强流脉冲离子束模型及辐照靶材能量沉积的模拟研究

强流脉冲离子束(IPIB)及其在靶材中沉积的能量是研究束流与靶材作用的基础.根据三束材料改性国家重点实验室从俄罗斯引进TEMPⅡ型加速器实测的磁绝缘二极管(MID)的加速电压波形及法拉第杯检测到的MID焦点处离子流密度波形,对其进行拟合得到高斯脉冲分布模型,以此为基础采用Monte Carlo方法模拟了离子在铝靶内沉积的能量,得到了一个脉冲内靶材内沉积的能量的时空演化规律.计算了单能离子束以20°～40°角入射铝靶情形.不同能量的单能H+束和C+束以一定角度入射时的最大射程比垂直入射时都要小,表面处单位长度沉积的能量随入射角的增加而增多.IPIB入射铝靶时变化规律同单能离子束.同时对H+和C+二维入射靶材情况也进行了模拟研究.     

小型离子源中膜孔静电透镜系统仿真研究

离子源是各种类型质谱仪、离子加速器、离子注入机、离子束刻蚀机等电真空设备不可缺少的部件,静电透镜系统是离子源的重要组成部分。本文基于圆孔膜片透镜理论及带电粒子在静电场中的运动理论,利用多重物理场软件COMSOL对一种小型化离子源的离子加速系统进行了仿真研究。分析了离子加速区透镜片数为4片、23片时不同位置的圆孔膜片透镜电压对离子束能量及发散角的影响。计算结果表明,离子加速区膜孔透镜数量为4片时,更易于通过透镜电压调节离子束光斑尺寸,当膜孔透镜相对位置为12 mm、透镜电压为510 V时,离子束发散角最小值为3°,离子能量最高值为480 eV。     

考虑齿顶修形和时变中心距的渐开线直齿轮振动特性研究

针对渐开线直齿轮,考虑时变中心距推导了动态啮合角、动态间隙的解析表达式,考虑时变转速、时变中心距和齿顶修形,并采用解析方法得到了齿轮的动态啮合刚度,在此基础上建立了齿轮啮合模型。考虑几何偏心、齿向偏载力矩和陀螺力矩,建立了单级齿轮传动系统10自由度横-扭-摆耦合非线性动力学模型。将非线性动力学模型和齿轮啮合模型进行耦合计算,对比分析了转速和扭矩对不同修形齿轮振动特性的影响。结果表明:当转速超过某临界值,短修形齿轮的振动载荷大于无修形齿轮,而长修形齿轮不存在临界转速;随着扭矩的增加,无修形齿轮的啮合力峰峰值呈线性比例增加,短修形齿轮和长修形齿轮的啮合力峰峰值近似呈先减小后增大的趋势变化,说明在某扭矩下修形齿轮的振动载荷最小,且长修形对应的扭矩大于短修形;短修形和长修形齿轮均存在临界扭矩,当扭矩小于该临界值时,修形齿轮的振动载荷大于无修形齿轮,且长修形对应临界扭矩小于短修形。     

磁流变抛光连续加工状态下去除函数稳定控制

在长时间连续加工情况下,即使稳定控制工艺参数,磁流变抛光材料去除效率仍会出现下降.通过仿真认为,去除效率的下降对于大口径工件的高精度修形而言不可忽略.通过材料去除机理分析、磁流变液微粒观测以及X射线衍射测试,认为去除函数发生变化是磁流变液中抛光颗粒消耗所致.基于液体抛光效率随抛光颗粒浓度增大而趋于饱和的规律,提出了定时定量添加过饱和磁流变抛光液使去除函数得到稳定控制的方法.通过实验,去除函数体积去除效率在达到饱和后波动率小于1!.最后对大口径光学元件进行修形,验证了控制方法的有效性.     

