电子助进化学气相沉积金刚石中发射光谱的蒙特卡罗模拟

采用蒙特卡罗方法，对源料气体为CH4/H2混合气的电子助进化学气相沉积（EACVD）中 的氢原子(H)、碳原子(C)以及CH基团的发射过程进行了模拟.研究了CH4浓度、反应室气压 和衬底偏压等工艺参数对发射光谱及成膜的影响.研究发现，CH基团可能是有利于金刚石薄 膜生长的活性基团，而碳原子不是；偏压的升高可提高电子平均温度及衬底表面附近氢原子 的相对浓度；通过氢原子谱线可测定电子平均温度并找到最佳成膜实验条件.该结果对EACVD 生长金刚石薄膜过程中实时监测电子平均温度，有效控制工艺条件，生长出高质量的金刚石 薄膜具有重要的意义. 关键词： 蒙特卡罗模拟 金刚石薄膜 发射光谱     

投影电子束光刻中电子穿透掩膜的Monte Carlo模拟

利用基于Mott散射截面和介电函数模型的Monte Carlo方法模拟了电子穿透掩膜的能量损失分布，其计算结果与实验结果符合很好. 由此进一步计算了角度限制投影电子束光刻(SCALPEL)掩膜的穿透率和衬度，结果表明：散射体的厚度对衬度的影响较大，衬度随散射体厚度的增加而增强，而支撑体对衬度的影响较小；增大限制孔的孔径角时，透射率相应增大，但衬度会降低；衬度随入射电子的能量增加而减小. 关键词： Monte Carlo模拟 电子束光刻 掩膜     

用分子自组装技术制备的单电子器件的Monte Carlo模拟

用分子自组装技术制备出纳米金单电子器件,并测量了其伏安特性,根据单电子系统的半经典理论,用MonteCarlo法对其结果进行了模拟.结果表明,模拟出的伏安曲线与实测的伏安曲线有较好的一致性,反映了模拟方法用于单电子器件研究的合理性,此外发现,虽然单电子器件两电极间含有众多的纳米粒子,但在低压区,其伏安特性只与少数纳米粒子有关 关键词： 单电子器件 MonteCarlo模拟 分子自组装     

Monte Carlo simulation of electron avalanches and avalanche size distributions in methane

The simulation of electron avalanches and avalanche size distributions in methane is presented in this paper. A model for electron transport under the influence of a constant electric field based on the Monte Carlo method is described in detail. The model is verified and then used to simulate the avalanche development, to calculate the number of electrons in the avalanche (avalanche size), and to determine the avalanche size distribution. The simulated avalanche size distributions in methane are compared with the experimental results, and a good agreement is observed. The influence of inter‐electrode distance, pressure, and reduced electric field on the shape of the avalanche size distribution is discussed. The assumption from the literature that for a constant reduced electric field the shape of the reduced avalanche size distribution is independent of the mean size of the avalanche is confirmed for a wide range of experimental conditions. The simulations have shown that avalanche size distributions depend only on the reduced electric field, confirming the similarity principle.     

金刚石薄膜中二次电子输运的蒙特卡罗模拟

本文通过编写的二维MATLAB蒙特卡罗程序, 对倍增的二次电子在金刚石薄膜中的输运特性进行了初步模拟. 研究表明: 二次电子的迁移率对温度和外加电场的大小很敏感, 在杂质浓度比较低时(<10¹⁷/cm^-3)受杂质浓度的影响不大. 模拟得到的 二次电子的饱和速度为1.88×10⁷ cm/s, 无外加电场时的迁移率为3732 cm² /V.s. 同时, 通过对二次电子束团在金刚石薄膜中的整体输运特性的模拟, 证明了束团电荷密度在应用要求的范围内时, 空间电荷力的影响可以忽略不计.     

低能电子在固体表面背散射系数的直接Monte Carlo方法模拟

应用单次碰撞的直接Monte Carlo方法计算能量范围从100 eV~10 keV的电子在固体Al,Si,Au表面的背散射系数,其中低能电子在固体中的弹性散射和非弹性散射截面分别应用Mott散射截面和Born近似下的广义振子强度计算模型得到.通过与压缩历史Monte Carlo方法的模拟计算结果及实验值的比较,结果表明,对于100 eV~10 keV范围的低能区电子,采用直接方法计算得到的电子背散射系数与实验值符合较好,直接方法比压缩历史方法更适合于能量在10 keV以下的电子输运计算.     

