石墨烯基杂化复合材料的可控制备及其场发射增强机制研究

Since graphene was obtained by Geim and Novoselov using a mechanical exfoliation method in 2004, graphene is expected to be a new generation of field emission cathode materials, due to its extremely high electronic mobility, highest theoretical specific surface area, excellent thermodynamic stability, and great elasticity. Carbon nanotubes have potential advantages as the electron emitting sources. Moreover，in graphene nanosheet, a strong direction-dependent electrical transport property with extremely low out-of-plane conductivity as a result of the presence of strong covalent bond in the carbon plane and the much weaker van der Waals interaction between the layers. Therefore, the electron emission is mostly from the edges of graphene, which implies the emission current can be improved by changing the morphology and microstructure of graphene to increase the emission sites. And，graphene nanosheets are expected as the promising candidate for large-area field emitters free from Joule heating, due to the high aspect ratio and high in-plane continuity of the wall structures. In this work, we considered from three aspects to improve the field emission properties of cathode materials. First is how to decrease the contact resistance between substrate and cathode material. Second is how to decrease the contact resistance between the unit materials in cathode material. Third is how to optimize the size and growth density of emission sites. Then, we will synthesize graphene nanosheets-CNTs-graphene hybrid composites by using Co as the catalyst via RF-PECVD method. Co has the same work function of carbon (5eV) that can reduce the contact resistance between Co and CNTs（graphene or graphene nanosheets）. We will try to reveal the growth mechanism experimentally and theoretically, and we will find the influence factors on improving the field emission properties of this hybrid composite. This investigation will make a contribution to the practical application of graphene based field emission cathode materials.

自石墨烯被发现以来，越来越多的科研工作者致力于石墨烯基材料的制备和性能开发。石墨烯极高的电子迁移率、极大的比表面积、良好的导热性等，使其有望成为新一代的场发射阴极材料。由于碳纳米管大的长径比，优异的导电和导热性，在场发射领域具有潜在的发展优势；石墨烯片中电子的传输具有方向性，且大的比表面积可以提高散热面积，将石墨烯与碳纳米管复合，可以减弱场发射时碳纳米管尖端所受的焦耳热损坏作用。本项目从降低基底与阴极材料、阴极材料各组元间的接触电阻和优化场发射尖端尺寸及生长密度三方面考虑，拟采用射频等离子体增强化学气相沉积法，以与碳具有相同功函数的金属钴为催化剂将碳纳米管根部与石墨烯、碳纳米管顶端与石墨烯片杂化复合，制备具有优良场发射性能的石墨烯片-碳纳米管-石墨烯杂化复合材料；揭示生长机理；探讨场发射增强机制。为石墨烯基场发射阴极材料的实际应用做出贡献。

石墨烯特殊的结构和优异的物理性能，使石墨烯及石墨烯基复合材料在电子及光电子器件和能量储存器件等领域具有广泛的应用前景。目前，虽然在理论和实验上石墨烯基复合材料在场发射方面的相关研究已经有了很大的进步，然而，如何对石墨烯的结构进行调制，从而进一步开发或提高石墨烯基复合材料的性能仍然待于探讨和研究。本项目主要采用等离子体增强化学气相沉积方法，制备了石墨烯-镍和石墨烯-钴杂化复合材料，并探究了杂化复合材料结构、形貌、生长机理及场发射增强机制。在此基础上，我们研究了石墨烯-碳纳米管杂化复合材料及铜修饰的石墨烯-碳纳米管杂化复合材料的场发射性能。我们重点分析了这些复合材料的结构特性对场发射性能的影响，获得了通过构筑多种杂化结构提高场发射性能的有效方法，本项目将为新型石墨烯基复合材料在场发射方面的应用提供新的思路和指导。此外，利用等离子体增强化学气相沉积及电化学沉积相结合的方法，优化了氢氧化钴/石墨烯片正极电极材料，构建了新型的、具有更高能量密度的非对称式超级电容器，本部分工作将为石墨烯基复合电极材料在超高性能超级电容器方面的应用提供了一种简便有效的方法。