Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session M34: Thin Films of Block Copolymers and Hybrid Materials: Directed Assembly I |
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Sponsoring Units: DPOLY Chair: Bradley Olsen, Massachusetts Institute of Technology Room: 342 |
Wednesday, March 20, 2013 8:00AM - 8:12AM |
M34.00001: Inverse Solution for Directed Self-Assembly of Thin Film Cylindrical Morphology Block Copolymers Adam Hannon, Kevin Gotrik, Alfredo Alexander-Katz, Caroline Ross Using topographical templates, the directed self-assembly of thin film cylinder forming block copolymers has allowed for the fabrication of complex patterns with the sub-20nm length scales necessary for nanolithography. However, the templates for these circuit-like patterns have been developed from empirical methods that require either experimental examination of many input templates or time-consuming simulations over a wide parameter space. To address this problem, we have developed an inverse self-assembly algorithm that allows for the prediction of the template necessary to obtain a desired target pattern which includes bends, junctions, and terminals. The model system has been optimized for comparison with a cylindrical PDMS-PS block copolymer (45.5 kg/mol molecular weight and PDMS volume fraction 33.5{\%} ) under equilibrium neutral solvent annealing conditions. Example target structures are shown with the resulting predicted template found from the algorithm and compared with traditional simulation methods using those templates. [Preview Abstract] |
Wednesday, March 20, 2013 8:12AM - 8:24AM |
M34.00002: Directed Assembly of Block Copolymer Ordering on Rough and Patterned Flexible Substrates Arzu Hayirlioglu, Manish Kulkarni, Alamgir Karim Directed self-assembly of block copolymer (BCP) thin film on flexible substrates has potential in fabrication of flexible electronic devices due to its nanometer scale pattern formation capability. We studied the BCP ordering properties of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) films on a flexible substrate, where the PS-b-PMMA films are initially coated on a smooth poly(dimethylsiloxane) (PDMS) substrate, whose surface energy (SE) was tuned between (20-69) mJ/m2 by UV-ozone (UVO) exposure. This range of SE allows for controlled wettability and orientation of the BCP overlayer. Further, we replicated different patterned media and observed perpendicular lamellar BCP orientation and parallel cylindrical BCP orientation on patterned flexible PDMS in the wetting SE regime. Rough surface structures created by silica xerogels were replicated on PDMS. RMS roughness of the xerogels is tuned by controlling sol-gel catalyst concentration and aging time. Effect of the aspect ratio of the rough PDMS substrates on the orientation of BCP films was studied. Surface morphology of the BCP films was studied by optical microscopy and Atomic Force Microscope (AFM), while orientation of the film's interior was studied using Grazing-Incidence Small Angle X-ray Scattering (GISAXS) [Preview Abstract] |
Wednesday, March 20, 2013 8:24AM - 8:36AM |
M34.00003: Consequences of Surface Neutralization in Thin Film Block Copolymers Sangwon Kim, Paul Nealey, Frank Bates Changes in boundary conditions have been found to induce novel physical phenomena in numerous systems. In this presentation, the consequences of surface neutralization to the structures of thin-film block copolymers were investigated using partially epoxidized poly(styrene-$b$-isoprene) (PS-PI) diblock copolymers. The thickness dependence of thin-film structures, prepared on non-preferential and preferential underlying brushes, were studied using scanning electron microscopy and atomic force microscopy. The PS-PI precursor, without epoxidation, exhibited parallel, layer-by-layer structures covered with one component, and the corresponding hole/island structures had step heights of one bulk lamellar periodicity (L$_{\mathrm{0}})$, consistent with previous studies. On the other hand, the thin films of epoxidized PS-PI showed perpendicular ordering independent of the thickness above non-preferential brushes, indicative of surface neutralization at both interfaces. The parallel lamellae of epoxidized PS-PI above preferential brushes were characterized as hole/island structures of 0.5 L$_{\mathrm{0}}$ step heights and the free surface wetting by both components of the diblock copolymers. The formation of the distinctive relief structures was attributed to the surface neutralization from the chemical modification. [Preview Abstract] |
Wednesday, March 20, 2013 8:36AM - 9:12AM |
