Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session S25: Block Copolymer Thin Films |
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Sponsoring Units: DPOLY Chair: Thomas H. Epps, University of Delaware Room: Colorado Convention Center 203 |
Wednesday, March 7, 2007 2:30PM - 2:42PM |
S25.00001: Surfactant Assisted Orientation of PS-b-PMMA Block Copolymer Thin Films Jeong Gon Son, Xavier Bulliard, Huiman Kang, Paul F. Nealey, Kookheon Char Block copolymers are well known to spontaneously form a wide range of nanostructures. In thin films, they are additionally affected by the presence of a substrate and a free surface. This often leads to the morphology oriented in the direction parallel to the substrate. However, for the fabrication of functional nanostructures, the perpendicular orientation is preferred. In this study, we present a new route based on the use of surfactants in order to control the morphology of polystyrene-\textit{block}-poly(methylmethacrylate) (PS-$b$-PMMA) thin films. The addition of surfactants, interacting more favorably with the PMMA domains and modifying the surface and interfacial energy of the system, induces the perpendicular orientation of block copolymer thin film microdomains regardless of the chemistry of the substrate. For the high aspect ratio and the defect-free perpendicular orientation, we combine the surfactant assisted self-assembly with the directed self-assembly on chemically nanopatterned substrates. [Preview Abstract] |
Wednesday, March 7, 2007 2:42PM - 2:54PM |
S25.00002: Controlled Alignment of Lamellar Phase in Thin Films of a Block Copolymer and a Silica Precursor Mixture H.-C. Kim, C. Rettner, J. Cheng, O.-H. Park, L. Sundstrom Thin films of block copolymers containing self-assembled microdomains have emerged as a promising method for generating patterns of sub-optical lithographic length scales. Of great interest in semiconductor industry is the line pattern from lamellar phase of block copolymers due to their potential application to fabricate devices with length scales much smaller than those that traditional optical lithography can offer. One of the great challenges in evolving the line patterns from block copolymers into a practically viable device fabrication is the control over alignment of the lamellar microdomains on substrates. In this presentation, we report a simple method to create and control the alignment of robust inorganic line patterns of 20nm half-pitch on surfaces. We used a mixture of an organic diblock copolymer (poly(styrene-b-ethylene oxide), PS-b-PEO) and an organosilicate precursor which is selectively miscible with PEO of the block copolymer. Lamellar phase of the mixture was obtained by controlling the mixing composition. We could control the orientation of lamellar microdomains by applying energetically \textit{neutral} interface between thin films and substrate surface. In-plane alignment of the lamellae was achieved by using a topographic prepatterns generated using an E-beam lithography. We report the energetic calculation to cause the alignment of lamellae on surface along with a simple computational simulation [Preview Abstract] |
Wednesday, March 7, 2007 2:54PM - 3:06PM |
S25.00003: Defect structures in block copolymer thin films epitaxially assembled on chemically nanopatterned surfaces Sang Ouk Kim, Bong Hoon Kim, Kwanghyon Kim, Mark Stoykovich, Paul Nealey, Harun Solak Epitaxial self-assembly of block copolymer thin film is gathering a lot of attention as a successful strategy for nanofabrication. Chemically nanopatterned surfaces has been applied to guide the self-assembly of block copolymer thin films to form defect-free nanoscale patterns over an arbitrarily large area [S. O. Kim et al. \textit{Nature} \textbf{424}, 411-414, 2003]. The commensurability between the periods of block copolymer nanostructure and surface pattern has been turned out to act crucial role in determining the final nanostructure. Deviation of surface pattern period from the natural period of block copolymer nanostructure led to various types of defects. The defects in the block copolymer thin film self-assembled on the striped nanopattern of neutral/preferential wetting behavior, are presented. When the surface pattern period was slightly smaller, dipole of two edge dislocations with opposite sign appeared as a dominant defect structure. When the surface pattern period was slightly bigger, tilted lamellae appeared. The origin of the defect evolution is discussed [S. O. Kim et al. \textit{Macromolecules} \textbf{39}, 5466-5470, 2006]. [Preview Abstract] |
