Directed Assembly of Block Copolymer Blends into Nonregular Device-Oriented Structures

Highly Ordered Eutectic Mesostructures via Template-Directed Solidification within Thermally Engineered Templates

Template-directed self-assembly of solidifying eutectics results in emergence of unique microstructures due to diffusion constraints and thermal gradients imposed by the template. Here, the importance of selecting the template material based on its conductivity to control heat transfer between the template and the solidifying eutectic, and thus the thermal gradients near the solidification front, is demonstrated. Simulations elucidate the relationship between the thermal properties of the eutectic and template and the resultant microstructure. The overarching finding is that templates with low thermal conductivities are generally advantageous for forming highly organized microstructures. When electrochemically porosified silicon pillars (thermal conductivity < 0.3 Wm-1K-1) are used as the template into which an AgCl-KCl eutectic is solidified, 99% of the unit cells in the solidified structure exhibit the same pattern. In contrast, when higher thermal conductivity crystalline silicon pillars (≈100 Wm-1K-1) are utilized, the expected pattern is only present in 50% of the unit cells. The thermally engineered template results in mesostructures with tunable optical properties and reflectances nearly identical to the simulated reflectances of perfect structures, indicating highly ordered patterns are formed over large areas. This work highlights the importance of controlling heat flows in template-directed self-assembly of eutectics.

Droplet dynamics affecting the shape of patterns formed spontaneously by transforming UV-curable emulsions

Forming large pitch and depth patterns spontaneously based on a bottom-up approach is a challenging task but with great industrial value. It is possible to spontaneously form an uneven (concave-convex) patterns with submillimeter-to-millimeter-scale pitches and depths by the direct pattern exposure of a UV-curable oil-in-water (O/W) emulsion liquid film. UV irradiation generates a latent pattern of a cured particle aggregation in the liquid film, and an uneven structure is spontaneously formed during the subsequent drying process. This process does not require any printing and embossing plates or development process. In this report, we presented an example of unevenness formation with a maximum pattern depth of approximately 0.4 mm and a maximum pitch width of 5 mm. The patterns formed by this method have raised edges in the exposed areas and fogging in unexposed areas. The pattern shapes become conspicuous under overexposure conditions, but the formation mechanism has not yet been understood in detail and needs to be investigated. In this study, we focused on the exposure process and clarified the mechanism of pattern formation by analyzing the dynamics of emulsion droplets in the medium by an in situ microscopy observation method. As a result, we found that the fogging was mainly caused by light leakage from the exposed area, and the raised pattern edges were caused by droplets transported from the unexposed area to the exposed area. Furthermore, the convection caused by the heat generated from polymerization is a determining factor affecting all these phenomena. By controlling the pattern shape related to convection utilizing direct projection exposure, we showed an example of eliminating raised pattern edges with a height difference of approximately 0.1 mm. By devising and selecting exposure methods, we can expand the range of design applications such as interior decorative patterns.

Focused solar annealing for block copolymer fast self-assembly

Block copolymer (BCP) self-assembly has tremendous potential applications in next-generation nanolithography. It offers significant advantages, including high resolution and cost-effectiveness, effectively overcoming the limitations associated with conventional optical lithography. In this work, we demonstrate a focused solar annealing (FSA) technique that is facile, eco-friendly, and energy-efficient for fast self-assembly of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) thin films. The FSA principle involves utilizing a common biconvex lens to converge incident solar radiation into a high-temperature spot, which is directly used to drive the microphase separation of PS-b-PMMA thin films. As a result, PS-b-PMMA undergoes self-assembly, forming ordered nanostructures in a vertical orientation at seconds timescales on silicon substrates with a neutral layer. In addition, the FSA technique can be employed for grafting neutral polymer brushes onto the silicon substrate. Furthermore, the FSA's compatibility with graphoepitaxy-directed self-assembly (DSA) of BCP is also demonstrated in the patterning of contact holes. The results of contact hole shrinking show that contact hole prepatterns of ∼60.4 nm could be uniformly shrunk to ∼20.5 nm DSA hole patterns with a hole open yield (HOY) of 100 %. For contact hole multiplication, doublet DSA holes were successfully generated on elliptical templates, revealing an average DSA hole size of ∼21.3 nm. Most importantly, due to the direct use of solar energy, the FSA technique provides many significant advantages such as simplicity, environmental friendliness, solvent-free, low cost, and net-zero carbon emissions, and will open up a new direction for BCP lithography that is sustainable, pollution-free, and carbon-neutral.

