Control of interfacial interactions leads to a dramatic change in shape and morphology for particles based on poly(styrene-b-2-vinylpyridine) diblock copolymers. Key to these changes is the addition of Au-based surfactant nanoparticles (SNPs) which are adsorbed at the interface between block copolymer-containing emulsion droplets and the surrounding amphiphilic surfactant to afford asymmetric, ellipsoid particles. The mechanism of formation for these novel nanostructures was investigated by systematically varying the volume fraction of SNPs, with the results showing the critical nature that the segregation of SNPs to specific interfaces plays in controlling structure. A theoretical description of the system allows the size distribution and aspect ratio of the asymmetric block copolymer colloidal particles to be correlated with the experimental results.

We use self-consistent field theory (SCFT) to study the directed self-assembly of laterally confined diblock copolymers. In this study, we focus on systems in which the self-assembled lamellae are oriented parallel to selective sidewalls in a channel. While well-ordered, perfect lamellae are observed in narrow channels both experimentally and numerically, undesirable defective structures also emerge. We therefore investigate the energetics of two categories of isolated defects (dislocations and disclinations) for various segregation strengths and channel dimensions, and establish conditions that favor the formation of defects. We also determine the energy barrier and the transition path between defective and perfect states using the string method. We find that only a few kT of energy are necessary to overcome the kinetic barrier and remove a defect, sharply contrasting with the large gain in free energy (many tens of kT) that is necessary for the formation of a defect from the pristine state.

Over the last few years, the directed self-assembly of block copolymers by surface patterns has transitioned from academic curiosity to viable contender for commercial fabrication of nextgeneration nanocircuits by lithography. Recently, it has become apparent that kinetics, and not only thermodynamics, plays a key role for the ability of a polymeric material to self-assemble into a perfect, defect-free ordered state. Perfection, in this context, implies not more than one defect, with characteristic dimensions on the order of 5 nm, over a sample area as large as 100 cm 2 . In this work, we identify the key pathways and the corresponding free energy barriers for eliminating defects, and we demonstrate that an extraordinarily large thermodynamic driving force is not necessarily sufficient for their removal. By adopting a concerted computational and experimental approach, we explain the molecular origins of these barriers and how they depend on material characteristics, and we propose strategies designed to overcome them. The validity of our conclusions for industrially relevant patterning processes is established by relying on instruments and assembly lines that are only available at state-of-the-art fabrication facilities, and, through this confluence of fundamental and applied research, we are able to discern the evolution of morphology at the smallest relevant length scales-a handful of nanometers-and present a view of defect annihilation in directed self-assembly at an unprecedented level of detail.directed self-assembly | copolymer | defect | minimum free energy path | string method O ver the last decade, the directed self-assembly (DSA) of block copolymers has rapidly evolved from mere intellectual curiosity (1-4) to a potentially crucial step in the commercial fabrication of next-generation electronic circuits. Indeed, the characteristic length scale of ordered self-assembled copolymer domains is in the range of 5-50 nm. Furthermore, their size and shape can be manipulated through simple processing steps, thereby making them attractive for the production of semiconductor devices, nanofluidic devices, or high-density storage media (5, 6). The general idea behind copolymer DSA is that a surface patternchemical or topographic-can be used to guide the assembly of a polymeric material into an ordered, device-like structure that is free of defects. In so-called "density multiplication" patterning strategies (7,8), the spacing or pitch of the surface features can be much larger than the characteristic dimensions of the copolymer of interest. One can thus prepare coarse surface patterns, which are easier to create, and rely on the copolymer to self-assemble into features whose density is considerably larger. Fig. 1 shows a schematic representation of the process for obtaining a lamellar morphology on a stripe-patterned substrate under a one-to-three (or 3X) density multiplication strategy. Patterned stripes interact preferentially with one of the blocks and guide the assembly of thin copolymer films into ordered lam...

Solvent annealing provides an effective means to control the self-assembly of block copolymer (BCP) thin films. Multiple effects, including swelling, shrinkage, and morphological transitions, act in concert to yield ordered or disordered structures. The current understanding of these processes is limited; by relying on a theoretically informed coarse-grained model of block copolymers, a conceptual framework is presented that permits prediction and rationalization of experimentally observed behaviors. Through proper selection of several process conditions, it is shown that a narrow window of solvent pressures exists over which one can direct a BCP material to form well-ordered, defect-free structures.

