| 초록 |
The hole-in-hole hierarchical structures of block copolymer such as polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) thin films are known to be initiated by the lateral strain due to the evaporation of residual high-boiling solvent, toluene (Tb = 110oC), with low spin rate after the fast formation of parallel lamellar. Generally the morphology of hole-in-hole structures are known to show the shape of rounded holes. In present study, we observed the various surface morphologies and different kinds of holes such as intriguing fractal holes and rounded holes with different annealing temperature and various initial thicknesses using optical microscopy (OM) and atomic force microscopy (AFM). With controlled factors, fractal holes were observed in various thickness region at low annealing temperature (140oC), however, only in quantized thickness region, t0 = (n+1/2)L0, where L0 is the lamellar period and n is an integer at high annealing temperature (180oC). This is believed to be related to the degree of imposed strain. At lower annealing temperature, imposed strain is weaker due to lower evaporation rate of residual solvent . Even in higher annealing temperature, as block copolymer favors a quantized thickness, imposed strain in quantized thickness is weaker than in off-quantized thickness region, which induce fractal holes. |
