Graphene Synthesis By Ion Implantation Technique

Graphene is a two-dimensional single layer of sp2carbon atoms bound in hexagonal honeycomb lattice crystalline. It has excellent electrical and optical physics properties due to its unique band structure. In order to take advantage of graphene, it is necessary to develop various methods for the growth of high quality graphene films over large areas. The typical methods include mechanical exfoliating highly oriented pyrolytic graphene (HOPG), thermal decomposition of SiC, chemical vapor deposition (CVD), reduction of graphite oxide, pulsed laser deposition (PLD) and unzipping the carbon nano tube (CNT), et. al. All of them have pros and cons. We tried to use ion implantation method for synthetic graphene. The ion implantation has some special characters for the growth of graphene:i) Ion implantation is a non-equilibrium process without limitation of solid solubility. ii) The amount of doped atoms is controlled by ion current integration with the level of accuracy error less than2%. iii) The depth distribution of the doped atoms is adjusted by the implanted ion energy. iv) The uniformity deviation of ion implanted doping can be better than2%after an accurate X-Y scanning.v) Ion implantation is a direct doping process, it is not necessary to decompose the carbon gaseous precursor for graphene as in CVD method. vi) Ion implantation as a mature technique in large scale integrated circuit (IC) production. If ion implantation synthesis of large area graphene is successful, then the graphene-based nano-device or hybrid device formation will be compatible with existing IC production techniques based on Si technology. In the present dissertation, we focused on a series of investigation on graphene synthesis by ion implantation method. The dissertation is divided into three parts:Part One, introduction of graphene-its theory and application; Part Two, introduction of ion implantation technology and its application for synthesis of graphene; Part Three, graphene synthesis by ion beam implantation, which gives the innovating work in this dissertation in details. Part One and Part Two are separate single chapters. The Part Three alone decomposes into three sub-chapters.1) Graphene synthesis with low defects:After the modification and improvement of low energy injector of Tandetron tandem accelerator, the negative cluster ion beams were extracted and implanted into Ni films covered on SiO2. Subsequently, graphene synthesized on Ni films upon annealing process. Combined with the low energy and nonlinear damage effect, the graphene layer by cluster ion implantation shows lower defects than that by monomer ion implantation.2) Direct graphene synthesis on insulators:A series of doses of monomer carbon ions were implanted into Ni films on SiO2substrate with optimal annealing condition and thickness of Ni films. Graphene formed between Ni films and substrates besides on Ni surface. The graphene films on the Ni films were etched by oxygen plasma, followed by aqueous HC1solution for etching Ni films. The graphene direct growth on SiO2was confirmed. This method provides an approach for direct graphene synthesis on insulating substrates, avoiding any transferring process.3) Epitaxial growth of graphene on6H-SiC substrates at lower temperature:Taking advantage of radiation damages on specimens in ion implantation, several ion species, such as carbon monomer and cluster ions, Ar and Si ions were implanted into single-crystal C-face6H-SiC substrates at room temperature. After high temperature annealing process in Ar atmosphere, epitaxial graphene formed on implanted SiC substrates at a decreasing temperature compared to the non-implanted ones.