With Professor Lian Yu and his group, we are studying crystal growth in thin films of organic glasses. We have found evidence for fast crystal growth at the surface. Another interesting feature of this surface crystal growth is the way in which the crystals grow more than 100 nm out of the surface. This striking behavior seems to require either that the crystal is pushed out of the glass or that molecules climb up the sides of the crystal to attach to the top. The Yu lab has performed measurements of surface diffusion for several of these systems and shown that surface diffusion can exceed bulk diffusion by more than 7 orders of magnitude.
The surface diffusion coefficients correlate very well with the rate of crystal growth at the surface, indicating that surface mobility allows the rapid crystal growth to occur.
We anticipate that the fast surface diffusion detected by these experiments is related to the surface mobility that allows the formation of highly stable glasses by physical vapor deposition.