基于氧化还原功能性纳米膜的电化学纳米加工研究

In order to meet the demand for large-scale planarization and complex 3-dimensional nano-structure at nano-precision, this project proposes to develop a new nano-machining method from the principle innovation. A new strategy for electrochemical nano-machining will be taken by fabricating (or modifying) a redox functional nano-film on the tool-electrode (mold electrode). In the case of its uniform thickness, the redox film surface is able to reflect the nano-structure of the electrode surface at a high resolution. When such a film is used as a middle layer between the tool-electrode and the workpiece, a high-precision interval will be easily achieved and/or controlled. Moreover, the unique electron-hopping transfer of the redox film will prevent the electrochemically anodic oxidation of the workpiece that indirectly links with electrochemical workstation. It is also duo to electron-hopping transfer that all of functional groups within the film can take part in the electrochemically reversible reaction. After being electrochemically oxidized, the functional groups chemically oxidize the workpiece only at the point where they are touching. The chemical etch thus is confined at nano-precision and finally results in a fully complementary surface between the tool-electrode and the workpiece. This project plans to systematically study on several key issues, including the accurate fabrication of the redox functional nano-film, the precision control of the interval between the tool-electrode and the workpiece, the physical chemistry behavior of the redox functional nano-film within the interval, etc. It is expected to clarify both the physical chemistry reaction process of the confined etch and the formation mechanism of the high quality surface, to find the key factors for the nano-machining efficiency and the surface quality,to establish the new electrochemical nano-machining means, and to provide the advanced theory and technology for high-precision nano-machining.

为满足未来对纳米精度大面积平坦化和复杂三维纳米结构的批量加工需求，本项目拟从原理创新发展电化学纳米加工方法。拟采取的策略是在工具(模板)电极表面制备一层氧化还原功能性纳米膜。均一的膜厚既能使膜面反映出电极表面纳米结构，又易使工具和工件间形成高精度间隔；氧化还原膜独特的电子传导方式，既能防止通过膜层间接接入电化学系统的工件发生电化学阳极氧化，又能使膜上所有功能基团被电化学氧化还原；电化学氧化后的基团仅能化学氧化与之接触的工件表面，实现高精度约束刻蚀，以纳米精度将电极表面结构加工复制在工件表面。本项目拟通过对大面积氧化还原纳米膜的精确制备、固-固表面纳米间隙的精密控制，以及间隙内氧化还原纳米膜的物理化学行为等关键理论问题开展系统研究，阐明约束刻蚀加工的物理化学反应过程和高精度高质量表面的形成机理，弄清影响纳米加工效率、表面质量的关键因素，建立可控的加工方法，为高精度纳米加工提供先进理论与技术。

本课题从原理创新发展了一种电化学与化学相结合距离敏感的刻蚀方法，能够实现大面积的纳米加工，并可避免现有纳米加工技术的局限和缺陷。方法要点是在模板电极表面电化学产生的刻蚀剂扩散至工件表面并化学刻蚀之；实现距离敏感的前提是刻蚀剂扩散是整个加工过程的决速步。采用氧化还原水合凝胶膜作为刻蚀剂/前驱体是简单可行的方案，因电子以跳迁方式在锚定于膜内的氧化还原基团间慢速传导；仅靠模板电极自重和软质水合膜就可在模板电极和工件表面间形成高平行度的微/纳间隙。 .通过机械研磨和旋涂热解光刻胶制出了多尺度(Φ6-50.8 mm)的表面均为三维曲面纳米结构的碳模板电极。采用电化学聚合和旋涂成膜，在模板电极表面形成厚度可控的([Ru(bpy)2(vpy)2]2+)n和([Ru(bpy)2(PVP)5Cl]+)n两种水合凝胶薄膜；其在0.2 M H2SO4工作溶液中的电子扩散系数(D)在10E-10 cm/s 量级比自由扩散小四个量级。实验结果证明：采用两种膜在高电位(+1.0 - +1.4 V vs. SCE)下加工铜工件，极限刻蚀电流密度(Ilim)均与膜厚(A)成反比关系，符合Ilim = nFDC/A；刻蚀能以约1.2 nm/min的速度和4 nm的精度在铜工件表面加工出与模板电极表面三维曲面完全互补的结构。高质表面的形成机理是工件表面各点的刻蚀速度与各点到模板电极表面的最短距离成反比，将使各点的最短距离最终达等同。由于提高刻蚀电位不会增加电极边缘区域Ilim，增加的槽压将消除膜的侧向电阻引起的电极中心区域的电场屏蔽现象，因此有效加工面积可达Φ 50.8 mm。刻蚀产物是影响表面质量的关键因素，原因是形成的Cu2+ ·5H2O被电迁移至膜外消耗膜内水，并且Cu2+也可刻蚀铜工件生成Cu+，形成与氧化还原膜并行作用的刻蚀体系。采用持续的恒电位刻蚀方法将因缺水而使刻面粗糙且无法进行，只有采用循环电位刻蚀方法利用膜氧化还原时SO42电迁移带水入膜，或采用微流控方法供给膜内水方可使大面积的刻蚀加工持续。在工件和模板电极间隙被完全填满氧化还原水凝胶膜后，此方法可以进行大面积(Φ50.8 mm)平面、曲面和三维浅浮雕的纳米加工；对刻蚀产物不与工件发生反应的体系可加工高深宽比的三维纳米结构。