石墨烯薄膜的表面粘着特性调控与磨损机制

There are two main classes of MEMS devices: sensors and actuators.Sensors-based MEMS have only sensing elements, whereas the actuators-based MEMS have elements that undergo relative mechanical motion. Sensors-based MEMS devices are already commercialized. However, the actuators-based MEMS have not been commercialized yet, due to the fact that there is no robust lubrication solutions at microscale to solve adhesion,friction and wear issues of MEMS to assure the devices operated smoothly and reliably. In the past decades,many efforts have been done to develop solutions to restrict the adhesion, to reduce the friction, and to prolong the wear durability of MEMS elements.For examples, self-assembled monolayers of organic molecules,diamond like carbon thin films fabricated via physical and chemical vapor deposition, or high voltage decomposition of organic compounds,have been investigated extensively, however,owing to their inherent shortcomings or the fabrication process is not compatible with microelectron fabrication processes,they could not satisfy the demands of MEMS. Based on the above analyses, we think the graphene-based thin films fabricated via electrophoresis could be considered as solid lubricant for MEMS since the electrophoresis is compatible with microelectron fabrication processes,the surface chemistry could be controlled according to the chemical modification,and the carbon thin films inherently possess low friction and low wear.In this study,the target is to probe the surface adhesion and wear mechanism of graphene thin films, including to make the graphene to be charged through surface chemical modification,then to be deposited to thin films via electrophoresis; to investigate the correlation between surface chemistry and adhesion characters of graphene thin films,to examine the friction and wear properties of the graphene thin films,to probe the evolution of the graphene layers during the friction process, to understand the wear mechanism of the graphene thin films, so as to construct graphene thin films with low adhesion, low friction and long wear resistance.

针对MEMS存在的表面粘着与摩擦磨损问题，分析多年来在有机分子自组装薄膜、气相沉积类金刚石薄膜、液相高电压解离沉积类金刚石薄膜等的研究进展和存在缺点，提出液相电泳沉积石墨烯类薄膜有望成为MEMS良好的固体润滑薄膜，解决其粘着与摩擦磨损问题。申请项目拟开展石墨烯基薄膜的表面粘着特性与磨损机制研究，通过表面化学修饰或掺杂使石墨烯表面带电荷，利用电泳方法沉积制备石墨烯基薄膜，研究薄膜表面特性与其粘着特性的关系，考察石墨烯表面化学特性对其摩擦磨损性能的影响规律，揭示石墨烯在摩擦过程中的结构演变，深入认识其摩擦磨损机制，建立低粘着、低摩擦、耐磨损石墨烯固体润滑薄膜制备方法。

特征尺寸在微/纳米的微电子机械系统（MEMS/NEMS）由于具备尺寸微型化、功能集成化等优点，已经成为近几十年的一个重要发展方向。但是由于MEMS/NEMS尺寸很小，粘着和磨损问题已经成为其广泛应用的最大挑战。在过去的几十年中，分子自组装膜（SAMs）和类金刚石碳（DLC）薄膜曾被广泛研究，期望用来解决这些问题，石墨烯由于具备优异的摩擦学性能，被认为是最薄的固体润滑薄膜。但是，传统的气相沉积法制备的石墨烯薄膜不仅成本昂贵，而且面临膜的转移等难题。针对以上问题，本项目开展了一系列的研究工作，主要研究内容和结果如下：.1.利用氧化石墨烯（GO）在水介质中能形成带负电荷的稳定胶体溶液这一本征特性，运用阳极电泳沉积法（EPD）直接在硅基底上制备出纳米级厚度可控的氧化石墨烯薄膜（GOF）。研究结果表明，GOF的厚度可以通过调节电泳电压进行精确控制（如50~400nm）；GOF具有优异的力学性能和摩擦学性能，可有效降低硅材料表面的摩擦系数（从0.31降低到0.05）和磨损体积（从8.32×10-13m3降低到3.38×10-14m3），显著提高硅的磨损寿命。.2.探索出了分析和研究氧化石墨烯薄膜上不同种类含氧官能团的实验方法，揭示了氧化石墨烯薄膜含氧官能团种类和其摩擦学性能之间的相关性规律。.3.基于GOF的制备原理，将EPD技术拓展到多种杂原子（如H, Cl, F, N, S等）掺杂的有机羧酸分子（CAM）薄膜的制备。重点研究了氟元素的引入对CAM薄膜形貌、表面性质、抗湿特性、力学和摩擦学性能的影响；与SAMs相比，氟取代的三氟乙酸分子膜具有较低的摩擦系数（0.047 vs.0.12）和粘着力（5.3nN vs.16nN），可显著提高硅材料的磨损寿命（>466min）和抗湿能力。.4.通过研究电泳沉积的三氯乙酸分子膜退火前后的表面形貌、微观结构和结晶状态的变化，证明经过简单的退火处理可将有机分子膜转变为厚度可控的碳膜。与退火前的三氯乙酸分子膜相比，转变成的碳膜不仅与硅基底有更强的结合力（从2.7N提高到了7.6N），而且表现出更低的摩擦系数（从0.116降低到0.052）、更低的磨损率（从5.48×10-4mm3/Nm降低到2.17×10-4mm3/Nm）及更长的磨损寿命（从85min增长到175min）。