精细积分法在一维光子晶体数值模拟中的应用

应用精细积分法对含各种介质材料的一维光子晶体进行了数值模拟,并对结果进行了分析.计算时将光子晶体分成不同的区段,引入区段势能和区段混合能,利用精细积分法求出各个区段的出口刚度矩阵,然后将各个区段的刚度矩阵合并,再结合边界条件便可求解问题.利用透射率和反射率之间的关系,判断了本算法的准确度,数值计算结果表明,对于一维光子晶体的数值模拟,此方法准确、有效、适用性强.     

精细积分法在一维光子晶体数值模拟中的应用

应用精细积分法对含各种介质材料的一维光子晶体进行了数值模拟,并对结果进行了分析.计算时将光子晶体分成不同的区段,引入区段势能和区段混合能,利用精细积分法求出各个区段的出口刚度矩阵,然后将各个区段的刚度矩阵合并,再结合边界条件便可求解问题.利用透射率和反射率之间的关系,判断了本算法的准确度,数值计算结果表明,对于一维光子晶体的数值模拟,此方法准确、有效、适用性强.     

High dose implantations of antimony for buried layer applicationsrrr

A computer simulation of low energy implantation is presented. The method of calculation takes into account the inelastic processes and vacancies in the crystal lattice.

The described simulation was used for a nitrogen implanted molybdenum single crystal. From the result of the calculation the possible positions of implanted nitrogen on the surface and in the bulk were obtained. The results of simulations are compared with those measured by SIMS and AES.     

基于GEANT4的CsI(Tl)闪烁体探测器的Monte Carlo模拟

对闪烁光在晶体内的传输以及光电子倍增过程进行了建模,基于GEANT4软件包对CsI(T1)闪烁体探测器进行了蒙特卡罗模拟, 得到了不同形状、尺寸和包装的CsI(Tl)晶体测量γ射线的能谱。对比模拟和测试结果,两者得到了很好的符合,从而验证了模拟参数的合理性和可靠性。该模拟程序的建立为闪烁体探测器的设计提供了更精确的开发工具。 With the modeling of the light transportation in crystal and electron multiplication in the PMT, a Monte Carlo simulation of CsI(Tl) scintillator detector has been implemented with Geant4 toolkit. The energy spectra simulated with different crystal shape, size and wrappings are obtained. And the reliability of the simulation parameters is confirmed by comparing with the measurements. The simulation code can be used as an reliable tool for the design of scintillator detectors.     

The influence of stimulated temperature-dependent emission cross section on intracavity optical parametric oscillator

In this paper, the influence of temperature on the intracavity optical parametric oscillator(IOPO) is investigated by using the stimulated temperature-dependent emission cross section of laser crystal. The rate equations under plane wave approximation have been used for simulation of signal output pulse. Results show that the signal output pulse width is decreased by increasing the laser crystal temperature. Also, the signal output energy is increased by the increasing of the laser crystal temperature. The simulation results for IOPO based on Nd:YAG and Nd:YVO_4, show that the signal pulse energies are increased by 3.2 and 5.6 times respectively when the laser crystal temperature increased from 15℃ to 300℃. The presented model indicates that the temperature sensitivity of Nd:YVO_4-based IOPOs is more than that of Nd:YAG-based IOPOs which is expected from a physical point of view.     

典型金属纳米结构的电子能量损失谱研究

利用格林函数推导出金属纳米结构电子能量损失谱的计算公式,基于时域有限差分方法对几种典型的结构进行建模仿真,数值模拟运动电荷和结构的距离、液晶环境材料对电子能量损失谱的调节作用.仿真结果表明:当增加电子与纳米结构的距离时,电子能量损失谱谱峰降低;当添加液晶材料或各向同性衬底材料时,电子能量损失谱的峰值发生明显红移,但液晶的光轴倾角改变对峰值的调制作用有限.通过计算电子能量损失谱研究金属纳米结构表面等离子激元共振特性,为高度复杂的等离子体激元纳米结构的设计提供了理论基础.     

