  We present a systematical study via scanning tunneling microscopy (STM) and
low-energy electron diffraction (LEED) on the effect of the exposure of Lithium
(Li) on graphene on silicon carbide (SiC). We have investigated Li deposition
both on epitaxial monolayer graphene and on buffer layer surfaces on the
Si-face of SiC. At room temperature, Li immediately intercalates at the
interface between the SiC substrate and the buffer layer and transforms the
buffer layer into a quasi-free-standing graphene. This conclusion is
substantiated by LEED and STM evidence. We show that intercalation occurs
through the SiC step sites or graphene defects. We obtain a good quantitative
agreement between the number of Li atoms deposited and the number of available
Si bonds at the surface of the SiC crystal. Through STM analysis, we are able
to determine the interlayer distance induced by Li-intercalation at the
interface between the SiC substrate and the buffer layer.
