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Cholesteric liquid crystals (CLCs) are compelling responsive materials with applications in next-generation sensing, imaging, and display technologies. While electric fields and surface treatments have been used to manipulate the molecular organization and, subsequently, the optical properties of CLCs, their response to controlled fluid flow has remained largely unexplored. Here, we investigate the influence of microfluidic flow on the structure of thermotropic CLCs that can exhibit structural coloration. We demonstrate that the shear forces that arise from microfluidic flow align the helical axis of CLCs; alignment is a prerequisite for harnessing the promising photonic properties of CLCs. Moreover, we show that microfluidic flow can generate non-equilibrium structures exhibiting photonic band gaps that are inaccessible in the stationary cholesteric phase. Our findings have implications for the use of CLCs in applications involving flow processing such as additive manufacturing.

The self-assembly of thin films of block copolymers (BCPs) with perpendicular domain orientation offers a promising approach for nanopatterning on a variety of substrates, which is required by advanced applications such as ultrasmall transistors in integrated circuits, nanopatterned materials for tissue engineering, and electrocatalysts for fuel cell applications. In this study, we created BCPs with an A- b -(B- r -C) architecture that have blocks with equal surface energy ( γ air ) and that can bind to the substrate, effectively creating a non-preferential substrate coating via self-brushing that enables the formation of through-film perpendicular domains in thin films of BCPs. We employed a thiol-epoxy click reaction to functionalize polystyrene- block -poly(glycidyl methacrylate) with a pair of thiols to generate an A- b -(B- r -C) BCP and tune γ air of the B- r -C block. The secondary hydroxyl and thiol ether functionality generated by the click reaction was utilized to bind the BCP to the substrates. Scanning electron microscopy revealed that perpendicular orientation was achieved by simply annealing a thin film of the BCP on the bare substrate without the usual extra step of coating a random copolymer brush on the substrate. The self-brushing capability of the BCP was also examined on gold, platinum, titanium, aluminum nitride, and silicon nitride surfaces. These results demonstrate that self-brushing is a promising approach for achieving perpendicular domain orientation in thin films of BCP for nanopatterning on a variety of useful surfaces.

Hierarchical structure-within-structure assemblies offer a route toward increasingly complex and multifunctional materials while pushing the limits of block copolymer self-assembly. We present a detailed study of the self-assembly of a series of fluorinated high-χ block copolymers (BCPs) prepared via postmodification of a single poly(styrene)- block -poly(glycidyl methacrylate) (S- b -G) parent polymer with the fluorinated alkylthiol pendent groups containing 1, 6, or 8 fluorinated carbons (termed trifluoro-ethanethiol (TFET), perfluoro-octylthiol (PFOT), and perfluoro-decylthiol (PFDT), respectively). Bulk X-ray scattering of thermally annealed samples demonstrates hierarchical molecular assembly with phase separation between the two blocks and within the fluorinated block. The degree of ordering within the fluorinated block is highly sensitive to synthetic variation; a lamellar sublattice was formed for S- b -GPFOT and S- b -GPFDT. Thermal analyses of S- b -GPFOT reveal that the fluorinated block exhibits liquid crystal-like ordering. The complex thin-film self-assembly behavior of an S- b -GPFOT polymer was investigated using real-space (atomic force microscopy and scanning electron microscopy) and reciprocal-space (resonant soft X-ray scattering (RSoXS), grazing incidence small- and wide-angle scattering) measurements. After thermal annealing in nitrogen or vacuum, films thicker than 1.5 times the primary lattice spacing exhibit a 90-degree grain boundary, exposing a thin layer of vertical lamellae at the free interface, while exhibiting horizontal lamellae on the preferential (polystyrene brush) substrate. RSoXS measurements reveal the near-perfect orthogonality between the primary and sublattice orientations, demonstrating hierarchical patterning at the nanoscale.

This study explores how conformational asymmetry influences the bulk phase behavior of linear-brush block copolymers. We synthesized 60 diblock copolymers composed of poly(trifluoroethyl methacrylate) as the linear block and poly[oligo(ethylene glycol) methyl ether methacrylate] as the brush block, varying the molecular weight, composition, and side-chain length to introduce different degrees of conformational asymmetry. Using small-angle X-ray scattering, we determined the morphology and phase diagrams for three different side-chain length systems, mainly observing lamellar and cylindrical phases. Increasing the side-chain length of the brush block from three to nine ethylene oxide units introduces sufficient asymmetry between the blocks to alter the phase behavior, shifting the lamellar-to-cylindrical transitions toward lower brush block compositions and transitioning the brush block from the dense comb-like regime to the bottlebrush regime. Coarse-grained simulations support our experimental observations and provide a mapping between the composition and conformational asymmetry. A comparison of our findings to strong stretching theory across multiple phase boundary predictions confirms the transition between the dense comb-like regime and the bottlebrush regime., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

The optical properties of liquid crystals serve as the basis for display, diagnostic, and sensing technologies. Such properties are generally controlled by relying on electric fields. In this work, we investigate the effects of microfluidic flows and acoustic fields on the molecular orientation and the corresponding optical response of nematic liquid crystals. Several previously unknown structures are identified, which are rationalized in terms of a state diagram as a function of the strengths of the flow and the acoustic field. The new structures are interpreted by relying on calculations with a free energy functional expressed in terms of the tensorial order parameter, using continuum theory simulations in the Landau-de Gennes framework. Taken together, the findings presented here offer promise for the development of new systems based on combinations of sound, flow, and confinement.

To form nanopatterns with self-assembled block copolymers (BCPs), it is desirable to have through-film domains that are oriented perpendicular to the substrate. The domain orientation is determined by the interfacial interactions of the BCP domains with the substrate and with the free surface. Here, we use thin films of two different sets of BCPs with A -block- (B- random -C) architecture matched with a corresponding B- random -C copolymer nanocoating on the substrate to demonstrate two distinct wetting behaviors. The two sets of A -b- (B- r -C) BCPs are made by using thiol-epoxy click chemistry to functionalize polystyrene -block- poly(glycidyl methacrylate) with trifluoroethanethiol (TFET) and either 2-mercaptopyridine (2MP) or methyl thioglycolate (MTG). For each set of BCPs, the composition ratio of the two thiols in the BCP (φ 1 ) is found that results in the two blocks of the modified BCP having equal surface energies (Δγ air = 0). The corresponding B- r -C random copolymers were synthesized and used to modify the substrate, and the composition ratio (φ 2 ) values that resulted in the two blocks of the BCP having equal interfacial energy with the substrate (Δγ sub = 0) were determined with scanning electron microscopy. The correlation between each block's γ sub value and the interaction parameter, χ, is employed to explain the different wetting behaviors of the two sets of BCPs. For the thiol pair 2MP and TFET, the values of φ 1 and φ 2 that lead to Δγ air = 0 and Δγ sub = 0, respectively, are significantly different. A similar difference was observed between the φ 1 and φ 2 values that lead to Δγ air = 0 and Δγ sub = 0 for the BCPs made with the thiol pair MTG and TFET. In the latter case, for Δγ sub = 0 two windows of φ 2 are identified, which can be explained by the thermodynamic interactions of the specific thiol pair and the A- b -(B- r -C) architecture.

