Generating Surface Energy Gradients for Block Copolymer Thin Film Studies

The development of block copolymer materials for future nanotechnologies requires an understanding of how surface energetics affect block copolymer thin film phase behavior. Combinatorial studies of these effects can be accomplished with surface energy gradients. These gradients can be used to identify transitions in thin film phase behavior and microstructure orientation. In this work, gradients are created by vapor deposition of functionalized chlorosilanes on UVO-cleaned silicon substrates under dynamic vacuum. The diffusion profiles of the chlorosilanes are manipulated by the location of the chlorosilane reservoirs in the deposition chamber. X-ray photoelectron spectroscopy (XPS) and diiodomethane contact angle are used to characterize the resulting chemical and surface energy gradients. Then, thin films of cylinder-forming poly(styrene-b-methyl methacrylate) (PS-b-PMMA) are flow coated on the gradient substrates, and the resulting phase behavior is characterized by atomic force microscopy (AFM).