The Effect Of The Pressure On The Growth Of Graphene Using The CVD Method

Graphene is a two dimensional nanocrystal consisted of a single layer of carbon atoms arranged in a hexagonal lattice with a sp~2 hybrid orbital.It has a great potential application in electronic devices,energy storage materials,and biomedical fields due to its excellent electrical,mechanical,thermal,and optical properties originated from its special two-dimensional structure.The new methods which can produce graphene with large scale,low cost and high quality have attracted more and more attention.In present,a series of methods to grow graphene have been explored after many years of hard work for researcher,including mechanical cleavage,the chemical method,epitaxy on SiC,and chemical vapor deposition(CVD).Among them,the CVD method has aroused great attention due to it is potential as a procedure where it is not only possible to grow graphene with high controllability,mass production and simple production process but also to realize the large scale industrialized production.Two research areas have been gained a great of interesting in graphene grown by CVD method.One is to produce single crystal graphene with large scale and high quality,even with industrialized production;the other is to study the growth mechanism by analyzing microstructure and even realize graphics in graphene.The single crystal graphene with a centimeter size has been controllable achieved in recently.However,the graphene growth mechanism has been uncovered due to it has too many impact factors to grow graphene using CVD method such as the substrate,growth temperature,hydrogen concentration,carbon source concentration,carrier gas oxygen content,pressure,and so on.There are few reports researched on pressure due to it is difficult to be controlled while other factors have been systematically studied in past few years.In this paper,the impact of the pressure in the CVD method has been systematically investigated.In the steady state pressure,the square graphene has been successfully grown by controlling the pressure in the growth process.Under the dynamic pressure,the circular graphene has been synthesized by controlling the increase rate of the pressure in the growth process.The square graphene and circular graphene can be tansformed to each other by tuning the grow process in the steady state pressure or under the dynamic pressure.The results illustrated here may advance the understanding of the role of the pressure and further revealing the growth mechanism,and even realizing the production of the single crystal graphene with large scale.The main contents are demonstrated below:First,the impact of pressure on the growth of graphene was studied and the square graphene with high quality was successfully synthesized in the steady state pressure.The pressure in the reaction system is able to be controlled by the flow rate of the hydrogen or the high vacuum valve at the air outlet end using the CVD method.The experiment results shown that the square graphene with rough bound was obtained in the low pressure,and the boundary become much sharper when the pressure increases.The shape of the graphene transformed from the square to the polygon with the dendritic boundary if the growth pressure continued increase.The hexagonal graphene with sharp boundary was obtained if the growth pressure further increase finally.The above results demonstrated that the morphology of the graphene was able to be gained by controlling the growth pressure,and even the square graphene with high quality can be obtained.Second,the influence of the change rate of the pressure to the graphene has been investigated and the circular graphene has been prepared under the dynamic pressure.A two-step method to grow graphene was adopted.At first,the hexagonal graphene domains grown in the same conditions were obtained and used as the precusor.Then,the influence of the dynamic pressure on the growth of graphene nanostructure was carefully investigated by controlling the pressure under the dynamic state through tuning the high vacuum valve.The results demonstrated that the shape of the graphene transformed from the polygon with sharp bound to the circle with smooth boundary when the dynamic pressure rate increases.And the ellipse graphene with smooth bound was obtained finally if the pressure increased rate further increase.Therefore,it can be seen that the boundary of the graphene can be effective controllable and the single crystal circle graphene can be obtained at last.Third,the square graphene and circular graphene can be tansformed to each other which may give a useful guidance to reveal the growth mechanism by combining the growth condition with the steady state pressure and the dynamic pressure.The hexagonal,square and circle graphene can be tansformed to each other using multiple step methods by tuning growth pressure based on the successfully synthesized the hexagonal,square and circle graphene.The hexagonal graphene can be tansformed to square or circle graphene by controlling the growth condition in the steady state pressure or under the dynamic pressure in the second step.The square graphene can be tansformed to the hexagonal graphene by controlling the growth condition in the steady state pressure in the second step.Therefore,the different graphene nanostructure tansformed to each other have been realized and the graphics in graphene can be achieved,which may give a significant help to further understand the growth mechanism.