Preparation And Modification Of Graphene Films

With plenty of unique properties,graphene plays an important role in investigating the physical characteristics of two-dimensional?2D?materials and promoting the development of next general electronic and optoelectronic devices.For practical applications,graphene should be prepared not only with high quality and scalable productivity,but also by using eco-friendly and economical approaches.In investigating several key issues about the growth and modification of graphene films,this thesis focuses on the growth mechanism,structure modulation and performance optimization of chemical vapor deposition?CVD?grown graphene films.A series of studies on solid and liquid carbon sources in the CVD process have been carried out.The performance stability and properties improvement of CVD graphene films are investigated to advance the cost-effective uses for future wide-range applications of graphene.Graphene films with transmittance of 89%?93% and sheet resistance of 1150?2600?/sq are prepared from solid carbon sources?water-soluble polymers?by a direct CVD process.The growth mechanism of graphene has been systematically studied.The oxygenated functional groups and nitrogen atoms in carbon sources benefit enhancing the crystallinity of graphene and forming in-situ nitrogen doping in graphene,respectively.In the rapid thermal treatment process,the metal-binding functional groups in water-soluble polymers hinder the growth of graphene.A simple yet effective carbon feeding device is designed to help realizing controllable feeding of liquid carbon source.When using acetone as a liquid carbon source,nitrile-phenolic resin matrix is introduced to control the volatilization speed of acetone.Uniform monolayer graphene film with high crystallinity and low sheet resistance??500?/sq?is obtained.Meanwhile,continuous graphene film with over 80%bi-layer coverage is obtained by adjusting the growth parameters.The growth mechanisms of mono-and bi-layer graphene are systematically analyzed.The oxidation of copper foil and the reacticity atmosphere on its both sides significantly influence the growth of ad-layer graphene.With FeCl₃ intercalation,graphene film with well-maintained high transmittance??95%?and enhanced electrical conductivity?sheet resistance:?190?/sq?is obtained.The structure of FeCl₃ intercalated graphene is systematically studied.When served for graphene/silicon photodetector,FeCl₃intercalated graphene shows better performance,comparing to pristine graphene.Based on long-term resistance monitoring?500 days?,graphene films on SiO₂/Si substrate show excellent electrical stability in ambient air.The resistance of graphene film shows tiny and reversible oscillation?the relative resistance changes are no more than 10%?.In conclusion,this thesis will guide the preparation of graphene and other 2D materials,especially when liquid carbon sources are used.Strategies for further improving the quality of graphene and the controllability of CVD process are proposed.