**1. Introduction**

Graphene belongs to the extensive realm of nanostructured allotropes of carbon. It is a 2D nanomaterial conformed of sp2 -bonded carbon atoms arranged in a hexagonal pattern, each carbon atom bonds in the plane to other three atoms, forming a chicken-wire network only one-atom thick. This amazing nanomaterial was isolated in 2004 by Novoselov and Geim [1], who later, in 2010, were awarded the Nobel Prize in Physics. Perhaps the most natural way to obtain graphene is by exfoliating a layer from graphite, such was the method used by Novoselov and Geim. This method, however, poses intrinsic disadvantages such as the low yield, the time required to find monocrystals, and the irreproducibility of the shapes of the crystals. Scientists realized that a method to produce graphene in a more controlled, reproducible, and

scalable way was necessary. Among the many techniques available to produce nanomaterials, the chemical vapor deposition (CVD) method has proven to be advantageous for the production of carbon nanostructures, it has been used to produce carbon nanotubes, carbon nanospheres, nanoribbons, fullerenes, and in 2009, the production of multilayer graphene (MLG) was reported on top of nickel (Ni) films [2, 3]. Later the same year, the synthesis of large-area graphene films was reported using Cu foils by the group of R.S. Ruoff [4], ever since, most CVD-graphene reports use copper foils as catalysts. The basics of the technique, the roles of the precursor, the catalysts, and the synthesis gases are reviewed in detail in the following paragraphs.

Early reports of CVD-graphene accounted for continuous films with regions of single-layer, bilayer, and few-layer graphene (SLG, BLG, FLG, respectively). Characterization of these films revealed that the BLG and FLG do not respect an AB stacking of the layers, the stacking from highly oriented pyrolytic graphite (HOPG); the orientation between adjacent layers is random in CVD-grown films. Another peculiarity of these graphene films is their polycrystallinity, as will be described below in detail.
