Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session S55: Block Copolymer Thin Films Integrated with new Material Platforms II: Annealing, Architecture, and Multi-LayersFocus
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Sponsoring Units: DPOLY Chair: Gregory Doerk, Brookhaven Natl Lab Room: LACC 515A |
Thursday, March 8, 2018 11:15AM - 11:27AM |
S55.00001: Robust Gyroid Morphology in Triblock Terpolymer Films During Solvent Vapor Annealing Ilja Gunkel, James Dolan, Karolina Korzeb, Morgan Stefik, Ulrich Wiesner, Bodo Wilts, Ullrich Steiner Controlled solvent annealing is known to effectively generate ordered block copolymer films. In addition, films of desired morphology (spheres, cylinders, gyroids, or lamellae) can be produced by annealing films using solvent mixtures of tuned selectivity. While this has been investigated in detail for diblock copolymers, the effect of selective solvent annealing has not yet been studied for the next more complicated family of linear block copolymers, triblock terpolymers. We present the results of in situ GISAXS during solvent annealing of gyroid-forming polyisoprene-b-polystyrene-b-poly(ethylene oxide) triblock terpolymer films. The selectivity was adjusted by using mixed vapor ratios of tetrahydrofuran and methanol. In contrast to diblock copolymers, we found the gyroid morphology irrespective of the solvent vapor ratios used for annealing of the terpolymer film. Furthermore, we show that the robust nature of the gyroid morphology allows for generating films with long-range order. |
Thursday, March 8, 2018 11:27AM - 11:39AM |
S55.00002: Solvent-Mediated Self-Assembly in Thin Films of Block Copolymer-Based Supramolecules Katherine Evans, Ting Xu Block copolymer-based supramolecules offer a versatile platform to generate hierarchical assemblies. However, the system is complex and there is a limited understanding of the self-assembly process which is critical for precise control of the nanostructure. Here, we investigate the effects of small molecule loading and the solvent annealing condition on thin films of supramolecules on flat and patterned substrates. The studies show that small molecule loading and the solvent annealing condition greatly affect the assembly rate, grain size, and feature size. On the line-patterned surface, the microdomains can be macroscopically aligned with an order parameter as high as 0.9 without sacrificing commensurability between the pattern feature size and periodicity. Rather, the supramolecule self-assembles into structures with two distinct periodicities. The feature sizes are 0.9 and 1.33 times of that on a flat surface in the trench and on the mesa, respectively. The observed heterogeneous nanostructures are attributed to the redistribution of the small molecule and self-adaptation of the supramolecule to release energy costs that arise from incommensurability. The present study opens a new path to enrich the diversity of morphologies afforded by a single self-assembly system |
Thursday, March 8, 2018 11:39AM - 11:51AM |
S55.00003: Self-Assembly beyond 2D – Interactions in Multi-Layered Arrays of Block Copolymer Films Arkadiusz Leniart, Andrzej Sitkiewicz, Kevin Yager, Pawel Majewski Block copolymers (BCPs) offer a promising way for creating nanostructured periodic patterns on various substrates. Ordered BCP films are frequently utilized as etching or deposition masks or as synthetic templates in the fabrication of various functional nanomaterials. Unfortunately, the range of morphologies offered by typical diblock copolymer thin films is rather limited and does not meet the need for more refined structures required in many applications. Without resorting to more complex system e.g. multi-block copolymers, the two most commonly employed 2D motifs in the diblock systems are periodic “lines” and hexagonally-packed “dots”. To extend the library of structural motifs offered by the BCPs, we propose a strategy in which multiple monolayers are stacked, co-annealed, and ultimately converted to inorganic nanomaterials. We are investigating the process of mutual interactions between the layers of BCPs of distinct morphology and composition in which the polymers are initially in their disordered as-cast state or preordered using our directed self-assembly setup. |
Thursday, March 8, 2018 11:51AM - 12:27PM |
