# Study of Implantation Defects in CVD Graphene by Optical and Electrical Methods
## 1 Introduction  
Ion implantation is a useful tool for changing graphene parameters. Examples of usefulness of ion implantation are modification of graphene electrochemical activity [1] or production of nano-sieves for water desalination [2]. The principal effect of the ion implantation is generation of crystal lattice disorder, which is connected with modification of the hexagonal carbon sp\({}^{2}\) structure. In the most cases graphene, which have been used for implantation experiments was grown on Cu and later transferred on glass [3]. Such graphene already contains of many defects connected with growth and transfer process.  
It is known that the best epitaxial graphene is obtained on SiC (0001) [4; 5]. However, the epitaxial growth of graphene on SiC (0001) substrates is connected with the formation of a buffer layer [6; 7]. The buffer layer comprised carbon atoms that are covalently bonded to the underlying SiC substrate and does not show graphitic electronic properties [6; 7]. The electronically inactive reconstructed buffer layer on SiC (0001) may be converted into quasi-free-standing monolayer graphene after hydrogen intercalation [8]. It was demonstrated that hydrogen can migrate underneath epitaxial graphene and the interface layer, bind to the Si atoms of the SiC (0001) surface and decouple epitaxial graphene from its substrate. Intercalation of hydrogen atoms below the buffer layer forms weakly coupled bilayer graphene, leading to a completely sp\({}^{2}\) hybridized graphene layers with improved electronic properties.  
It was found that after intercalation by hydrogen graphene layer become p-type [8]. The hydrogen intercalation opened up the possibility to produce quasi-free-standing epitaxial graphene on large SiC wafers. Such quasi-free-standing graphene was used in our implantation experiments. Using such graphene increase probability that defects present in it are generated by ion implantation, and allows to connect electrical measurements with optical ones.  
Several experimental observations of defects induced in graphene by ion and electron irradiation show that defects consisting of different polygons may be formed under energetic particles bombardment [9; 10; 11; 12; 13]. Presented in [11; 12; 13] experimentally observed atomic configurations of the induced defects have areas essentially larger than vacancy or even divacancy, showing that even such large structures of the defects are possible.  
However, defects generated by ion implantation have to modify the electrical properties of graphene as well. In this work, Raman spectroscopy was used to define the carrier concentrations [14] and confronted with the results of electrical measurements. It was already reported that the Raman spectroscopy is a useful tool for investigation of ion beam induced defects in graphene [3]. The most important parameter that connects defects generated by ion implantation with electrical properties of graphene is carrier mobility. The main motivation of this work is to connect density of defects generated by ion implantation with electrical properties of the defected graphene.