Synthesis And N-doping Of Graphene Ribbons By Regulating The Solid State Dewetting Of Confined Metal

Graphene has become the focus of attention and scholars’research since it was discovered,because of its excellent optical,thermal,electrical,and mechanical properties.At present,chemical vapor deposition（CVD）is the most effective method for synthesizing large-scale,high-quality graphene films.To further promote the use of graphene in optoelectronic devices,it is necessary to prepare patterned graphene ribbons with fixed directions and positions,and adjustable electronic structures.Moreover,the properties of graphene,such as electrical conductivity and optical transparency are functions of its number of layers.Therefore,guided by the perspective of patterned graphene,this work prepared graphene ribbon arrays with a uniform width,high aspect ratio,and the controllable number of layers by the CVD.Furthermore,the lack of bandgap restricts the application of graphene in the field of semiconductor devices,and thus the graphene ribbons are modified by nitrogen doping so that it has more application scenarios.In this study,SiO₂/Si wafer with trapezoidal grooves etched was used as a template to construct a band-shaped metal catalyst substrate,and then graphene ribbons were grown by CVD.Firstly,the dewetting phenomenon of Cu upon a growth substrate in the grooves has been investigated by changing the heating method,sputtering time,sputtering mode（preheating sputtering）,groove type（V-shaped groove）,reaction temperature,and reaction time.Then the growth conditions were optimized to prepare single-layer graphene ribbons.Secondly,the influence of dewetting of Cu Ni alloy substrate under different Cu sputtering time,reaction temperature and reaction time was explored,and nitrogen-doped graphene ribbons were prepared by using NH₃ as a nitrogen source.The main research results are as follows:First,when Cu is used as the growth substrate,the rapid heating treatment can keep the Cu strip intact after CVD.The longer the sputtering time of Cu,the thicker the film and the lower the degree of dewetting.If the substrate is heated during sputtering,the Cu film will form a crystalline structure,which promotes the occurrence of dewetting.The trapezoidal groove has a flatter bottom than the V-shaped groove,so it is more suitable for the preparation of the growth substrate.Both the temperature and the time of reaction affect the morphology of the Cu band and the quality of the graphene ribbon.High temperature and long time will break the edge of the Cu band,whereas low temperature or short time is not suitable for the growth of graphene ribbons.The small methane flow rate facilitates the growth of single-layer graphene ribbons.Second,after adding a Ni adhesion layer between the Cu film and SiO₂ layer,the adhesion between the Cu metal and the groove substrate increases,which prevents the occurrence of dewetting.Compared with pure Cu substrate,Cu Ni substrate can maintain the integrity of metal ribbons at a shorter sputtering time,higher reaction temperature,and longer reaction time.In addition,the graphene ribbons grown on the Cu Ni substrate have better uniformity and less defects,due to the smaller surface roughness of the substrate after CVD.Moreover,the control over the number of layers of un-doped and nitrogen-doped graphene ribbons can be achieved by adjusting reaction parameters such as the relative thickness of the Cu film and the Ni film,the reaction time,and the nitrogen doping time.The Selected Area Electron Diffraction（SAED）shows that the single-layer nitrogen-doped graphene ribbons have two dominated lattice orientation angles of 0°and 30°,the nitrogen doping amount is 1.72 at.%,of which pyridine nitrogen,pyrrole nitrogen,and graphitic nitrogen account for 4.01 at.%,59.91at.%,36.08 at.%,respectively.The nitrogen-doped graphene ribbons exhibit obvious fluorescence effects in the red and near-infrared regions at room temperature.