Charge Reconfiguration in Isolated Quantum Dot Arrays

A high level of tunability and control over arrays of quantum dots are key ingredients toward the goal of scalable‐based qubit architectures. Increasing array size simultaneously increases the parameter space and therefore the tuning complexity. The electron reconfiguration behavior of quantum dot arrays isolated from the electron reservoirs is studied experimentally. Isolating a quantum dot array from the reservoirs does not only enable a high degree of control over the tunnel couplings but at the same time drastically simplifies the stability diagrams for small numbers of electrons trapped in the array. Experimental results on double, triple, and quadruple quantum dot arrays are presented and complementary model calculations allow the identification of all transitions observed in the experiment. Highly tunable long‐range transitions are observed in isolated triple quantum dots and evidence of higher‐order cotunneling is found for the quadruple quantum dot array.     

线型离子阱中空间电荷效应的理论分析

线型离子阱中的离子在射频场作用下做宏观的久期运动,久期运动频率与实验参数有关.但当离子阱中囚禁大量同种电荷的离子时,空间电荷效应会导致离子间存在相互排斥的库仑力,使离子的运动频率发生漂移.本文通过求解泊松方程计算了空间电荷产生的附加电场的解析表达式,在小振动近似下理论计算了该附加电场对久期运动频率的影响,模拟了不同离子云中心密度下久期频率的漂移,讨论了离子云的数目、温度与实验参数之间的关系.对用离子阱进行的频标实验、碰撞实验和其他方面的研究都具有重要的指导意义.     

氧化锌电阻阀片中ZnO(002)/β-Bi_2O_3(210)界面结构的第一性原理研究

为了从物质微观结构上了解氧化锌避雷器阀片的性能,采用基于密度泛函理论的第一性原理方法对ZnO(002)/β-Bi_2O_3(210)界面结构进行弛豫和电子结构计算.结果表明弛豫后,原子间的键长发生改变.界面区域差分电荷密度图和原子布居分析可得ZnO层片中Zn原子电荷缺失,β-Bi_2O_3层片中O原子电荷富集,ZnO层片向β-Bi_2O_3层片转移电子电荷23.61e.晶界结构的内建电场由ZnO层片指向β-Bi_2O_3层片,内建电场是ZnO电阻阀片具有非线性伏安特性的重要原因.界面附近态密度表明界面的结合主要依靠ZnO层片中Zn原子与β-Bi_2O_3层片中O原子相互作用.计算显示ZnO(002)/β-Bi_2O_3(210)界面结合较强,界面能约为-4.203 J/m~2.本文研究结果对于研制高性能非线性伏安特性氧化锌电阻片提供了机理解释和理论支持.     

外电场下交联聚乙烯电介质材料分子结构变化及其电老化微观机理研究

为了从微观角度分析交联聚乙烯(XLPE)材料的电树枝老化,本文采用分子模拟方法计算并优化得到了XLPE分子结构.沿着聚乙烯链施加不同大小电场强度,分析交联聚乙烯分子的几何结构、偶极矩、极化率、电荷分布、前线轨道能量和红外光谱变化规律.计算结果表明,随着外电场的增大,交联聚乙烯分子红外光谱发生较大变化;当外施电场达到0.026a.u.后,红外光谱图中出现虚频,表明分子空间结构不再稳定,易发生断键;另外从前线轨道图的变化可以看出断键现象最先发生在交联聚乙烯链端部;沿着电场方向,原子所带电荷量由交联处向端部转移,当外施电场达到0.029a.u.后,链端部的C-H和C-C键断裂产生H·和CH_3·自由基.游离的自由基会形成空间电荷并发生积聚,产生局部较大场强,从而进一步影响交联聚乙烯链的空间结构.而电介质内部微观特性的变化必定会导致交联聚乙烯材料绝缘性能的下降,这些变化对揭示交联聚乙烯电缆电树枝形成的微观规律具有重要研究意义.     

The impact of crystal defects towards oxide semiconductor photoanode for photoelectrochemical water splitting

Photoelectrochemical (PEC) water oxidation for sustainable clean energy and fuel production is a potential solution to the demands of organic pollutant removal and growing energy consumption. Development of high performance photoanodes, which is a key component in the system, is one of the central topics in the area. The crystal defect is an old concept but fruiting new understanding with promotive impact to the development of high performance photoanodes. In this review, we elucidated the typical defects involved in the photoanode with the position where they play the roles in the structure and how the properties of photoanode are influenced. In addition, we summarized the feasible protocols to maximize the pros but reduce the cons brought by having defects to the photoanode performance based on recent most prominent research advancements in the field. Finally, we briefly sketched the future perspective with the challenges of this topic when in the scenario of possible developments into practical applications.     

