  X-ray reflectivity measurements of the binary liquid Ga-Bi alloy reveal a
dramatically different surface structure above and below the monotectic
temperature $T_{mono}=222^{\circ}$ C.
  A Gibbs-adsorbed Bi monolayer resides at the surface at both regimes.
However, a 30 {\AA} thick, Bi-rich wetting film intrudes between the Bi
monolayer and the Ga-rich bulk for $T > T_{mono}$.
  The internal structure of the wetting film is determined with {\AA}
resolution, showing a theoretically unexpected concentration gradient and a
highly diffuse interface with the bulk phase.

Statistical Mechanics;Materials Science