Orientation-dependent growth mechanisms of graphene islands on Ir(111).

Using low-energy electron microscopy, we find that the mechanisms of graphene growth on Ir(111) depend sensitively on island orientation with respect to Ir. In the temperature range of 750-900 degrees C, we observe that growing rotated islands are more faceted than islands aligned with the substrate. Further, the growth velocity of rotated islands depends not only on the C adatom supersaturation but also on the geometry of the island edge. We deduce that the growth of rotated islands is kink-nucleation-limited, whereas aligned islands are kink-advancement-limited. These different growth mechanisms are attributed to differences in the graphene edge binding strength to the substrate.