Illuminating Recent Progress in Nanotransfer Printing: Core Principles, Emerging Applications, and Future Perspectives

As the demand for diverse nanostructures in physical/chemical devices continues to rise, the development of nanotransfer printing (nTP) technology is receiving significant attention due to its exceptional throughput and ease of use. Over the past decade, researchers have attempted to enhance the diversity of materials and substrates used in transfer processes as well as to improve the resolution, reliability, and scalability of nTP. Recent research on nTP has made continuous progress, particularly using the control of the interfacial adhesion force between the donor mold, target material, and receiver substrate, and numerous practical nTP methods with niche applications have been demonstrated. This review article offers a comprehensive analysis of the chronological advancements in nTP technology and categorizes recent strategies targeted for high-yield and versatile printing based on controlling the relative adhesion force depending on interfacial layers. In detail, the advantages and challenges of various nTP approaches are discussed based on their working mechanisms, and several promising solutions to improve morphological/material diversity are presented. Furthermore, this review provides a summary of potential applications of nanostructured devices, along with perspectives on the outlook and remaining challenges, which are expected to facilitate the continued progress of nTP technology and to inspire future innovations.

Roll-to-plate 0.1-second shear-rolling process at elevated temperature for highly aligned nanopatterns

The shear-rolling process is a promising directed self-assembly method that can produce high-quality sub-10 nm block copolymer line-space patterns cost-effectively and straightforwardly over a large area. This study presents a high temperature (280 °C) and rapid (~0.1 s) shear-rolling process that can achieve a high degree of orientation in a single process while effectively preventing film delamination, that can be applied to large-area continuous processes. By minimizing adhesion, normal forces, and ultimate shear strain of the polydimethylsiloxane pad, shearing was successfully performed without peeling up to 280 °C at which the chain mobility significantly increases. This method can be utilized for various high-χ block copolymers and surface neutralization processes. It enables the creation of block copolymer patterns with a half-pitch as small as 8 nm in a unidirectional way. Moreover, the 0.1-second rapid shear-rolling was successfully performed on long, 3-inch width polyimide flexible films to validate its potential for the roll-to-roll process.

Morphologies of Surface Perforations and Parallel Cylinders Coexisting in Terraced Films of Block Copolymer/Homopolymer Blends with Oxygen Plasma Etching

This study has demonstrated how oxygen plasma etching carves surface structures for thin films of polystyrene-block-poly(methyl methacrylate)/homopolystyrene blends. By tuning the weight-fraction ratio, blend films form perforations and cylinders on the SiOx/Si substrate. Since perforations exist only on the free surface and substrate interface, short exposure to oxygen plasma to quickly etch the PMMA component produces distorted hexagonal arrays of nanodots on the free surface. The interior of the blend films forms polygrain micro-structures composed of parallel cylinders with an in-plane random orientation. Oxygen plasma etching imposed on the fractured surfaces results in five morphologies: (i) distorted hexagonal arrays of nanoholes, (ii) layer-by-layer stacks, (iii) zigzag-like arrays, (iv) intertwined rectangular arrays of nanodots and nanoholes, and (v) intertwined parallelogram arrays of nanodots and nanoholes. The morphologies suggest synergic effects of grain orientations, stresses, spatial confinement, local segregation of chains, and etching kinetics on the terraced films with oxygen plasma etching.

Emerging exotic compositional order on approaching low-temperature equilibrium glasses

The ultimate fate of a glass former upon cooling has been a fundamental problem in condensed matter physics and materials science since Kauzmann. Recently, this problem has been challenged by a model with an extraordinary glass-forming ability effectively free from crystallisation and phase separation, two well-known fates of most glass formers, combined with a particle-size swap method. Thus, this system is expected to approach the ideal glass state if it exists. However, we discover exotic compositional order as the coexistence of space-spanning network-like structures formed by small-large particle connections and patches formed by medium-size particles at low temperatures. Therefore, the glass transition is accompanied unexpectedly by exotic compositional ordering inaccessible through ordinary structural or thermodynamic characterisations. Such exotic compositional ordering is found to have an unusual impact on structural relaxation dynamics. Our study thus raises fundamental questions concerning the role of unconventional structural ordering in understanding glass transition.

