Molecular ordering and domain morphology of molecularly thin triacontane films at SiO2/air interfaces

The molecular ordering and the domain morphology of molecularly thin triaco ntane Rims at SiO2/air interfaces has been investigated at room temperature by scanning force microscopy, X-ray diffraction, and X-ray reflexion. Our results suggest that the room temperature structure is influenced by the su rface freezing behaviour of triacontane, i.e. its solidification adjacent t o the interface already some degrees (approximate to 69 degreesC) above the bulk melting temperature (approximate to 66 degreesC). Depending on the am ount of alkane available either a closed monolayer topped by separated chun ks of bulk (solidified droplets) or, in the case of only submonolayer alkan e coverage fractal, seaweed-shaped domains are observed. In both cases, adj acent to the interface the molecules are oriented upright and packed in a r ectangularly centered unit cell with a lateral correlation of much more tha n 200 molecules. A fractal dimension of 1.64 +/- 0.06 indicates that the do mains are formed by diffusion-limited aggregation.