Research On The Growth Mechanism Of Vertically Oriented Graphene On Nanocrystalline Diamond Films

As a new carbon material,graphene has many excellent mechanical and electrochemical properties.However,these properties are easily affected by the placement state and substrate of the graphene.Therefore,the selection of placement state and substrate of the graphene are critical to the effective utilization of the large surface area,the extraordinary electrical,chemical,optical and mechanical properties of graphene.The unique orientation of the vertically orientied graphene allows graphene to maintains its inherent characteristics and has other excellent additional characteristics,has broad application prospects in capacitors and electrochemical electrodes,and use diamond as the substrate can retain the electronic properties of graphene to the greatest extent.However,the mechanism of growing vertically oriented graphene on diamond substrate is still unclear,and it is difficult to effectively control the morphology and thickness of vertically orientied graphene,which is the main challenge to realize its application.In order to solve the above problems,it is proposed to use nanocrystalline diamond film as substrate which the vertically oriented graphene is grown on by controlling the flow of growth gas source and growth power.The growth process of the vertically oriented graphene was studied by controlling the growth time to investigate its growth mechanism.The specific results of this paper are as follows:The growth gas source and growth power were adjusted by Hot Filament chemical vapor deposition（HFCVD）to prepare the vertically oriented graphene,and the effects of the growth gas source flow rate and growth power on the vertically oriented graphene were systematically investigated.The results show that the hydrogen flow rate plays a decisive role in the growth of the vertical oriented graphenes.When the hydrogen flow rate is too large,the vertical oriented graphene cannot grow due to the preferential etching of hydrogen to the graphite phase.The carbon source flow also plays an important role in vertically oriented graphene.When the hydrogen flow rate is 0 sccm and the carbon source flow rate is greater than 25sccm,the vertically oriented graphene begin to form,and as the carbon source flow rate further increases,the amount of the vertically oriented graphene is increasing.When a sufficient carbon source（100 sccm）is provided,the most of the graphene stop growing.The growth power affects the structure of the vertically oriented graphene.When the growth power is too low,the sheet structure cannot be formed due to the gas cannot be dissociated.When the growth power is too high（more than1800 W）,the amount of the vertically oriented graphene has increased significantly,but due to the excessive amount,the inter-sheet extrusion will cause the morphology to become corrugated.The optimal growth process of the vertically oriented graphene grown on nanocrystalline diamond films is as follows:the carbon source flow rate is100 sccm,and the growth power is 1800 W.The growth time of the vertically oriented graphene was systematically studied by the HFCVD system to control the growth time.The results show that the vertically oriented graphene growth has periodic changes.First,the diamond particles nucleate and grow soft graphite structure to become the vertically oriented graphene.The graphite structure gradually becomes rigid and becomes a needle-like graphite structure with time.During this period,the structure of graphite wrapped with small diamond particles(NCD-G_or)is formed around the graphite needle structure.As amount of the structure increases,the sheet structure disappears and the graphite-diamond phase transformation may occur on it.Further growth time,the small diamond particles again nucleate and grow a soft graphite structure,which circulates cyclically and forms a periodic change.The nucleation mechanism of vertically oriented graphene on diamond was discovered for the first time,which provided a new explanation for the nucleation mechanism of vertically oriented graphene.The growth power and growth time were regulated for slow down the phase transition process by HFCVD system in order to observe the graphite-diamond phase transformation process.The results show that when the growth time is extended to 8min,the coexistence state of graphite and diamond was observed at different positions of the graphite needle structure,and the diamond structure on the graphite became obvious with the change of position,indicating that the graphite was transformed into diamond.The spectrum of EELS further proves the transition.It shows that under certain growth conditions,graphite can be transformed into diamond under low temperature and low pressure.This finding has added a new idea for the the way to prepare diamond under low temperature and low pressure conditions.