We report the first experimental evidence of size effects in the glass transition of thin films of an organic molecule grown from the vapor phase. In as-deposited films grown at 90 K (0.80Tg), both the fictive temperature, Tf, and the onset of the glass transition, Ton, decrease with thickness. The thinnest layers (~4 nm) exhibit the highest thermodynamic and lowest kinetic stability. Films refrozen at 2000 K/s after being heated to the liquid state during a previous scan demonstrate no size effects. The width of the glass transition for both as-deposited and refrozen films is independent of the film thickness down to 4 nm. Our heat capacity data suggest that ultrathin vapor-deposited glasses transform into liquid by a faster dynamic influenced by the outer film surface. © 2009 American Chemical Society.
- Nanoparticles and nanostructures