Highly conductive tissue-like hydrogel interface through template-directed assembly

Over the past decade, conductive hydrogels have received great attention as tissue-interfacing electrodes due to their soft and tissue-like mechanical properties. However, a trade-off between robust tissue-like mechanical properties and good electrical properties has prevented the fabrication of a tough, highly conductive hydrogel and limited its use in bioelectronics. Here, we report a synthetic method for the realization of highly conductive and mechanically tough hydrogels with tissue-like modulus. We employed a template-directed assembly method, enabling the arrangement of a disorder-free, highly-conductive nanofibrous conductive network inside a highly stretchable, hydrated network. The resultant hydrogel exhibits ideal electrical and mechanical properties as a tissue-interfacing material. Furthermore, it can provide tough adhesion (800 J/m²) with diverse dynamic wet tissue after chemical activation. This hydrogel enables suture-free and adhesive-free, high-performance hydrogel bioelectronics. We successfully demonstrated ultra-low voltage neuromodulation and high-quality epicardial electrocardiogram (ECG) signal recording based on in vivo animal models. This template-directed assembly method provides a platform for hydrogel interfaces for various bioelectronic applications.

Direct Visualization of the Self-Alignment Process for Nanostructured Block Copolymer Thin Films by Transmission Electron Microscopy

Herein, this work aims to directly visualize the morphological evolution of the controlled self-assembly of star-block polystyrene-block-polydimethylsiloxane (PS-b-PDMS) thin films via in situ transmission electron microscopy (TEM) observations. With an environmental chip, possessing a built-in metal wire-based microheater fabricated by the microelectromechanical system (MEMS) technique, in situ TEM observations can be conducted under low-dose conditions to investigate the development of film-spanning perpendicular cylinders in the block copolymer (BCP) thin films via a self-alignment process. Owing to the free-standing condition, a symmetric condition of the BCP thin films can be formed for thermal annealing under vacuum with neutral air surface, whereas an asymmetric condition can be formed by an air plasma treatment on one side of the thin film that creates an end-capped neutral layer. A systematic comparison of the time-resolved self-alignment process in the symmetric and asymmetric conditions can be carried out, giving comprehensive insights for the self-alignment process via the nucleation and growth mechanism.

Tip-Induced Nanopatterning of Ultrathin Polymer Brushes

Patterned, ultra-thin surface layers can serve as templates for positioning nanoparticlesor targeted self-assembly of molecular structures, for example, block-copolymers. This work investigates the high-resolution, atomic force microscopebased patterning of 2 nm thick vinyl-terminated polystyrene brush layers and evaluates the line broadening due to tip degradation. This work compares the patterning properties with those of a silane-based fluorinated self-assembled monolayer (SAM), using molecular heteropatterns generated by modified polymer blend lithography (brush/SAM-PBL). Stable line widths of 20 nm (FWHM) over lengths of over 20000 µm indicate greatly reduced tip wear, compared to expectations on uncoated SiO_x surfaces. The polymer brush acts as a molecularly thin lubricating layer, thus enabling a 5000 fold increase in tip lifetime, and the brush is bonded weakly enough that it can be removed with surgical accuracy. On traditionally used SAMs, either the tip wear is very high or the molecules are not completely removed. Polymer Phase Amplified Brush Editing is presented, which uses directed self-assembly to amplify the aspect ratio of the molecular structures by a factor of 4. The structures thus amplified allow transfer into silicon/metal heterostructures, fabricating 30 nm deep, all-silicon diffraction gratings that could withstand focused high-power 405 nm laser irradiation.

Enhanced etching resolution of self-assembled PS-b-PMMA block copolymer films by ionic liquid additives

Polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) is one of the most widely studied block copolymers for direct self-assembly because of its excellent compatibility with traditional processes. However, pattern transfer of PS-b-PMMA block copolymers (BCPs) remains a great challenge for its applications due to the insufficient etching resolution. In this study, the effect of ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate (HMHF) additives on the line edge roughness (LER) performances of PS-b-PMMA self-assembled patterns was studied. Trace addition of HMHF kept the photolithography compatibility of PS-b-PMMA block copolymer films, but obviously increased their Flory-Huggins interaction parameter (χ) and enabled phase separation of disordered low molecular weight BCPs. LER value was effectively decreased by blending HMHF directly with PS-b-PMMA or from a supplying top layer of polyvinylpyrrolidone containing HMHF additives. This study shows an excellent strategy to improve the deficiencies of existing block copolymers.

Non-Bulk Morphologies of Extremely Thin Block Copolymer Films Cast on Topographically Defined Substrates Featuring Deep Trenches: The Importance of Lateral Confinement

Directed self-assembly of block copolymers is evolving toward applications that are more defect-tolerant but still require high morphological control and could benefit from simple, inexpensive fabrication processes. Previously, we demonstrated that simply casting ultra-thin block copolymer films on topographically defined substrates leads to hierarchical structures with dual patterns in a controlled manner and unraveled the dependence of the local morphology on the topographic feature dimensions. In this article, we discuss the extreme of the ultraconfined thickness regime at the border of film dewetting. Additional non-bulk morphologies are observed at this extreme, which further elaborate the arsenal of dual patterns that could be obtained in coexistence with full placement control. It is shown that as the thickness confinement approaches its limit, lateral confinement imposed by the width of the plateaus becomes a critical factor influencing the local morphology.

