  Graphene nanoribbons (GNRs) are considered one of the most promising
materials for next generation electronics, however a reliable and controllable
synthesis method is still lacking. Here, we report the CVD growth of GNRs on a
copper surface and the corresponding mechanisms of growth. One-dimensional GNR
growth is enabled by a vapor-liquid-solid (VLS) graphene growth guided by
on-surface propagation of a liquid catalyst particle. Controlling the
suppression of vapor-solid-solid (VSS) graphene growth along the width
direction of the GNR by tuning the flow of H2 during growth gives rise to a
spear head-shaped graphene that we term graphene nanospears (GNSs). The
real-time visual and spatially resolved observations confirm the VSS growth of
graphene can be fully suppressed and lead to GNR formation on Cu surface. These
findings reveal key insight into the growth mechanism of graphene and open a
door for achieving a facile and scalable method of synthesizing free standing
GNRs.
