  While the basal plane of graphene is inert, defects in it are centers of
chemical activity. An attractive application of such defects is towards
controlled functionalization of graphene with foreign molecules. However, the
interaction of the defects with reactive environment, such as ambient,
decreases the efficiency of functionalization and makes it poorly controlled.
Here, we report a novel approach to generate, monitor with time resolution, and
functionalize the defects $\textit{in situ}$ without ever exposing them to the
ambient. The defects are generated by an energetic Argon plasma and their
properties are monitored using $\textit{in situ}$ Raman spectroscopy. We find
that these defects are functional, very reactive, and strongly change their
density from $\approx 1\cdot10^{13} cm^{-2}$ to $\approx 5\cdot10^{11} cm^{-2}$
upon exposure to air. We perform the proof of principle $\textit{in situ}$
functionalization by generating defects using the Argon plasma and
functionalizing them $\textit{in situ}$ using Ammonia functional. The
functionalization induces the n-doping with a carrier density up to
$5\cdot10^{12} cm^{-2}$ in graphene and remains stable in ambient conditions.