M34.00004: Block Copolymer Directed Assembly for Nanomaterials and Nanodevices Invited Speaker: Sang Ouk Kim Block copolymer nanopatterning is a promising technology that can complement the inherent limitations of conventional photolithography. The spontaneous and parallel assembly of block copolymers may generate densely packed, periodic 10-nm-scale nanodomains in a scalable way. Furthermore, laterally ordered, device-oriented nanostructures are attainable by the directed self-assembly principles employing prepatterned substrates. In this presentation, the overview of my research achievements associated to block copolymer nanopatterning will be presented. My research group demonstrated the world-first successful integration of block copolymer nanopatterning with 193 nm ArF lithography. We also developed soft-graphoepitaxy, which generates highly aligned nanoscale metal and semiconductor nanostructures without any trace of structure-directing topographic pattern. Soft-graphoepitaxy could be further developed to ultralarge-area nanopatterning, where micrometer scale photoresist pattern can be completely transformed into large-area block copolymer nanopattern. My research group also developed various pattern transfer methods for block copolymer nanopatterning. Mussel-inspired block copolymer nanopatterning exploiting universal natural adhesive of mussel polydopamine enables the nanopatterning of low surface energy materials, such as gold, Teflon and graphene. Our recent transferrable and flexible nanopatterning employing chemically modified graphene films as pattern substrates makes it possible to apply block copolymer nanopatterning onto arbitrary nonplanar and flexible geometries and generates ideal three-dimensional assembly of carbon nanotubes and graphene. [Preview Abstract] |
Wednesday, March 20, 2013 9:12AM - 9:24AM |
M34.00005: Self-annihilation of defects in block-copolymer thin films induced by corrugated substrates Georges Hadziioannou, Guillaume Fleury, Karim Aissou, Jonah Saver, Giles Pecastaings, Cyril Brochon, Christophe Navarro, Stephane Grauby, Jean-Michel Rampnoux, Stefane Dilhaire Ultradense perfectly ordered structures with nanometric periodicity are of crucial importance for applications such as microelectronics, data storage media or meta-materials. Herein we demonstrate the use of a polymeric guiding pattern to control the self-assembly of block copolymers into highly-ordered 2D arrays. For this, a sinusoidal surface-relief grating was interferometrically inscribed onto an azobenzene containing copolymer sub-layer. A poly(styrene-$b$-ethylene oxide), PS-$b$-PEO, film was cast on top, resulting in cylinders with a 6-fold coordination. When film thickness reaches a critical value where the PS-$b$-PEO free-surface is smooth and no hint of the underlying sinusoidal pattern is apparent, a defect-free 2D-array of PS-$b$-PEO cylinders is observed over a large surface. Our results show that the surface deformation induced by the topological pattern controls the diffusion of defects and consequently their annihilation. [Preview Abstract] |
Wednesday, March 20, 2013 9:24AM - 9:36AM |
M34.00006: Directed Self-assembly of High-Molecular-Weight Block Copolymer Films Du Yeol Ryu, Eunhye Kim, Hyungju Ahn, Sungmin Park, June Huh, Joona Bang, Byeongdu Lee The solvent-vapor annealing of block copolymer (BCP) films facilitates the mobility of highly entangled polymer chains, or the path-way barriers to the formation of well-ordered structures. In this study, the microdomain orientation of BCP films has been studied by in-situ grazing incidence small angle x-ray scattering (GISAXS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). We demonstrate the rapid evolution of a perpendicularly oriented lamellar morphology in high-molecular-weight (up to 1,000,000 g/mol) block copolymer films, to achieve topographically patterned BCP substrates. [Preview Abstract] |
Wednesday, March 20, 2013 9:36AM - 9:48AM |
M34.00007: Directed Assembly of block copolymers on topologically complex surfaces: A self-consistent field theoretic study Xianggui Ye, Bamin Khomami The self-assembly of a lamella-forming diblock copolymer guided by topological complexity, namely, substrates composed of trenches with different heights and widths via self-consistent field theoretic simulations has been studied. In general, when the substrate is neutral to both blocks of the copolymer, the perpendicular lamella morphology is obtained. However, natural substrate usually has a preferred affinity to one of the blocks, and parallel lamella morphology is often obtained. Tuning the substrate roughness has proven useful in creating the