曲率诱导的微纳米表面形貌演化机理研究

A large amount of experimental phenomena at micro/nano scales reveal that surface morphology evolution caused by diffusion and adsorption has a close relation with curvature. Studying the mechanism of inner relation has an important theoretical significance in micro/nano fabrication technology. Applicant abstracts surface diffusion as curved surface body/on surface particle model, and abstracts surface absorption as curved surface body/an outside particle model. Based on differential geometry, the terms of curvatures are substituted into diffusion equations and the controlling mechanism of curvatures on micro/nano surface morphology evolution is built theoretically. Innovation point is that curvature invariants are imported into the surface evolution equations based on fundamental assumptions at micro/nano scales and the geometrization of evolution dynamics is realized. The main research contents are as follows: Based on curved surface body/on surface particle model, the curvature based surface tension and chemical potential are derived. The effect of curvatures on diffusion direction and speed is studied by solving curvature based surface diffusion equations. Based on curved surface body/ an outside particle model, the chemical potential outside body is derived as a function of curvatures, the relation between curvatures and moving direction as well as critical temperature of adsorption are built. The model of evolution dynamics of high temperature oxidation problem is built. Molecular simulation method is used to confirm the reliability of theory. Through these studies, the geometry induced mechanism of surface evolution is built and its applications in MEMS/NEMS are forecasted theoretically.

微纳米尺度大量实验现象表明扩散、吸附引起的表面形貌演化与曲率之间有着密切的关联，澄清其内在机理对于微纳米制造技术有着重要意义。本项目将表面扩散抽象为“曲面体/体上粒子”模型，将表面吸附抽象为“曲面体/体外粒子”模型，结合微分几何，将曲率项引入扩散演化方程，从理论上建立曲率对表面微纳米形貌演化的调控机理。创新点在于基于微纳米尺度的基本假设，将曲率不变量引入演化方程，实现微纳米演化动力学的几何化。主要研究内容有：基于“曲面体/体上粒子”模型，推导曲率化的表面张力及化学势，代入表面扩散方程，研究曲率对扩散方向、速率的影响；基于“曲面体/体外粒子”模型，推导曲率化的体外化学势，研究曲率与运动方向、吸附临界温度之间的关系；建立高温氧化的表面演化动力学模型；结合分子动力学模拟方法，验证理论的可靠性。通过这些研究，建立微纳米尺度表面形貌演化的几何驱动机制，为MEMS/NEMS技术提供理论指导。

本项目以微纳米尺度的反常演化现象为背景，以粒子间的短程相互作用为物理基础，以微分几何刻画卷曲空间形式，研究了曲率对粒子吸附、表面扩散的作用机理。取得了如下标志性成果：.1、基于粒子间短程作用对势，证实高度弯曲微纳米表面的表面能是曲率的函数，将表面能的尺度效应与几何内秉参数相关联，并研究了曲面体/体外粒子与曲面体/表面粒子间的作用势，证实曲率诱导的反常驱动力，是导致高度卷曲曲面体外粒子吸附与表面扩散反常现象的本质原因；该结果为揭示微纳尺度表面吸附、扩散现象的尺度效应提供了理论解释，为建立小尺度的本构模型提供了修正。.2、实现了任意曲面间的范德华相互作用势的曲率化，通过分析碳管/碳管、椭球颗粒/平面、球形分子/波浪状表面之间的相互作用，解释了相关实验中观察到的现象，为研究微尺度的表面演化、相分离等现象提供了理论模型；.3、通过分子动力学模拟与理论推导，证实微纳米波动表面上存在着一种反常运动现象-速度锁定效应，解释了微尺度表面上的高速扩散现象，为设计微通道的高速输运提供了一种新思路。.4、与德国亥姆霍兹研究所合作，从理论与实验两个方面证实了受限纳米空间中非极性分子的取向性排列与压强之间的关系，为纳米尺度调控结晶化提供了一种新方法。.5、本项目注重多学科交叉研究，通过多尺度本构建模的交叉研究，建立了新型智能聚合物材料的本构模型，成功刻画了光弹力本构关系，并实现控振等工程应用。