| 초록 |
The use of self-assembly has attracted much interest due to the ease of accessing complex structure with small feature size for a variety of potential applications. Block copolymers self-assemble on length scales of a few tens of nanometers into several morphology, and therefore, they can provide a versatile route to fabricating functional nanoscopic structures. However, it is essential that both orientation and lateral ordering of the nanoscopic domains be controlled in order to fully utilize the potential of these materials. Unfortunately, the presence of preferential interaction with one component of block copolymers at the interfaces hinders the microdomains from having perpendicular orientation with respect to the film surface which is more desirable for building nanostructured templates and scaffolds rather than the parallel orientation. Moreover, the lack of long-range order limits their applications requiring addressability. Here we have used cylinder-forming poly(styrene-b-ethylene oxide) (PS-b-PEO) diblock copolymerto provide several effective routes to controlling the orientation and lateral order of microdomains in copolymer thin films. Since the PEO block has the preferential interaction with the silicon substrate, PS-b-PEO thin films will naturally have the parallel orientationunless additional efforts are made. First, the end-functionalized random copolymer of PS and PMMA (PS-r-PMMA) was used as a neural brush just like in the case of PS-b-PMMA films to tune interfacial energy. Due to the miscibility between PEO and PMMA, PS-r-PMMA was found to be able to act as a neutral brush for PS-b-PEO films at its appropriate composition, and we observedthe perpendicular orientation of PEO microdomains in the PS matrix. Secondly, PS-b-PEO films were produced onthe substrate which was covered with hydroxy-terminated polystyrene homopolymer. In this case, we have seen similar effects to the first one, depending on the surface coverage by the homopolymer. Finally, the ionic salts were added to the PS-b-PEO solution where added salts were expected to bind PEO blocks. This complexation was found to effectively screen the preferential interaction of PEO block and enables the micodomains to change their orientation from parallel to perpendicular direction. In all cases, through exposing the films to solvent vapor or "solvent annealing", highly ordered arrays of cylindrical microdomains with long-range lateral order could be achieved. |
