具有周期性褶皱的石墨烯的构筑及其在力学传感中的应用探索

Graphene, which is not attached to any substrate, are thermodynamically unstable. Wrinkling or folding in the third dimension of graphene leads to an increase in elastic energy but minimizes the total free energy which enables the stable existence of graphene. Wrinkled graphene have unique tip structure and properties. It has a broad application prospects in the field of sensors, electron emission, etc, where a conducive tip structures are required. At present, the wrinkled graphene can be fabricated based on the previously prepared substrate with a special microstructure, but the relationship between the wrinkled structures and the properties of graphene, and the formation mechanism of wrinkles in graphene need to be further revealed. The height, shape and distribution of the wrinkles in graphene cannot be precisely controlled. At present, we can fabricate wrinkled graphene using a liquid-phase assembly method. In this research proposal, we propose to control the formation of wrinkled graphene with periodic folds using the liquid-phase interface assembly method. This project will achieve the precise control of the height, distribution and the formation location of the wrinkles in graphene, and the transfer of wrinkled graphene to different target substrate. This project also could analyze the effect of the wrinkled structures on the properties of graphene. Through physical modeling and theoretical calculation, we will reveal the mechanism and key factors for the forming ordered wrinkles in graphene based on liquid-phase method. This fabrication method could be a universal method, which can be used to prepare of periodic wrinkle structure for other two-dimensional materials. Furthermore, we will construct a piezoresistive mechanical sensor based on the wrinkled graphene with periodic folds. We will examine the effect of the graphene tip structures and wrinkles distribution on the performance of the sensor, thus revealing the physical properties of wrinkled graphene in the deformed state.

不依附于衬底的石墨烯容易在第三维度上起伏，而形成褶皱状结构。褶皱状石墨烯具有独特的尖锥结构和物性，使其在传感、电子发射等需要导电尖端的应用领域大有作为。目前虽然基于预先制备的具有特殊结构的衬底，能够组装出褶皱状石墨烯。但是褶皱结构与物性之间的关系、褶皱的形成机理有待进一步揭示。石墨烯中褶皱的高度、形成位置和分布有待精确控制。本项目拟在前期可控制备褶皱状石墨烯的基础上，实现基于液相界面组装具有周期性褶皱的石墨烯，实现对褶皱的高度、分布和形成位置可控，并可转移至不同目标衬底。分析褶皱结构对石墨烯物性的影响规律。通过物理建模和理论计算，从本质上揭示基于液相界面，石墨烯中形成有序褶皱结构的机制和关键因素，为其它二维材料制备出周期性褶皱结构提供一个普适方法。进一步，基于具有周期性尖锥结构的褶皱状石墨烯，构建压阻式力学传感器，探索尖锥结构及分布对传感器的性能的影响，揭示形变状态下褶皱状石墨烯的物性。

石墨烯具有独特的结构和优异的性能。在石墨烯中形成褶皱结构,将赋予其新的特性。褶皱状石墨烯中独特的尖锥结构，使其在可穿戴电子器件、柔性传感器件和环境监测等领域具有应用潜力。本项目提出了一种操作简易、有效和环境友好的制备褶皱状石墨烯的方法。该方法基于液/气界面，在溶液表面张力的作用下，使石墨烯自组装成褶皱状石墨烯。该自组装过程不依赖于生长基底或目标基底的形貌。通过将液/气界面上的石墨烯薄膜转移至预拉伸的聚合物基底上，实现了具有周期性褶皱结构的石墨烯薄膜的制备。项目深入研究了溶液浓度、溶液种类和溶液温度等工艺参数对褶皱状石墨烯中褶皱的高度以及表面粗糙度（RMS）的影响。结果表明，通过调控这些工艺参数，可以实现对褶皱的高度在20-300nm范围内，及褶皱的RMS在8-50nm范围内的调控；通过改变褶皱状石墨烯中褶皱结构的分布可以调控薄膜的光学和电学性能。此外，根据实验结果和理论分析，发现褶皱状石墨烯自组装形成的主要原因：一是表面张力变化引起的界面扰动；二是有机溶剂挥发使溶液的上下液面存在温度梯度，从而导致在竖直方向上形成的Rayleigh-Bénard对流。项目基于褶皱状石墨烯，构建了应变传感器。该传感器具有灵敏度高、稳定性好、可重复性高等特点。其可以检测大范围（50 %）和微小的应变（<1 %），灵敏度系数最高达348.6。其性能在循环拉伸5000次后仍保持稳定。项目以双层周期性褶皱状石墨烯薄膜为例，系统研究了拉伸过程中褶皱状石墨烯薄膜的形貌变化，分析了上下层薄膜中褶皱在拉伸过程中的变化及裂痕的形成。本项目开发的褶皱状石墨烯的制备和应用，也为其他二维材料，如过渡金属碳氮化合物（MXenes）和过渡金属硫族化合物（TMDs）等微结构的构筑、性质研究和实际应用提供了新的思路和途径。