  Is there a low-density region ('gap') between water and a hydrophobic
surface? Previous X-ray/neutron reflectivity results have been inconsistent
because the effect (if any) is sub-resolution for the surfaces studied. We have
used X-ray reflectivity to probe the interface between water and more
hydrophobic smooth surfaces. The depleted region width increases with contact
angle and becomes larger than the resolution, allowing definitive measurements.
Large fluctuations are predicted at this interface; however, we find that their
contribution to the interface roughness is too small to measure.
