Studies On Synthesis And Properties Of Graphene Nanoribbon

Graphene has been a hot research topic in recent years since researchers managed to prepare graphene by tape method in 2004.Graphene is known as the most thinnest material and is very strong and hard.As an element,its electron transfer speed is faster than any known del conductor at room temperature.Graphene has certain special electrical,optical and mechanical properties.As a one-dimensional material derived from graphene,the graphene nanoribbon is the thin strips of graphene.The band gap of graphene nanoribbon will increase with the decrease of the bandwidth,which has different electrical properties from graphene.Chemical vapor deposition is widely utilized to synthesize graphene with controlled properties for many applications.And it is one of the most important methods for the preparation of graphene with high quality in large area.Cu substrate is the most commonly used for the preparation of graphene in chemical vapor deposition.As we know,the properties of graphene are greatly affected by the number of layers.However,the synthesize and mechanism of bi-layer and multi-layer graphene on Cu substrate are also in debating.And how to make a breakthrough to realize the controllable synthesis of bi-layer and multi-layer graphene on Cu substrate has become a direction for many researchers.In this work,we reported bi-layer and multi-layer graphene on Cu substrate by atmospheric pressure chemical vapor deposition.Firstly,the Cu foil was put into the quartz slides of the tube furnace and heated to 1000 °C with a speed of 15 °C/min.After reaching 1000 °C,the Cu foil was annealed 2 hours with the mixture gas of hydrogen(20 sccm)and argon(380 sccm).After that,the graphene growth was carried out at 1000 °C under a 80 sccm mixture gas of argon and ethanol.Then,the samples were cooled to the room temperature with a speed of 100 °C/min with the protection gas of hydrogen and argon,and then taken out of the furnace.The graphene is prepared on the Cu foils and finally transferred onto the SiO2 / Si substrates.The quality and number of layers of the as-produced graphene were assessed by field emission scanning electron microscopy(SEM),transmission electron microscopy(TEM),Raman spectroscopy,and optical microscopy.By tuning the graphene growth,the monolayer,bi-layer and multi-layer graphene with higer quality and better continu-ity were obtained.And the growth time of monolayer,bi-layer,four-layers graphene was respectively 25 s,40 s,60 s.And we found that the graphene layer will be increased in the process of insulation.The growth mechanisms of bi-layer and multi-layer graphene on copper substrate by atomspheric pressure chemical vapor deposition are also discussed.There will be some indiffusible carbon atoms or radicals near the copper foil surface due to the small molecular diffusion mean free path under normal pressure.We suggested that the bi-layer and multi-layer graphene grown on copper substrate by atmospheric pressure chemical vapor deposition is dominated by Van der Waals epitaxial mechanism.This work provides a reference for improving the quality of chemical vapor deposition monolayer,bi-layer and multi-layer graphene.We used the copper nanowire as a mask to etch the graphene around the mask by reactive ion etching on the base that can grow and transfer high quality graphene in a large area.After the removal of the mask,the graphene nanoribbon with a width of about 200-300 nm,which is close to the diameter of copper nanowire,and a smooth edge with good quality are left on the substrate.The Focused Ion Beam(FBI)deposition was used to connect the graphene nanoribbons with the electrodes,and the conductivity,gas sensitivity and semiconductor thermal sensitivity were measured and analyzed.The characterization of the morphology of graphene nanoribbon shows that the copper nanowire can play a mask role well,which makes the finally formed graphene with a complete structure and clean surface.The conductivity test results show that the electrode of Focused Ion Beam deposition can be well used to connect graphene nanoribbons with electrodes.We also measured and analyzed the gas sensitivity and semiconductor thermal sensitivity of graphene nanoribbon.In addition,the process of preparing other graphene nano materials,including nanoporous graphene and graphene nano disk array was explored.What's more,we successfully prepared the nano porous graphene and graphene nanodisk array.