α-B晶体的Lennard-Jones对势和对势型多体势构建

精确原子间相互作用势函数的建立是分子动力学模拟的核心. 针对α-B晶体(R3m群), 分别构建Lennard-Jones (L-J)型对势和对势型多体势, 这两类势函数的构建仅需考虑晶体的原子平均结合能和几何构型参数. 前者取最近邻原子间距的势函数为最小值; 后者采用负指数(L-J型)函数和分段插值多项式形式来分别构造势函数, 在近邻处为势能极小值, 相邻极小值位置的中点引入势垒. 针对完整的α-B 晶体和偏离完整α-B晶体结构, 首先利用第一性原理计算结果来确定势函数的参数, 然后借助分子动力学的能量最小化方法优化结构, 并对这两类势函数以及Tersoff 势函数进行比较. 结果表明: L-J对势和Tersoff势的结果与α-B晶体构型有较大偏离; 而对势型多体势, 无论初始晶体构型完整与否, 其结果与完整α-B晶体构型比较一致.     

Temperature effect in antiproton channeling

The temperature dependence of axially channeled antiprotons in a Si crystal is studied using computer simulation. The number of channeled particles and the energy and angular distributions are calculated for antiprotons with an energy of 300 keV in the temperature range of 100 to 1000 K in the 〈100〉, 〈110〉, and 〈111〉 channels. The roles of the potential and atomic thermal vibrations are studied thoroughly. It is found that dechanneling depends on the crystal temperature. There exists an optimal temperature, which is dependent on the axis direction, for which dechanneling is minimal.     

Computer simulation of intrinsic defects in YAlO3 single crystal

Computer simulation techniques were used to investigate intrinsic defects in YAlO₃ single crystal. A set of short-range potential parameters were derived using a relaxed fitting procedure incorporating with the known crystal properties. These parameters were then applied within the framework of the shell model. The simulation results reveal that oxygen Frenkel disorder and the antisite defect of Al ion substituting the Y ion dominate the intrinsic defects in YAlO₃. An analysis of redox reactions corroborate that the oxidation is most likely to occur via forming interstitial oxygen, while the oxidation via filling oxygen vacancies and reduction reaction may predominate at high temperature. The activation energy of oxygen vacancy migration on conduction was also studied.     

一维光子晶体能流密度与透射率特性

设计不同介电常数材料构成的一维光子晶体,数值模拟探究一维光子晶体的能流密度和透射率特性。研究结果为人工电磁材料的设计提供了理论依据。     

Potential energy of interaction between a fast multiply charged ion and crystal atoms with regard for the Pauli principle

Expressions for the potential energy of interaction between a fast neutral atom or a multiply charged ion and a crystal atom are obtained, both with and without regard for the Pauli principle. Results from computer simulation of the heating of silver ions with a fixed value of the charge state in passing through the (110) planar channel of a silicon crystal are presented. It is shown that the rate of dechanneling can be estimated by the form of the potential energy of interaction of an incident ion with a continuous potential of the planar crystal channel.     

Energy transfer under impact load studied by molecular dynamics simulation

The process of amorphous silica clusters impact on a crystal silicon substrate is studied by molecular dynamics simulation, focusing on the energy transfer between clusters and the substrate under different impact conditions such as cluster size, impact velocity, and incidence angle. The impact process is divided into cluster deformation stage, cluster resilience stage, and cluster rebound stage according to the courses of energy change during the impact process. The simulation elucidates that the time of impact process of every cluster is only related to cluster size and is independent of impact velocity and incidence angle. The translational energy loss of the cluster and the potential energy increment of the substrate during cluster deformation stage, and the dissipation energy of system are independent of cluster size under the same impact energy and incidence angle. And the translational energy loss of the cluster during cluster rebound stage changes from energy absorption to energy release after the incidence angle becomes more than 60°. The rotational energy of the cluster may be omitted when the incidence angle is less than 15°. The ratios of the rotational energy increment of the cluster, the kinetic energy increment, and the potential energy increment of the substrate to the translational energy loss of the cluster are obviously influenced by impact conditions. And the ratios of the increment of the other categories of energy to the translational energy loss of the cluster are not sensitive to impact conditions.     