Reaction rate between 1D migrating self-interstitial atoms: an examination by kinetic Monte Carlo simulation

The rate equation approach is useful for semi-quantitatively simulating long-term processes of accumulation or recovery of lattice defects in crystalline materials upon irradiation or annealing. This approach has been developed and applied to a large number of systems, including 3D or 1D migrating self-interstitial atoms (SIAs) and 1D migrating SIA clusters. The dimensionality of the migration of mobile species significantly affects the forms of the reaction rate. For reactions related to 1D migrating SIAs and clusters, only their reactions with stationary traps have been considered. However, the reactions between 1D migrating SIAs (or clusters) cannot be ignored, especially for processes in metals, in which the most stable configuration of an SIA is the crowdion, under electron and ion irradiations at comparatively high dose rate. In the present study, we use the object kinetic Monte Carlo (KMC) method to find the approximate form of the reaction rate between 1D migrating SIAs. For this purpose, we examine the average time for one SIA to encounter another SIA, in systems where the spatial distribution of SIAs is kept homogeneous, as a function of the concentration of SIAs. The approximate form of the reaction rate between 1D migrating SIAs primarily and effectively reflects the 2D migration process. In addition, it is shown that, in the systems composed of all reactive SIAs under annealing, the absolute value of the reaction rate by KMC becomes slightly lower than the solution of the derived form after longer times, due to the spatial correlation among SIAs.     

多分散高浓度介质偏振光后向扩散散射的Monte Carlo仿真

建立了针对多分散高浓度介质偏振光后向扩散散射的Monte Carlo仿真模型，导出了多分散 系统的有效自由程分布函数. 给出了半径为50nm与550nm及其三种不同体积浓度比混合的聚 苯乙烯微球作为散射粒子的高浓度介质的仿真结果. 定性地分析了多分散介质偏振光后向扩 散散射的光强空间分布特征与粒子的体积浓度比的关系. 关键词： 后向扩散散射 偏振光 多分散高浓度介质 Monte Carlo仿真     

低速多电荷态离子He2+、O2+和Ne2+与W靶表面

本文报道了He2+,O2+和Ne2+与W靶表面相互作用中的动能电子产额随离子入射速度变化的实验测量结果.结果表明：在本实验的入射速度范围内,对同一入射离子,动能电子产额随入射离子的速度增大而线性增加.基于动能电子发射的机理,我们分析了影响动能电子产额的因素,理论上得出动能电子产额与入射速度增长呈线性增加的关系,取得了实验上和理论上一致的结果.     

Monte Carlo simulation of the enantioseparation process

By means of Monte Carlo simulation, a study of enantioseparation by capillary electrophoresis has been carried out. A simplified system consisting of two enantiomers S (R) and a selector chiral C, which reacts with the enantiomers to form complexes RC (SC), has been considered. The dependence of Δμ$\Delta \mu$ (enantioseparation) with the concentration of chiral selector and with temperature have been analyzed by simulation. The effect of the binding constant and the charge of the complexes are also analyzed. The results are qualitatively satisfactory, despite the simplicity of the model.     

Monte Carlo study of single-barrier structure based on exclusion model full counting statistics

Different from the usual full counting statistics theoretical work that focuses on the higher order cumulants computation by using cumulant generating function in electrical structures, Monte Carlo simulation of single-barrier structure is performed to obtain time series for two types of widely applicable exclusion models, counter-flows model, and tunnel model. With high-order spectrum analysis of Matlab, the validation of Monte Carlo methods is shown through the extracted first four cumulants from the time series, which are in agreement with those from cumulant generating function. After the comparison between the counter-flows model and the tunnel model in a single barrier structure, it is found that the essential difference between them consists in the strictly holding of Pauli principle in the former and in the statistical consideration of Pauli principle in the latter.     

