Self-assembly is an effective strategy for the creation of periodic structures at the nanoscale. However, because microelectronic devices use free-form design principles, the insertion point of self-assembling materials into existing nanomanufacturing processes is unclear. We directed ternary blends of diblock copolymers and homopolymers that naturally form periodic arrays to assemble into nonregular device-oriented structures on chemically nanopatterned substrates. Redistribution of homopolymer facilitates the defect-free assembly in locations where the domain dimensions deviate substantially from those formed in the bulk. The ability to pattern nonregular structures using self-assembling materials creates new opportunities for nanoscale manufacturing.

Block-copolymer lithography refers to the use of the selfassembling domain structure in thin films of block copolymers to template dense patterns into materials at the scale of 5±50 nm. Applications of this technology include the fabrication of quantum dots, [1,2] photonic crystals, [3,4] nanowires, [5,6] magnetic-storage media, [7] silicon capacitors, [8] and flash memory devices. [9,10] The major challenges facing block-copolymer lithography and its potential impact with respect to the fabrication of nanometer-scale devices is the emulation of the following essential attributes of current photolithographic materials and processes: 1) nearly perfect patterning over very large areas, and 2) registration of the pattern with features of the underlying substrate. Some of the strategies that are pursued in order to increase the length scale over which the domains in block-copolymer films are desirably oriented and ordered include graphoepitaxy, [11±13] in-plane electric fields, [14] directional solidification, [15] solvent evaporation, [16] and chemical surface patterns.[17] Recently we demonstrated that perpendicularly oriented lamellar domains in blockcopolymer films could be induced to assemble such that the ordering of domains was perfect over arbitrarily large areas and each domain was registered with the underlying substrate.[17] Imaging layers were patterned with advanced lithography in order to produce stripes of different chemical functionality. Adjacent stripes exhibited neutral wetting and preferential wetting towards the blocks of the copolymer, and if the period of the stripes, L s , closely matched the bulk lamellar period of the block copolymer, L o , then the domain structure in the film self-assembled in an epitaxial manner with respect to the chemically nanopatterned substrate. Here we demonstrate the process latitude of epitaxial block-copolymer lithography, that is, the range of dimensions of features (or periodicity of structures) that can be patterned with perfection using the same composition and molecular weight block copolymer, is significantly improved by increasing the contrast in interfacial energy or wetting behavior between adjacent chemically patterned regions onto which the polymer films self-assemble. The impact of incommensurate periods, L s and L o , on domain ordering, and the types of defects that occur due to incommensurability have been investigated both experimentally [18±20] and theoretically. [21±27] In epitaxial assembly of lamellar structures onto neutral/preferential wetting striped surfaces consisting of self-assembled monolayers, perfect epitaxial assembly occurred only if L s was within a few percent of L o .[17] If L s = 45 nm and L o = 48 nm, pairs of dislocation defects were observed in the compressed lamellae, and if L s was greater than 52.5 nm and L o was 48 nm, herring-bone defects, tilted domains, and domains unregistered with the surface pattern were observed. Rockford et al. [18] investigated the structure of 30 nm thick films of block copolymers of differe...

We report a method to fabricate high-quality patterned magnetic dot arrays using block copolymer lithography, metal deposition, and a dry lift-off technique. Long-range order of cylindrical domains oriented perpendicular to the substrate and in hexagonal arrays was induced in the block copolymer films by prepatterning the substrate with topographic features and chemically modifying the surface to exhibit neutral wetting behaviour towards the blocks of the copolymer. The uniformity of the domain size and row spacing of block copolymer templates created in this way was improved compared to those reported in previous studies that used graphoepitaxy of sphere-forming block copolymers. The pattern of block copolymer domains was transferred to a pattern of magnetic metal dots, demonstrating the potential of this technology for the fabrication of patterned magnetic recording media.

Thin films of a nearly symmetric lamellae-forming diblock copolymer of poly(styrene-b-methyl methacrylate) (PS-b-PMMA) having a bulk repeat period, L O, were directed to assemble vertically away from chemically nanopatterned striped substrates (having a periodicity L S) that consisted of alternating stripes that were preferentially wet by the two blocks of the copolymer. The relative widths of the adjacent stripes were systematically varied such that the normalized line width of the chemical surface pattern, defined as the width of the stripe that was wet by the styrene block of the block copolymer, W, divided by the constant chemical surface pattern period, L s had values between 0.30 and 0.65. On chemical surface patterns with L S ≈ L O the diblock copolymer domains formed defect-free perpendicular arrays if the normalized line width W/L S, was between 0.36 and 0.63. On chemical surface patterns with L S ≠ L O, the range of W/L S capable of inducing defect free arrays decreased as the difference between L S and L O increased. Single-chain-in-mean-field (SCMF) simulations provided information on the dimensions and shapes of the block copolymer domains. The SCMF simulations indicated that the widths of the lamellae at half film thickness were 0.47L S independent of W/L S and the angle of the interface between the vertically oriented domains remained within 11° of the substrate normal over the range of experimentally relevant values of W/L S.

A morphological transition from cylinders to spheres was induced in an asymmetric diblock copolymer, poly(styrene)-block-poly(tert-butyl acrylate) (PS-b-PtBA). The periodic arrays of the poly(tert-butyl acrylate) (PtBA) domains were transformed to the ordered poly(acrylic anhydride) (PAA) spheres via the thermal deprotection of tert-butyl acrylate linkages and the subsequent volume change of the minority block. Coupled with techniques to direct the assembly of cylinder-forming block copolymers, this finding provides new routes to fabricate ordered geometries of nanodot arrays.

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Lamellae forming diblock copolymer domains can be directed to assemble without defects and in registration with chemically nanopatterned substrates. Initially, thin films of the lamellar poly(styrene-b-methyl methacrylate) block copolymer form hexagonally close-packed styrene domains when annealed on chemical nanopatterned striped surfaces. These styrene domains then coalesce to form linear styrene domains that are not fully registered with the underlying chemical surface pattern. Defects coarsen, until defect-free directed assembly is obtained, by breaking linear styrene domains and reforming new structures until registered lamellae have been formed. At all stages in the process, two factors play an important role in the observed degree of registration of the block copolymer domains as a function of annealing time: the interfacial energy between the blocks of the copolymer and the chemically nanopatterned substrate and the commensurability of the bulk repeat period of the block copolymer and the substrate pattern period. Insight into the time-dependent three-dimensional behavior of the block copolymer structures is gained from single chain in mean field simulations.

This article gives an overview of recent progress in the self-assembly of nanocrystals. Classic self-assembly of nanocrystals, so-called colloidal crystallization driven by van der Waals interactions, is highlighted first with an emphasis on the recent realization of binary colloidal crystals. Next, new developments in the integration of nanocrystals into clusters based on electrostatic interactions, hydrogen bonding and dipole-dipole interactions are summarized, shedding light on the defined control of the interactions between the nanocrystals. Finally, the fabrication of heterogenous nanocrystals, obtained via either phase selective modification at the water/oil interface or facet-selective crystal growth on non-spherical nanocrystals is discussed. These last materials may provide significant building blocks for mimicking molecular self-assembly.