Kinetics of chain organization in ultrathin poly(di-n-hexylsilane) films

The effect of film thickness on the organization kinetics of ultrathin (50-1000 Å thick) spin-cast polymer films was studied using poly(di-n-hexylsilane) and UV absorption spectroscopy. We found an extensive reduction in the crystallinity as well as a reduction in the rate of crystallization for film thicknesses below 500 Å resulting from the constrained geometry. Modeling using polymer crystallization theories elucidated the surface-induced phenomena. We found that the dimensionality of the growth depended both on the film thickness and on the crystallization temperature. At low crystallization temperatures (below 0°C) and for films thicker than 220 Å, the nucleation is bulk and the growth is three-dimensional. However, at higher crystallization temperatures (above 3°C) and for low film thickness (below 150 Å), the growth is one-dimensional and heterogeneous nucleation becomes important. For 500 Å thick films, the transition between the two nucleation regimes occurs abruptly around 3°C.