  Recent experiments have convincingly demonstrated the existence of surface
nanobubbles on submerged hydrophobic surfaces. However, classical theory
dictates that small gaseous bubbles quickly dissolve because their large
Laplace pressure causes a diffusive outflux of gas. Here we suggest that the
bubbles are stabilized by a continuous influx of gas near the contact line, due
to the gas attraction towards hydrophobic walls (Dammer & Lohse, PRL96, 206101
(2006); Zhang {\it et al.}, PRL98, 136101 (2007); Mezger {\it et al.}, J.\
Chem. Phys. 128, 244705 (2008)). This influx balances the outflux and allows
for a meta-stable equilibrium, which however vanishes in thermodynamic
equilibrium. Our theory predicts the equilibrium radius of the surface
nanobubbles, as well as the threshold for surface nanobubble formation as a
function of hydrophobicity and gas concentration.
