  We report on the capillary-driven levelling of a topographical perturbation
at the surface of a free-standing liquid nanofilm. The width of a stepped
surface profile is found to evolve as the square root of time. The hydrodynamic
model is in excellent agreement with the experimental data. In addition to
exhibiting an analogy with diffusive processes, this novel system serves as a
precise nanoprobe for the rheology of liquids at interfaces in a configuration
that avoids substrate effects.
