With the ever diminishing size scale of device elements, the directed self-assembly of block copolymers (BCPs), a highly parallel process, offers a simple, robust, and rapid route for generating nanostructured materials that overcomes the intrinsic technological and economic limits associated with large-scale “top down” lithographic approaches. See, e.g., J. Bang, U. Jeong, D. Y. Rue, T. P. Russell, C. J. Hawker, Advanced Materials, volume 21, page 1 (2009). The future of the directed self-assembly hinges on the ability to manipulate self-assemblies over large areas in an efficient, cost-effective manner and to make block copolymer self-assemblies compatible with industrial strategies like roll-to-roll processing and nanoimprint lithography.
Addressable arrays of elements with perfect, long-range lateral ordering, though essential for some applications, have yet to be achieved by self-assembly over macroscopic areas. A nanoscopic line pattern, though the simplest pattern and a key element for semiconductor, magnetic, and optical devices, is still a challenge to prepare over large areas. See, e.g., H.-C. Kim, C. T. Rettner, L. Sundström, Nanotechnology, volume 19, page 235301 (2008); and V. Pelletier, K. Asakawa, M. Wu, D. H. Adamson, R. A. Register, P. M. Chaikin, Applied Physics Letters, volume 88, page 211114 (2006). Chemical and topographic patterning and shearing have been used to direct the ordering and orientation of cylindrical and lamellar BCP microdomains. See, e.g., H.-C. Kim, C. T. Rettner, L. Sundström, Nanotechnology, volume 19, page 235301 (2008); R. A. Segalman, H. Yokoyama, E. J. Kramer, Advanced Materials, volume 13, page 1152 (2001); R. Ruiz, H. Kang, F. A. Detcheverry, E. Dobisz, D. S. Kercher, T. R. Albrecht, J. J. de Pablo, P. F. Nealey, Science, volume 321, page 936 (2008); M. A. Villar, D. R. Rueda, F. Ania, E. L. Thomas, Polymer, volume 43, page 5139 (2002); I. Bita, J. K. W. Yang, Y. S. Jung, C. A. Ross, E. L. Thomas, K. K. Berggren, Science, volume 321, page 939 (2008); J. Y. Cheng, A. M. Mayes, C. A. Ross, Nature Materials, volume 3, page 823 (2004); L. Rockford, Y. Liu, P. Mansky, T. P. Russell, M. Yoon, S. G. J. Mochrie, Physical Review Letters, volume 82, page 2602 (1999); L. Rockford, S. G. J. Mochrie, T. P. Russell, Macromolecules, volume 34, page 1487 (2001); S. O. Kim, H. H. Solak, M. P. Stoykovich, N. J. Ferrier, J. J. de Pablo, P. F. Nealey, Nature, volume 424, page 411 (2003); S. Xiao, X. Yang, E. W. Edwards, Y.-H. La, P. F. Nealey, Nanotechnology, volume 16, page 5324 (2005); D. E. Angelescu, J. H. Waller, D. H. Adamson, P. Deshpande, S. Y. Chou, R. A. Register, P. M. Chaikin, Advanced Materials, volume 16, page 1736 (2004); Y. S. Jung, C. A. Ross, Nano Letters, volume 7, page 2046 (2007). While shearing is the only technique that can produce nanoscopic line patterns over areas greater than one square-millimeter in a rapid, cost-effective manner, it is limited by the thickness of the films required and defects, like dislocations. Consequently, obtaining one-dimensional arrays of lines with perfect order over macroscopic areas represents an unmet challenge.
Single grains of hexagonally packed cylindrical microdomains oriented normal to the surface in BCP thin films have been prepared over macroscopic areas using the faceted surfaces of reconstructed, single-crystalline materials, like sapphire and silicon, or their replicas on polymer surfaces. See, e.g., S. Park, D. H. Lee, J. Xu, B. Kim, S. W. Hong, U. Jeong, T. Xu, T. P. Russell, Science, volume 323, page 1030 (2009); and S. Park, D. H. Lee, T. P. Russell, Advanced Materials, volume 22, page 1882 (2010). Perfection in the orientational order of the lattice was achieved, but only improved local translational order. The faceted surface topography could be transferred to the surface of a broad range of inexpensive, flexible polymeric substrates with exceptional fidelity, making the process amenable to roll-to-roll and nanoimprint and capillary force lithographic processes. S. Park, D. H. Lee, T. P. Russell, Advanced Materials, volume 22, page 1882 (2010). Only the size of the single crystal limited the area over which such ordered arrays could be produced. Consequently, the atomic level ordering of a single crystal could be transferred to the ordering of the BCP microdomains through the surface facets. However, long-range translational order was not realized for hexagonally-packed cylindrical microdomains oriented normal to the surface. There therefore remains a need for methods of forming nanoscopic line patterns with high degrees of long-range order over macroscopic areas.