  Using X-ray photoelectron spectroscopy, thermal desorption spectroscopy, and
scanning tunneling microscopy we show that upon keV Xe + irradiation of
graphene on Ir(111), Xe atoms are trapped under the graphene. Upon annealing,
aggregation of Xe leads to graphene bulges and blisters. The efficient trapping
is an unexpected and remarkable phenomenon, given the absence of chemical
binding of Xe to Ir and to graphene, the weak interaction of a perfect graphene
layer with Ir(111), as well as the substantial damage to graphene due to
irradiation. By combining molecular dynamics simulations and density functional
theory calculations with our experiments, we uncover the mechanism of trapping.
We describe ways to avoid blister formation during graphene growth, and also
demonstrate how ion implantation can be used to intentionally create blisters
without introducing damage to the graphene layer. Our approach may provide a
pathway to synthesize new materials at a substrate - 2D material interface or
to enable confined reactions at high pressures and temperatures.
