The role of surface morphology on nucleation density limitation during the CVD growth of graphene and the factors influe
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.73
The role of surface morphology on nucleation density limitation during the CVD growth of graphene and the factors influencing graphene wrinkle formation Sajith Withanage*, Tharanga Nanayakkara, U. Kushan Wijewardena, Annika Kriisa, and R. G. Mani Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303, U.S.A.
*Corresponding author: [email protected]
ABSTRACT
CVD graphene growth typically uses commercially available cold-rolled copper foils, which includes a rich topography with scratches, dents, pits, and peaks. The graphene grown on this topography, even after annealing the foil, tends to include and reflect these topographic features. Further, the transfer of such CVD graphene to a flat substrate using a polymer transfer method also introduces wrinkles. Here, we examine an electropolishing technique for reducing native foil defects, characterize the resulting foil surface, grow single-crystal graphene on the polished foil, and examine the quality of the graphene for such defects.
INTRODUCTION Since the first preparation of tiny flakes of exfoliated graphene from graphite, this 2-D material has attracted enormous attention due to its unique electrical, chemical, and physical characteristics, which are promising for a variety of applications in nanophotonics, nano-electronics, optoelectronics.[1-14] For such applications, the desirable features of graphene include high mechanical strength, chemical stability, high optical transparency, and gate-controllable electrical transport characteristics. [7, 8, 13, 15] It turns out that large-area graphene can be fabricated by chemical vapor deposition (CVD) techniques on thin metallic catalyst surfaces like copper (Cu) or nickel (Ni). Thus, the CVD process has become an attractive means for producing large-area graphene due to
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its simplicity and relatively low cost. [16-18] However, one of the significant drawbacks of CVD graphene is the presence of grain boundaries, defects, and wrinkles in the polycrystalline graphene, which adversely affects electrical transport and structural properties. CVD graphene grown on copper turns out to be polycrystalline because of the high nucleation density on the copper foil surface, which is typically ∼106 sites/cm2. [19] In order to realize better quality LPCVD graphene, this nucleation density needs to be reduced to ∼1-2 sites/cm2, so that single crystals can grow to a much larger cm-scale size, before coalescing with neighboring graphene flakes. Previous studies have demonstrated that substrate pre-treatments [19-22] and control of the gaseous precursors [23-27] can be used to limit the nucleation density to a great extent. These studies also have demonstrated that the presence of oxygen on the surface of the m
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