扫描式氩离子枪的电子光学系统研究

扫描式离子枪是样品表面清洁、表面刻蚀和深度分析的常用部件,加速电压在500V到3kV之间可调,具有效率高、性能可靠等优点。电子光学系统是离子枪的重要组成部分,是决定离子束流品质的重要因素。本文利用计算机模拟软件CST对离子枪整体结构进行建模,研究了离子枪聚焦系统不同结构和电压参数对离子束电流密度和束斑尺寸的影响,同时得到了离子枪偏转系统在不同电压分布下的离子分布情况,通过仿真分析确定了电子光学系统的设计方案,并进行了实验验证。结果表明：工作距离为25mm、氩气工作气压为6×10^-3Pa、加速电压为3kV时,氩离子束的束流大小为3μA;束斑大小在7mm到12mm之间可调;当偏转电压为300V时,偏转角度为4.6°。实验与仿真结果基本对应,同时该离子枪的性能指标可获得表面原子精度构造。     

聚焦离子束的束径测量

报道了聚焦离子束装置的束径测量方法和典型测量结果。偏转离子束使其扫过金属栅网的边缘 ,由法拉第筒接收到的离子流强度变化所形成的S形电流曲线可确定束径大小。在数据处理中 ,采用了快速傅立叶变换滤波的办法来消除微小电流测量结果中的噪声 ,从而可以对S形电流曲线进行微分 ,得到束流密度空间分布。在改变透镜光阑口径而维持靶室离子流强度不变的测量模式中 ,证实了离子间库仑相互作用增大束径的效应     

小角度偏转离子能量分析器性能仿真研究北大核心CSCD

能量分析器是对荷能粒子进行分析的重要仪器,其在空间粒子探测方面有着越来越广泛的应用。本文基于带电粒子在静电场中的运动理论以及粒子碰撞理论,利用多物理场仿真软件COMSOL,对一种小角度偏转离子能量分析器进行了仿真研究。模拟计算了不同入射离子能量下的离子运动轨迹,分析了不同入射离子能量和微通道板电压对分析器带电粒子通过率和分辨率的影响,同时分析了温度变化对分析器工作性能的影响。计算结果表明,偏转电压与离子能量之间存在线性变化关系;微通道板电压为-300 V时,分析器的能量分辨率效果较好;温度的变化不改变分析器的能量分辨率,但对分析器的离子通过率有影响。     

小角度偏转离子能量分析器性能仿真研究

能量分析器是对荷能粒子进行分析的重要仪器,其在空间粒子探测方面有着越来越广泛的应用。本文基于带电粒子在静电场中的运动理论以及粒子碰撞理论,利用多物理场仿真软件COMSOL,对一种小角度偏转离子能量分析器进行了仿真研究。模拟计算了不同入射离子能量下的离子运动轨迹,分析了不同入射离子能量和微通道板电压对分析器带电粒子通过率和分辨率的影响,同时分析了温度变化对分析器工作性能的影响。计算结果表明,偏转电压与离子能量之间存在线性变化关系;微通道板电压为-300 V时,分析器的能量分辨率效果较好;温度的变化不改变分析器的能量分辨率,但对分析器的离子通过率有影响。     

离子束倾斜入射抛光对表面粗糙度的影响

基于光学元件离子束高精度确定性抛光技术,在自行研制的离子束抛光机床上,本文研究了离子束倾斜入射抛光对光学材料熔石英表面粗糙度的影响.为了在离子束抛光中改善表面粗糙度,采用了0°～80°之间不同入射角度的离子束倾斜抛光和倾斜45°入射均匀去除两种实验方案进行研究,其中不同入射角度抛光实验研究结果表明:离子束垂直入射抛光较难改善表面粗糙度,倾斜入射抛光可以较好地改善表面粗糙度,入射角为30°～60°之间时抛光效果最佳,表面粗糙度得到明显改善;倾斜45°入射均匀去除抛光实验结果表明表面粗糙度的RMS值由抛光前(0.92±0.06)nm下降到(0.48±0.04)nm,提高了光学零件的表面质量,验证了离子束倾斜入射抛光可以较好地改善表面粗糙度,实现了离子束倾斜抛光超光滑表面的生成.     

