Directed Assembly of Lamellae Forming Block Copolymer Thin Films near the Order–Disorder Transition

The impact of thin film confinement on the ordering of lamellae was investigated using symmetric poly­(styrene-<i>b</i>-[isoprene-<i>ran</i>-epoxyisoprene]) diblock copolymers bound by nonpreferential wetting interfaces. The order–disorder transition temperature (<i>T</i>_ODT) and the occurrence of composition fluctuations in the disordered state are not significantly affected by two-dimensional confinement. Directed self-assembly using chemical patterning is demonstrated near <i>T</i>_ODT. These results establish the minimum feature size attainable using directed self-assembly of a given diblock copolymer system

Decoupling Bulk Thermodynamics and Wetting Characteristics of Block Copolymer Thin Films

The consequences on certain physical properties of controlled levels of epoxidation of the poly­(isoprene) blocks in poly­(styrene-<i>b</i>-isoprene) (PS-PI) diblock copolymers and poly­(isoprene) (hPI) homopolymers have been studied, where the products after epoxidation are denoted PS-PIxn and hPIxn, respectively. The effective interaction parameters χ_eff between the PS and the PIxn blocks were estimated by applying mean-field theory to the lamellar periodicities identified by small-angle X-ray scattering and to the order-to-disorder transition temperatures determined by dynamic mechanical spectroscopy. These results were fit to a binary segment–segment interaction parameter model indicating a nonlinear change in χ_eff with percent epoxidation. In contrast, contact angle measurement on hPIxn and lamellar orientations of thin-film PS-PIxn suggest that the surface energy of PIxn increases linearly with epoxidation. This decoupling of bulk and thin-film thermodynamic behaviors is attributed to the different roles that a random copolymer architecture plays in establishing three-dimensional order versus wetting at a two-dimensional surface

Free Energy of Defects in Ordered Assemblies of Block Copolymer Domains

We investigate commonly occurring defects in block copolymer thin films assembled on chemically nanopatterned substrates and predict their probability of occurrence by computing their free energies. A theoretically informed 3D coarse grain model is used to describe the system. These defects become increasingly unstable as the strength of interactions between the copolymer and the patterned substrate increases and when partial defects occur close to the top surface of the film. The results presented here reveal an extraordinarily large thermodynamic driving force for the elimination of defects. When the characteristics of the substrate are commensurate with the morphology of the block copolymer, the probability of creating a defect is extremely small and well below the specifications of the semiconductor industry for fabrication of features having characteristic dimensions on the scale of tens of nanometers. We also investigate how the occurrence of defect changes when imperfections arise in the underlying patterns and find that, while defects continue to be remarkably unstable, stretched patterns are more permissive than compressed patterns

Directed Self-Assembly of High χ Poly(styrene‑<i>b</i>‑(lactic acid-<i>alt</i>-glycolic acid)) Block Copolymers on Chemical Patterns via Thermal Annealing

We demonstrated the synthesis and directed self-assembly (DSA) of poly­(styrene-<i>b</i>-(lactic acid-<i>alt</i>-glycolic acid)) (PS-<i>b</i>-PLGA). Lamellae-forming PS-<i>b</i>-PLGAs with a range of molecular weights were synthesized by ring-opening polymerization (ROP) of LGA (d,l-3-methyl-1,4-dioxane-2,5-dione) from hydroxy-terminated polystyrene (PS–OH) with stannous octoate as the catalyst and characterized by ¹H NMR spectroscopy, GPC, DSC, TGA, SAXS, and rheometry. The order–disorder transition temperatures (<i>T</i>_ODT) of four PS-<i>b</i>-PLGA block copolymers were determined by temperature sweep measurements and verified by variable-temperature SAXS, which were used to determine the temperature dependence of χ. The χ value of PS-<i>b</i>-PLGA is twice as large as that of poly­(styrene-<i>b</i>-<i>racemic</i> lactide) (PS-<i>b</i>-PDLLA) at 150 °C, while the surface energies (γ) of PS and PLGA are nearly equal. Thin films of PS-<i>b</i>-PLGA were successfully directed to assemble on stripe chemical patterns with a range of pattern periods (<i>L</i>_S) upon thermal annealing. SEM analysis of the assembled films revealed that long-range ordered perpendicularly oriented lamellae were registered on chemical patterns with 2× density multiplication. These results qualify PS-<i>b</i>-PLGA as an attractive candidate for next-generation lithography with sub-10 nm resolution

Light-Activated Replication of Block Copolymer Fingerprint Patterns

A strategy to replicate fingerprint patterns formed by the self-assembly of lamella-forming block copolymer (BCP) was investigated. To accomplish this, liquid conformal layers were placed between the surfaces of a “master” BCP film and a transparent “replica” substrate that solidified and covalently bonded to the BCP upon exposure to light. The benzophenone-containing conformal layer enabled pattern replication over areas limited only by the size of the samples and exposure field. The replication step is light activated, occurs below the glass transition of the BCP, and takes less than 1 h. This demonstration used a poly­(styrene-<i>b</i>-methyl methacrylate) BCP with a bulk domain periodicity of 42 nm, but it is possible that the chemistry may be generalized to many other BCPs. Control experiments conducted with alternative conformal layer compositions indicate that interfacial photosensitization of the BCP by excited benzophenone, followed by propagation to residual acrylate groups present in the conformal layer, is the primary mechanism by which pattern replication takes place