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., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Electrostatic interactions in polymeric systems are responsible for a wide range of liquid-liquid phase transitions that are of importance for biology and materials science. Such transitions are referred to as complex coacervation, and recent studies have sought to understand the underlying physics and chemistry. Most theoretical and simulation efforts to date have focused on oppositely charged linear polyelectrolytes, which adopt nearly ideal-coil conformations in the condensed phase. However, when one of the coacervate components is a globular protein, a better model of complexation should replace one of the species with a spherical charged particle or colloid. In this work, we perform coarse-grained simulations of colloid-polyelectrolyte coacervation using a spherical model for the colloid. Simulation results indicate that the electroneutral cell of the resulting (hybrid) coacervates consists of a polyelectrolyte layer adsorbed on the colloid. Power laws for the structure and the density of the condensed phase, which are extracted from simulations, are found to be consistent with the adsorption-based scaling theory of hybrid coacervation. The coacervates remain amorphous (disordered) at a moderate colloid charge, Q , while an intra-coacervate colloidal crystal is formed above a certain threshold, at Q > Q *. In the disordered coacervate, if Q is sufficiently low, colloids diffuse as neutral nonsticky nanoparticles in the semidilute polymer solution. For higher Q , adsorption is strong and colloids become effectively sticky. Our findings are relevant for the coacervation of polyelectrolytes with proteins, spherical micelles of ionic surfactants, and solid organic or inorganic nanoparticles., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Polyelectrolyte complexation plays an important role in materials science and biology. The internal structure of the resultant polyelectrolyte complex (PEC) phase dictates properties such as physical state, response to external stimuli, and dynamics. Small-angle scattering experiments with X-rays and neutrons have revealed structural similarities between PECs and semidilute solutions of neutral polymers, where the total scattering function exhibits an Ornstein-Zernike form. In spite of consensus among different theoretical predictions, the existence of positional correlations between polyanion and polycation charges has not been confirmed experimentally. Here, we present small-angle neutron scattering profiles where the polycation scattering length density is matched to that of the solvent to extract positional correlations among anionic monomers. The polyanion scattering functions exhibit a peak at the inverse polymer screening radius of Coulomb interactions, q * ≈ 0.2 Å -1 . This peak, attributed to Coulomb repulsions between the fragments of polyanions and their attractions to polycations, is even more pronounced in the calculated charge scattering function that quantifies positional correlations of all polymer charges within the PEC. Screening of electrostatic interactions by adding salt leads to the gradual disappearance of this correlation peak, and the scattering functions regain an Ornstein-Zernike form. Experimental scattering results are consistent with those calculated from the random phase approximation, a scaling analysis, and molecular simulations.

Blue phase (BP) liquid crystals are chiral fluids wherein millions of molecules self-assemble into cubic lattices that are on the order of hundred nanometers. As the unit cell sizes of BPs are comparable to the wavelength of light, they exhibit selective Bragg reflections in the visible. The exploitation of the photonic properties of BPs for technological applications is made possible through photopolymerization, a process that renders mechanical robustness and thermal stability. We review here the preparation and characterization of stimuli-responsive, polymeric photonic crystals based on BPs. We highlight recent studies that demonstrate the promise that polymerized BP photonic crystals hold for colorimetric sensing and dynamic light control. We review using Landau-de Gennes simulations for predicting the self-assembly of BPs and the potential for using theory to guide experimental design. Finally, opportunities for using BPs to synthesize new soft materials, such as highly structured polymer meshes, are discussed.

The self-assembly of block copolymers (BCPs) is dictated by their segregation strength, χ N , and while there are well-developed methods for determining χ in the weak and strong segregation regimes, it is challenging to accurately measure χ of copolymers with intermediate segregation strengths, especially when copolymers have inaccessible order-disorder transition temperatures. χ eff is often approximated by using strong segregation theory (SST), but utilizing these values to estimate the interface width ( w m ) of BCPs in the intermediate segregation regime often results in predictions that deviate significantly from measured values. Therefore, we propose using the extent of mixing, quantified as the normalized interface width w m / L 0 , where L 0 is the block copolymer pitch, as a thermodynamic parameter. We experimentally measure w m and L 0 for a series of lamellar A- b -(B- r -C) copolymers via resonant soft X-ray reflectivity and extract values of χ eff N based on previous data collected for A- b -B copolymers. The composition profiles measured via reflectivity match the extracted χ eff N values, while those calculated with SST predict much more mixed composition profiles. The extracted χ eff values agreed quantitatively between copolymers of different molecular weights. We believe that this methodology will be well-suited for block copolymers used in lithographic applications due to their inaccessible order-disorder transition temperatures, intermediate values of χ N , and the importance of w m for line edge roughness metrics.

We report a method for the directed self-assembly (DSA) of block copolymers (BCPs) in which a first BCP film deploys homopolymer brushes, or "inks", that sequentially graft onto the substrate's surface via the interpenetration of polymer molecules during the thermal annealing of the polymer film on top of existing polymer brushes. By selecting polymer "inks" with the desired chemistry and appropriate relative molecular weights, it is possible to use brush interpenetration as a powerful technique to generate self-registered chemical contrast patterns at the same frequency as that of the domains of the BCP. The result is a process with a higher tolerance to dimensional and chemical imperfections in the guiding patterns, which we showcase by implementing DSA using homopolymer brushes for the guiding features as opposed to more robust cross-linkable mats. We find that the use of "inks" does not compromise the line width roughness, and the quality of the DSA as a lithographic mask is verified by implementing a robust "dry lift-off" pattern transfer.

Leveraging the self-assembling behavior of liquid crystals designed for controlling ion transport is of both fundamental and technological significance. Here, we have designed and prepared a liquid crystal that contains 2,5-bis(thien-2-yl)thieno[3,2- b ]thiophene (BTTT) as mesogenic core and conjugated segment and symmetric tetra(ethylene oxide) (EO4) as polar side chains for ion-conducting regions. Driven by the crystallization of the BTTT cores, BTTT/dEO4 exhibits well-ordered smectic phases below 71.5 °C as confirmed by differential scanning calorimetry, polarized optical microscopy, temperature-dependent wide-angle X-ray scattering, and grazing incidence wide-angle X-ray scattering (GIWAXS). We adopted a combination of experimental GIWAXS and molecular dynamics (MD) simulations to better understand the molecular packing of BTTT/dEO4 films, particularly when loaded with the ion-conducting salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Ionic conduction of BTTT/dEO4 is realized by the addition of LiTFSI, with the material able to maintain smectic phases up to r = [Li + ]/[EO] = 0.1. The highest ionic conductivity of 8 × 10 -3 S/cm was attained at an intermedium salt concentration of r = 0.05. It was also found that ion conduction in BTTT/dEO4 is enhanced by forming a smectic layered structure with irregular interfaces between the BTTT and EO4 layers and by the lateral film expansion upon salt addition. This can be explained by the enhancement of the misalignment and configurational entropy of the side chains, which increase their local mobility and that of the solvated ions. Our molecular design thus illustrates how, beyond the favorable energetic interactions that drive the assembly of ion solvating domains, modulation of entropic effects can also be favorably harnessed to improve ion conduction.

