  We evaluate how a second graphene layer forms and grows on Cu foils during
chemical vapor deposition (CVD). Low-energy electron diffraction and microscopy
is used to reveal that the second layer nucleates and grows next to the
substrate, i.e., under a graphene layer. This underlayer mechanism can
facilitate the synthesis of uniform single-layer films but presents challenges
for growing uniform bilayer films by CVD. We also show that the buried and
overlying layers have the same edge termination.
