Enhanced photogalvanic effect in the two-dimensional MgCl2/ZnBr2 vertical heterojunction by inhomogenous tensile stress

The photogalvanic effect (PGE) occurring in noncentrosymmetric materials enables the generation of a dc photocurrent at zero bias with a high polarization sensitivity, which makes it very attractive in photodetection. However, the magnitude of the PGE photocurrent is usually small, leading to a low photoresponsivity, and therefore hampers its practical application in photodetection. Here, we propose an approach to largely enhancing the PGE photocurrent by applying an inhomogenous mechanical stretch, based on quantum transport simulations. We model a two-dimensional photodetector consisting of the wide-bandgap MgCl₂/ZnBr₂ vertical van der Waals heterojunction with the noncentrosymmetric C_3v symmetry. Polarization-sensitive PGE photocurrent is generated under the vertical illumination of linearly polarized light. By applying inhomogenous mechanical stretch on the lattice, the photocurrent can be largely increased by up to 3 orders of magnitude due to the significantly increased device asymmetry. Our results propose an effective way to enhance the PGE by inhomogenous mechanical strain, showing the potential of the MgCl₂/ZnBr₂ vertical heterojunction in the low-power UV photodetection.     

豫南山区典型森林类型土壤水分变化规律研究

采用连续定位观测的研究方法,对豫南低山区天然落叶阔叶林土壤水分变化规律进行了研究.结果表明,10cm,20cm,30cm,50cm四个不同测定深度处的土壤水分随季节变化均发生明显的周期性变异,土壤水分含量50cm20cm30cm10cm;变异幅度随深度增加而增加,即50cm30cm20cm10cm;垂直变化差异显著.土壤水分含量与降雨量存在显著的回归关系,10cm,20cm,30cm,50cm四个测定深度土壤水分含量与降雨量的线性回归方程相关系数分别达到0.727,0.772,0.786,0.626.     

晶圆键合和激光剥离工艺对GaN基垂直结构发光二极管芯片残余应力的影响

GaN基发光二极管(LED)中的残余应力状态对器件的性能和稳定性有很大影响. 通过使用三种不同的键合衬底(Al₂O₃衬底, CuW衬底和Si衬底)以及改变键合温度(290 ℃, 320 ℃, 350 ℃和380 ℃), 并且使用不同的激光能量密度(875, 945和1015 mJ·cm^-2) 进行激光剥离, 制备了不同应力状态的GaN基LED器件. 对不同条件下GaN LED进行弯曲度、Raman 散射谱测试. 实验结果表明, 垂直结构LED中的残余应力的状态是键合衬底和键合金属共同作用的结果, 而键合温度影响着垂直结构LED中的残余应力的大小. 激光剥离过程中, 一定能量密度下激光剥离工艺一般不会对芯片中的残余应力造成影响, 但是如果该工艺对GaN 层造成了微裂缝, 则会在一定程度上起到释放残余应力的作用. 使用Si衬底键合后, 外延蓝宝石衬底翘曲变大, 对应制备的GaN基垂直结构 LED中的残余应力为张应力, 并且随着键合温度的上升而变大; 而Al₂O₃和CuW衬底制备的LED中的残余应力为压应力, 但使用Al₂O₃衬底键合制备的LED中压应力随键合温度上升而一定程度变大, CuW 衬底制备的LED中压应力随键合温度上升而下降.     

垂直向列型彩色滤光膜硅覆液晶微显示器的三维光学建模

针对垂直向列型彩色滤光膜硅覆液晶微显示器件中的微型彩色像素建立了三维光学模型. 首先, 对彩色液晶器件的机电特性进行了分析; 其次, 利用扩展琼斯矩阵计算出器件的光反射率; 最后, 采用标准RGB协议将所研究的垂直向列型彩色滤光膜硅覆液晶微显示器件中各像素点的光反射特性还原成彩色图像. 用上述过程所建立的三维光学模型进行了垂直向列型彩色滤光膜硅覆液晶微显示器件的光学特性研究, 并与实验数据进行了比较. 比较结果显示, 模拟得到的垂直向列型彩色滤光膜硅覆液晶微显示器件的光学特性与实验结果非常符合.     