The ability to impart multiple covarying properties into a single material represents a grand challenge in manufacturing. In the design of block copolymers (BCPs) for directed self-assembly and nanolithography, materials often balance orthogonal properties to meet constraints related to processing, structure and defectivity. Although iterative synthesis strategies deliver BCPs with attractive properties, identifying materials with all the required attributes has been difficult. Here we report a high-throughput synthesis and characterization platform for the discovery and optimization of BCPs with A-block-(B-random-C) architectures for lithographic patterning in semiconductor manufacturing. Starting from a parent BCP and using thiol-epoxy 'click' chemistry, we synthesize a library of BCPs that cover a large and complex parameter space. This allows us to readily identify feature-size-dependent BCP chemistries for 8-20-nm-pitch patterns. These blocks have similar surface energies for directed self-assembly, and control over the segregation strength to optimize the structure (favoured at higher segregation strengths) and defectivity (favoured at lower segregation strengths)., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

A peripheral nerve injury results in disruption of the fiber that usually protects axons from the surrounding environment. Severed axons from the proximal nerve stump are capable of regenerating, but axons are exposed to a completely new environment. Regeneration recruits cells that produce and deposit key molecules, including growth factor proteins and fibrils in the extracellular matrix (ECM), thus changing the chemical and geometrical environment. The regenerating axons thus surf on a newly remodeled micro-landscape. Strategies to enhance and control axonal regeneration and growth after injury often involve mimicking the extrinsic cues that are found in the natural nerve environment. Indeed, nano- and micropatterned substrates have been generated as tools to guide axons along a defined path. The mechanical cues of the substrate are used as guides to orient growth or change the direction of growth in response to impediments or cell surface topography. However, exactly how axons respond to biophysical information and the dynamics of axonal movement are still poorly understood. Here we use anisotropic, groove-patterned substrate topography to direct and enhance sensory axonal growth of whole mouse dorsal root ganglia (DRG) transplanted ex vivo. Our results show significantly enhanced and directed growth of the DRG sensory fibers on the hemi-3D topographic substrates compared to a 0 nm pitch, flat control surface. By assessing the dynamics of axonal movement in time-lapse microscopy, we found that the enhancement was not due to increases in the speed of axonal growth, but to the efficiency of growth direction, ensuring axons minimize movement in undesired directions. Finally, the directionality of growth was reproduced on topographic patterns fabricated as fully 3D substrates, potentially opening new translational avenues of development incorporating these specific topographic feature sizes in implantable conduits in vivo.

In-plane tungsten oxide nanostructures, including hexagonally patterned cylinders and holes in a matrix, were fabricated via sequential infiltration synthesis (SIS) on self-assembled block copolymer templates. Using the tailored morphology and porosity of these model electrodes with in situ grazing incidence small-angle X-ray scattering, the intrinsic structural change of nanoscale active materials during the conversion reaction of WO 3 + 6Li ↔ W + 3Li 2 O was investigated at controlled electrochemical conditions. Reversible electrode volume expansion and contraction was observed during lithiation and delithiation cycles, respectively. The potential where the electrode's thickness expansion started was ∼1.6 V, which is close to the thermodynamically expected one for the conversion reaction of WO 3 with lithium (1.65 V). The temporal evolution of the electrode volume at constant electrode potentials revealed high overpotential for bulk lithiation and slow conversion reaction kinetics, despite the tailored porosity of the SIS electrodes. Oxide cylinders showed a smaller overall electrode thickness change, likely due to unconstrained lateral volume change, as compared to a matrix with holes. On the other hand, better connectivity and guided volume change of the latter electrode morphology provided improved cycling stability. In addition, heterogeneity in an electrode, from internal pores and density gradients, was found to aggravate the fragmentation of the electrode during the conversion reaction. Insights into oxide conversion reaction kinetics and the relationship between electrode mesostructure and cycling behavior obtained from this study can help guide the more rational design of conversion electrodes for high-performing batteries.

Directed self-assembly (DSA) of block copolymers is one of the most promising patterning techniques for patterning sub-10 nm features. However, at such small feature sizes, it is becoming increasingly difficult to fabricate the guiding pattern for the DSA process, and it is necessary to explore alternative guiding methods for DSA to achieve long-range ordered alignment. Here, we report the self-aligned assembly of a triblock copolymer, poly(2-vinylpyridine)- b -polystyrene- b -poly(2-vinylpyridine) (P2VP- b -PS- b -P2VP) on neutral graphene nanoribbons with the gap consisting of a P2VP-preferential silicon oxide (SiO 2 ) substrate via solvent vapor annealing. The assembled P2VP-b-PS-b-P2VP demonstrated long-range, one-dimensional alignment on the graphene substrate in a direction perpendicular to the boundary of the graphene and substrate with a half-pitch size of 8 nm, which greatly alleviates the lithography resolution required for traditional chemoepitaxy DSA. A wide processing window is demonstrated with the gap between graphene stripes varying from 10 to 100 nm, overcoming the restriction on widths of guiding patterns to have commensurate domain spacing. When the gap was reduced to 10 nm, P2VP- b -PS- b -P2VP formed a straight-line pattern on both the graphene and the substrate. Monte Carlo simulations showed that the self-aligned assembly of the triblock copolymer on the graphene nanoribbons is guided at the boundary of parallel and perpendicular lamellae on graphene and SiO 2 , respectively. Simulations also indicate that the swelling of a system allows for rapid rearrangement of chains and quickly anneal any misaligned grains and defects. The effect of the interaction strength between SiO 2 and P2VP on the self-assembly is systematically investigated in simulations.

Interactions between polymers and surfaces can be used to influence properties including mechanical performance in nanocomposites, the glass transition temperature, and the orientation of thin film block copolymers (BCPs). In this work we investigate how specific interactions between the substrate and BCPs with varying substrate affinity impact the interfacial width between polymer components. The interface width is generally assumed to be a function of the BCP properties and independent of the surface affinity or substrate proximity. Using resonant soft X-ray reflectivity the optical constants of the film can be controlled by changing the incident energy, thereby varying the depth sensitivity of the measurement. Resonant soft X-ray reflectivity measurements were conducted on films of polystyrene- b -poly(2-vinylpyridine) (PS- b -P2VP) and PS- b -poly(methyl methacrylate) (PS- b -PMMA), where the thickness of the film was varied from half the periodicity ( L 0 ) of the BCP to 5.5 L 0 . The results of this measurement on the PS- b -P2VP films show a significant expansion of the interface width immediately adjacent to the surface. This is likely caused by the strong adsorption of P2VP to the substrate, which constrains the mobility of the junction points, preventing them from reaching their equilibrium distribution and expanding the observed interface width. The interface width decays toward equilibrium moving away from the substrate, with the decay rate being a function of film thickness below a critical limit. The PMMA block appears to be more mobile, and the BCP interfaces near the substrate match their equilibrium value.

