  Edge engineering is important for both fundamental research and applications
as the device size decreases to nanometer scale. This is especially the case
for graphene because a graphene edge shows totally different electronic
properties depending on the atomic structure and the termination. It has
recently been shown that an atomically precise zigzag edge can be obtained by
etching graphene and graphite using hydrogen (H) plasma. However, edge
termination had not been studied directly. In this study, termination of edges
created by H-plasma is studied by high-resolution electron energy loss
spectroscopy (HREELS) to show that the edge is $\mathrm{sp}^{2}$ bonded and the
edge carbon atom is terminated by only one H atom. This suggests that an ideal
zigzag edge, which is not only atomically precise but also $\mathrm{sp}^{2}$
bonding, can be obtained by H-plasma etching. Etching of the graphite surface
with plasma of a different isotope, deuterium (D), is also studied by scanning
tunneling microscopy (STM) to show that D-plasma anisotropically etches
graphite less efficiently, although it can make defects more efficiently, than
H-plasma.
