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The catalyst-free synthesis of graphene on dielectrics prevents the damageinduced by the transfer process. Although challenging, to master this synthesiswould boost the integration of graphene on consumer electronics since defectshinder its optoelectronic properties. In this work, the influence of thedifferent surface terminations of c-plane sapphire substrates on the synthesisof graphene via plasma-enhanced chemical vapour deposition (PECVD) is studied.The different terminations of the sapphire surface are controlled by a plasmaetching process. A design of experiments (DoE) procedure was carried out toevaluate the major effects governing the etching process of four differentparameters: i.e. discharge power, time, pressure and gas employed. In thecharacterization of the substrate, two sapphire surface terminations wereidentified and characterized by means of contact angle measurements, being ahydrophilic (hydrophobic) surface the fingerprint of an Al- (OH-) terminatedsurface, respectively. The defects within the synthesized graphene wereanalysed by Raman spectroscopy. Notably, we found that the ID/IG ratiodecreases for graphene grown on OH-terminated surfaces. Furthermore, twodifferent regimes related to the nature of graphene defects were identified anddepending on the sapphire terminated surface are bound either to vacancy orboundary like defects. Finally, studying the density of defects and thecrystallite area, as well as their relationship with the sapphire surfacetermination paves the way for increasing the crystallinity of the synthesizedgraphene.

Plasma induced surface modification of sapphire and its influence on graphene grown by PECVD