At small size scales, traditional "top-down" approaches for patterning features such as photolithography become extremely difficult and expensive.[1] However, the self-assembly of block copolymers (BCPs) into highly ordered morphologies represents a good example of a "bottom-up" process, providing a possible alternative for patterning features with nanoscale dimensions. Over the past decade, tremendous effort has been focused on generating well-organized nanoscopic structures over large scales by the self assembly of BCPs, using external stimuli such as electric fields, [2][3][4][5] solvent evaporation, [6,7] temperature gradients, [8] graphoepitaxy, [9][10][11] crystallization, [12,13] chemical patterning of surfaces, [14][15][16] controlled interfacial interactions, [17][18][19] or the addition of a second component. [20][21][22][23][24][25][26] However, simple and inexpensive procedures to generate highly ordered structures are still needed for microelectronics fabrication. Here, we demonstrate a simple approach to generate highly ordered hexagonally packed cylindrical microdomains normal to the substrate surface mediated by the addition of a small amount of salt to the BCP. An asymmetric diblock copolymer of polystyrene-blockpoly(2-vinylpyridine) (PS-b-P2VP) with a number-average molecular weight of 7.35×10 4 g mol -1 , a PS weight fraction of 0.75, and a polydispersity of 1.06 has been used as received (Polymer Source). The nitrogen atom in the pyridine ring can be used for functionalization or interactions with different compounds through hydrogen bonding [20,22] or coordination bonding. [21,27,28] This characteristic makes this specific BCP an attractive candidate for the fabrication of high-density storage devices. However, achieving control over the orientation of the microdomains is critical. PS-b-P2VP thin films (ca. 200 nm in thickness) spin-coated from a toluene solution followed by annealing in CHCl 3 for 24 h show mixed structures with most of the cylindrical microdomains parallel to the surface, [29] as indicated by the scanning force microscopy (SFM, Digital Instruments Dimension 3100 microscope) phase image in Figure 1a. Owing to the strong interfacial interactions, even the application of large external fields does not lead to reorientation of the domains through the entire film. However, upon the incorporation of a small amount of LiCl into the P2VP microdomains, a totally different morphology has been observed. 10 vol% LiCl methanol solutions (0.622, 3.11, and 6.22 mg mL -1 ) have been added to a 6 wt% PS-b-P2VP toluene so- Figure 1b indicates the formation of reoriented P2VP cylindrical microdomains perpendicular to the surface but without any long-range order, as indicated by the diffuse ring in the Fourier transform image (inset) and the numerous types of defects in the Voronoi diagram shown in Figure 1c. Figure 1d shows that the distribution of the center-to-center distances is quite broad with a standard deviation of 0.52. No parallel cylindrical domains have been observed in this case....
