THE FREE-SURFACE OF THIN DIBLOCK COPOLYMER FILMS - EXPERIMENTAL AND THEORETICAL INVESTIGATIONS ON THE FORMATION AND GROWTH OF SURFACE-RELIEF STRUCTURES

We have investigated both experimentally and theoretically the formati on and subsequent growth of surface relief structures on thin diblock copolymer films. The surface pattern appearing upon annealing is chara cterized by the average domain radius R. Using atomic force microscopy , we have obtained time-dependent topographs from which the critical e xponent a in the growth law R proportional to t(a) has been determined . The values are significantly lower than the ones usually predicted f or a in such films. We have discussed theoretically both the nucleatio n and formation stage of the process in detail, also considering the i deal situation (all domains belong to the same lamellar layer, and no additional defects are present). In particular the dependence of the g rowth law on the surface fraction Phi occupied by domains was addresse d. For the ideal situation three main values of the exponent alpha wer e predicted: 1/4, 1, and 1/3. However, we show that several factors ca n be responsible for a decrease in the apparent exponent a, such as li ne defects, semi-islands, and the multilayer character of the domain p attern. A crucial role of the line defects, especially for small value s of Phi, is predicted. Theoretical results are in qualitative agreeme nt with the experimental data.