  Graphene on the substrate can form bubbles rising above the sheet. In some
cases, the bubble is a perfect spherical surface crown, and its radius can be
adjusted by external electric field. In this manuscript, we theoretically
investigate the voltage dependence of the spherical bubble's radius. The
calculated results are in good agreement with recent experiments on the
graphene bubble controlled by applied gate voltage [Appl. Phys. Lett. 99,
093103 (2011)].
