Dependence of Morphology on Initial Film Thickness

Looking at Fig. 11.4, it is certainly intriguing to note that the same kind of square shaped envelope as in Figs. 11.2 and 11.3 is also observed for much thinner films, even thinner than the height of the lamella. (Depending on crystallisation temperature, the lamella thickness varied between about 20 nm 

Wlien using thicker films (see Fig. 11.5), we qualitatively can find many similarities to the previous Figs. 11.2 to 11.4. The conditions (film thickness and crystallisation temperature) are similar to Fig. 11.3. However, this sample 

Although the sample shown in Fig. 11.7 was crystallized under almost the same conditions as the one in Fig. 11.6, the fact that it could grow at a higher rate (due to the higher number of available molecules the film was about 11 nm thicker the crystal front moved faster) the crystal front is more prone to become unstable. Therefore, the square-shape envelope of the crystal is not established. Nonetheless, some features hke the four-fold symmetry and the dominance of the diagonals are reproduced also in this situation. The ripples are also clearly visible. 

3 The Kinetics of Crystal Growth and the Effect of Cheinging Temperature 

In order to visualize how dendritic crystals grow and how a square-shape envelope is formed from such dendritic structures, we have superposed two images from the same crystal taken at an interval of 95 sec (see Fig. 11.8). As we want to focus on single crystals only, we have chosen a rather thin film of about 40 nm in order to avoid growth front nucleation (GFN) [13,14j. GFN depends on the number of molecules present. Thus, in such thin films the transition from poly-crystals to single crystals can occur at lower temperatures than in the 108 nm thick 111 ins discussed above. 

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