基于紧密耦合理论的3端分子桥的传导特性

利用基于紧密耦合理论的格林函数方法，考虑到每一个碳原子的π轨道电子，对3苯环构成的纳米分子桥的量子传输特性进行了理论研究。得出了从分子桥的一个端点到另外两个端点的电子传输概率。 利用基于Fisher-Lee公式的流密度方法，在传输概率出现峰值的能量点E=±0.42, ±1.06 和±1.5处，计算了分子桥内部的电流分布。其数值结果用图形模拟表示出来。我们发现传输谱与入射电子能量相关，并且紧密地依赖与分子能级。其结果显示电子流分布完全符合Kirchhoff量子动量守恒定律。     

四端纳米分子桥的量子传输特征

利用基于Greenfunction的Tight-binding方法，对由平面共轭分子连结而成的有四个端子的纳米分子桥进行了理论研究和数值模拟，得出了入射电子通过纳米分子桥传输到各个端点的电子透射概率.利用Fisher-Lee关系式和电子流密度理论，在透射概率出现峰值的四个能量点E=±12,E=±149处计算了分子桥内的电子流分布.不仅得出了键电子流的最大值，而且揭示了分子内环路电子流生成和存在是由于分子轨道波函数的位相差使电子流的大小和方向发生变化而引起的. 关键词： 纳米分子桥 量子传输 电子透射概率 环路电子流     

多注速调管的3维数值计算

 用KARAT-3D全电磁PIC程序，对多注速调管设计模型波束相互作用的物理过程进行3维数值模拟，给出了输出功率、电流等基本的物理参数。在输入电压14 kV，电流20.8 A时候，得到了128 kW的峰值输出功率，峰值效率是43.8％。考察了电子在高频场的运动和电流调制，分析了电流在各互作用腔中的调制，并对多注速调管不同发射度时电子传输进行了研究。结果表明：电子均匀发射时高频场的调制对电流传输效率影响不大，电流和电场调制随着腔的增加而增加。电子能量在输出腔的位置减小很多，电子有一部分能量转化为微波。     

基于NEPTUNE3D开展的脉冲功率装置汇流区三维PIC数值模拟

大型脉冲功率装置真空汇流区的电子输运过程对于电流汇聚有重要的影响，在高性能计算集群的帮助下，使用NEPTUNE3D软件开展三维全电磁PIC模拟进行了研究，模拟区域（34 cm×34 cm×18 cm）包括双层柱-孔盘旋（DPHC）结构和部分内、外磁绝缘传输线等关键位置。计算结果清晰地展示了零磁位区分布和电子输运轨迹，电子主要由外磁绝缘传输线阴极表面发射，在洛伦兹力作用下向中心漂移并损失在零磁位区处；对电子能量沉积的统计结果表明，受电子流轰击最严重的位置在DPHC结构下层阳极柱表面，来自大型脉冲功率装置的实验结果证实了上述结论。根据计算结果，最大电流损失率（437 kA，27%）发生在电流传输的早期时刻（～15 ns），而电流峰值时刻损失率则仅有0.48%，此时磁绝缘已完全生效，表明DPHC结构在峰值电流的汇聚与传输上有很高的效率。     

多端耦合量子点分子桥的量子输运特性研究

利用非平衡格林函数方法,对五个量子点连结而成的有四个终端的耦合量子点分子桥进行了理论研究和数值模拟,得出了入射电子通过耦合量子点分子桥传输到各个终端的电子隧穿概率的规律. 关键词： 耦合量子点分子桥 非平衡格林函数 量子输运     

氮等离子体枪中电子输运行为的蒙特卡罗模拟

采用蒙特卡罗模拟,对氮等离子体枪的两个环形电极间的氮气辉光放电过程中电子的输运过程进行研究.计算在不同平均电场与粒子数密度的比值(E/N)下,电子与氮分子发生不同碰撞的概率、出射电子的平均能量、方向角分布和电子的能量分布.结果表明,电子能量近似服从玻尔兹曼分布.随着E/N的升高,电子平均能量升高,发生激发、离化、电离和离化电离碰撞的概率增大;非均匀分布的电场使分子获得更高的离化率,同时显著增强出射电子的能量.模拟结果为等离子体应用设计提供了参考依据.     

量子环中量子比特的性质

通过精确求解能量本征方程获得量子环的电子能态，并利用电子的基态和第一激发态构造一个量子比特.对InAs/GaAs量子环的数值计算表明：当环尺寸给定时，量子比特内电子的概率密度分布与坐标位置及时间有关，在环内中心位置处电子出现的概率最大，电子的概率密度随柱坐标内的转角作周期性变化，并且各个空间点处的概率密度均随时间做周期性振荡. 关键词： 量子环 能量本征方程 电子能态 量子比特     