Recently there has been significant interest in manipulating the self-assembly behavior of block copolymers to obtain structures that are not observed in the bulk. Here we explore the conditions for which self-assembly in laterally confined thin block copolymer films results in tetragonal square arrays of standing up cylinders. More specifically, we used self-consistent field theory (SCFT) to study the equilibrium phase behavior of thin films composed of a blend of AB block copolymer and A homopolymer laterally confined in square wells. By using suitable homopolymer additives and appropriately sized wells, we observed square lattices of upright B cylinders that are not stable in pure 1 AB block copolymer systems. We further investigated the optimal conditions and parameters that lead to defect-free, in-plane tetragonal ordering. Considering the potential application of such films in block copolymer lithography, we also conducted numerical SCFT simulations of the role of line edge roughness at the periphery of the square well on feature defect populations. Our results indicate that the tetragonal ordering observed under square confinement is robust to a wide range of boundary perturbations.

While self-assembling block copolymer thin films have attracted attention as a promising high resolution lithographic tool, the self assembly of mixed polymer brushes for lithography is relatively unexplored. Here we study the directed self-assembly of a mixed polymer brush using self-consistent field theory (SCFT) simulations. Using the model equations and numerical methods introduced and verified in our previous study, the bulk phase behavior of a mixed melt brush is studied in depth through full three dimensional calculations. We assume that the mixed A/B polymer chains, which are of the same length, are exposed to a neutral top surface and are uniformly grafted at a high density. We identify phase-separated morphologies and calculate a phase diagram for the mixed brush under melt conditions as a function of the segregation force and composition. The observed lateral microphase separation is similar to that in block copolymer thin films, but the phase separation occurs at a smaller segregation force and the transition between cylindrical and spherical morphologies are quite different than the first-order phase transition in block copolymers. We demonstrate that lateral confinement can induce long-range, in-plane order in mixed brushes and suggest promising directed self-assembly methods for the application of self-assembled mixed polymer brushes in next-generation information storage and electronic devices.

A modular and hierarchical self-assembly strategy using block copolymer blends (AB/B'C) with tunable supramolecular interactions is reported. By combining supramolecular assembly of hydrogenbonding units with controlled phase separation of diblock copolymers, highly ordered square arrays or hexagonal arrays of cylindrical domains were obtained for mixtures of poly(ethylene oxide)-b-poly(styrene-r-4-hydroxystyrene) (PEO-b-P(S-r-4HS)) and poly(styrene-r-4-vinylpyridine)-b-poly(methyl methacrylate) (P(S-r-4VP)-b-PMMA) diblock copolymers under solvent annealing with controlled high humidity. The fraction of the H-bonded phenolic and pyridyl units was shown to be critical for both the generation of longrange order and controlling the spatial arrangement of the cylindrical domains. Both low absolute numbers and a near-stoichiometric ratio of pyridyl-to-phenolic groups are needed to produce ordered square arrays with separated PEO and PMMA domains, whereas a low ratio of pyridyl-to-phenolic groups facilitated the formation of ordered hexagonal arrays with mixed PEO and PMMA domains. Self-consistent field theory simulations suggest that the effective Flory-Huggins parameters between the various blocks control the stability of the different packing structures in this system. The modularity and tunability of this supramolecular block copolymer blending approach is a unique and powerful strategy to fabricate diverse nanostructures for a variety of applications such as block copolymer lithography.

Defects in highly ordered self-assembled block copolymers represent an important roadblock toward the adoption of these materials in a wide range of applications. This work examines the pathways for annihilation of defects in symmetric diblock copolymers in the context of directed assembly using patterned substrates. Past theoretical and computational studies of such systems have predicted minimum free energy pathways that are characteristic of an activated process. However, they have been limited to adjacent dislocations with opposite Burgers vectors. By relying on a combination of advanced sampling techniques and particle-based simulations, this work considers the long-range interaction between dislocation pairs, both on homogeneous and nanopatterned substrates. As illustrated here, these interactions are central to understanding the defect structures that are most commonly found in applications and in experimental studies of directed self-assembly. More specifically, it is shown that, for dislocation dipoles separated by several lamellae, multiple consecutive free energy barriers lead to effective kinetic barriers that are an order of magnitude larger than those originally reported in the literature for tightly bound dislocation pairs. It is also shown that annihilation pathways depend strongly on both the separation between dislocations and their relative position with respect to the substrate guiding stripes used to direct the assembly.