Dewetting-Induced Hierarchical Self-Assembly of Block Copolymers Templated by Colloidal Crystals

Recent advances in high-performance flexible electronic devices have increased the demand for more diverse and complex nanofabrication methods; high-resolution, high-efficiency, and low-cost patterning strategies for next-generation devices are therefore required. In this study, we demonstrate the formation of dewetting-induced hierarchical patterns using two self-assembled materials: block copolymers (BCPs) and colloidal crystals. The combination of the two self-assembly methods successfully generates multiscale hierarchical patterns because the length scales of the periodic colloidal crystal structures are suitable for templating the BCP patterns. Various concentric ring patterns were observed on the templated BCP films, and a free energy model of the polymer chain was applied to explain the formation of these patterns relative to the template width. Frequently occurring spiral-defective features were also examined and found to be promoted by Y-junction defects.

Synthesis of MAPbBr3 -Polymer Composite Films by Photolysis of DMF: Toward Transparent and Flexible Optical Physical Unclonable Functions (PUFs) with Hierarchical Multilevel Complexity

Physical entities with inherent randomness have been investigated as anti-counterfeiting labels based on physical unclonable functions (PUFs). Herein, a transparent and flexible optical PUF label associated with multilevel complexity is demonstrated by taking advantage of the optical properties of hierarchical morphologies of the composite film composed of metal halide perovskite nanoparticles (MAPbBr₃ NPs) and the intrinsic spinodal-decomposition-like phase separation of polymer blend (PMMA/PS blend). Due to the combinatorial effects of the photolysis synthesis of MAPbBr₃ and the thermodynamic instability of the PMMA/PS blend, randomized patterns emerge at two-level scales. These patterns are intrinsically non-deterministic, and therefore, the PUF labels from the multilevel random patterns are challenging to replicate. This is mainly attributed to random spot patterns (higher-level patterns) confined within intricate bicontinuous patterns (lower-level patterns).

Autonomous discovery of emergent morphologies in directed self-assembly of block copolymer blends

The directed self-assembly (DSA) of block copolymers (BCPs) is a powerful approach to fabricate complex nanostructure arrays, but finding morphologies that emerge with changes in polymer architecture, composition, or assembly constraints remains daunting because of the increased dimensionality of the DSA design space. Here, we demonstrate machine-guided discovery of emergent morphologies from a cylinder/lamellae BCP blend directed by a chemical grating template, conducted without direct human intervention on a synchrotron x-ray scattering beamline. This approach maps the morphology-template phase space in a fraction of the time required by manual characterization and highlights regions deserving more detailed investigation. These studies reveal localized, template-directed partitioning of coexisting lamella- and cylinder-like subdomains at the template period length scale, manifesting as previously unknown morphologies such as aligned alternating subdomains, bilayers, or a "ladder" morphology. This work underscores the pivotal role that autonomous characterization can play in advancing the paradigm of DSA.

Hierarchically engineered nanostructures from compositionally anisotropic molecular building blocks

The inability to synthesize hierarchical structures with independently tailored nanoscale and mesoscale features limits the discovery of next-generation multifunctional materials. Here we present a predictable molecular self-assembly strategy to craft nanostructured materials with a variety of phase-in-phase hierarchical morphologies. The compositionally anisotropic building blocks employed in the assembly process are formed by multicomponent graft block copolymers containing sequence-defined side chains. The judicious design of various structural parameters in the graft block copolymers enables broadly tunable compositions, morphologies and lattice parameters across the nanoscale and mesoscale in the assembled structures. Our strategy introduces advanced design principles for the efficient creation of complex hierarchical structures and provides a facile synthetic platform to access nanomaterials with multiple precisely integrated functionalities.

Study of the ordered assembly morphologies of diblock copolymers on the same substrate

With the development of frontier technology in emerging semiconductor processes, self-assembling (SA) and directed self-assembly (DSA) of block copolymers (BCPs) have attracted great attention from scientific researchers and become promising candidates for advanced photolithography. Using an optimal coating and baking process, highly ordered assembly morphologies (e.g., cylinder and lamella) of two BCPs in thin films were obtained without an additional topcoat material layer. Moreover, the whole experimental study also provides an optimal process for integrating the two BCPs into the same topographic guiding pattern substrate fabricated by electron beam lithography (EBL) to achieve specific self-assembly. This topographic guiding substrate achieves not only lamellar micro-domains aligned perpendicular to the sidewalls of trench edges but also cylindrical micro-domains (PMMA phase in a PS matrix) aligned parallel to trench edges respectively, which provides insights and valuable information for further applications in lithography and electronic devices.