Directed self-assembly (DSA) of block copolymers (BCP) has attracted considerable interest from the semiconductor industry because it can achieve semiconductor-relevant structures with a relatively simple process and low cost. However, the self-assembling structures can become kinetically trapped into defective states, which greatly impedes the implementation of DSA in high-volume manufacturing. Understanding the kinetics of defect annihilation is crucial to optimizing the process and eventually eliminating defects in DSA. Such kinetic experiments, however, are not commonly available in academic laboratories. To address this challenge, we perform a kinetic study of chemoepitaxy DSA in a 300 mm wafer fab, where the complete defectivity information at various annealing conditions can be readily captured. Through extensive statistical analysis, we reveal the statistical model of defect annihilation in DSA for the first time. The annihilation kinetics can be well described by a power law model, indicating that all dislocations can be removed by sufficiently long annealing time. We further develop image analysis algorithms to analyze the distribution of dislocation size and configurations and discover that the distribution stays relatively constant over time. The defect distribution is determined by the role of the guiding stripe, which is found to stabilize the defects. Although this study is based on polystyrene- b -poly(methyl methacrylate) (PS- b -PMMA), we anticipate that these findings can be readily applied to other BCP platforms as well.

Block copolymer electrolytes (BCE) such as polystyrene- block -poly(ethylene oxide) (SEO) blended with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and composed of mechanically robust insulating and rubbery conducting nanodomains are promising solid-state electrolytes for Li batteries. Here, we compare ionic solvation, association, distribution, and conductivity in SEO-LiTFSI BCEs and their homopolymer PEO-LiTFSI analogs toward a fundamental understanding of the maximum in conductivity and transport mechanisms as a function of salt concentration. Ionic conductivity measurements reveal that SEO-LiTFSI and PEO-LiTFSI exhibit similar behaviors up to a Li/EO ratio of 1/12, where roughly half of the available solvation sites in the system are filled, and conductivity is maximized. As the Li/EO ratios increase to 1/5 the conductivity, of the PEO-LiTFSI drops nearly 3-fold, while the conductivity of SEO-LiTFSI remains constant. FTIR spectroscopy reveals that additional Li cations in the homopolymer electrolyte are complexed by additional EO units when the Li/EO ratio exceeds 1/12, while in the BCE, the proportion of complexed and uncomplexed EO units remains constant; Raman spectroscopy data at the same concentrations show that Li cations in the SEO-LiTFSI samples tend to coordinate more to their counteranions. Atomistic-scale molecular dynamics simulations corroborate these results and further show that associated ions tend to segregate to the SEO-LiTFSI domain interfaces. The opportunity for "excess" salt to be sequestered at BCE interfaces results in the retention of an optimum ratio of uncompleted and complexed PEO solvation sites in the middle of the conductive nanodomains of the BCE and maximized conductivity over a broad range of salt concentrations.

Bottlebrush block copolymers (BBCPs) are intriguing architectural variations on linear BCPs with highly tunable structure. Confinement can have a significant impact on polymer assembly, giving rise to changes in morphology, assembly kinetics, and properties like the glass transition. Given that confinement leads to significant changes in the persistence length of bottlebrush homopolymers, it is reasonable to expect that BBCPs will see significant changes in their structure and periodicity relative to the bulk morphology. Understanding how confinement influences assembly will be important for designing BBCPs for thin film applications including membranes, integrated photonic structures, and potentially BCP lithography. In order to study the effects of confinement on BBCP conformation and morphology, a blade coating was used to prepare films with continuous variation in film thickness. Unlike thin films of linear BCPs, islands/holes were not observed, and instead mixtures of parallel and perpendicular morphologies emerge after annealing. The lamellar periodicity ( L 0 ) of the morphologies is found to be thickness dependent, increasing L 0 with decreasing film thickness for blade coated films. Films coated out of tetrahydrofuran (THF) resulted in a single well-defined lamellar periodicity, verified through atomic force microscopy (AFM) and grazing incidence small-angle X-ray scattering (GISAXS), which increases dramatically from the bulk value (30.6 nm) and continues to increase as the film thickness decreases. The largest observed L 0 was 65.5 nm, and this closely approaches the estimated upper limit of 67 nm corresponding to a fully extended backbone in a bilayer arrangement. Films coated out of propylene glycol methyl ether acetate (PGMEA) resulted in a mixture of perpendicular lamellae and a smaller, likely cylindrical morphology. The lamellar portion of the film shows the same thickness dependence as the lamellae observed in the THF coated films. The scaling of the lamellar L 0 with respect to film thickness follows predictions for confined semiflexible polymers with weak excluded volume interactions and can be related to models for confinement of DNA. Spin coated films shows the same reduction in periodicity, although at very different film thicknesses. This result suggests that the material has shallow free-energy barriers to transitioning between different L 0 and morphologies, a property that could be taken advantage of for patterning diverse structures with a single material.

Engineering the thermal conductivity of amorphous materials is highly essential for the thermal management of future electronic devices. Here, we demonstrate the impact of ultrafine nanostructuring on the thermal conductivity reduction of amorphous silicon nitride (a-Si 3 N 4 ) thin films, in which the thermal transport is inherently impeded by the atomic disorders. Ultrafine nanostructuring with feature sizes below 20 nm allows us to fully suppress contribution of the propagating vibrational modes (propagons), leaving only the diffusive vibrational modes (diffusons) to contribute to thermal transport in a-Si 3 N 4 A combination of the phonon-gas kinetics model and the Allen-Feldmann theory reproduced the measured results without any fitting parameters. The thermal conductivity reduction was explained as extremely strong diffusive boundary scattering of both propagons and diffusons. These findings give rise to substantial tunability of thermal conductivity of amorphous materials, which enables us to provide better thermal solutions in microelectronic devices., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution License 4.0 (CC BY).)

Directed self-assembly of block copolymers (BCPs) enables nanofabrication at sub-10 nm dimensions, beyond the resolution of conventional lithography. However, directing the position, orientation, and long-range lateral order of BCP domains to produce technologically-useful patterns is a challenge. Here, we present a promising approach to direct assembly using spatial boundaries between planar, low-resolution regions on a surface with different composition. Pairs of boundaries are formed at the edges of isolated stripes on a background substrate. Vertical lamellae nucleate at and are pinned by chemical contrast at each stripe/substrate boundary, align parallel to boundaries, selectively propagate from boundaries into stripe interiors (whereas horizontal lamellae form on the background), and register to wide stripes to multiply the feature density. Ordered BCP line arrays with half-pitch of 6.4 nm are demonstrated on stripes >80 nm wide. Boundary-directed epitaxy provides an attractive path towards assembling, creating, and lithographically defining materials on sub-10 nm scales.