S55.00004: Directed Self-Assembly (DSA) of Block Copolymer Films with Direct Immersion Annealing Invited Speaker: Alamgir Karim The self-assembly of block copolymers into periodic nanostructures has long been studied for their potential use in integrated circuits, nanofiltration devices, metamaterials, energy and data storage devices, and many more applications. Their use, however, is limited by a number of structural and kinetics challenges. The present research describes how a recently developed annealing technique, Direct Immersion Annealing (DIA), can be used to address these challenges. The mechanism that leads to a reduction in domain size of up to as much as 60% for a range of molecular weights of block copolymer during DIA is examined for 1D, 2D, and 3D morphologies. We find that the chain orientation within a structure has a significant impact on the structural rearrangements that occur as the result of constrained swelling. This leads to a reduction of the domain size for out-of-plane structure and an increase in domain size for in-plane structure in the dry film. The non-equilibrium state of the morphology that leads to the reduced domain size leaves the chains in a non- equilibrium conformation that deviates from shape traditionally observed in block copolymers. SANS analysis confirms that the chains take on a flattened disc-like shape in this state. The solvent presence during DIA also presents the ability to tune the interaction parameter of the block, where it is shown that the interface width between domains can be reduced by almost 30% using a selective solvent. Finally, the kinetics of DIA are examined for its ability to rapidly order (30s in best case) neat and nanofilled block copolymer systems. The rapid ordering kinetics of direct immersion annealing are limited to the molecular weight regime where chains are unentangled. At higher molecular weights, the ordering diffusion coefficient scales as N-2.9. |
Thursday, March 8, 2018 12:27PM - 12:39PM |
S55.00005: In-Situ Grazing-Incidence Small-Angle X-ray Scattering of Electrospray Deposited Block Copolymer Thin Films Kristof Toth, Youngwoo Choo, Manesh Gopinadhan, Ruipeng Li, Kevin Yager, Masafumi Fukuto, Chinedum Osuji Electrospray deposition (ESD) enables the growth of block copolymer (BCP) thin films in a precise and continuous manner by the delivery of sub-micron droplets of dilute polymer solutions to a heated substrate. It also allows the fabrication of uniquely structured films by sequential deposition. We report here the results of in-situ grazing-incidence small-angle X-ray scattering (GISAXS) measurements of BCP thin films during ESD. A custom ESD apparatus was used to obtain synchrotron GISAXS data that provide information regarding the domain spacing and orientation of the developing BCP thin films during film deposition. We examined microstructural evolution during the deposition of a homopolymer, polystyrene (PS), of varying molecular weights onto a lamellae-forming polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) film in the ESD apparatus. The combined thin film exhibited a transition from lamellae to cylinders for low molecular weight PS and loss of structural order above a critical thickness of the deposited PS “top-coat.” We attribute this to volume fraction changes on swelling with PS during ESD. This methodology advanced here enables studies of ordering pathways and the real-time exploration of structure development in thin films fabricated by ESD. |
Thursday, March 8, 2018 12:39PM - 12:51PM |
S55.00006: Vapor phase assisted polymer deposition for generating hierarchical block copolymer nanostructures Zhe Qiang, Muzhou Wang The ability of block copolymers (BCPs) to self-assemble into uniform nanostructures has rendered them highly attractive for a wide variety of technologies. Many applications such as information technology require the assembly of BCPs in thin films with different regions containing different features (domain spacing and morphology). Previous methods for generating complex nanopatterns on one substrate usually rely on either multiple processing steps or locally controlling the orientation/degree of ordering of polymer patterns, which are challenging with increasing complexity of the desired nanopatterns. Here, we adapt common BCP solvent vapor annealing processes to develop a vapor-phase photo-controlled deposition technique for producing homopolymers in BCP film matrices. The amount of deposited homopolymers and their molecular weight can be controlled by the processing time and irradiation energy. The synthesized homopolymers blend with BCPs, which change the underlying polymer chemistry and alter the BCP morphology and domain spacing. This method can be applied to different BCP systems. We will also demonstrate how to generate different nanopatterns (both sizes and shapes) from one block copolymer on different regions of one substrate using this technique. |