Vacuum-Driven Orientation of Nanostructured Diblock Copolymer Thin Films

This work aims to demonstrate a facile method for the controlled orientation of nanostructures of block copolymer (BCP) thin films. A simple diblock copolymer system, polystyrene-block-polydimethylsiloxane (PS-b-PDMS), is chosen to demonstrate vacuum-driven orientation for solving the notorious low-surface-energy problem of silicon-based BCP nanopatterning. By taking advantage of the pressure dependence of the surface tension of polymeric materials, a neutral air surface for the PS-b-PDMS thin film can be formed under a high vacuum degree (∼10^-4 Pa), allowing the formation of the film-spanning perpendicular cylinders and lamellae upon thermal annealing. In contrast to perpendicular lamellae, a long-range lateral order for forming perpendicular cylinders can be efficiently achieved through the self-alignment mechanism for induced ordering from the top and bottom of the free-standing thin film.

Dual Block Copolymer Morphologies in Ultrathin Films on Topographic Substrates: The Effect of Film Curvature

The ability to create mixed morphologies using easily controlled parameters is crucial for the integration of block copolymers in advanced technologies. We have previously shown that casting an ultrathin block copolymer film on a topographically patterned substrate results in different deposited thicknesses on the plateaus and in the trenches, which leads to the co-existence of two patterns. In this work, we highlight the dependence of the dual patterns on the film profile. We suggest that the steepness of the film profile formed across the plateau edge affects the nucleation of microphase-separated domains near the plateau edges, which influences the morphology that develops on the plateau regions. An analysis of the local film thicknesses in multiple samples exhibiting various combinations of plateau and trench widths for different trench depths enabled the construction of phase diagrams, which unraveled the intricate dependence of the formed patterns not only on the curvature of the film profile but also on the fraction of the film that resides in the trenches. Our analysis facilitates the prediction of the patterns that would develop in the trenches and on the plateaus for a given block copolymer film of known thickness from the dimensions of the topographic features.

Hybrid Time-Dependent Ginzburg–Landau Simulations of Block Copolymer Nanocomposites: Nanoparticle Anisotropy

Block copolymer melts are perfect candidates to template the position of colloidal nanoparticles in the nanoscale, on top of their well-known suitability for lithography applications. This is due to their ability to self-assemble into periodic ordered structures, in which nanoparticles can segregate depending on the polymer–particle interactions, size and shape. The resulting coassembled structure can be highly ordered as a combination of both the polymeric and colloidal properties. The time-dependent Ginzburg–Landau model for the block copolymer was combined with Brownian dynamics for nanoparticles, resulting in an efficient mesoscopic model to study the complex behaviour of block copolymer nanocomposites. This review covers recent developments of the time-dependent Ginzburg–Landau/Brownian dynamics scheme. This includes efforts to parallelise the numerical scheme and applications of the model. The validity of the model is studied by comparing simulation and experimental results for isotropic nanoparticles. Extensions to simulate nonspherical and inhomogeneous nanoparticles are discussed and simulation results are discussed. The time-dependent Ginzburg–Landau/Brownian dynamics scheme is shown to be a flexible method which can account for the relatively large system sizes required to study block copolymer nanocomposite systems, while being easily extensible to simulate nonspherical nanoparticles.

Thin film block copolymer self-assembly for nanophotonics

The nanophotonic engineering of light-matter interactions has profoundly changed research behind the design and fabrication of optical materials and devices. Metasurfaces-arrays of subwavelength nanostructures that interact resonantly with electromagnetic radiation-have emerged as an integral nanophotonic platform for a new generation of ultrathin lenses, displays, polarizers and other devices. Their success hinges on advances in lithography and nanofabrication in recent decades. While existing nanolithography techniques are suitable for basic research and prototyping, issues of cost, throughput, scalability, and substrate compatibility may preclude their use for many metasurface applications. Patterning via spontaneous self-assembly of block copolymer thin films offers an enticing alternative for nanophotonic manufacturing that is rapid, inexpensive, and applicable to large areas and diverse substrates. This review discusses the advantages and disadvantages of block copolymer-based nanopatterning and highlights recent progress in their use for broadband antireflection, surface enhanced Raman spectroscopy, and other nanophotonic applications. Recent advances in diversification of self-assembled block copolymer nanopatterns and improved processes for enhanced scalability of self-assembled nanopatterning using block copolymers are also discussed, with a spotlight on directions for future research that would enable a wider array of nanophotonic applications.