Knowledge of intrinsic properties is of central importance for materials design and assessing suitability for specific applications. Self-assembling block copolymer electrolytes (BCEs) are of great interest for applications in solid-state energy storage devices. A fundamental understanding of ion transport properties, however, is hindered by the difficulty in deconvoluting extrinsic factors, such as defects, from intrinsic factors, such as the presence of interfaces between the domains. Here, we quantify the intrinsic ion transport properties of a model BCE system consisting of poly(styrene- block -ethylene oxide) (SEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt using a generalizable strategy of depositing thin films on interdigitated electrodes and self-assembling fully connected parallel lamellar structures throughout the films. Comparison between conductivity in homopolymer poly(ethylene oxide) (PEO)-LiTFSI electrolytes and the analogous conducting material in SEO over a range of salt concentrations ( r , molar ratio of lithium ion to ethylene oxide repeat units) and temperatures reveals that between 20% and 50% of the PEO in SEO is inactive. Using mean-field theory calculations of the domain structure and monomer concentration profiles at domain interfaces-both of which vary substantially with salt concentration-the fraction of inactive PEO in the SEO, as derived from conductivity measurements, can be quantitatively reconciled with the fraction of PEO that is mixed with greater than a few volume percent of polystyrene. Despite the detrimental interfacial effects for ion transport in BCEs, the intrinsic conductivity of the SEO studied here ( ca . 10 -3 S/cm at 90 °C, r = 0.085) is an order of magnitude higher than reported values from bulk samples of similar molecular weight SEO ( ca . 10 -4 S/cm at 90 °C, r = 0.085). Overall, this work provides motivation and methods for pursuing improved BCE chemical design, interfacial engineering, and processing.

Studies have demonstrated that the thermal conductivity (κ) of crystalline semiconductor materials can be reduced by phonon scattering in periodic nanostructures formed using templates fabricated from self-assembled block copolymers (BCPs). Compared to crystalline materials, the heat transport mechanisms in amorphous inorganic materials differ significantly and have been explored far less extensively. However, thermal management of amorphous inorganic solids is crucial for a broad range of semiconductor devices. Here we present the fabrication of freestanding amorphous silicon nitride (SiN x ) membranes for studying κ in an amorphous solid. To form a periodic nanostructure, directed self-assembly of cylinder-forming BCPs is used to pattern in the SiN x highly ordered, hexagonally close packed nanopores with pitch and neck width down to 37.5 and 12 nm, respectively. The κ of the nanoporous SiN x membranes is 60% smaller than the classically predicted value based on just the membrane porosity. In comparison, holes with much larger neck widths and pitches patterned by e-beam lithography lead to only a slight reduction in κ, which is closer to the classical porosity-based prediction. These results demonstrate that κ of amorphous SiN x can be reduced by introducing periodic nanostructures that behave as a phononic crystal, where the relationship between the smallest dimension of the nanostructure and the length scale of the mean-free paths of the dominant, heat-carrying phonons is critical. Additionally, changing the orientation of the hexagonal array of nanopores relative to the primary direction of heat flow has a smaller impact on amorphous SiN x than was previously observed in silicon.

Three-dimensional (3D) structures at the nanometer length scale play a crucial role in modern devices, but their fabrication using traditional top-down approaches is complex and expensive. Analogous to atomic lattices, block copolymers (BCPs) spontaneously form a rich variety of 3D nanostructures and have the potential to substantially simplify 3D nanofabrication. Here, we show that the 3D superlattice formed by BCP micelles can be controlled by lithographically defined 2D templates matching a crystallographic plane in the 3D superlattice. Using scanning transmission electron microscopy tomography, we demonstrate precise control over the lattice symmetry and orientation. Excellent ordering and substrate registration can be achieved, propagating through 284-nanometer-thick films. BCP epitaxy also showed exceptional lattice tunability, with a continuous Bain transformation from a body-centered cubic to a face-centered cubic lattice. Lattice stability was mediated by molecular packing frustration, and surface-induced lattice reconstruction was observed, leading to the formation of a unique honeycomb lattice., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

Liquid crystal blue phases (BPs) are three-dimensional soft crystals with unit cell sizes orders of magnitude larger than those of classic, atomic crystals. The directed self-assembly of BPs on chemically patterned surfaces uniquely enables detailed in situ resonant soft x-ray scattering measurements of martensitic phase transformations in these systems. The formation of twin lamellae is explicitly identified during the BPII-to-BPI transformation, further corroborating the martensitic nature of this transformation and broadening the analogy between soft and atomic crystal diffusionless phase transformations to include their strain-release mechanisms., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

This work represents a joint computational and experimental study on a series of n -ethylene glycol (PEO n )-terminated quaterthiophene (4T) oligomers for 1 < n < 10 to elucidate their self-assembly behavior into a smectic-like lamellar phase. This study builds on an earlier study for n = 4 that showed that our model predictions were consistent with experimental data on the melting behavior and structure of the lamellar phase, with the latter consisting of crystal-like 4T domains and liquid-like PEO4 domains. The present study aims to understand how the length of the terminal PEO n chains modulates the disordering temperature of the lamellar phase and hence the relative stability of the ordered structure. A simplified bilayer model, where the 4T domains are not explicitly described, is put forward to efficiently estimate the disordering effect of the PEO domains with increasing n ; this method is first validated by correctly predicting that layers of alkyl (PE)-capped 4T oligomers (for 1 < n < 10) stay ordered at room temperature. Both 4T-domain implicit and explicit model simulations reveal that the order-disorder temperature decreases with the length of the PEO capping chains, as the associated increase in conformational entropy drives a tendency toward disorder that overtakes the cohesive energy, keeping the ordered packing of the 4T domains.

The challenges of patterning next generation integrated circuits have driven the semiconductor industry to look outside of traditional lithographic methods in order to continue cost effective size scaling. The directed self-assembly (DSA) of block copolymers (BCPs) is a nanofabrication technique used to reduce the periodicity of patterns prepared with traditional optical methods. BCPs with large interaction parameters ( χ eff ), provide access to smaller pitches and reduced interface widths. Larger χ eff is also expected to be correlated with reduced line edge roughness (LER), a critical performance parameter in integrated circuits. One approach to increasing χ eff is blending the BCP with a phase selective additive, such as an Ionic liquid (IL). The IL does not impact the etching rates of either phase, and this enables a direct interrogation of whether the change in interface width driven by higher χ eff translates into lower LER. The effect of the IL on the layer thickness and interface width of a BCP are examined, along with the corresponding changes in LER in a DSA patterned sample. The results demonstrate that increased χ eff through additive blending will not necessarily translate to a lower LER, clarifying an important design criterion for future material systems.

We report on the use of a selective, non-volatile ionic liquid (IL) to enhance the self-assembly via solvent annealing of a low molecular weight block copolymer (BCP) of styrene and 2-vinylpyridine (2VP) suitable for generating sub-10 nm features. Diblock and triblock copolymers of different molecular weights of styrene and 2VP are individually blended with the IL and then solvent annealed in acetone, a non-preferential solvent for the BCPs. Differential scanning calorimetry indicates that the IL selectively resides in the 2VP block of the BCP, resulting in a decrease of the block's Tg and an increase of the effective Flory-Huggins parameter (χeff) of the BCP. The influence of the IL on the non-preferential window of a random copolymer brush used to treat the substrate for self-assembly of the BCPs is also analyzed. Well-defined lamellar patterns form when the optimal weight ratio of IL (∼1%) is added to the BCPs. A detailed analysis of the orientational correlation length and pitch size of the BCPs quantitatively shows that the addition of the IL enhanced the microphase separation of the low molecular weight version of the BCP. Subsequent treatment of the self-assembled BCP with sequential infiltration synthesis yields sub-10 nm AlOx lines.

