  Monolayer graphene epitaxially grown on SiC(0001) was etched by H-plasma and
studied by scanning tunneling microscopy and spectroscopy. The etching created
partly hexagonal nanopits of monatomic depth as well as elevated regions with a
height of about 0.12 nm which are stable at $T$ = 78 K. The symmetric tunnel
spectrum about the Femi energy and the absence of a $6\times6$ corrugation on
the elevated regions suggest that in these regions the carbon buffer layer is
decoupled from the SiC substrate and quasi-free-standing bilayer graphene
appears at originally monolayer graphene on the buffer layer. This is a result
of passivation of the SiC substrate by intercalated hydrogen as in previous
reports for graphene on SiC(0001) heat treated in atomic hydrogen.
