Dewetting on Patterned Substrates

One possibility to prepare regular dewetted patterns on rough substrates is by pattern transfer. A regular pattern is formed on mica, on which then another substrate is placed. The pattern is released from the mica and fixed on the other substrate at the original droplet positions [49]. 

In the course of time (see Fig. 2.2a-d) these nucleated holes grew in size and eventually reached the periphery of the patch where dewetting stopped. The dewetted material form the patch was collected in a rim surrounding the dewetted patch. Thus, after dewetting reached the periphery of the patch and stopped, patches were enclosed by a circular rim, as can be clearly seen in Fig. 2.2e. The shape of the holes formed in such thin films was circular with both a diameter and a distribution on the substrate identical to the pattern of the imprinted domains. Some tiny droplets within the dewetted region resulted from the coalescence of rims of multiple holes nucleated within this area. Therefore, dewetting allowed to transform a quasi-two... 

The experimental results presented here impressively demonstrate that a simple dewetting process of a thin polymer film on a chemically patterned substrate allows to transform a smooth layer of material into various stmctures. For increasing thickness of the layer the chemical pattern produces the following sequence (see Fig. 2.14) Cylindrical holes—droplets with the shape of a spherical cap—toroids. 

Kargupta, K., Sharma, A. Morphological self-organization by dewetting in thin films on chemically patterned substrates. J. Chem. Phys. 116, 3042-3051 (2002)... 

The two approaches are in fact quite similar. The difference is that in the repelling method, water is added to the monomer solution for the dewetting process, and in the dipping method, the sample with applied undiluted monomer is dipped into a water reservoir accurate control of the dipping speed is achieved through a motorized stage. If the monomer film dewets in air, the monomer remains on the hydrophilic domains of the substrate. This is the case with the withdrawal method [15,16] in which the patterned substrate is completely immersed in the monomer and pulled out at a fixed angle and a controlled speed into ambient air. 

In a coupled AFM/XPS study of patterned collagen layers obtained by adsorption and dewetting on a PS substrate, AFM provided information on the thickness of the collagen pattern (t = 7.5nm), which showed a net-like structure. This allowed a surface coverage of 13% to be computed from the A/C ratio measured by XPS. This value could be compared with the surface coverage observed on the AFM images, which was of the order of 28% but was overestimated due to the broadening effect of the AFM probe." ... 

Figure11.6 Structures formed by dewetting of a 6 nm-thick, rubbed PS film on a photolithographically patterned substrate, with the rubbing direction (a) orthogonal and...

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