In general, synthesis of graphene follows the two major routeways: top-down and bottom-up techniques. Topdown methods break down bulk graphite into individual graphene layers using various methodologies such as liquid-phase exfoliation , electrochemical exfoliation , and ball milling . These synthesis routes are scalable and cheaper. However, both these approaches introduce structural defects in graphene and are not suitable for applications that require graphene of a high degree of purity. In contrast to this top-down approach, the bottom-up technique in CVD , epitaxial growth will build up graphene from carboncontaining precursors; while yielding high-quality graphene with fewer defects, the process is more expensive and difficult to use in scalable processing. Both techniques have their advantages, and application usually determines which process is followed.