硬X射线透射晶体谱仪的设计性能参数

激光等离子体相互作用高分辨硬X射线光谱的测量通常采用柱面透射弯晶谱仪实现。利用几何光学模型对柱面透射弯晶谱仪的关键技术参数进行了理论计算和数值模拟,给出了谱仪弯晶曲率半径、光源到晶体的距离、光源尺寸和探测器的位置等因素对谱仪测谱范围和分辨能力的影响情况,分析了光谱分辨水平随能点的变化。分析结果表明:晶体曲率半径对测谱范围和谱分辨能力影响大,在光源尺寸较小时,随着探测器与罗兰圆距离的增加,谱线之间距离增加的速度大于光谱线宽增加的速度,使得分辨能力增加。     

Ranges and profiles of distribution of low-energy ions channeling in metal and semiconductor single crystals

In the present work peculiarities of trajectories and energy losses, ranges and profiles of distribution of low-energy different-mass ions channeling in thin single crystals of metals and semiconductors have been thoroughly studied by computer simulation in binary collision approximation. The character of oscillations of channeled-ion trajectories depending on their energies, aiming points from the axis of a channel, kind of interaction potential, crystal lattice type and temperature has been determined. It has been found that, in the case of light ions even at low energy, the main contribution to energy loss is made by inelastic energy losses, whereas for heavy ions, already at E < 10 keV, elastic energy losses exceed inelastic ones. Profiles of the distribution of channeled ions have been calculated depending on crystal lattice type, kind of ions and their energy.     

Localization of light energy of a femtosecond laser pulse upon generation of the second harmonic in a one-dimensional nonlinear photonic crystal with alternating nonlinear response

A possibility of localization of the light energy upon generation of the second harmonic of a femtosecond laser pulse in a one-dimensional photonic crystal, some layers of which are either quadratic or cubic nonlinear, is demonstrated in computer simulation. It is shown that there exist light energy localization modes at one of the interacting frequencies and at both interacting frequencies simultaneously. The formation of solitons in separate layers of the photonic crystal is the basis of light energy localization. Logical operations of Boolean algebra can be implemented based on the discovered effect.     

Influence of quantum fluctuations on the motion of relativistic protons in crystals

The influence of multiple scattering and quantum fluctuations in the transverse coordinate, momentum, and energy on the channeling of relativistic protons in a silicon crystal have been studied by computer simulation.     

Flexoelectric-Induced Voltage Shift in Hybrid Aligned Nematic Liquid Crystal Cell

Flexoelectric-induced voltage shift in a weak anchoring hybrid aligned nematic liquid crystal cell is investigated theoretically. Based on the elastic theory of liquid crystal and the variation method, the equations for the bulk and the boundary of the cell are derived. By computer simulation, the dependence of the
shift voltage on the sum of the flexoelectric coefficients and the anchoring energy strength is obtained. As a result, a novel method to determine the sum of the flexoelectric coefficients by measuring the shift voltage is put forward.     

CuI晶体及其缺陷态电子结构的模拟

利用相对论密度泛函理论和嵌入分子团簇方法,模拟计算了具有闪锌矿结构的γ态CuI晶体及其缺陷态的电子结构。结果显示晶体的本征能级结构:价带顶主要由I5p和Cu3d轨道杂化组成,导带底由Cu4s轨道组成,禁带宽度为3.1eV,该结果与实验相符。在不同缺陷态的计算中,四面体间隙铜缺陷相对其他间隙缺陷更易于在晶体中形成,其中Cu3d→4s跃迁能量为3.2eV,推测与CuI晶体发光密切相关。     

On the self-consistent statistical theory of vacancies

We report here a new method of describing the effect of the presence of vacancies on the structure, dynamics and thermodynamics of a crystal. The unsymmetrized self-consistent approximation is used to determine the potential energy in which the defective structure and the anharmonicity appear from the beginning. In order to stress the power of this method, we calculate the free energy of formation of a vacancy and the concentration of vacancy in a two-dimensional triangular Lennard-Jones crystal. A comparison with Monte Carlo simulation is given and a possible application to experimentally accessible systems is discussed.     

On the construction of a bias potential for atomic system simulation by the hyperdynamics method

Hyperdynamics is the method of accelerated molecular dynamics simulation based on lowering energy barriers while performing the dynamic simulation of a nano/atomic system. A system with reduced energy barriers between different states is obtained by changing the potential of interaction, namely, by constructing the so-called bias potential. An approach allowing a bias potential to be obtained is considered. To demonstrate this method, the hyperdynamics simulation of the diffusion of an atom, adsorbed on a 2D crystal surface, and a vacancy, located in its bulk, is carried out. The results are compared with relevant results obtained by molecular dynamics. It is shown that the hyperdynamics approach makes it possible to obtain statistical results, similar to those provided by molecular dynamics. This allows the accelerated simulation of atomic systems to be conducted with minor losses in the accuracy of results.