Influence of helium on the evolution of irradiation-induced defects in tungsten: An object kinetic Monte Carlo simulation

Understanding the evolution of irradiation-induced defects is of critical importance for the performance estimation of nuclear materials under irradiation. Hereby, we systematically investigate the influence of He on the evolution of Frenkel pairs and collision cascades in tungsten (W) via using the object kinetic Monte Carlo (OKMC) method. Our findings suggest that the presence of He has significant effect on the evolution of irradiation-induced defects. On the one hand, the presence of He can facilitate the recombination of vacancies and self-interstitial atoms (SIAs) in W. This can be attributed to the formation of immobile He-SIA complexes, which increases the annihilation probability of vacancies and SIAs. On the other hand, due to the high stability and low mobility of He-vacancy complexes, the growth of large vacancy clusters in W is kinetically suppressed by He addition. Specially, in comparison with the injection of collision cascades and He in sequential way at 1223 K, the average sizes of surviving vacancy clusters in W via simultaneous way are smaller, which is in good agreement with previous experimental observations. These results advocate that the impurity with low concentration has significant effect on the evolution of irradiation-induced defects in materials, and contributes to our understanding of W performance under irradiation.     

降雨融化层后向散射的蒙特卡罗仿真

云层上端冰雪粒子的融化形成了降雨融化层，随着粒子的下落融化过程开始，因此融化层的微观特性在垂直方向上是连续变化的.建立了降雨融化层的仿真模型，应用更为切合实际的三层球形粒子代替了融化层中的粒子.根据降雨过程中雨滴的尺寸分布推导了融化层中融化粒子的尺寸分布.根据Mie理论，计算了降雨率小于12.5 mm/h时，降雨融化层对5，10，35，94 GHz电磁波的雷达反射率和特征衰减因子的垂直廓线.计算结果表明，当电磁波频率高于20 GHz时，将无法观测到“雷达亮带”，这与实验结果相符.根据辐射传输理论，应用蒙特卡罗方法计算了垂直方向微观特性连续变化的降雨融化层对不同频率电磁波的反射率，比较了两种不同尺寸分布(Gamma分布和Marshall-Palmer分布)融化层反射率的差别，这为利用高频电磁波对降雨融化层进行遥感提供了理论和数值依据. 关键词： 降雨融化层 蒙特卡罗方法 后向散射 电磁波     

Quantum Monte Carlo study of a proton in an electron gas

The polarization of jellium by a fixed proton impurity at 0 K is determined for an electron density range from metallic to dilute using the quantum Monte Carlo algorithm. Preliminary results show the correct H^– binding limit for the impurity in a dilute electron gas. The screening indicates transitions from two-to one-electron binding and from localized to delocalized electrons as the jellium density increases. The results are compared to density functional calculations. Pair distribution functions, Friedel oscillations, and binding energies are discussed.     

Monte Carlo simulation of magnetic nanostructured thin films

Using Monte Carlo simulation, we have compared the magnetic properties between nanostructured thin films and two-dimensional crystalline solids. The dependence of nanostructured properties on the interaction between particles that constitute the nanostructured thin films is also studied. The result shows that the parameters in the interaction potential have an important effect on the properties of nanostructured thin films at the transition temperatures.     

Monte Carlo simulation of hydrogen adsorption on Ni surfaces

In the present paper the adsorption kinetics of the hydrogen molecule on the (111) and (100) surfaces have been studied with the model proposed by Panczyk and the grand canonical Monte Carlo simulation method. The equilibrium adsorption isotherms are calculated at five different temperatures ranging from 314 K to 376 K and compared with the experimental equilibrium adsorption isotherms. The effects of temperature and pressure on coverage are also analyzed.      

Monte Carlo simulation of exposure factor

In this paper, we simulate the exposure factor by a simple model of a free-air ionization chamber with the Monte Carlo programme Geant4. Special emphasis is placed on the discussion of the exposure factor related to parameters of the chamber model. The reason for the variation in exposure factor with incident ray energy is also analysed in terms of reaction cross section for different types of reactions. The obtained results indicate that our simulation is accurate in the calculation of the exposure factor and can serve as a reference in designing air ionization chambers.     

Monte Carlo simulation of ramified aggregates onhetero-substrates

We have studied the aggregation of particles on a hetero-substrate consisting of two different substrates A and B with finite surface barriers E_AB and E_BA between the AB and BA boundaries, respectively. With the diffusion energy limited aggregation (DELA) model, we find that the number of clusters and the mean radius of gyration of the clusters are dependent on the surface barriers E_AB and E_BA. For the case with a constant of E_BA, a series of minima are summarized as E_AB= (E₀- k_BAE_BA)/ k_AB with k_AB and k_BA being two integers, for main minima (k_BA=k_AB- 1) and two local minima (k_BA=k_AB and k_BA=k_AB + 1) between two neighbouring main minima.