基于垂直晶体管结构的低电压并五苯光电探测器

并五苯(Pentacene)具有优良的场效应晶体管特性及在可见光区的高吸收系数, 被广泛应用于光敏(电)晶体管中. 垂直晶体管的沟道长度可做到纳米量级, 能有效提高器件的性能和工作频率, 同时降低能耗. 本文制备了一种基于垂直晶体管结构的低电压并五苯光电探测器ITO(S)/Pentacene/Al(G)/Pentacene/Au(D). 实验发现, 在工作电压低至-3 V时, 并五苯光电探测器ITO/Pentacene (80 nm)/Al(15 nm)/ Pentacene(80 nm)/Au 的阈值电压为-0.9 V, “开/关”电流比为10⁴, 表现出了良好的P型晶体管特性以及低电压调控性能. 在350-750 nm的不同波长单色光照射下, 器件的“明/暗”电流比和响应度随入射波长而变化; 在350 nm单色光照射下, 该光电探测器的“明/暗”电流比的最大值达到308, 其对应的响应度为219 mA·W^-1, 大于标准硅基探测器在350 nm 单色光照射下的探测率. 这为制备低电压下工作的高灵敏度全有机光电探测器提供了一种可行的方法.     

Vertical vibrations of elastic foundation resting on saturated half-space

This paper is mainly concerned with the dynamic response of an elastic foun- dation of finite height bounded to the surface of a saturated half-space.The foundation is subjected to time-harmonic vertical loadings.First,the transform solutions for the governing equations of the saturated media are obtained.Then,based on the assumption that the contact between the foundation and the half-space is fully relaxed and the half- space is completely pervious or impervious,this dynamic mixed boundary-value problem can lead to dual integral equations,which can be further reduced to the Fredholm integral equations of the second kind and solved by numerical procedures.In the numerical exam- ples,the dynamic compliances,displacements and pore pressure are developed for a wide range of frequencies and material/geometrical properties of the saturated soil-foundation system.In most of the cases,the dynamic behavior of an elastic foundation resting on the saturated media significantly differs from that of a rigid disc on the saturated half-space. The solutions obtained can be used to study a variety of wave propagation problems and dynamic soil-structure interactions.     

Tautomeric forms of adenine: Vertical ionization energies and Dyson orbitals

For the MP2/6‐311++g(2df,p) optimized geometry of all the 14 adenine tautomers, the first three vertical ionization energies have been calculated using several electron propagator decouplings. The corresponding Dyson orbitals provide detailed insight into the role of structural variations in different adenine tautomers. Changes in the electron binding energies and the corresponding Dyson orbital amplitudes have been correlated with tautomeric proton shifts and changes in conjugation patterns. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Dynamics of a stochastic SIR model with both horizontal and vertical transmission

A stochastic mathematical model with both horizontal and vertical transmission is proposed to investigate the dynamical behavior of SIR disease. By employing theories of stochastic differential equation and inequality techniques, the threshold associating on extinction and persistence of infectious diseases is deduced for the case of the small noise. Our results show that the threshold completely depends on the stochastic perturbation and the basic reproductive number of the corresponding deterministic model. Moreover, we find that large noise is conducive to control the spread of diseases and the persistent disease in deterministic model may eliminate ultimately due to the effect of large noise. Finally, numerical simulations are performed to illustrate the theoretical results.     

Plasma position control in SST1 tokamak

For long duration steady state operation of SST1, it would be very crucial to maintain the plasma radial and vertical positions accurately. For designing the position controller in SST1 we have adopted the simple linear RZIP control model. While the vertical position instability is slowed down by a set of passive stabilizers placed closed to the plasma edge, a pair of in-vessel active feedback coils can adequately control vertical position perturbations of up to 1 cm. The shifts in radial position arising due to minor disruptions would be controlled by a separate pair of poloidal field (PF) coils also placed inside the vessel, however the controller would ignore fast but insignificant changes in radius arising due to edge localised modes. The parameters of both vertical and radial position control coils and their power supplies are determined based on the RZIP simulations.     

考虑横纵向一体化的港航联盟的收益模型

随着港航业竞争的加剧,港口间的联盟与合作、港口与航运企业纵向一体化不断发展。尤其是,航运企业以收购或投资模式参与港口间的资源整合,形成了更为复杂的港航混合联盟。针对港口间的资源整合与竞争、航运企业与港口一体化等因素,构建港航混合联盟模式的收益模型,对比分析在区域港口竞争模式和港航混合联盟模式下港口和航运企业的收益变化,揭示地理位置、内陆运输成本、航运企业投资效果等因素的作用。结果表明,港航混合联盟模式能够实现整合港口和航运企业的双赢。同时,当港口与内陆的集疏运基础设施薄弱、航运企业的影响力较大时,非合作港口也会受益,此时港航横纵向混合联盟模式有利于推动整个区域港口经济的发展。