perpendicular lamellar morphology. To this end, it has been shown that the perpendicular lamellae vertical to the trench direction is preferred when the trench size is relatively large. However, the orientation of the highly sought after perpendicular lamellar morphology can be changed by manipulation of the trench size, i.e., when the trench size is comparable to the natural periodic spacing of diblock copolymer, the perpendicular lamellae parallel to the trench direction is the preferred morphology. Overall this study clearly demonstrates the impact of this class of simulations in rational design of morphologies in thin multi-component polymeric films with application to technologies such as ultra-high-density magnetic recording media, metal nanostructures for metamaterials and plasmonic circuits, and sensors. [Preview Abstract] |
Wednesday, March 20, 2013 9:48AM - 10:00AM |
M34.00008: Topcoat approaches for directed-assembly of copolymer films with blocks exhibiting differences in surface energy Hyo Seon Suh, Jeong In Lee, Abelardo Ramirez-Hernandez, Yasuhiko Tada, Hiroshi Yoshida, Lei Wan, Ricardo Ruiz, Juan de Pablo, Paul Nealey Fabricating patterns with feature dimensions smaller than 10 nm scale using block copolymer lithography requires the use of materials with large Flory-Huggins interaction parameters. Because such block copolymers (BCPs) typically show the large differences in surface energy between the blocks, one block (with lower surface energy) tends to segregate to the free surface of films and precludes the assembly of the desired through-film perpendicularly oriented structures. Here we describe a generalizable strategy to overcome this limitation. By coating the BCP film with an additional layer, a topcoat, thermodynamically favorable boundary conditions at the top surface of the film can be engineered for directed self-assembly. The allowable properties of the topcoats depend on the interfacial energies of the layer with the blocks of the copolymer, and the block-block interfacial energy. The strategy is demonstrated experimentally by directing the assembly of polystyrene-block-poly-2-vinylpyridine (PS-$b$-P2VP) films on chemically nanopatterned substrates with different topcoat materials. [Preview Abstract] |
Wednesday, March 20, 2013 10:00AM - 10:12AM |
M34.00009: Bad-solvent Induced Tunable Nanoscale Roughness in Polymer, Block Co-polymer and Carbon Thin Films Manish Kulkarni, Chandrashekhar Sharma, Alamgir Karim Nanoscale surface roughness of a material plays significant role in various applications such as adhesion, micro-/nano-electromechanical systems and antireflective coatings. We demonstrate here a novel and simple method for tuning nanoscale surface roughness of polymer coatings using a modified flow coater assembly. A dual-blade flow coating assembly was used to coat films of Poly(styrene) (PS), poly(methylmethacrylate) (PMMA) and PS-b-PMMA block co-polymer (BCP) dissolved in toluene on silicon substrates with a secondary blade flow coating a bad-solvent (water, ethanol) on top of the polymer film after a controlled delay. The bad-solvent and good--solvent miscibility and evaporation dynamics dictates the surface roughness/porosity in the polymer-liquid-air-interface. Combination of miscible ethanol-toluene solvents led to PS-chain formation of iterated function system (IFS) like fractal patterns with a root-mean-square (RMS) roughness $\sim$ 250 nm. However, PS films with much smaller roughness (\textless\ 20nm) were obtained for immiscible water and toluene solvents. The rough polymer coatings were also pyrolysed under optimized conditions to obtain carbon films with similar morphologies. Surface morphology and chemistry of the polymer and carbonized films were studied using AFM and XPS. [Preview Abstract] |
Wednesday, March 20, 2013 10:12AM - 10:24AM |
M34.00010: Orientation of Microdomains in Cylinder-Forming PS-PHMA Thin Films Raleigh Davis, Richard Register, Paul Chaikin There is much interest in the study of self-assembled block copolymer thin films for uses in nanofabrication. For many applications control of the microdomain order is required. One method to achieve long-range orientational order in thin films is through the use of shear, which has been shown to orient block copolymer microdomains in the direction of the applied shear. A particular interest is shear-alignment of cylinder-forming poly(styrene)-poly(hexylmethacrylate) (PS-PHMA) thin films, which are effective masks for nanofabrication via reactive-ion etching. The present work examines the effects of changing PS block volume fraction, within the cylinder-forming region of the phase diagram, to both modulate the range of film thicknesses over which in-plane vs. out-of-plane cylinders are observed as well as improve the quality of in-plane alignment post-shear. Increasing the volume fraction of PS, away from the cylinder-sphere boundary, increased the range of film thicknesses over which the cylinders orient in-plane. The effects of the substrate wetting condition on cylinder orientation were also examined through grafting of PS and PHMA brushes to the substrate before deposition of the PS-PHMA film. [Preview Abstract] |