Large-Area Uniform 1-nm-Level Amorphous Carbon Layers from 3D Conformal Polymer Brushes. A "Next-Generation" Cu Diffusion Barrier?

A reliable method for preparing a conformal amorphous carbon (a-C) layer with a thickness of 1-nm-level, is tested as a possible Cu diffusion barrier layer for next-generation ultrahigh-density semiconductor device miniaturization. A polystyrene brush of uniform thickness is grafted onto 4-inch SiO₂ /Si wafer substrates with "self-limiting" chemistry favoring such a uniform layer. UV crosslinking and subsequent carbonization transforms this polymer film into an ultrathin a-C layer without pinholes or hillocks. The uniform coating of nonplanar regions or surfaces is also possible. The Cu diffusion "blocking ability" is evaluated by time-dependent dielectric breakdown (TDDB) tests using a metal-oxide-semiconductor (MOS) capacitor structure. A 0.82 nm-thick a-C barrier gives TDDB lifetimes 3.3× longer than that obtained using the conventional 1.0 nm-thick TaN_x diffusion barrier. In addition, this exceptionally uniform ultrathin polymer and a-C film layers hold promise for selective ion permeable membranes, electrically and thermally insulating films in electronics, slits of angstrom-scale thickness, and, when appropriately functionalized, as a robust ultrathin coating with many other potential applications.

A Single Crystal 2D Hexagonal Array in a Centimeter Scale with a Self-Directed Assembly of Diblock Copolymer Spheres

The creation of a single-grain two-dimensional (2D) nanoarray over a large area (∼1 cm²) has been only realized with expensive lithographic fabrication involving a complicated multichemical process. In this work, we report the production of a highly aligned single-grain 2D crystalline nanoarray over a centimeter-scale large area with a concept of self-directed assembly (SDA) in block copolymer (BCP) thin films. No lithographic guiding pattern is employed in SDA. A sphere-forming BCP is first transformed to transient-cylinders and aligned with shear. The aligned cylinders act as a guiding pattern to restore the sphere-morphology producing a single-grain 2D crystalline array with the following solvent vapor annealing. The SDA process has two governing parameters: orientational order of guiding patterns in the first step and the lattice matching between the transient guiding cylinders and the restored spheres. The successful application of SDA yields a single-grain of 2D crystalline hexagonal nanoarray with an exceptional long-range order, which is confirmed by employing image treating algorithms and grazing incidence small-angle X-ray scattering (GISAXS) measurements. The suggested SDA strategy is found to be effective for large-scale nanopatterning with no lithographic tools.

Soft-Shear-Aligned Vertically Oriented Lamellar Block Copolymers for Template-Free Sub-10 nm Patterning and Hybrid Nanostructures

The template-free unidirectional alignment of lamellar block copolymers (l-BCPs) for sub-10 nm high-resolution patterning and hybrid multicomponent nanostructures is important for technological applications. We demonstrate a modified soft-shear-directed self-assembly (SDSA) approach for aligning pristine l-BCPs and l-BCPs with incorporated polymer-grafted nanoparticles (PGNPs), as well as the l-BCP conversion to aligned gold nanowires, and hybrid of metallic gold nanowire and dielectric silica nanoparticle in the form of line-dot nanostructures. The smallest patterns have a half-pitch as small as 9.8 nm. In all cases, soft-shear is achieved using a high-molecular-mass polymer topcoat layer, with support on a neutral bottom layer. We also show that the hybrid line-dot nanostructures have a red-shifted plasmonic response in comparison to neat gold nanowires. These template-free aligned BCPs and nanowires have potential use in nanopatterning applications, and the line-dot nanostructures should be useful in the sensing of biomolecules and other molecular species based on the plasmonic response of the nanowires.

Block Copolymer Nanopatterning for Nonsemiconductor Device Applications

Block copolymer (BCP) nanopatterning has emerged as a versatile nanoscale fabrication tool for semiconductor devices and other applications, because of its ability to organize well-defined, periodic nanostructures with a critical dimension of 5-100 nm. While the most promising application field of BCP nanopatterning has been semiconductor devices, the versatility of BCPs has also led to enormous interest from a broad spectrum of other application areas. In particular, the intrinsically low cost and straightforward processing of BCP nanopatterning have been widely recognized for their large-area parallel formation of dense nanoscale features, which clearly contrasts that of sophisticated processing steps of the typical photolithographic process, including EUV lithography. In this Review, we highlight the recent progress in the field of BCP nanopatterning for various nonsemiconductor applications. Notable examples relying on BCP nanopatterning, including nanocatalysts, sensors, optics, energy devices, membranes, surface modifications and other emerging applications, are summarized. We further discuss the current limitations of BCP nanopatterning and suggest future research directions to open up new potential application fields.