Thursday, March 8, 2018 12:51PM - 1:03PM |
S55.00007: Epitaxy of Incommensurate Block Copolymer Dot Arrays: Preferential Alignment and Moire Superstructures Erik Luber, Cong Jin, Brian Olsen, Jillian Buriak In this work we investigated the directed self-assembly of dot forming block copolymers (BCP) deposited in a sequential layer-by-layer fashion. Samples were fabricated by first spin-casting a dot forming BCP (PS-b-PDMS) and converting it to a hexagonal array of silica dots, this non-planar substrate was then used to direct the self-assembly of a second dot forming BCP layer. It was found that the top layer of dots adopted a preferential orientation relative to the bottom dot array, resulting in well-defined Moire superstructures. The observed preferential orientations were shown to be statistically meaningful, as the distributions of the relative rotation angles between the BCP dot arrays were determined using large-area helium-ion microscopy (> 106 dots). Moreover, the preferential rotation angle of these Moire superstructures was found to be uniquely determined by the pitch ratio of the two lattices and relative sizes of the dot features. A systematic investigation into the bottom layer dot features was performed using electron beam lithography, where it was found that three different pattern forming regimes exist depending on the size of the bottom layer features. |
Thursday, March 8, 2018 1:03PM - 1:15PM |
S55.00008: Thru-thickness Vertically Ordered Lamellar Block Copolymer Films with Dynamic Thermal Annealing Monali Basutkar, Saumil Samant, Joseph Strzalka, Kevin Yager, Gurpreet Singh, Alamgir Karim Template-free directed self-assembly of ultrathin lamellar block copolymer (l-BCP) films into vertically oriented nanodomains holds much technological relevance for fabrication of next-generation devices from nanoelectronics to nanomembranes. We report the formation of thru-thickness vertically oriented lamellae in polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) thin films on quartz substrate, without any PMMA-block wetting layer formation, quartz surface modification or system modifications. A molecular relaxation induced vertical l-BCP ordering occurs under a transient macroscopic vertical strain field, imposed by sharp thermal gradient (▽T) cold zone annealing (CZA-S). The parametric window for vertical ordering is quantified via a coupling constant, C (= v.▽T), whose range is established in terms of ▽T above a threshold value, and an optimal dynamic sample sweep rate (v ~ d/τ), where τ = l-BCP’s longest molecular relaxation time and d = Tg,heat-Tg,cool distance. This study also reports a thorough understanding of the dynamic molecular mechanisms involved in the nanostructure formation and morphology evolution of vertically oriented l-BCP along the CZA-S ▽T tracked in real-time by in-situ GISAXS. |
Thursday, March 8, 2018 1:15PM - 1:27PM |
S55.00009: Unconventional Phase Behaviors of Linear-Dendritic Copolymer due to Extremely High Frustration Yicheng Qiang, Wei-hua Li Among the various ordered structures formed by the self-assembly of block copolymer, spherical phases occupy relatively minor regions in the phase diagram. Some new spherical phases, e.g. Frank-Kasper phases, can only be obtained in a wide region of spherical phases. Several mechanisms have been established to expand the spherical region thus stabilizing the Frank-Kasper phases, while the effect of these mechanisms is still limited. Aiming to widen the phase regions of these desired new spherical phases drastically, we design a kind of linear-dendritic block copolymer and investigate its self-assembly behaviors by the self-consistent field theory (SCFT). With the optimized control parameters, the spherical phase region is expanded to be overwhelming in the phase diagram, reaching the volume fraction of 0.7, which means that the spherical domain is formed with the major component. Along with the exploration of many exotic new phases, this renews our insight into the intricate mechanism of the self-assembly of block copolymer. |
Thursday, March 8, 2018 1:27PM - 1:39PM |
