著的变化，这对于实际应用有着非常重要的意义。将官能化线性低密度聚乙烯与金属铝进行复合，测定了其剥离强度。结果表明：由于引入了极性基团，其与铝复合的剥离强度大大提高。接枝率、粘合时间、粘合温度和压力等均会对剥离强度产生较大影响。利用SEM 和 XPS对剥离表面进行了研究，发现剥离的铝表面有一个新的Al_(2p)峰，并且其谱图变宽。剥离铝表面O_(1S)结合能与纯铝表面及剥离 LLDPE-g-AA 表面的O_(1S)结合能不同，说明其处于不同的环境中。上述结果证明 LLDPE-g-AA 与铝在界面处可能发生了反应，从而使其剥离强度大大提高。

南沙群岛海区NS97-13柱样沉积物磁化率各向异性研究

二类水体光学活性成分的复杂性导致了水体光学特性的复杂性。通过对太湖区域

低能离子束沉积制备GaAs:Gd的研究

对室温条件下用低能离子束沉积得到的GaAs∶Gd样品,借助X射线衍射(XRD)和高分辨X射线衍射(HR-XRD)进行了结构分析,结果表明没有出现新的衍射峰,并且摇摆曲线的形状与Gd的注入计量密切相关.运用X光电子能谱仪对比分析了Gd注入后,衬底中主要元素Ga2p和As3d的化学位移,以及不同计量的样品中注入的Gd4d芯能级束缚能的变化,并分析了铁磁性产生的可能原因.

Direct Numerical Simulation of Shock/Turbulent Boundary Layer Interaction in a Supersonic Compression Ramp

A direct numerical simulation of the shock/turbulent boundary layer interaction flow in a supersonic 24-degree compression ramp is conducted with the free stream Mach number 2.9. The blow-and-suction disturbance in the upstream wall boundary is used to trigger the transition. Both the mean wall pressure and the velocity profiles agree with those of the experimental data, which validates the simulation. The turbulent kinetic energy budget in the separation region is analyzed. Results show that the turbulent production term increases fast in the separation region, while the turbulent dissipation term reaches its peak in the near-wall region. The turbulent transport term contributes to the balance of the turbulent conduction and turbulent dissipation. Based on the analysis of instantaneous pressure in the downstream region of the mean shock and that in the separation bubble, the authors suggest that the low frequency oscillation of the shock is not caused by the upstream turbulent disturbance, but rather the instability of separation bubble.