【作者】 杨晔；

【导师】 赵万生；

【作者基本信息】 上海交通大学 ， 机械制造及其自动化， 2014， 博士

【摘要】 基于SPM（Scanning Probe Microscope，扫描探针显微镜）的纳米电刻蚀加工技术具有成本低，操作灵活，精度高，加工尺寸可控，加工去除能力与材料强度和硬度无关等优势，适用于各种金属，非金属导体和半导体材料表面的纳米尺度加工和改性，因此在纳米尺度器件的加工领域中具有广阔的应用前景。目前该加工方法尚处于实验室研究阶段，还需要进行大量相关的基础实验和机理研究才能可靠和高效地应用于实际纳米尺度结构的加工中。本文针对基于SPM的电刻蚀加工方法进行了系统的实验研究和相关的机理研究，分别采用了STM（Scanning TunnelingMicroscope，扫描隧道显微镜）和AFM（Atomic Force Microscope，原子力显微镜）两种系统装置，致力于解决三方面的关键性问题，即研究基于SPM纳米电刻蚀加工方法在加工石墨样品中的实验规律，优化加工参数，从而提高加工的可控性，成像精度，加工效率和加工稳定性；有效区分基于SPM纳米电刻蚀加工方法在电化学和放电两种原理下进行加工的实验条件，从而在指定加工原理下获得可控的纳米结构；探究材料加工蚀除的微观过程，对局域纳米加工间隙中的电场和热场分布进行有限元计算和分析，并且采用分子动力学方法对基于放电原理的加工中热源作用下材料蚀除过程的原子运动轨迹进行模拟。主要完成的工作有以下几个方面：1.采用基于STM的电刻蚀加工方法在大气环境中对石墨样品表面进行了系统的加工实验研究，加工间隙控制在0.6nm至3nm间。在样品正极性下可以进行样品材料的蚀除加工和改性，而在样品负极性下，样品表面材料无法被去除或改性，但是可以对针尖进行尖锐化的修整，有效地提高针尖的使用寿命。实验还研究了加工偏压幅值，脉宽，加工间距，针尖几何构型，大气湿度等加工参数对电刻蚀加工结果的影响规律，同时通过研究加工过程中检测出的实时电流来进一步地分析加工状态和机理。在加工实验中可以获得深径比为0.04~0.4的蚀坑结构，其中加工获得最小尺寸的蚀坑直径为10nm，深度约为1nm。而加工获得最浅线槽结构的深度约为1nm，相当于几个石墨片层的厚度。2.采用基于AFM的电刻蚀加工方法在大气环境中对石墨样品表面进行了系统的加工实验研究，针尖和样品间处于接触模式下，相互作用力控制在10nN以内。在样品正极性下，对AFM探针几何构型，加工偏压幅值，加工速度和大气湿度等过程参数进行了系统的实验研究。这种加工方式不仅可以获得各种尺寸的纳米蚀坑和蚀槽结构，还可以在电化学原理下可控地获得凸起或凹陷的纳米线结构，其中线凸起结构具有绝缘特性，加工宽度约为40~60nm，高度约为1~3nm。并且检测出电化学和放电原理下的实时电加工电流具有明显差异。还对比了基于STM和AFM两种电刻蚀加工方法的特点，加工精度以及针尖寿命等。3.通过J.G. Simmons的通用计算公式获得了纳米尺度加工间隙中的电流密度-电压曲线，结合实验加工结果，获得了不同原理加工区域的加工电流密度阈值，并由此得到不同加工间隙下的加工电压阈值。并且采用有限元方法对基于SPM的纳米电刻蚀加工进行建模，计算得到不同针尖几何构型下纳米尺度间隙中的电场分布，获得了最佳电加工状态下的针尖曲率半径值。还通过有限元热电耦合计算获得了样品表面的温度场分布，并根据相变计算结果估算出纳米放电加工中，不同的加工偏压，加工间隙，针尖几何构型和样品材料下局域材料蚀除量的大小。将有限元模拟预测结果与实际加工结果进行对比，一致性较好。4.采用分子动力学方法对纳米放电加工中热效应作用下原子尺度的材料蚀除过程进行了模拟。分别以石墨和铜样品材料作为模拟对象，研究了在放电焦耳热源作用下局域样品表面的原子运动轨迹，从而确定了材料蚀除的纳观机理。并且研究和分析了热源能量大小以及不同样品晶格结构对于材料蚀除过程的影响。更多还原