Wednesday, March 20, 2013 10:24AM - 10:36AM |
M34.00011: Tunable-Morphology Block Copolymer Thin Films with Controlled Solvent Vapor Annealing for Lithographic Applications Brian Stahl, Nathaniel Lynd, Edward Kramer, Craig Hawker Solvent annealing is an alternative to thermal annealing for improving long-range order and reducing defect density in block copolymer thin films. However, the fundamentals of block-copolymer self-assembly under solvent annealing conditions have yet to be studied in detail. We have developed a specialized hardware platform to perform solvent annealing experiments with active and precise control over solvent vapor saturation which allows us to quantitatively understand the structure-processing relationship during different stages of solvent annealing. Using polystyrene-b-polyethylene oxide/water/toluene as a model system and AFM, TEM and GISAXS characterization, we have found that a decrease in water vapor saturation during the post-annealing quenching step induces a change in domain spacing and reduction in long-range order. We have also found that by changing the water vapor saturation during steady-state annealing we are able to tune the domain spacing over a wide range and that this spacing remains after quenching. This controlled approach to solvent annealing affords considerable control over the morphology of annealed block copolymer thin films and a deeper understanding of the fundamentals of the process, making this technique more relevant to industrial applications. [Preview Abstract] |
Wednesday, March 20, 2013 10:36AM - 10:48AM |
M34.00012: Ultrathin block copolymer films under shear Marco Pinna, Roberta Dessi, Andrei Zvelindovsky Ultrathin block copolymer films of 1-2 microdomains thick were investigated by means of a large scale coarse grained computer simulation, Cell Dynamics Simulation. Our simulation method allowed to computationally reach the size scale of experimental samples and to explain some recent experiments on sheared lamellae and cylindrical block copolymer morphologies. A detailed dynamical phase diagram, which covered parallel and perpendicular lamellae and cylinders, as well as perforated lamellae, was constructed. The crucial role of defects in orientation phase transitions and structure ordering and non-trivial defects dynamics was found. Our results provide detailed insights into how to use shear to control and manipulate block copolymer structure in thin films. [Preview Abstract] |
Wednesday, March 20, 2013 10:48AM - 11:00AM |
M34.00013: Continuity and Network Morphologies of Lamellar Nanostructures Self-assembled in Block Copolymer Thin Films: Comparison of Processing by Thermal and Solvent Annealing Ian Campbell, Chunlin He, Mark Stoykovich Self-assembled block copolymers in thin films have advantages for nanolithography including tunable and scalable feature sizes below 50 nm, parallel patterning over large areas, inexpensive material costs, and attractive processability. One process for inducing order in block copolymer thin films is solvent annealing, in which a film is swollen with solvent and domain ordering is induced as the solvent evaporates from the film. Solvent annealing is advantageous compared to thermal processing because it occurs rapidly and enables the use of polymer constituents that may be thermally unstable. Here the continuity of lamellar networks formed in thin films of poly(styrene-block-methyl methacrylate) with volume fractions of PMMA ranging from 0.45 to 0.55 will be shown to be favored in the block with a higher volume fraction. Network characteristics such as branch point density and end point density correlate with continuity, but at lower densities in solvent annealed than thermally annealed thin films of identical composition. Further comparison between thermal and solvent annealed morphologies sheds light on the mechanism through which ordering is achieved in solvent annealing and allows for additional control over the nanoscale features formed by block copolymers in thin films. [Preview Abstract] |
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