Visualization of nonsingular defect enabling rapid control of structural color

Stimuli-interactive structural color (SC) of a block copolymer (BCP) photonic crystal (PC) uses reversible alteration of the PC using external fluids and applied forces. The origin of the diffusional pathways of a stimulating fluid into a BCP PC has not been examined. Here, we directly visualize the vertically oriented screw dislocations in a one-dimensional lamellar BCP PC that facilitate the rapid response of visible SC. To reveal the diffusional pathway of the solvent via the dislocations, BCP lamellae are swollen with an interpenetrated hydrogel network, allowing fixation of the swollen state and subsequent microscopic examination. The visualized defects are low-energy helicoidal screw dislocations having unique, nonsingular cores. Location and areal density of these dislocations are determined by periodic concentric topographic nanopatterns of the upper surface-reconstructed layer. The nonsingular nature of the interlayer connectivity in the core region demonstrates the beneficial nature of these defects on sensing dynamics.

Spontaneous patterning method utilizing transformation of UV-curable emulsion

A self-organizing structure is important for imparting functions and simplifying the manufacturing process. The development of spontaneous structures with a roll-to-roll process capability is a challenging task. We propose a novel patterning method utilizing the destruction of the emulsion structure. An oil-in-water (O/W) UV-curable emulsion liquid film was partially exposed to UV, resulting in aggregation and immobilization of the emulsion in the medium. Emulsion droplets in the unexposed area are coalesced by removing water. Coalesced emulsion droplets expand and spontaneously permeate into the pores formed in the aggregated structure of UV-cured emulsion particles, causing an uneven structure. An uneven pattern can be formed by direct UV exposure of the liquid film and the subsequent drying process without requiring a development process.

Blending Linear and Cyclic Block Copolymers to Manipulate Nanolithographic Feature Dimensions

Block copolymers (BCPs) consist of two or more covalently bound chemically distinct homopolymer blocks. These macromolecules have emerging applications in photonics, membrane separations, and nanolithography stemming from their self-assembly into regular nanoscale structures. Theory suggests that cyclic BCPs should form features up to 40% smaller than their linear analogs while also exhibiting superior thin-film stability and assembly dynamics. However, the complex syntheses required to produce cyclic polymers mean that a need for pure cyclic BCPs would present a challenge to large-scale manufacturing. Here, we employ dissipative particle dynamics simulations to probe the self-assembly behavior of cyclic/linear BCP blends, focusing on nanofeature size and interfacial width as these qualities are critical to nanopatterning applications. We find that for mixtures of symmetric cyclic and linear polymers with equivalent lengths, up to 10% synthetic impurity has a minimal impact on cyclic BCP feature dimensions and interfacial roughness. On the other hand, blending with cyclic BCPs provides a route to "fine-tune" linear BCP feature sizes. We analyze simulated blend domain spacings within the context of strong segregation theory and find significant deviations between simulation and theory that arise from molecular-level packing motifs not included in theory. These insights into blend self-assembly will assist experimentalists in rationally designing BCP materials for advanced nanolithography applications.

Selective Deposition of Copper on Self-Assembled Block Copolymer Surfaces via Physical Vapor Deposition

Block copolymer (BCP) self-assembly produces chemically and topographically patterned surfaces which are used to guide the formation of Cu nanostructures by exploiting differences in the mobility of vapor-deposited species on each microdomain. Cu metal films a few nm thick were deposited on three different BCP surfaces self-assembled from poly(styrene-b-methyl methacrylate) (PS-b-PMMA) and polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP). For PS-b-PMMA, the effects of chemical heterogeneity dominate over the effects of the 2 nm peak-to-valley topography, and sputtered Cu preferentially wets the PS block. PS-b-P2VP has greater chemical and topographical contrast and shows a wider process window for selective deposition. Cu grown by evaporation has less surface mobility, and shadowing effects are believed to dominate pattern formation. The hierarchical self-assembly process of thin metal films on BCP surfaces provides a route to fabricating heterogeneous metallic nanostructures.

