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Highly asymmetric lamellar microdomains, such as those required for many lithographic line patterns, cannot be straightforwardly achieved by conventional block copolymer self-assembly. We present a conceptually new and versatile approach to produce highly asymmetric lamellar morphologies by the use of binary blends of block copolymers whose components are capable of hydrogen bonding. We first demonstrate our strategy in bulk systems and complement the experimental results observed by transmission electron microscopy and small-angle X-ray scattering with theoretical calculations based on strong stretching theory to suggest the generality of the strategy. To illustrate the impact on potential lithographic applications, we demonstrate that our strategy can be transferred to thin film morphologies. For this purpose, we used solvent vapor annealing to prepare thin films with vertically oriented asymmetric lamellar patterns that preserve the bulk morphological characteristics. Due to the highly asymmetric lamellar microdomains, the line width is reduced to sub-10 nm scale, while its periodicity is precisely tuned.

We synthesized, via anionic coupling reaction, poly(3-dodecylthiophene)-block-poly(methyl methacrylate) copolymers (P3DDT-b-PMMA) having narrow molecular weight distribution and several block compositions. P3DDT was chosen because of moderate rod/rod interaction compared with a weak interaction of poly(3-(2′-ethyl)hexylthiophene) (P3EHT) or a strong interaction of poly(3hexylthiophene) (P3HT). The moderate rod/rod interaction of P3DDT enables us to investigate final morphologies affected by crystallization arising from the rod/rod interaction of P3DDT or the microphase separation between P3DDT and PMMA blocks. When the weight fraction (w P3DDT ) of P3DDT block of P3DDT-b-PMMAs was smaller than ∼0.6, various microdomains such as body-centered-cubic spheres, hexagonally packed cylinders, and lamellae were observed similar to those reported in conventional coil−coil type block copolymers. Interestingly, these microdomains were maintained even after P3DDT blocks were crystallized, indicating that P3DDT crystals were successfully confined within P3DDT microdomains. On the other hand, when w P3DDT was high (e.g., w P3DDT ∼ 0.76), the rod/rod interaction became dominant over microphase separation between two blocks. As a result, only fibril structure was found after the crystallization of P3DDT block.

The phase behavior of 18-arm star-shaped polystyrene-block-poly(methyl methacrylate) copolymers ((PS-b-PMMA)18) with various volume fractions of PMMA block (f PMMA) was investigated by transmission electron microscopy and small-angle X-ray scattering. (PS-b-PMMA)18 was synthesized by atom transfer radical polymerization from α-cyclodextrin (α-CD) having 18 functional groups for the initiation. We also prepared the corresponding linear PS-b-PMMAs by cutting the ester groups connecting α-CD and PS chains in (PS-b-PMMA)18 through the hydrolysis. The microdomains of (PS-b-PMMA)18 changed from body-centered-cubic spheres (BCC), hexagonally packed cylinders (HEX), perforated lamellae (PL), and lamellae (LAM), with increasing f PMMA from 0.3 to 0.8. Interestingly, (PS-b-PMMA)18 with f PMMA of 0.77 showed highly asymmetric lamellar microdomains, while the corresponding linear PS-b-PMMA with the same volume fraction should not have lamellar microdomains. Thus, the microdomains are highly affected by the molecular architecture of block copolymer. The experimental results are discussed with the prediction based on the self-consistent mean-field theory.

We investigated, via scanning and transmission electron microscopy, the arrangement of the microdomains of symmetric polystyreneblock-poly(methyl methacrylate) copolymer (PS-b-PMMA) confined in hemispherical cavities. The hemispherical cavities were prepared by using anodic aluminum oxide (AAO) template, where the inner surface of the cavities was modified by thin brush layers of PS, PMMA, and PS-ran-PMMA copolymer. When the inner surface of the cavity is strongly selective to PS chains, concentric rings consisting of PS and PMMA microdomains are formed, replicating the confined geometry of hemisphere. However, as the selectivity of a brush to PS chains becomes weaker, various interesting morphologies are formed that have not been reported in the literature. The experimentally observed microdomain arrangement confined inside the hemispherical cavities was compared with the simulation results based on the dynamic Metropolis Monte Carlo method.

We fabricated a high density array of concentric silver nanorings in a large area (over in. 2 ) with uniform gap distance by utilizing half onion-shaped microdomains prepared by symmetric polystyrene-block-poly(methyl methacrylate) copolymers (PS-b-PMMA) confined within hemispherical cavities in anodized aluminum oxide (AAO) template. Silver nanoparticles with 6 nm height were selectively deposited only on the PS microdomains by thermal evaporation. The gap distance of two neighboring silver nanorings was controlled from 12 to 24 nm by changing the total molecular weight of PS-b-PMMAs. The substrate showed high surface-enhanced Raman scattering (SERS) enhancement factor as high as 4.3 × 10 7 with good reproducibility (±7%). It could be used for biosensing, detection of trace-level explosive and hazardous chemicals, and reaction monitoring.

We introduce a novel method to improve the device performance of P3HT:CdSe hybrid solar cells by using selenourea (SeU) for ligand exchange. SeU induces interconnection of CdSe nanorods in the nanoscale range without severe aggregation. The power conversion efficiency of the devices with SeU is improved from 1.71% to 2.63% due to efficient charge transport through interconnected CdSe nanorods.

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