Light-Activated Replication of Block Copolymer Fingerprint Patterns

A strategy to replicate fingerprint patterns formed by the self-assembly of lamella-forming block copolymer (BCP) was investigated. To accomplish this, liquid conformal layers were placed between the surfaces of a “master” BCP film and a transparent “replica” substrate that solidified and covalently bonded to the BCP upon exposure to light. The benzophenone-containing conformal layer enabled pattern replication over areas limited only by the size of the samples and exposure field. The replication step is light activated, occurs below the glass transition of the BCP, and takes less than 1 h. This demonstration used a poly­(styrene-<i>b</i>-methyl methacrylate) BCP with a bulk domain periodicity of 42 nm, but it is possible that the chemistry may be generalized to many other BCPs. Control experiments conducted with alternative conformal layer compositions indicate that interfacial photosensitization of the BCP by excited benzophenone, followed by propagation to residual acrylate groups present in the conformal layer, is the primary mechanism by which pattern replication takes place

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A strategy to replicate fingerprint patterns formed by the self-assembly of lamella-forming block copolymer (BCP) was investigated. To accomplish this, liquid conformal layers were placed between the surfaces of a “master” BCP film and a transparent “replica” substrate that solidified and covalently bonded to the BCP upon exposure to light. The benzophenone-containing conformal layer enabled pattern replication over areas limited only by the size of the samples and exposure field. The replication step is light activated, occurs below the glass transition of the BCP, and takes less than 1 h. This demonstration used a poly­(styrene-<i>b</i>-methyl methacrylate) BCP with a bulk domain periodicity of 42 nm, but it is possible that the chemistry may be generalized to many other BCPs. Control experiments conducted with alternative conformal layer compositions indicate that interfacial photosensitization of the BCP by excited benzophenone, followed by propagation to residual acrylate groups present in the conformal layer, is the primary mechanism by which pattern replication takes place

Light-Activated Replication of Block Copolymer Fingerprint Patterns

A strategy to replicate fingerprint patterns formed by the self-assembly of lamella-forming block copolymer (BCP) was investigated. To accomplish this, liquid conformal layers were placed between the surfaces of a “master” BCP film and a transparent “replica” substrate that solidified and covalently bonded to the BCP upon exposure to light. The benzophenone-containing conformal layer enabled pattern replication over areas limited only by the size of the samples and exposure field. The replication step is light activated, occurs below the glass transition of the BCP, and takes less than 1 h. This demonstration used a poly­(styrene-<i>b</i>-methyl methacrylate) BCP with a bulk domain periodicity of 42 nm, but it is possible that the chemistry may be generalized to many other BCPs. Control experiments conducted with alternative conformal layer compositions indicate that interfacial photosensitization of the BCP by excited benzophenone, followed by propagation to residual acrylate groups present in the conformal layer, is the primary mechanism by which pattern replication takes place

Self-Assembled Nanoparticle Arrays on Chemical Nanopatterns Prepared Using Block Copolymer Lithography

We present a high-throughput and inexpensive fabrication approach that uses self-assembled block copolymer (BCP) films as templates to generate dense nanoscale chemical patterns of polymer brushes for the selective immobilization of Au nanoparticles (NPs). A cross-linked random copolymer mat that contains styrene and methyl methacrylate units serves both as a base layer for perpendicular assembly of nanoscale domains of poly­(styrene-<i>block</i>-methyl methacrylate) (PS-<i>b</i>-PMMA) films and as a nonadsorbing background layer that surrounds the chemical patterns. The selective removal of the PMMA block and the underlying mat via oxygen plasma etching generates binding sites which are then functionalized with poly­(2-vinylpyridine) (P2VP) brushes. Au NPs with a diameter of 13 nm selectively immobilize on the patterned P2VP brushes. An essential aspect in fabricating high quality chemical patterns is the superior behavior of methyl methacrylate containing cross-linked mats in retaining their chemistry during the grafting of P2VP brushes. The use of BCPs with different molecular weights and volume fractions allows for preparation of chemical patterns with different geometries, sizes, and pitches for generating arrays of single particles that hold great promise for applications that range from molecular sensing to optical devices

Entropic Penalty Switches Li⁺ Solvation Site Formation and Transport Mechanisms in Mixed Polarity Copolymer Electrolytes

Emerging solid polymer electrolyte (SPE) designs for efficient Li-ion (Li+) conduction have relied on polarity and mobility contrast to improve conductivity. To further develop this concept, we employ simulations to examine Li+ solvation and transport in poly(oligo ethylene methacrylate) (POEM) and its copolymers with poly(glycerol carbonate methacrylate) (PGCMA). We find that Li+ is solvated by ether oxygens instead of the highly polar PGCMA, due to lower entropic penalties. The presence of PGCMA promotes single-chain solvation, thereby suppressing interchain Li+ hopping. The conductivity difference between random copolymer PGCMA-r-POEM and block copolymer PGCMA-b-POEM is explained in terms of a hybrid solvation site mechanism. With diffuse microscopic interfaces between domains, PGCMA near the POEM contributes to Li+ transport by forming hybrid solvation sites. The formation of such sites is hindered when PGCMA is locally concentrated. These findings help explain how thermodynamic driving forces govern Li+ solvation and transport in mixed SPEs