利用PECVD法“缝合”石墨烯晶界及其薄膜的光电性能研究

The scattering of charge carriers at the graphene grain boundaries (BGs) is one of the major factors that lowers the charge mobilities in a graphene-based transparent conductive films (TCFs). The charge scattering is inevitable in a graphene-based TCF fabricated by existing methods (solution process and CVD-transfer process). In the graphene-based TCFs a big number of BGs are randomly distributed leading to reduction of optical transparency and electrical conductivity. To this respect, this project proposes that stitching the graphene grains using plasma-enhanced chemical vapor deposition (PECVD), which covalently bonds the adjacent or overlapping graphene nanosheets via C-C. The plasma physics and chemistry are diagnosed using optical emission spectroscopy. The atoms, bonds, and nucleation are studied using advanced techniques such as high-resolution electron microscopy. Based on the gas-solid physical picture of the interaction between plasma and graphene, a kinetic model of the reactions is established, and the stitching method is eventually controllable. Transistors based on the stitched graphene films are fabricated and characterized. Combined with the study of Hall mobility, the charge transport properties are investigated. This project reveals the mechanism of improvement on the optoelectronic performance of the stitched thin films. The results will provide new route and model for fabrication of high-quality TCFs.

电荷在石墨烯晶界处的散射一直以来是影响石墨烯薄膜透光率和载流子迁移率的主要因素之一。目前采用溶液法、CVD-转移法等方法制备的石墨烯透明导电薄膜都不可避免地包含有大量的晶界，导致薄膜的透光率和电性能明显下降。为了解决这一问题，本项目提出利用等离子增强化学气相沉积（PECVD）法“缝合”石墨烯的晶界，即通过C-C共价键的方式将相邻或交叠的石墨烯片连接起来，提高薄膜的光学和电学性能。通过光学发射光谱等等离子体诊断手段和高分辨电镜等表征技术，研究等离子体的物理化学特性及其对石墨烯晶界的原子、化学键、成核等因素的影响，描绘等离子体与石墨烯的“气相-固相”相互作用的物理图像，建立反应动力学模型，实现石墨烯晶界“缝合”的可控性；通过研究薄膜的晶体管特性和Hall迁移率，研究载流子在“缝合”石墨烯薄膜中的输运特性，揭示“缝合”方法提高薄膜光电性能的物理机制，为制备高效透明导电薄膜提供新的思路和理论模型。

湿法制备石墨烯薄膜是获得石墨烯薄膜的一种重要途径，即通过旋涂、喷涂、点涂等技术制备氧化石墨烯（GO）的薄膜，再经过还原得到还原氧化石墨烯（RGO）薄膜。但是湿法制得的RGO薄膜通常包含大量的结构缺陷，其电学性能很差，远未达到很多实际应用的要求。因此有研究者提出，如果修复或减少RGO薄膜中的缺陷，就可以提高其石墨烯薄膜的导电性。.本项目采用等离子增强化学气相沉积（PECVD）技术对RGO进行修复，对其中的科学问题开展了一系列研究工作：.一，用密度泛函理论DFT计算，研究了等离子体修复RGO的最佳动力学通道；.二，研究了温度和氢气对RGO修复的作用，证明了氢气去除无定形碳的作用，和温度作为影响修复-刻蚀反应平衡的动力学因子；.三，研究了压强对RGO修复的作用，揭示了压强作为修复-刻蚀竞争性平衡的动力学影响因子；.四，研究了对RGO修复和刻蚀之后，其电学性质和光学性质的变化；.五，以优化的参数在单模石英光纤端面直接生长石墨烯薄膜，并研究了其可饱和吸收特性和超快激光脉冲的产生。.项目发表SCI论文9篇，授权发明专利2项，研究成果多次在学术会议中演讲报告。