S55.00010: Design Block Copolymers for Unconventional Ordered Phases Wei-hua Li, Chao Duan, Bin Zhao The self-assembly of block copolymers provides a powerful platform for the fabrication of ordered nanostructures. To design block copolymers for desired new ordered phases presents an interesting but challenging task. In our previous work, we have demonstrated that many prototypical structures of hard crystals can be recasted by the self-assembly of purposely designed block copolymers following some useful guiding principles. In this presentation, three block copolymers, including linear ABAB tetrablock copolymer, a nonlinear AB-type copolymer composed of AB diblock tethered by an additional A-block onto the B-block, are designed to target some unconventional ordered phases: the hybrid lamella-sphere phase, perforated-lamella phase and two-dimensional quasicrystal-like phase. The stability of these targeted phases is identified using the self-consistent field theory. In particular, their stabilization mechanisms are elucidated by analyzing the segment distributions as well as the different contributions of free energy. These successful examples further demonstrates that architecture design provides a huge space for the self-assembly block copolymers. |
Thursday, March 8, 2018 1:39PM - 1:51PM |
S55.00011: Dodecagonal Quasicrystal Phase in Block Copolymers: Stable or Metastable? Chao Duan, Mingtian Zhao, Yicheng Qiang, Lei Chen, Wei-hua Li In the last decade, quasicrystal (QC) phases as a special kind of ordered aperiodic structures have been observed in various soft matter systems including self-assembling block copolymer(BCP) melts. However, the thermodynamic stability of QC is a long-standing problem in the community of condensed matter physics. In this presentation, the relative stability of cylindrical dodecagonal quasicrystal (DDQC) phase formed by ABCB tetrablock terpolymers is studied using the self-consistent field theory (SCFT). To circumvent the aperiodicity, the free energy of DDQC is determined by SCFT coupled with the Stampfli self-similarity construction, and it is compared with a series of competitive periodic DDQC approximants. Additionally, the cluster model originally from hard DDQCs is introduced to quantitatively analyze the relative stabilities between DDQC and its approximants, revealing a general conclusion of metastable DDQC in BCP melt systems as well as a robust mechanism of packing frustration closely related to the mismatch of lattice constants. |
Thursday, March 8, 2018 1:51PM - 2:03PM |
S55.00012: Impact of Topological Constraint on the Self-Assembly Behavior of AB-Type Block Copolymers Wenbo Jiang, Yicheng Qiang, Lei Chen, Wei-hua Li Chain topology has an important impact on the phase behaviors of block copolymers, even for two-component AB-type ones. To demonstrate this impact, a special type of AB-type copolymers is purposely devised by tethering an additional A block onto the B-block of AB diblock copolymer. With the tethering position at the junction point of AB, the copolymer becomes A2B miktoarm star while it becomes ABA linear triblock with the tethering position at the end of B-block. The phase diagrams of the AB-type copolymers with various grafting positions are constructed using the self-consistent field theory. Surprisingly, the perforated lamellar (PL) phase with perforated A-layer becomes stable and completely replaces gyroid at relatively strong segregation for the AB-type copolymer with a proper tethering position, which is in obvious contrast to a tiny stability channel in A2B or no stability region in ABA. It is elucidated that PL is stabilized by the local segregation of the two divided B-blocks, accommodating to the distinct interfaces with highly different curvatures. |
Thursday, March 8, 2018 2:03PM - 2:15PM |
S55.00013: Directing assembly of semiconductor colloidal quantum dots with short-chain amphiphilic block copolymers Stacy Copp, Christina Hanson, Jennifer Hollingsworth, Gabriel Montano Block copolymers are promising agents for controlling the assembly of photonic materials. In particular, low molecular weight copolymers may allow for nanoscale spacing of nanoparticles and molecules, a requirement for engineering inter-particle interactions. Recent studies show that short-chain amphiphilic block copolymers can direct assembly of chromophores into photonic systems that exhibit energy transfer [2,3]. We explore the utility of similar block copolymers to arrange another photonic nanomaterial: semiconductor “giant” colloidal quantum dots [4]. By exploiting hydrophobic effects, quantum dots are driven into the hydrophobic core of extended micelles, solubilizing the nanoparticles in water. The length and type of hydrophobic and hydrophilic polymer blocks tune the structures of these polymer-nanoparticle hybrid structures. We show that this polymer-mediated control of quantum dot assembly also tunes the photophysics of the quantum dots. |
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