Engineering the grain boundaries of crystalline materials represents an enduring challenge, particularly in the case of soft materials. Grain boundaries, however, can provide preferential sites for chemical reactions, adsorption processes, nucleation of phase transitions, and mechanical transformations. In this work, "soft heteroepitaxy" is used to exert precise control over the lattice orientation of three-dimensional liquid crystalline soft crystals, thereby granting the ability to sculpt the grain boundaries between them. Since these soft crystals are liquid-like in nature, the heteroepitaxy approach introduced here provides a clear strategy to accurately mold liquid-liquid interfaces in structured liquids with a hitherto unavailable level of precision., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

Directed self-assembly of block copolymers and self-aligned double patterning are two commonly used pitch scaling techniques to increase the density of lithographic features. In this work, both of these pitch scaling techniques were combined, enabling patterning at even higher densities. In this process, directed self-assembly of a high-χ block copolymer was used to form a line/space pattern, which served as a template for mandrels. Via these mandrels, atomic layer deposition was used to deposit a thin aluminium oxide spacer. By this method, a total pitch scaling factor of 8, equivalent to a 10.5 nm full pitch, was reached. The types of defects and the line roughness at the different steps of the process were discussed.

Developing soft materials with both ion and electron transport functionalities is of broad interest for energy-storage and bioelectronics applications. Rational design of these materials requires a fundamental understanding of interactions between ion and electron conducting blocks along with the correlation between the microstructure and the conduction characteristics. Here, we investigate the structure and mixed ionic/electronic conduction in thin films of a liquid crystal (LC) 4T/PEO4, which consists of an electronically conducting quarterthiophene (4T) block terminated at both ends by ionically conducting oligoethylenoxide (PEO4) blocks. Using a combined experimental and simulation approach, 4T/PEO4 is shown to self-assemble into smectic, ordered, or disordered phases upon blending the materials with the ionic dopant bis(trifluoromethane)sulfonimide lithium (LiTFSI) under different LiTFSI concentrations. Interestingly, at intermediate LiTFSI concentration, ordered 4T/PEO4 exhibits an electronic conductivity as high as 3.1 × 10 -3 S/cm upon being infiltrated with vapor of the 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) molecular dopant while still maintaining its ionic conducting functionality. This electronic conductivity is superior by an order of magnitude to the previously reported electronic conductivity of vapor co-deposited 4T/F4TCNQ blends. Our findings demonstrate that structure and electronic transport in mixed conduction materials could be modulated by the presence of the ion transporting component and will have important implications for other more complex mixed ionic/electronic conductors.

Nanoparticle assemblies have generated intense interest because of their novel optical, electronic, and magnetic properties that open up numerous opportunities in fundamental and applied nanophotonics, -electronics, and -magnetics. However, despite the great scientific and technological potential of these structures, it remains an outstanding challenge to reliably fabricate such assemblies with both nanometer-level structural control and precise spatial arrangements on a macroscopic scale. It is the combination of these two features that is key to realizing nanoparticle assemblies' potential, particular for device applications. To address this challenge, we propose a hierarchical assembly approach consisting of both template-particle and particle-particle interactions, whereby the former ensures precise addressability of assemblies on a surface and the latter provides nanometer-level structural control. Template-particle interactions are harnessed via chemical-pattern-directed assembly, and the particle-particle interactions are controlled using DNA-directed self-assembly. To demonstrate the potential of this hierarchical assembly approach, we demonstrate the fabrication of a particularly fascinating assembly: the nanoparticle heterodimer, which possesses a surprisingly rich set of plasmonic properties and is a promising candidate to enable a variety of imaging and sensing applications. Each heterodimer is placed on the surface at predetermined locations, and the precise control of the nanogaps is confirmed by far-field scattering measurements of individual dimers. We further demonstrate that the gap size can be effectively tuned by varying the DNA length. By correlating measured spectra with finite-difference time-domain (FDTD) simulations, we determine the gap sizes to be 4.2 and 5.0 nm-with subnm deviation-for the two DNA lengths investigated. This is one of the best gap uniformities ever demonstrated for surface-bound nanoparticle assemblies. The estimated surface-enhanced Raman scattering (SERS) enhancement factor of these heterodimers is on the order of 10 5 -10 6 with high reproducibility and predictable polarization-dependence. This hierarchical fabrication technique-employing both template-particle and particle-particle interactions-constitutes a novel platform for the realization of functional nanoparticle assemblies on surfaces and thereby creates new opportunities to implement these structures in a variety of applications.

Ion conducting block copolymers can overcome traditional limitations of homopolymer electrolytes by phase separating into nanoarchitectures that can be simultaneously optimized for two or more orthogonal material properties such as high ionic conductivity and mechanical stability. A key challenge in understanding the ion transport properties of these materials is the difficulty of extracting structure-function relationships without having complete knowledge of all nanoscale transport pathways in bulk samples. Here we demonstrate a method for deriving structure-transport relationships for ion conducting block copolymers using thin films and interdigitated electrodes. Well-defined and directly imaged structure in films of poly(styrene)- block -poly(2-vinylpyridine) is controlled using techniques of directed self-assembly then the poly(2-vinylpyridine) is selectively converted into an ion conductor. The ion conductivity is found to be directly proportional to the total number of connected paths between electrodes and the path length. A single defect such as a dislocation anywhere in the path of an ion conducting route disconnects and precludes that pathway from contributing to the conductivity and results in an increase in the dielectric parameter of the film. When all the ion conduction pathways are blocked between electrodes, the conductivity is negligible, 4 orders of magnitude lower compared to a completely connected morphology and the dielectric parameter increases by a factor of 50. These results have profound implications for the interpretation, design, and processing of block copolymer electrolytes for applications as ion conducting membranes.

Chemically patterned surfaces can be used to selectively stabilize blue phases as macroscopic single crystals with a prescribed lattice orientation. By tailoring the interfacial free energy through the pattern characteristics, it is possible to set, with nanoscale precision, the optimal conditions to induce spontaneously blue-phase crystal nucleation on the patterned substrate where a uniform, defect-free, blue-phase single crystal is finally formed in a matter of seconds. The chemical patterns taken into consideration in this work are made up of alternated stripelike regions of homeotropic and planar anchoring. By varying the stripe pattern dimension, including the period and ratio of the planar/homeotropic anchoring width, it is possible to generate blue-phase I single crystals with (110) lattice orientation and blue-phase II single crystals with either the (100), (110), or (111) lattice orientation. Continuum mean-field calculations of the studied systems serve to explain, in terms of the free energy of the systems, how the pattern dimensions favor certain crystallographic orientations while penalizing the others. We found that a small free-energy difference is sufficient to drive the nucleation and growth of blue phases into a certain lattice orientation. Therefore, a processing window for obtaining arbitrary large blue-phase single crystals with predesigned lattice orientation, highly aligned reflective peaks, and significantly short forming time is provided here, which is essential for manufacturing and modulating optical devices and photonics.

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.

