Single-crystal graphene growth from mobile hot-wire-assisted CVD system

Abstract

For the last decade, graphene have been emerging as one of ideal materials for the building block of the forthcoming nanotechnology, due to their unique electrical, mechanical and mechanical properties. Although various graphene synthesis method was developed, the intrinsic properties of graphene is limited by the defect generation during growth and transfer process. Due to the uncontrollable random nucleation and sequential growth of graphene grains on catalytic substrate, grain boundaries are generated in graphene films. Most of studies report that grain boundaries in graphene film impede the electric transport of graphene. Therefore, minimizing the grain boundaries is one of the key techniques for high-quality graphene growth. For obtaining large single-crystal graphene grain, we improve the conventional CVD system by locating mobile hot-wire on bottom substrate for separately control the nucleation and growth of graphene at initial growth stage. After optimizing the graphene growth condition, high-angle tilt boundary graphene domain was observed through recrystallization-like stitching of graphene grains. For the purpose of achieving single-crystal graphene, pre-treatment of catalytic substrate was conducted before graphene growth. Cu-Ni alloy substrate was used for nucleation of small domain which facilitate to rotation of initially grown graphene grains. Furthermore, Cu(111) substrate was employed in order to nucleate the aligned graphene domain at initial growth stage. As a result, high angle tilt boundary graphene domain in graphene film was reduced compared to polycrystalline pure copper. In case of transfer-free growth of graphene, carbon-containing polymers such as PE, PEG, PMMA, PS was used for solid carbon source. Owing to the dual heating system in our CVD, uniform graphene was obtained on dielectric substrate. The effect the vapor pressure of catalytic metal on crystallinity of graphene is also studied by using catalytic metal wire. The primary factor for graphene growth is catalytic reaction of metal nanoparticle and carbon precursor in vapor phase. Although the metal nanoparticle was not fully etched from as-grown graphene, uniform and low-defect graphene was directly grown on dielectric substrate. We believe our report offers a significant contribution to understanding the growth mechanism of graphene and would be a fundamental technology for growth of high quality two dimensional materials.