Graphene produced from graphite
As graphene is a subunit of graphite, it makes sense that the earliest and simplest approach to its synthesis would be direct extraction from bulk graphite. At the start, it should be noted that not all graphite is created equal. There are two important varieties of graphite: natural and synthetic. The highest quality natural graphite possesses single crystalline domains with in-plane dimensions exceeding 1 mm and, consequently, single-layer graphene sheets obtained from natural sources are of exceptional crystal quality.[17] In particular, the absence of in-plane grain boundaries in this graphene enhances performance in electronic devices. The difficulty is that while the crystal dimensions are roughly 1 mm in-plane, they are typically much less than 1 mm out-of-plane; material this thin can be difficult to work with. Thus, much of the work done on graphene has proceeded from large-area synthetic graphite, namely highly ordered pyrolytic graphite (HOPG) and Kish graphite.