第十九讲 真空溅射镀膜

<正>(接2015年第5期第80页)综合分析图28和图29可以看出,在高速磁控溅射中,靶上施加的产生放电的溅射电压,使离子获得的能量,能产生最大的功率密度,而且在这一电压范围内,便于输入较大的功率。靶发热、辐射和二次电子发射等"无用"功在总输入功率中所占比例很小。3低能溅射由于靶上施加的阴极电压低,等离子体被磁场束缚在阴极附近的空间中,从而抑制了高能带电粒子向基片一侧入射。因此,由带电粒子轰击     

Ion beam figuring of high-slope surfaces based on figure error compensation algorithm

In a deterministic figuring process, it is critical to guarantee high stability of the removal function as well as the accuracy of the dwell time solution, which directly influence the convergence of the figuring process. Hence, when figuring steep optics, the ion beam is required to keep a perpendicular incidence, and a five-axis figuring machine is typically utilized. In this paper, however, a method for high-precision figuring of high-slope optics is proposed with a linear three-axis machine, allowing for inclined beam incidence. First, the changing rule of the removal function and the normal removal rate with the incidence angle is analyzed according to the removal characteristics of ion beam figuring (IBF). Then, we propose to reduce the influence of varying removal function and projection distortion on the dwell time solution by means of figure error compensation. Consequently, the incident ion beam is allowed to keep parallel to the optical axis. Simulations and experiments are given to verify the removal analysis. Finally, a figuring experiment is conducted on a linear three-axis IBF machine, which proves the validity of the method for high-slope surfaces. It takes two iterations and about 9 min to successfully figure a fused silica sample, whose aperture is 21.3 mm and radius of curvature is 16 mm. The root-mean-square figure error of the convex surface is reduced from 13.13 to 5.86 nm.     

Ion-beam machining of millimeter scale optics

An ion-beam microcontouring process is developed and implemented for figuring millimeter scale optics. Ion figuring is a noncontact machining technique in which a beam of high-energy ions is directed toward a target substrate to remove material in a predetermined and controlled fashion. Owing to this noncontact mode of material removal, problems associated with tool wear and edge effects, which are common in conventional machining processes, are avoided. Ion-beam figuring is presented as an alternative for the final figuring of small (<1-mm) optical components. The depth of the material removed by an ion beam is a convolution between the ion-beam shape and an ion-beam dwell function, defined over a two-dimensional area of interest. Therefore determination of the beam dwell function from a desired material removal map and a known steady beam shape is a deconvolution process. A wavelet-based algorithm has been developed to model the deconvolution process in which the desired removal contours and ion-beam shapes are synthesized numerically as wavelet expansions. We then mathematically combined these expansions to compute the dwell function or the tool path for controlling the figuring process. Various models have been developed to test the stability of the algorithm and to understand the critical parameters of the figuring process. The figuring system primarily consists of a duo-plasmatron ion source that ionizes argon to generate a focused (~200-mum FWHM) ion beam. This beam is rastered over the removal surface with a perpendicular set of electrostatic plates controlled by a computer guidance system. Experimental confirmation of ion figuring is demonstrated by machining a one-dimensional sinusoidal depth profile in a prepolished silicon substrate. This profile was figured to within a rms error of 25 nm in one iteration.     

宽束冷阴极离子源离子能量及能量分布的研究

介绍了一种用于离子束辅助沉积光学薄膜的新型宽束冷阴极离子源,详细叙述了该源的结构和工作过程.采用五栅网离子能量测试装置研究了离子源的离子能量及能量分布.结果表明,探针接收的离子最低能量随着引出电压和真空度的升高而升高.离子能量分布概率密度函数为单峰函数,其峰值位置随着真空度的降低向低能量方向移动,随着引出电压的升高向高能量方向移动.当引出电压为200～1200V时,离子平均能量为600～1600eV,呈线性规律变化.这种离子源的离子平均初始动能约为430～480eV.了解和掌握离子源的这些特性和参数,可以有效的对镀膜过程的微观环境(离子密度、离子能量等)进行控制,促进薄膜制备工艺更好地进行.     