Distributions of Deuterated Polystyrene Chains in Perforated Layers of Blend Films of a Symmetric Polystyrene-block-poly(methyl methacrylate)

We have examined the spatial distributions of polymer chains in blend films of weakly segregated polystyrene-block-poly(methyl methacrylate) [P(S-b-MMA)] and deuterated polystyrene (dPS). By fine-tuning the composition (ϕ_PS+dPS = 63.8 vol %) of the total PS/dPS component and annealing temperature (230 and 270 °C), P(S-b-MMA)/dPS blend films mainly form perforated layers with a parallel orientation (hereafter PLs^//). The distributions of dPS in PLs^// were probed by grazing-incidence small-angle neutron scattering (GISANS) and time-of-flight neutron reflectivity (ToF-NR). GISANS and ToF-NR results offer evidence that dPS chains preferentially locate at the free surface and within the PS layers for blend films that were annealed at 230 °C. Upon annealing at 270 °C, dPS chains distribute within PS layers and perforated PMMA layers. Nevertheless, dPS chains still retain a surface preference for thin films. In contrast, such surface segregation of dPS chains is prohibited for thick films when annealed at 270 °C.

Phase behavior in thin films of weakly segregated block copolymer/homopolymer blends

We have demonstrated the phase behavior of substrate-supported films of a symmetric weakly segregated polystyrene-block-poly (methyl methacrylate), P(S-b-MMA), block copolymer and its blends with homopolymer polystyrene (PS) at different compositions. Upon increasing the content of added PS in the blends, lamellae (L), perforated layers (PL), double gyroid (DG) and cylinders (C) are obtained in sequence for films. Among these nanodomains, PL and DG only exist in a narrow ϕ_PS region (ϕ_PS denotes the volume fraction of PS). At ϕ_PS = 64%, tuning film thickness and annealing temperature can produce parallel PL or DG with {121}_DG lattice planes being parallel to the substrate surface. The effects of annealing temperature and film thickness on the formation of PL and DG are examined. In thin films with n ≈ 3 (n denotes the ratio of initial film thickness to inter-domain spacing), the PL phase solely exists regardless of temperature. However, for thick films with n ≈ 6 and 10, thermal annealing at the most accessible temperature produces films containing both PL and DG of various fractions, but a low temperature tends to favor a greater fraction of PL. The PL phase becomes the only discernible phase if thick films are shortly annealed at 230 °C.

Orbital Angular Momentum from Self-Assembled Concentric Nanoparticle Rings

Ring-shaped nanostructures can focus, filter, and manipulate electromagnetic waves, but are challenging to incorporate into devices using standard nanofabrication techniques. Directed self-assembly (DSA) of block copolymers (BCPs) on lithographically patterned templates has successfully been used to fabricate concentric rings and spirals as etching masks. However, this method is limited by BCP phase behavior and material selection. Here, a straightforward approach to generate ring-shaped nanoparticle assemblies in thin films of supramolecular nanocomposites is demonstrated. DSA is used to guide the formation of concentric rings with radii spanning 150-1150 nm and ring widths spanning 30-60 nm. When plasmonic nanoparticles are used, ring nanodevice arrays can be fabricated in one step, and the completed devices produce high-quality orbital angular momentum (OAM). Nanocomposite DSA simplifies and streamlines nanofabrication by producing metal structures without etching or deposition steps; it also introduces interparticle coupling as a new design axis. Detailed analysis of the nanoparticle ring assemblies confirms that the supramolecular system self-regulates the spatial distribution of its components, and thus exhibits a degree of flexibility absent in DSA of BCPs alone, where structures are determined by polymer-pattern incommensurability. The present studies also provide guidelines for developing self-regulating DSA as an alternative to incommensurability-driven methods.

Influence of Osmotic Pressure on Nanostructures in Thin Films of a Weakly-Segregated Block Copolymer and Its Blends with a Homopolymer

We studied the influence of osmotic pressure on nanostructures in thin films of a symmetric weakly-segregated polystyrene-block-poly (methyl methacrylate), P(S-b-MMA), block copolymer and its mixtures with a polystyrene (PS) homopolymer of various compositions. Thin films were deposited on substrates through surface neutralization. The surface neutralization results from the PS mats, which were oxidized and cross-linked by UV-light exposure. Thus, thermal annealing produced perpendicularly oriented lamellae and perforated layers, depending on the content of added PS chains. Nevertheless, a mixed orientation was obtained from cylinders in thin films, where a high content of PS was blended with the P(S-b-MMA). A combination of UV-light exposure and acetic acid rinsing was used to remove the PMMA block. Interestingly, the treatment of PMMA removal inevitably produced osmotic pressure and consequently resulted in surface wrinkling of perpendicular lamellae. As a result, a hierarchical structure with two periodicities was obtained for wrinkled films with perpendicular lamellae. The formation of surface wrinkling is due to the interplay between UV-light exposure and acetic acid rinsing. UV-light exposure resulted in different mechanical properties between the skin and the inner region of a film. Acetic acid rinsing produced osmotic pressure. It was found that surface wrinkling could be suppressed by reducing film thickness, increasing PS content and using high-molecular-weight P(S-b-MMA) BCPs.