冲功率装置汇流区由电子发射导致的电流损失机制

面向大型脉冲功率装置聚龙一号(PTS装置),以电磁粒子模拟方法(PIC)为依托,围绕真空汇流区双层柱-孔盘旋(DPHC)结构区域,研究电子发射对DPHC结构在电流传输、汇聚过程中的影响。使用全三维大规模并行粒子模拟软件NEPTUNE3D,简化并建立DPHC结构的物理和几何模型,利用全电路数值模拟的方法获得PTS装置真空轴向绝缘堆处开路和短路电压波形曲线作为输入条件,计算得到DPHC结构中磁场强度分布。分别考虑是否存在电子发射过程,获得输出端电流损失随时间变化曲线,经过对比得到峰值时刻由阴极表面电子发射所导致的电流损失率为0.46%~0.48%。     

脉冲功率装置汇流区由电子发射导致的电流损失机制

面向大型脉冲功率装置聚龙一号(PTS装置),以电磁粒子模拟方法(PIC)为依托,围绕真空汇流区双层柱-孔盘旋(DPHC)结构区域,研究电子发射对DPHC结构在电流传输、汇聚过程中的影响。使用全三维大规模并行粒子模拟软件NEPTUNE3D,简化并建立DPHC结构的物理和几何模型,利用全电路数值模拟的方法获得PTS装置真空轴向绝缘堆处开路和短路电压波形曲线作为输入条件,计算得到DPHC结构中磁场强度分布。分别考虑是否存在电子发射过程,获得输出端电流损失随时间变化曲线,经过对比得到峰值时刻由阴极表面电子发射所导致的电流损失率为0.46%~0.48%。     

平行电磁场中H-光剥离电子轨道分岔现象的研究

当改变能量、位置或场强等参数时,电磁场中里德堡态的原子、分子和离子等体系将出现分岔现象,从而导致波函数在分岔点附近发散,半经典闭合轨道理论不再适用.本文分析并计算了平行电磁场中H-光剥离电子轨道的分岔现象,并采用统一近似的方法进行定域修正,从而消除了分岔点的奇异性,得到了合理的光剥离电子流的分布.     

First-principles predictions of the geometries and electronic structures of tungsten ditelluride nanoribbons

First-principles calculations are carried out to predict the structures and electronic properties of 2H- and Td-WTe₂ nanoribbons with different termination edges. It is found that the 2H-WTe₂ nanoribbon along the armchair direction and the Td-WTe₂ nanoribbon along the X direction show semiconducting characters with tunable band gaps. The 2H-WTe₂ nanoribbon along the zigzag direction and the Td-WTe₂ nanoribbon along the Y direction show metallic characters.     

An indirect probe of the possible half-metallic nature of LiFePO4 using resonant inelastic X-ray scattering

The Fe site in LiFePO₄ was probed resonantly and non-resonantly at the L_2,3 edge. A suspected half-metal, the experimental results were compared to band structure calculations to understand the electronic structure. We found that the probability of promoting an electron to the unoccupied band through simple photoexcitation or through scattering is highly influenced by magnon-exciton coupling. We have also found evidence that the correlation self-energy has a momentum-dependant component, causing spectral renormalization of the Fe 3d PDOS. Our experimental results are consistent with the predicted band, structure of LiFePO₄.     

Static response to a charge impurity near a metal surface finite-barrier treatment

Summary The static response to a charge impurity near a metal surface is computed in the RPA approximation for the case of a finite barrier. Particular attention is given to the problem of the correct infinite-volume limit and to the contribution of the one-particle states with energy higher than the potential barrier, which has been found to be not negligible. An integral equation for the self-consistent potential is derived and solved numerically. Results for Na and Zn are exhibited, showing remarkable difference with respect to the infinite-barrier case.

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Riassunto La risposta statica ad un'impurezza di carica in prossimità della superficie di un metallo è calcolata nell'approssimazione delle fasi a caso (RPA) nel caso di una barriera finita. Sono trattati con particolare cura i problemi del corretto limite di volume infinito e del contributo degli stati ad una particella con energia superiore alla barriera di potenziale, contributo che risulta non trascurabile. Si deriva e risolve numericamente un'equazione integrale per il potenziale autoconsistente. Sono presentati i risultati per Na e Zn, da cui si può rilevare una notevole differenza rispetto al caso della barriera infinita.

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Резюме В случае конечного барьера в приближении случайных фаз вычисляется статический отклик на заряженную примесь вблизи металлической поверхности. Особое внимание уделяется проблеме корректного предела бесконечного объема и вкладу одно-частичных состояний с энергией выше потенциального барьера, который, как получено, не является пренебрежимо малым. Выводится интегральное уравнение для самосогласованного потенциала и решается численно. Полученные результаы для Na и Zn обнаруживают значительное различие с результатами для случая бесконечного барьера.

     

Possibility of line radiation at the interface of MOS

Summary If the applied electric field is perpendicular to the surface of the MOS structure, the conduction band of the semiconductor near the oxide-semiconductor interface will be curved. The quantized energy levels for electrons in a surface potential well will be given by the triangular-potential-well approximation. For a moderately lightly doped semiconductor, the Fermi level will be sufficiently lower than the bottom of the conductor band. By adjusting the applied field, the surface quantized levels will be lifted up above the Fermi level and the radiative transition between the quantized levels will be possible. Thus the line emission at the submillimetre wave band will be expected.