Controlling the orientation of liquid crystal (LC) molecules towards contacting surfaces is a crucial requirement for the development of LC displays and passive electro-optical devices. Up to now, research has been focused on photo-responses of a LC azobenzene polymer system to obtain either planar or homeotropic orientation of LCs. It remains a challenge, however, to tune the polar angle of LC molecules on the solid surface and gain more insights about the polymer chain conformation extending in LC medium. Here, we deposit a liquid crystalline side chain polymer brush, poly(6-(4-methoxy-azobenzene-4'-oxy)hexyl methacrylate) (PMMAZO), onto the solid surface with film thickness varying between ∼3 nm and 13 nm; therefore, the grafting density of the brush layer ranges from 0.0219 to 0.0924 chains per nm2. When LCs are confined in hybrid cells with a top surface eliciting uniform homeotropic anchoring and a bottom surface covered by the PMMAZO brush, the out-of-plane polar angle of 4-pentyl-4'-cyanobiphenyl (5CB) on the brush layer gradually changes from ∼0° to ∼62° by simply increasing the grafting brush density. The surface forces apparatus (SFA) measurement is used to determine 5CB as a good solvent for the PMMAZO brush and understand the relationship between the chain conformation in 5CB and the anchoring behavior of LC molecules on the polymer brush layer. For high grafting density, the polymer chain in 5CB extends significantly away from the substrate, making the side chain mesogens on average almost parallel to the substrate; for the low-density case, the main chain extends in the narrow region around the surface for aligning the mesogens perpendicular to the substrate.

The transition temperatures of nanoscale polymeric films are measured from a leveling experiment where a designed nanostructure is heated from below. Surface tension forces drive the relaxation of the polymeric features, allowing direct measurement of the critical temperature of collapse, T flow , and indirect measurement of the glass transition temperature, T G . Small-angle X-ray scattering and atomic force microscopy are used to follow the leveling dynamics, whereas a mathematical model for the momentum balance is implemented to extract the viscosity of the polymer film as a function of temperature. Our methodology is illustrated in the context of films of poly(methyl methacrylate) that are patterned via nanoimprint lithography into dense gratings. We study how the glass transition temperature and the critical temperature of collapse vary as a function of the film size and the inclusion of the antiplasticizer, tris(2-chloropropyl) phosphate. The grating periods are varied consistently between 80 and 240 nm, whereas the antiplasticizer concentrations are 1, 3, 5, and 10 wt %. The solution of the momentum balance allows the detailed correlation between stresses, curvature, heating, and shear rates during leveling. We found that both temperatures, T G and T flow , decrease as the film size decreases or as the concentration of the antiplasticizer increases. In addition, antiplasticizer concentrations between 3 and 5 wt % stabilize the size dependence of T flow . We show that the nature of the antiplasticizer is effectively to increase the low-temperature viscosity of the film. However, during leveling, the antiplasticized film sustains its curvature, thereby driving a sudden relaxation, once T G is reached, and increasing the possibilities of defects.

Temperature sensors with micro- and nanoscale spatial resolution have long been explored for their potential to investigate the details of physical systems at an unprecedented scale. In particular, the rapid miniaturization of transistor technology, with its associated steep boost in power density, calls for sensors that accurately monitor heating distributions. Here, we report on a simple and scalable fabrication approach, based on directed self-assembly and transfer-printing techniques, to constructing arrays of nanodiamonds containing temperature-sensitive fluorescent spin defects. The nanoparticles are embedded within a low-thermal-conductivity matrix that allows for repeated use on a wide range of systems with minimal spurious effects. Additionally, we demonstrate access to a wide spectrum of array parameters ranging from sparser single-particle arrays, with the potential for quantum computing applications, to denser devices with 98 ± 0.8% yield and stronger photoluminescence signals, ideal for temperature measurements. With these, we experimentally reconstruct the temperature map of an operating coplanar waveguide to confirm the accuracy of these platforms.

Directed self-assembly (DSA) of block copolymers (BCPs) can achieve perfectly aligned structures at thermodynamic equilibrium, but the self-assembling morphology can become kinetically trapped in defective states. Understanding and optimizing the kinetic pathway toward domain alignment is crucial for enhancing process throughput and lowering defectivity to levels required for semiconductor manufacturing, but there is a dearth of experimental, three-dimensional studies of the kinetic pathways in DSA. Here, we combined arrested annealing and TEM tomography to probe the kinetics and structural evolution in the chemoepitaxy DSA of PS- b-PMMA with density multiplication. During the initial stages of annealing, BCP domains developed independently at first, with aligned structures at the template interface and randomly oriented domains at the top surface. As the grains coarsened, the assembly became cooperative throughout the film thickness, and a metastable stitch morphology was formed, representing a kinetic barrier. The stitch morphology had a three-dimensional structure consisting of both perpendicular and parallel lamellae. On the basis of the mechanistic information, we studied the effect of key design parameters on the kinetics and evolution of structures in DSA. Three types of structural evolutions were observed at different film thicknesses: (1) immediate alignment and fast assembly when thickness < L 0 ( L 0 = BCP natural periodicity); (2) formation of stitch morphology for 1.25-1.45 L 0 ; (3) fingerprint formation when thickness >1.64 L 0 . We found that the DSA kinetics can be significantly improved by avoiding the formation of the metastable stitch morphology. Increasing template topography also enhanced the kinetics by increasing the PMMA guiding surface area. A combination of 0.75 L 0 BCP thickness and 0.50 L 0 template topography achieved perfect alignment over 100 times faster than the baseline process. This research demonstrates that an improved understanding of the evolution of structures during DSA can significantly improve the DSA process.

We demonstrated the synthesis and directed self-assembly (DSA) of poly(styrene- b -(lactic acid- alt -glycolic acid)) (PS- b -PLGA). Lamellae-forming PS- b -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 1 H NMR spectroscopy, GPC, DSC, TGA, SAXS, and rheometry. The order-disorder transition temperatures ( T ODT ) of four PS- b -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- b -PLGA is twice as large as that of poly(styrene- b - racemic lactide) (PS- b -PDLLA) at 150 °C, while the surface energies (γ) of PS and PLGA are nearly equal. Thin films of PS- b -PLGA were successfully directed to assemble on stripe chemical patterns with a range of pattern periods ( L 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- b -PLGA as an attractive candidate for next-generation lithography with sub-10 nm resolution.

Polystyrene- block-poly(methyl methacrylate) (PS- b-PMMA) is one of the prototypical block copolymers in directed self-assembly (DSA) research and development, with standardized protocols in place for processing on industrially relevant 300 mm wafers. Scaling of DSA patterns to pitches below 20 nm using PS- b-PMMA, however, is hindered by the relatively low Flory-Huggins interaction parameter, χ. Here, we investigate the approach of adding small amounts of ionic liquids (ILs) into PS- b-PMMA, which selectively segregates into the PMMA domain and effectively increases the χ parameter and thus the pattern resolution. The amount of IL additive is small enough to result in limited changes in PS- b-PMMA's surface and interfacial properties, thus maintaining industry-friendly processing by thermal annealing with a free surface. Three different ILs are studied comparatively regarding their compositional process window, capability of increasing χ, and thermal stability. By adding ∼3.1 vol % of the champion IL into a low-molecular-weight PS- b-PMMA ( M n = 10.3k- b-9.5k), we demonstrated DSA on chemically patterned substrates of lamellar structures with feature sizes <8.5 nm. Compatibility of the PS- b-PMMMA/IL blends with the standardized processes that have been previously developed suggests that such blend materials could provide a drop-in solution for sub-10 nm lithography with the processing advantages of PS- b-PMMA.

