Precise Control And Property Investigation Of Graphene Layers Via Soft Plasma Technology

Graphene is a kind of two-dimensional crystal materials formed by sp~2 hybridized carbon atoms with a hexagonal honeycomb structure.This stable hexagonal structure makes it exhibit excellent electronic,optical and physical properties.Graphene has drawn great attention from both academia and industry since its discovery by Geim and Novoselov at the University of Manchester in England.Due to its unique properties,graphene shows great application potential in many fields,and may bring revolutionary effects on composites,microelectronics,energy storage industry,aerospace,and so on.Therefore,the fabrication and application of graphene have become one of the hottest research topics at present.Through continuous efforts and explorations,people have mastered several different methods to produce graphene and developed a deep understanding to the properties and applications of graphene.However,these preparation methods still remain imperfect,and thus restrict the rapid development of graphene industry.In this thesis,we report a simple and fast way to realize precise control of graphene layers and simultaneously obtain high quality monolayer or few-layer graphene samples based on a self-developed capacitively coupled electrodeless plasma(CCEP)technology.The theory and principle of the experiments are also analyzed.The main research content is summarized as follows.Firstly,we introduce several preparation methods of graphene currently used in laboratories and industry and discuss their advantages and disadvantages.Then we give a brief introduction to the unique properties and applications of graphene,as well as several methods of determining graphene layers.Particularly,the plasma discharge principle and a new soft plasma technology namely CCEP developed by our lab are introduced in details.Secondly,we use the soft plasma in the capacitive mode to etch the multilayer graphene samples.The results show that the soft plasma can effectively remove the top graphene due to the ion bombardment effect,and the etching process has good anisotropy.The number of graphene layers after etching is significantly reduced.The plasma power density,precursor gases and their flow ratios,etching time and other parameters can influence the experimental results.Therefore,the rapid etching and the slow-but-accurate etching of graphene materials can be achieved by controlling the precursor gases and plasma power density.Finally,we find that the lattice of graphene is kind of destroyed with defect generation during the plasma etching process by comparing the Raman characterization of the samples before and after plasma treatment.It is found that the high temperature post annealing under a nitrogen atmosphere can effectively repair the lattice defects produced during the etching process.High quality monolayer and few-layer graphene samples can be obtained after repairing.This work provides a new simple and reliable method for preparing high quality monolayer and few-layer graphene materials.