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Riassunto Se il campo eletrico applicato è perpendicolare alla superficie della struttura MOS, la banda di conduzione del semiconduttore vicino all'interfaccia ossido-semiconduttore sarà curva. I livelli di energia quantizzati per elettroni in un pozzo di potenziale di superficie saranno dati dall'approssimazione del pozzo di potenziale triangolare. Per un semiconduttore leggermente drogato, il livello di Fermi sarà sufficientemente piú basso del fondo della banda del conduttore. Sistemando il campo applicato, i livelli quantizzati di superficie saranno sollevati sopra il livello di Fermi e la transizione radiativa tra i livelli quantizzati sarà possibile. Così ci si attende l'emissione di linea alla banda d'onda submillimetrica.

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Резюме Если приложенное электрическое поле перпендикулярно поверхности МОП структуры, то зона проводимости полупроводника вблизи границы раздела окисел-полупроводник будет искривлена. Квантованные уровни энергии для электронов в потенциальной яме поверхности приближенно определяются треугольной потенциальной ямой. Для умеренно легированного полупроводника уровень Ферми будет существенно ниже, чем дно зоны проводимости. Изменяя величину приложенного поля, поверхностые квантованные уровни поднимаются выше уровня Ферми и становится возможным радиационный переход между квантованными уровнями. Таким образом, можно ожидать линейное излучение в области субмиллиметровых волн.

     

Lithium absorption on single-walled boron nitride,aluminum nitride,silicon carbide and carbon nanotubes: A first-principles study

Using the DFT-B3LYP calculations we investigate the adsorption of Li atom on CNT, BNNT, AlNNT and SiCNT. We found that Li atom can be chemisorbed on zig-zag SiCNT with binding energy of −2.358 eV and charge transfer of 0.842 |e|, which are larger than the results of other nanotubes. The binding energy of Li on SiCNT is foun to be stronger than activation energy barrier indicating that Li metal could be well dispersed on SiCNTs. Furthermore, the average voltage caused by the lithium adsorption on SiCNT demonstrated that SiCNTs could exhibit as a stable anode similar to the lithium metal anode. The binding nature has been rationalized by analyzing the electronic structures. Our findings demonstrate that Li-BNNT, Li-SiCNT and Li-AlNNT systems exhibit spin polarized behaviors and can fascinating potential application in future spintronics. Also, Li-SiCNT system with rather small band gap might be a promising material for optical applications and active molecule in its environment.     

The image potential in the weighted-density approximation

Summary We analyse the image potential of a metal surface in the weightede-density approximation and obtain an analytical expression for the position of the image plane which is independent of the surface electronic structure. We conclude that the position of the plane image given by this density functional approximation cannot be accepted as a physical result.     

Theoretically exploring the possible configurations,the electronic and transport properties of MoS2-OH bilayer

Inspired by MoS₂-OH bilayer framework (Zhu et al. 2019 [19]), first principles calculations are applied to explore its possible configurations as well as their electronic and transport properties. The calculated results indicate O-MoS₂ and OH…O-MoS₂ are two primary configuration in MoS₂-OH bilayer. It shows negligible difference in electronic structure between O-MoS₂ and pure MoS₂, but a flat band arise at the Fermi level in OH…O-MoS₂. Their contact characteristics show larger binding energy with selected metals and smaller contact barrier with Pt electrode. Besides, the currents of both O-MoS₂ and OH…O-MoS₂ are enlarged compared with that of pure MoS₂ in finite bias, indicating MoS₂-OH bilayer may be potential candidate for future electron device applications.     

发射光谱法研究无极灯等离子体参数分布

使用电感耦合放电装置和拍型明泡,以氩-汞混合气体作为工作气体,在低气压下点亮了无极灯.利用发射光谱法,研究了无极灯点灯5s时的电子温度和电子密度随轴向和径向位置的变化规律.等离子体电子温度变化通过分析Ar原子425.9和750.4nm谱线强度比值获得,等离子体电子密度的变化通过分析Ar原子750.4nm谱线强度变化得到...     

Polarizability of a hydrogenic donor impurity in a ridge quantum wire

We use in this paper the variational method to calculate the polarizability of a hydrogenic donor impurity, in the presence of electric field, in a V-groove GaAs/Al_xGa_1−xAs quantum wire. The carrier ground states are analytically obtained by an effective potential scheme together with a suitable coordinate transformation that allows the decoupling of the two-dimensional Schrodinger equation. According to the results obtained from the present work for polarizability and binding energy reveals that the impurity position and field direction play important roles.     

On the energy-dependent number of electronic states in a quantum-well laser diode under a perpendicular magnetic field

The number of electronic states in a quantum-well laser diode under a perpendicular, uniform and time-independent magnetic field is considered as a function of the electronic energy. Within this framework, the energy-averaged number of states is calculated over a suitable energy range. In particular, an expression for the above average number is given when the magnetic field is relatively weak and the devices are assumed to be quasi-one-dimensional.