离子束加工中驻留时间的求解模型及方法

驻留时间求解问题是离子束加工中的关键问题．通常,离子束加工过程可以描述为一个包含驻留时间的二维卷积方程,理论上通过反卷积即可以求解出驻留时间．然而,反卷积问题是一个病态问题,所以驻留时间一般较难很好地求解出．为了解决这个问题,介绍了一个离散的线性模型——CEH模型,分析了该模型的优点．提出应用截断奇异值分解法（TSVD）来求解CEH模型;深入分析了该方法的优点,并利用“L-曲线”分析了驻留误差和加工量之间的关系以及用“L-曲线”对CEH模型中去除点和驻留点的不同取法进行了评价．仿真结果表明,CEH模型和TSVD方法对于求解光学镜面离子束加工中的驻留时间很有效．     

Ion beam machining error control and correction for small scale optics

Ion beam figuring (IBF) technology for small scale optical components is discussed. Since the small removal function can be obtained in IBF, it makes computer-controlled optical surfacing technology possible to machine precision centimeter- or millimeter-scale optical components deterministically. Using a small ion beam to machine small optical components, there are some key problems, such as small ion beam positioning on the optical surface, material removal rate, ion beam scanning pitch control on the optical surface, and so on, that must be seriously considered. The main reasons for the problems are that it is more sensitive to the above problems than a big ion beam because of its small beam diameter and lower material ratio. In this paper, we discuss these problems and their influences in machining small optical components in detail. Based on the identification-compensation principle, an iterative machining compensation method is deduced for correcting the positioning error of an ion beam with the material removal rate estimated by a selected optimal scanning pitch. Experiments on ?10?mm Zerodur planar and spherical samples are made, and the final surface errors are both smaller than λ/100 measured by a Zygo GPI interferometer.     

Effect of assist ion beam voltage on intrinsic stress and optical properties of Ta2O5 thin films deposited by dual ion beam sputtering

The optical properties and intrinsic stress of Ta₂O₅ thin films deposited by dual ion beam sputtering (DIBS) were studied as a function of the assist ion beam voltage (250-650 V). When the assist ion beam voltage was in the range of 350-450 V, the transmittance at the quarter-wave point reached its highest value (lowest absorption). The refractive index increased to 2.185 as the assist ion beam voltage increased from 250 to 350 V, but decreased as the assist ion beam voltage was further increased from 350 to 650 V.     

Oberflächenpräzisionsbearbeitung mit Ionenstrahlen

Low energy ion beam processing becomes more and more established in the development and manufacturing of high precision surfaces as a final complementary step of the conventional surfaces polishing of special optical and mechanical parts. The presented paper gives a comprehensive overview about different ion beam processing techniques and demonstrates the applicability of the ion beam figuring to the final correction of high precision surfaces.     

Molecular dynamics simulations for gas cluster ion beam processes

Molecular dynamics (MD) simulations of large argon clusters impacting on silicon targets were performed. The characteristics of crater formation, a typical collisional effect with large cluster impact were examined from the viewpoint of incident energy, cluster size and incident angle. The MD simulation results suggested that the condition where an incident cluster penetrates into the solid target and causes a crater is mainly dominated by the incident energy-per-atom rather than total incident energy of the cluster. Additionally, the MD simulations of sequential multiple cluster impacts and grazing-angle cluster irradiation on irregular surface structures were studied to characterize the surface modification effects with large cluster ion beam process.     

一种新型复合加速离子注入动力学研究

提出了一种基于靶台(工件)二次加速的束线离子注入的新方法,基本原理是将传统束线离子注入和等离子体离子注入有效复合。采用二维Particle-in-cell(PIC)模型对这种注入方法进行了数值仿真研究。考察了靶台加负偏压情况下靶台表面空间电势、离子密度变化以及离子的运动状态的时空演化。统计分析了不同时刻离子注入剂量、注入能量和注入角度的分布规律。结果表明:靶台施加偏压对束流离子起到了很好的二次加速效果,束线离子复合加速离子注入这种新方法理论上是切实可行的。同时发现在靶台附近空间电场的作用下,离子束会发生小角度偏转,由柱状形逐渐变成"喇叭口"形,靶台表面有效注入范围扩大。靶台表面注入剂量分布呈中心区域高边缘区域低的趋势。这种新方法有助于减缓电源硬件加工的难度,增加了工艺的灵活性。