【作者】 宋晨飞；

【导师】 钱林茂；

【作者基本信息】 西南交通大学 ， 机械设计及理论， 2013， 博士

【摘要】 纳米科技与生物科技及信息科技并列为21世纪最具影响的三大领域,深刻地改变着人类社会进程。而纳米制造技术是实现纳米产品生产的先决条件,是纳米科技走向应用的关键和基础。随着器件微型化发展至纳米尺度,传统的纳米加工技术遇到了前所未有的挑战,比如分辨率难以提升、工艺复杂、加工损伤高等。因此,开发新的纳米加工技术不仅能满足纳米科技发展的需求,而且有望为我国在纳米时代的国际竞争中实现跨越式发展提供支撑。本论文主要研究石英表面低损伤的摩擦诱导纳米加工方法。首先,石英屈服前摩擦表面可直接形成纳米凸起结构,据此提出石英表面摩擦诱导直接加工方法。凸结构机械性能与基体接近,但化学稳定性降低。为进一步减少加工损伤,根据摩擦区域石英材料可被KOH溶液选择性去除的现象,提出了石英表面摩擦诱导选择性刻蚀加工方法。研究表明摩擦化学作用可显著降低摩擦诱导加工损伤,改善所加工结构的性能。文中阐明了扫描参数(载荷、扫描次数、扫描速度)和刻蚀温度对所提摩擦诱导纳米加工的影响规律。通过透射电镜观测、X射线光电子能谱分析等手段,揭示了摩擦诱导纳米加工机理。为验证所提出的摩擦诱导选择性刻蚀机理和化学作用对加工损伤的影响,分别在玻璃表面和砷化镓表面进行了摩擦诱导纳米加工研究。主要研究内容和创新点如下：(1)揭示出石英表面摩擦诱导纳米凸结构的形成机理,提出了摩擦诱导直接加工方法。利用金刚石探针在单晶石英表面摩擦可直接加工纳米凸结构,凸结构形成的有效赫兹接触压力范围为0.4Py到Py(Py是石英屈服时对应的赫兹接触压力)。所加工纳米结构高度随扫描次数和扫描载荷的增加而增加并逐步平稳。X射线光电子能谱和透射电镜观测结果表明摩擦导致的晶格变形主导了凸起结构的形成。通过控制探针扫描轨迹,实现了纳米点、线、面等各种纳米结构的可控加工。尽管加工区域弹性模量比单晶基体下降了1.1-11.6%,但仍能承受微机电系统典型的接触压力。由于加工区域含有晶格缺陷,凸结构可被KOH溶液选择性去除。(2)阐明了石英摩擦诱导区域材料刻蚀去除的规律和机理,建立了摩擦诱导选择性刻蚀加工方法。结合无磨损扫描和KOH溶液刻蚀,提出摩擦诱导选择性刻蚀加工。详细研究了其加工规律,发现刻蚀厚度随扫描载荷和扫描次数的增加而增加,随扫描速度的增加而减小。提高刻蚀温度有利于提高加工效率,但不影响最终加工深度。透射电镜观测表明晶格畸变层不能够被KOH溶液刻蚀,结合非晶石英的对比刻蚀结果,选择性刻蚀加工机理可归因于摩擦诱导非晶层在KOH溶液中的快速化学反应。刻蚀动力学分析发现载荷不改变刻蚀反应活化能,其反应机制和刻蚀剂在扫描区域的优先扩散有关。通过优化扫描参数和刻蚀温度,实现了线阵列、斜面、多级台阶等图案的低损伤、高效率可控加工。所加工结构具有高度的化学稳定性,刻蚀后弹性模量比单晶石英基体下降了仅0.2-2.6%,该方法更适合于石英表面低损伤纳米加工。(3)验证了摩擦诱导选择性刻蚀机理和摩擦化学作用对低损伤加工的意义,分别提出了玻璃和砷化镓表面摩擦诱导纳米加工方法。X射线光电子能谱分析表明玻璃扫描区域被HF溶液刻蚀后形成难溶物AlF3,该结果不仅验证了摩擦诱导选择性刻蚀加工机理和反应机制,而且为玻璃表面摩擦诱导纳米加工方法提供理论依据。基于化学作用对低损伤加工的影响,利用摩擦化学在砷化镓表面实现了低损伤摩擦诱导纳米加工,加工所需接触压力仅为砷化镓屈服时接触压力的11%。高分辨透射电镜观测显示砷化镓加工区域下方无位错存在。综上所述,本文基于摩擦引起的石英表面结构变化及化学性质变化,提出了摩擦诱导直接加工和摩擦诱导选择性刻蚀加工方法。探索了玻璃、砷化镓表面摩擦诱导纳米加工,加深了对摩擦化学作用降低加工损伤的认识。本论文的研究结果不仅有助于丰富纳米摩擦学的基础理论,而且有望推动低损伤摩擦诱导加工在石英等材料纳米加工领域的应用。更多还原