An environmental chamber equipped with an in situ spectroscopic ellipsometer, programmatic vapor pressure control, and variable temperature substrate holder has been designed for studying polymer coating behavior during an exposure to a solvent vapor and also for probing the residual solvent in the film afterwards. Both sorption-desorption cycle at a constant temperature and temperature programmed desorption (TPD) of the residual solvent manifest themselves as a change of the film thickness. Monitoring of ellipsometric angles of the coating allows us to determine the thickness as a function of the vapor pressure or sample temperature. The solvent vapor pressure is precisely regulated by a computer-controlled pneumatics. TPD spectra are recorded during heating of the film in an oil-free vacuum. The vapor pressure control system is described in detail. The system has been tested on 6-170 nm thick polystyrene, poly(methyl methacrylate), and poly(2-vinyl pyridine) films deposited on silicon substrates. Liquid toluene, water, ethanol, isopropanol, cyclohexane, 1,2-dichloroethane, and chlorobenzene were used to create a vapor atmosphere. Typical sorption-desorption and TPD curves are shown. The instrument achieves sub-monolayer sensitivity for adsorption studies on flat surfaces. Polymer-solvent vapor systems with strong interaction demonstrate characteristic absorption-desorption hysteresis spanning from vacuum to the glass transition pressure. Features on the TPD curves can be classified as either glass transition related film contraction or low temperature broad contraction peak. Typical absorption-desorption and TPD dependencies recorded for the 6 nm thick polystyrene film demonstrate the possibility to apply the presented technique for probing size effects in extremely thin coatings.

Directed self-assembly (DSA) of block copolymer (BCP) thin films is a promising approach to enable next-generation patterning at increasingly smaller length scales. DSA utilizes interfacial wetting layers to force the BCP domains to self-assemble with the desired orientation with respect to the substrate. Here, we demonstrate that initiated chemical-vapor-deposited (iCVD) polydivinylbenzene (pDVB) ultrathin films can direct the self-assembly of poly(styrene- block-methylmethacrylate). We found that the methyl radicals formed at increased filament temperatures during the iCVD process result in the backbone methylation of pDVB. By tuning the degree of backbone methylation, we systematically changed the wetting properties of the iCVD pDVB from a slight poly(methylmethacrylate) preference to complete poly(styrene) preference. Additionally, we utilize the conformal nature of the iCVD to form a wetting layer over a topographical line and space pattern, which is subsequently used to produce self-assembled BCP films with both perpendicular orientation and long-range alignment.

A block copolymer self-consistent field theory (SCFT) model is used for direct analysis of experimental X-ray scattering data obtained from thin films of polystyrene- b -poly(methyl methacrylate) (PS- b -PMMA) made from directed self-assembly. In a departure from traditional approaches, which reconstruct the real space structure using simple geometric shapes, we build on recent work that has relied on physics-based models to determine shape profiles and extract thermodynamic processing information from the scattering data. More specifically, an SCFT model, coupled to a covariance matrix adaptation evolutionary strategy (CMAES), is used to find the set of simulation parameters for the model that best reproduces the scattering data. The SCFT model is detailed enough to capture the essential physics of the copolymer self-assembly, but sufficiently simple to rapidly produce structure profiles needed for interpreting the scattering data. The ability of the model to produce a matching scattering profile is assessed, and several improvements are proposed in order to more accurately recreate the experimental observations. The predicted parameters are compared to those extracted from model fits via additional experimental methods and with predicted parameters from direct particle-based simulations of the same model, which incorporate the effects of fluctuations. The Flory-Huggins interaction parameter for PS- b -PMMA is found to be in agreement with reported ranges for this material. These results serve to strengthen the case for relying on physics-based models for direct analysis of scattering and light signal based experiments., Competing Interests: Conflicts of interest There are no conflicts of interest to declare.

Tungsten oxide (WO 3-x ) nanostructures with hexagonal in-plane arrangements were fabricated by sequential infiltration synthesis (SIS), using the selective interaction of gas phase precursors with functional groups in one domain of a block copolymer (BCP) self-assembled template. Such structures are highly desirable for various practical applications and as model systems for fundamental studies. The nanostructures were characterized by cross-sectional scanning electron microscopy, grazing-incidence small/wide-angle X-ray scattering (GISAXS/GIWAXS), and X-ray absorption near edge structure (XANES) measurements at each stage during the SIS process and subsequent thermal treatments, to provide a comprehensive picture of their evolution in morphology, crystallography and electronic structure. In particular, we discuss the critical role of SIS Al 2 O 3 seeds toward modifying the chemical affinity and free volume in a polymer for subsequent infiltration of gas phase precursors. The insights into SIS growth obtained from this study are valuable to the design and fabrication of a wide range of targeted nanostructures.

Three-dimensional (3D) mesoporous thin films with sub-100 nm periodic lattices are of increasing interest as templates for a number of nanotechnology applications, yet are hard to achieve with conventional top-down fabrication methods. Block copolymer self-assembly derived mesoscale structures provide a toolbox for such 3D template formation. In this work, single (alternating) gyroidal and double gyroidal mesoporous thin-film structures are achieved via solvent vapor annealing assisted co-assembly of poly(isoprene-block-styrene-block-ethylene oxide) (PI-b-PS-b-PEO, ISO) and resorcinol/phenol formaldehyde resols. In particular, the alternating gyroid thin-film morphology is highly desirable for potential template backfilling processes as a result of the large pore volume fraction. In situ grazing-incidence small-angle X-ray scattering during solvent annealing is employed as a tool to elucidate and navigate the pathway complexity of the structure formation processes. The resulting network structures are resistant to high temperatures provided an inert atmosphere. The thin films have tunable hydrophilicity from pyrolysis at different temperatures, while pore sizes can be tailored by varying ISO molar mass. A transfer technique between substrates is demonstrated for alternating gyroidal mesoporous thin films, circumventing the need to re-optimize film formation protocols for different substrates. Increased conductivity after pyrolysis at high temperatures demonstrates that these gyroidal mesoporous resin/carbon thin films have potential as functional 3D templates for a number of nanomaterials applications.

The kinetics of directed self-assembly of symmetric PS-b-PMMA diblock copolymer on chemically patterned templates were measured during in situ thermal annealing. Although these chemical guide patterns lead to well-aligned, defect-free lamellar patterns at thermodynamic equilibrium, in practice, challenges remain in understanding and optimizing the kinetic evolution for technological applications. High-speed, environmentally controlled atomic force microscopy imaging was used to track pattern evolution on the time scale of individual microdomain connections in real space and time, allowing the direct visualization of defect healing mechanisms. When we apply this highly general technique to films on chemically patterned substrates, we find that pattern alignment is mediated by a metastable nonbulk morphology unique to these samples, referred to as the "stitch" morphology. We observe diverse and anisotropic mechanisms for the conversion from this morphology to equilibrium lamellar stripes. Directed self-assembly on chemical templates is observed to follow exponential kinetics with an apparent energetic barrier of 360 ± 80 kJ/mol from 210-230 °C, a significant enhancement when compared with ordering rates on unpatterned substrates. Ultimately, from local imaging, we find that the presence of a chemical guiding field causes morphological ordering and lamellar alignment to occur irreversibly.