Improved eikonal approach for charge exchange reactions at intermediate energies

In order to describe charge exchange reactions at intermediate energies,we implemented as a first step the formulation of the normal eikonal approach.The calculated differential cross-sections based on this approach deviated significantly from the conventional DWBA calculations for CE reactions at 140 MeV/nucleon.Thereafter,improvements were made in the application of the eikonal approximation so as to keep a strict three-dimensional form factor.The results obtained with the improved eikonal approach are in good agreement with the DWBA calculations and with the experimental data.Since the improved eikonal approach can be formulated in a microscopic way,it is easy to apply to CE reactions at higher energies,where the phenomenological DWBA is a priori difficult to use due to the lack,in most cases,of the required phenomenological potentials.     

Triboelectrification of granular insulating materials as affected by dielectric barrier discharge (DBD) treatment

The aim of this paper is to point out the influence of dielectric barrier discharge treatment on tribocharging of granular insulating materials. Particles of Polyvinyl Chloride (PVC) and Polypropylene (PP) were subjected to an AC dielectric barrier discharge (DBD) plasma treatment in ambient airprior to tribocharging in a vibratory device. The charge to mass ratio was measured for treated and untreated materials. Electrostatic separation of a mixture of granular materials (PVC and PP) to measure the effectiveness of DBD treatment was evaluated by processing treated and untreated PVC/PP granular mixtures in a free-fall electrostatic separator. The obtained results clearly indicate that DBD has the capability to influence surface charging proprieties of polymer granular materials. In case of short treatment time, typically less than 3 s, a marked increase in the charge to mass ratios was observed for both PVC (about 35%) and PP (roughly 45%). In the same way, the quantity of DBD-treated materials, recovered after electrostatic separation, was increased by about 104% and 30% for PVC and PP, respectively, as compared to untreated case. The DBD treatment time is a key factor to increase the tribo electric effect.     

量子点发光二极管功能层厚度确定方法

为改善量子点发光二极管器件载流子注入平衡,提出一种量子点发光二极管各功能层厚度的确定方法.首先选定量子点发光层厚度,基于隧穿模型进行仿真分析确定电子传输层厚度;然后采用空间电荷限制电流模型进行仿真分析确定空穴传输层厚度.采用CdSe/ZnS量子点作为发光层、poly-TPD作为空穴传输层、Alq_3作为电子传输层,按照该方法仿真分析得到各功能层厚度进行旋涂-蒸镀法实物器件制备.对比实验结果表明:当poly-TPD、QDs及Alq_3厚度分别为45nm、25nm及35nm时,获得了较高的发光效率及色纯度,器件性能最好.该方法确定的各功能层厚度有助于减少载流子在发光界面积累,获得载流子的注入平衡,从而改善QLEDs发光性能.     

基于Visco-SCRAM模型的侵彻装药点火研究

针对弹体侵彻过程中装药的安全性,基于黏弹性统计裂纹力学(visco-statistical crack mechanics, Visco-SCRAM)模型计算装药整体温升、装药裂纹摩擦生热以及弹体装药与壳体摩擦生热,考察这3种机制对装药温升的贡献以及侵彻装药的点火机制,得到了装药点火对应的弹体侵彻临界初始速度。结果表明:(1)装药与弹体内壁摩擦生热对装药温升有一定贡献,随着弹体初始撞击速度的提高,摩擦生热对温升的贡献逐渐增大;(2)黏性、损伤和绝热体积变化导致的装药整体温升对装药点火的作用有限; (3)裂纹摩擦形成热点是侵彻装药点火的物理机制;(4)采用Visco-SCRAM模型可预测低强度、长脉冲载荷作用下的装药点火响应。     

Secondary plasmon resonance in graphene nanostructures

The plasmon characteristics of two graphene nanostructures are studied using time-dependent density functional theory (TDDFT). The absorption spectrum has two main bands, which result from π and σ + π plasmon resonances. At low energies, the Fourier transform of the induced charge density maps exhibits anomalous behavior, with a π phase change in the charge density maps in the plane of the graphene and those in the plane 0.3 ? from the graphene. The charge density fluctuations close to the plane of the graphene are much smaller than those above and beneath the graphene plane. However, this phenomenon disappears at higher energies. By analyzing the electronic properties, we may conclude that the restoring force for the plasmon in the plane of the graphene does not result from fixed positive ions, but rather the Coulomb interactions with the plasmonic oscillations away from the plane of the graphene, which extend in the surface-normal direction. The collective oscillation in the graphene plane results in a forced vibration. Accordingly, the low-energy plasmon in the graphene can be split into two components: a normal component, which corresponds to direct feedback of the external perturbation, and a secondary component, which corresponds to feedback of the Coulombic interaction with the normal component.