Controllable Synthesis And Physical Properties Of Bilayer Graphene From Solid Carbon Source

Most of the physicochemical properties of graphene are sensitive to its thickness and stacking order.It is well known that monolayer graphene is intrinsically a semimetal with a zero bandgap,which is unfavorable for its application in electronic devices because of the difficulty in turning off the current in graphene-based transistors In contrast,the electrical band gap opening or band overlap generated in few-layer graphene can be well modulated by vertical electric fields.In particular,the gate-induced insulating state in Bernal bilayer graphene opens a promising avenue for application of graphene in the electronic industry.Fabrication of industrial-level high-quality graphene with a controllable layer number is of fundamental importance for realizing its potential applications in nanoelectronic devices.Nevertheless,direct fabrication of high-quality large-area-uniform bilayer graphene on Cu foil is still a formidable challengeIn this work,we focused on the chemical vapor deposition(CVD)bilayer graphene.Based on the understanding the formation mechanism of domain,layer number,stacking order and defect,the controllable growth of CVD bilayer graphene was achieved,and then the effect mechanism of structure on the electrical transport properties of bilayer graphene was studied.The main research contents and results are summarized as follows.Fast growth of large-scale bilayer graphene sheets with a high AB-stacking ratio and high mobility on copper poses a tremendous challenge,which has to overcome the self-limiting effect.Here,we report a low-cost but facile method to rapidly synthesize bilayer Bernal graphene by chemical vapor deposition using polystyrene as the feedstock,which be well controllable from hexagonal single-crystal domains to wafer-scale homogeneous films.The bilayer graphene grains and continuous film obtained are of high quality and exhibit field-effect hole mobilities as high as 5700 and 2200 cm2V-1s-1 at room temperature,respectively.In addition,a synchronous growth mechanism of bilayer graphene is revealed by monitoring the growth process,resulting in a high surface coverage of nearly 100%for a near-perfect AB stacking order.In this process,the polystyrene plays a crucial role to give synchronous bilayer growth.The high carrier mobility,tunable bandgap,and ability for low-cost mass production pave the way for development of bilayer graphene nanoelectronic devices with high performance.Unfortunately,CVD graphene is intrinsically polycrystalline,with pristine graphene grains stitched together by disordered grain boundaries,which can be either a blessing or acurse.On the one hand,grain boundaries are expected to degrade the electrical and mechanical properties of polycrystalline graphene,rendering the material undesirable for many applications.On the other hand,they exhibit an increased chemical reactivity,suggesting their potential application to sensing or as templates for synthesis of one-dimensional materials.Therefore,it is important to gain a deeper understanding of the structure and properties of graphene grain boundaries.Here we study single-crystal bilayer graphene grains synthesized by ambient chemical vapour deposition on polycrystalline Cu,and show how individual boundaries between coalescing grains affect graphene's electronic properties.Magneto-transport properties in bilayer graphene was experimentally investigated by varying magnetic-field strength and a linear magnetoresistance(LMR)was observed.Bilayer graphene grain boundaries give a significant Raman D peak,impede electrical transport,and decrease de-phasing length in graphene.This study highlights the importance of domain interfaces,especially on the carrier transport properties in CVD graphene.