Directed self-assembly of block copolymers combining top-down and bottom-up approaches

The self-assembled nanostructures of block copolymers have been widely investigated because of their potential applications as templates for nanocomposites, optoelectronic devices, ultrahigh density nanodots or nanowire arrays, memory and capacitor devices, sensors, etc. Despite the advantages of block copolymer self-assembly such as parallel processing, molecular level resolution, and the capability to generate three dimensional structure, the lack of long range order of the block copolymer nanostructure have prevented the application to practical devices. Here, we review the strategy to combine top-down and bottom-up approaches as the method to obtain a block copolymer nanostructure with long range ordering. 'Graphoepitaxy' and 'epitaxial self-assembly' are demonstrated as the most successful strategies for well-ordered block copolymer nanostructures.