Graphene domains with different sizes and densities were successfully grown on Cu foils with use of a chemical vapor deposition method. We investigated the effects of volume ratios of argon to hydrogen during the annealing process on graphene growth, especially as a function of hydrogen partial pressure. The mean size and density of graphene domains increased with an increase in hydrogen partial pressure during the annealing time. In addition, we found that annealing with use of only hydrogen gas resulted in snowflake-shaped carbon aggregates. Energydispersive X-ray spectroscopy (EDX) and high-resolution photoemission spectroscopy (HRPES) revealed that the snowflake-shaped carbon aggregates have stacked sp 2 carbon configuration. With these observations, we demonstrate the key reaction details for each growth process and a proposed growth mechanism as a function of the partial pressure of H 2 during the annealing process.

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Anisotropic graphene domains are of significant interest since the electronic properties of pristine graphene strongly depend on its size, shape, and edge structures. In this work, considering that the growth of graphene domains is governable by the dynamics of the graphene-substrate interface during growth, we investigated the shape and defects of graphene domains grown on copper lattices with different indices by chemical vapor deposition of methane at either low pressure or atmospheric pressure. Computational modeling identified that the crystallographic orientation of copper strongly influences the shape of the graphene at low pressure, yet does not play a critical role at atmospheric pressure. Moreover, the defects that have been previously observed in the center of four-lobed graphene domains grown under low pressure conditions were demonstrated for the first time to be caused by a lattice mismatch between graphene and the copper substrate.As the electronic properties of pristine graphene are strongly dependent on its size, shape, and edge structures 1 , variously shaped graphene domains with defined edge configurations have attracted considerable attention 2-4 . They are expected to provide a pathway toward greater insight into the electronic properties of graphene and, hence, toward device performance optimization [5][6][7] . The edge geometry significantly affects the p-electron structure at the edge 1,8 ; the zigzag edge in a semi-infinite graphene sheet leads to a localized state and the armchair edge, on the other hand, shows no such localized state 8,9 . Consequently, graphene domains with edges of various geometries can be expected to exhibit unique reactivity, since they display unique physical characteristics such as particular electronic structures and magnetic properties 5 . With the consideration that the reactivity of graphene is governable by edges of various geometries, there have been many efforts to grow variously shaped graphene domains and define their edge structures. Of the various graphene synthesis techniques, Cu-assisted chemical vapor deposition (CVD) is the most reasonable and appropriate method to produce large-scale and low-defect graphene films 10,11 , since it is highly reproducible and yields high-quality films of controllable thickness and domain shapes 12,13 . Hexagonal graphene domains, which are usually synthesized using a CVD method, are believed to exhibit predominantly zigzag edge symmetry 4,14 . But, graphene domains with anisotropic geometries, such as rectangular 15 and two-lobed curvilinear structures 16 , are expected to exhibit both zigzag and armchair edge structures because the edges exhibit the same configuration if the angles between them are 2n × 30° (n = 1, 2, 3, …) 4,14 .Most CVD synthesis of graphene to date has been conducted using methane at either low pressure (LPCVD) or atmospheric pressure (APCVD), with these two conditions reported to produce very different results in terms of the domain shape and the growth mechanism. For instance, graphene domain...

Graphene has attracted great attention owing to its unique structural and electrical properties. Among various synthetic approaches of the graphene, metal assisted chemical vapor deposition (CVD) is the most reasonable and proper method to produce large-scale and low-defect graphene films. Until now, CVD from gaseous hydrocarbon sources has shown great promises for large-scale graphene growth, but high growth temperature is required for such growth. A recent work by using liquid benzene precursor has shown that monolayer graphene could be obtained at 300 degrees C by low pressure, required for high vacuum equipment. Here, we report the first successful attempt of atmospheric pressure CVD graphene growth on Cu foil using liquid benzene as a precursor. We investigated the effect of hydrogen partial pressure, growth time, and precursor temperature on the domain size of as-grown graphene. Also, micro-Raman analysis confirmed that these reaction parameters influenced the number of layer and uniformity of the graphene.