【Abstract】 The SPM (Scanning Probe Microscope)-based nano scale electrical machiningtechnique is of numerous advantages, such as low cost, flexible operation, high accuracy,controllable feature size and its material removal capability has nothing to do with thematerial strength and hardness. The machining method is applicable to a variety of metals,non-metallic conductive materials and the semiconductor materials to achieve thenanoscale surface modification and processing. Therefore, it has broad applicationprospects in the nanoscale device fabrication fields. Presently the SPM-based electricfabrication method is in the laboratory stage and still requires a lot of the relevantexperimental and mechanism researches to be reliably and efficiently applied to the actualnanoscale structure fabrication. In this dissertation, the two system devices of STM(Scanning Probe Microscope) and AFM (Atomic Force Microscope) are utilizedrespectively to perform the systematic experimental study and the mechanism research.This work is committed to address three key issues. That is firstly, through the study ofthe experimental laws and optimal processing parameters in the SPM-based electriclithography of the graphite sample, the enhancement of fabrication controllability,imaging precision, machining efficiency and reliability is achieved. Secondly, theexperimental conditions for determining the electrochemical-caused fabrication and theelectro discharge-caused fabrication during the SPM-based electric lithography areobtained and the controllable nanoscale structures are fabricated under the specificmachining mechanism. Finally, to explore the microscopic process of the local materialremoval and modifications, both of the FEM (finite element method) analysis of theelectric and thermal field distribution in the nanoscale machining gap and the MD(molecular dynamics) simulation of the atom trajectory under the heat sourcecorresponding to the electro spark-caused SPM-based fabrication are carried out. Major work completed in the dissertation is in the following areas:1. The experimental research of the STM-based electrical machining is performed onthe graphite surface in the ambient conditions with the machining gap controlled between0.6to3nm. For the fabrication conducted under the positive polarity of the sample, thesample material removal and modification can be obtained, while under the negativepolarity fabrication, the sample surface cannot be effectively removed or modified.However, the probe tip could be sharpened to effectively improve the lifetime of the tooltip. The machining parameters involving the bias voltage amplitude, pulse width,machining gap, tip geometry and the atmospheric humidity are experimentally studied todetermine their influence on the fabrication results. Furthermore, the real-time currentduring the machining process is also detected to analyze the machining status andmechainism. The nanoscale pits in the aspect ratio between0.04and0.4are obtained.The smallest pits fabricated are in the diameter of10nm and the depth of1nm or so. Theshallowest groove structure obtained is in the depth of1nm, equivalent to severalgraphite layer thicknesses.2. The experimental study of the AFM-based electric lithography is carried out on thegraphite sample in the atmosphere. The AFM probe tip and the sample are kept in thecontact mode and the interaction force is controlled within10nN. Under the positivepolarity fabrication, the process parameters including the AFM probe geometry, biasvoltage magnitude, scanning speed and the relative humidity are systematicallyinvestigated in the experiments. Not only the nanoscale pits and grooves of various sizescan be obtained, but also the bulged or the grooved nanowire sturcutres can becontrollably achieved in the electrochemical principle. The bulged nanolines possessingthe insulation properties are in the width of40~60nm and the height of1~3nm or so.And it can be observed that the current under the electrochemical-caused fabrication andthe electro discharge-caused machining has a significant difference. Moreover, theSTM-based and the AFM-based electrical machining methods are compared in theaspects of machining charateristics, machining accuracy, life time of the probe tip and soon.3. The current density-voltage (J-V) curve in the nanocale machining gap is obtainedthrough the J.G. Simmons general formula. Combined with the experimental results, thethreshold current density values for performing the machining under distinct mechanisms are acquired and thus to get the threshold voltage values under different machining gaps.The electric field distribution in the nanoscale gap is calculated under various tipgeometries using the FEM (finite element method) and the tip curvature radius forachieving optimal electro machining status is determined. Furthermore, through the FEMthermoelectric coupling calculation, the temperature distribution is obtained. The materialremoval size of the local sample surface during the electro discharge machining can beestimated through the phase change calculation under distinct bias voltages, machininggaps, tip geometries and sample materials. It is found out that the FEM calculation resultsare in good accordance with the experimental results.4. The MD (molecular dynamics) simulation method is utilized to simulate theatomic-scale thermal response and material removal process during the electro dischargemachining. The graphite sample and copper sample are taken as the simulation objectrespectively. The atomic trajectories under the Joule heating effect of the nanoscaleelectro discharge phenomena are studied to determine the microscopic mechanism ofmaterial removal and ablation. Moreover, the role of the heat source energy and thesample material in the material machining process are investigated in detail.更多还原