【Abstract】 Nanotechnology is one of the most important research topics in the21st century, which has a profound influence on the development of human society. Nanofabrication method is the foundation of the transition from nanoscience and nanotechnology to application. As the device dimension down to nanoscale, the traditional nanofabrication technologies have met serious technical challenges, such as poor resolution, complex processes and fabrication destruction etc. Researches on nanofabrication methods can not only meet the requirements of the nanotechnology, but also facilitate the great-leap-forward development of China in the violent international competition.In this doctoral thesis, low-destructive friction-induced nanofabrication methods on quartz are proposed. Firstly, hillock nano structures can be directly fabricated by scratching a diamond tip at the target area before the yield of quartz. The mechanical performance of the hillock is similar to the quartz substrate, but the chemical stability is weaker. To further reduce the fabrication destruction, friction-induced selective etching is developed by combination of the wearless scanning the quartz surface and selective etching the sample in KOH. The effects of the scan parameters and etching temperature on the fabrication are studied thoroughly. The fabrication mechanism is analyzed by transmission electron microscope observation, X-ray photoelectron spectroscope analysis and etc. Results show that the chemical etching can improve the fabrication quality. Finally, to discuss the mechanism of friction-induced selective etching and the role of chemistry in the low-destructive fabrication, the friction-induced nanofabrication is also practiced on glass and GaAs. The main contents of thesis are shown in follows.(1) Based on the clarification of the formation mechanism of friction-induced hillocks on quartz surface, the direct friction-induced nanofabrication on quartz is proposed.The protrusive nanostructures can be produced by sliding a diamond tip on quartz when the contact pressure is ranged from0.4Py to Py (Py is the critical yield pressure of quartz). The height of these nanostructures increases with the increase of the number of scratching cycles or the normal load. X-ray photoelectron spectroscopy and transmission electron microscope observation indicates that the mechanical interaction playes a dominating role during the fabrication. Various nanostructures such as nanodots, nanolines, surface mesas and nanowords can be fabricated by programming the tip traces according to the demanded patterns. Although the protrusive nanostructures exhibit a slightly lower elastic modulus than quartz substrate (decreased by1.1-11.6%), they can resist the typical contact pressure in MEMS. Such nanostructures can be selectively dissolved in20%KOH solution, which can provide an erasing technique for this method.(2) The fabrication rules and mechanism of the selective etching on scanned quartz surface are revealed, and the friction-induced selective etching on quartz surface is proposed.Nanofabrication on quartz can also be achieved by wearless scanning on a target area and post-etching in a KOH solution. The etching thickness on the wearless scan area increases with the increase of the scan load and scan cycles but decreases with the scan speed. Higher etching temperature below318K can improve the fabrication efficiency and does not change the final fabrication depth. Transmission electron microscope observation shows that the distorted lattice can not be etched by KOH. Combinning with the contradistinctive etching experiments, the fabrication mechanism could be summarized as the selective etching of friction-induced amorphous layer on fabrication surface. Chemical kinetics analysis shows that the dependence of the etching rate on the contact pressure should be mainly attributed to the variation of frequency factor and the concentration of reactants, rather than the decrease of the activation energy. The reaction pathway may be related to the preferential diffusion of solutes into the fabrication area. By optimizing the scan parameters and etching temperature, various nanostructures including line arrays, slops, hierarchical stages can be fabricated on quartz surface in a low-destruction and high efficiency way. These nanostructures have a stronger chemical stability and a better mechanical performance (the elastic modulus is only0.2-2.6%lower than the substrate). This means that the selective etching can reduce the fabrication destruction in higher level.(3) To further understand the friction-induced selective etching and the role of chemistry in the low-destructive fabrication, friction-induced nanofabrication is practiced on glass and GaAs.X-ray photoelectron spectroscopy shows that the fluorine species can preferentially diffuse into the scan area on glass and form AIF3. Such insoluble AIF3acts as a mask layer to prevent the etching of glass and then the protrusive nanostructures are formed on the fabrication area after HF etching. Therefore, the friction-induced selective etching is further verified and a maskless nanofabrication on glass is proposed. Another low-destructive method is attempted for fabricating "defect free" nanofabrication on GaAs based on the tribochemical reaction. Tribochemical reaction facilitates the removal of GaAs material when the contact pressure was only11%of the critical yield pressure of GaAs. Transmission electron microscope observation shows that there is no lattice damage beneath the fabrication area.In brief, based on the friction-induced structural and chemical modification, low-destructive nanofabrication methods are developed on quartz. The friction-induced nanofabrication of glass and GaAs deepens the understanding of the involved mechanism. The results in this thesis can not only enrich the nanotribology theory, but also encourage the application of the low-destructive friction-induced nanofabrication on quartz and other materials.更多还原