Wednesday, March 7, 2007 3:06PM - 3:18PM |
S25.00004: Graphoepitaxy of diblock-copolymers microdomains with chemical patterns Antonio Checco, Benjamin M. Ocko, Matthew Misner, Ji Xu, Thomas P. Russell Topographically patterned substrates have been used in recent years to laterally confine diblock copolymer (DBC) thin films in order to induce long-range lateral order of the DBC microdomain lattice with respect to a macroscopic reference. Here we demonstrate that surfaces with pure chemical patterns can be used to confine laterally diblock copolymers thin films through template-induced dewetting. A thin DBC film (PS-PEO) is spun cast on top of a surface chemically patterned with micron-sized, wettable domains prepared by oxidative nanolithography. Subsequently, annealing is used to direct the dewetting of the thin film into regions which are conformal to the patterns. We investigate the conditions (film thickness, annealing time) necessary to obtain dewetted structures reproducing the pattern shape with a high level of fidelity. In addition, we study the effect of pattern shape and size on the long-range order of DBC microdomains. [Preview Abstract] |
Wednesday, March 7, 2007 3:18PM - 3:30PM |
S25.00005: The Alignment of Ion-Complexed Symmetric Diblock Copolymer Thin Films under an Electric Field Jia-Yu Wang, Ting Xu, Julie Leiston-Belanger, Suresh Gupta, James Sievert, Thomas Russell In symmetric polystyrene-\textit{block}-poly(methyl methacrylate) (PS-$b$-PMMA) diblock copolymer thin films, lithium ions were successfully introduced to form lithium-PMMA complexes that markedly enhanced the alignment of BCP microdomains under a DC electric field, even adjacent to the two interfaces. The origin of improved alignment arises from the increased dielectric constant difference between the PS and PMMA blocks which reduces the critical field strength required to overcome interfacial interactions of the blocks. Furthermore, \textit{$\chi $} was significantly increased with the formation of the lithium-PMMA complexes, resulting in a transition in the orientation mechanism of the lamellar microdomains from a disruption and re-formation of the microdomains to a grain rotation mediated by movement of defects. The formation of large grains amplifies the ability of the external electric field to overcome preferential interfacial interactions and eliminate defects. Consequently, complete alignment of BCP microdomains can be achieved. By controlling the number of lithium-PMMA complexes, the microdomain alignment can be regulated in PS-$b$-PMMA thin films. [Preview Abstract] |
Wednesday, March 7, 2007 3:30PM - 3:42PM |
S25.00006: Shear-induced Long Range Order in Diblock Copolymer Thin Films Xuan Ding, Thomas Russell Shear is a well-established means of aligning block copolymer micro-domains in bulk; cylinder-forming block copolymers respond by orienting cylinder axes parallel to the flow direction, and macroscopic specimens with near-single-crystal texture can be obtained. A stepper motor is a brushless, synchronous electric motor that can divide a full rotation into a large number of steps. With the combination of a stepper motor and several gear boxes in our experiment, we can control the rotating resolution to be as small as $1 \times 10^{-4}$ degree/step. Also, with the help of a customized computer program we can control the motor speed in a very systematical way. By changing parameters such as the weight (or the uniform pressure) and the lateral force we can carry on experiment to examine the effect of lateral shear on different polymer systems such as PS-\emph{b}-PEO (large $\chi$) and PS-\emph{b}-P2VP (small $\chi$). [Preview Abstract] |
Wednesday, March 7, 2007 3:42PM - 3:54PM |
S25.00007: Control of Ordering Kinetics and Morphology using Zone Annealing of Thin Block Copolymer Films Alamgir Karim, Brian Berry, Ronald Jones A primary limitation of block copolymer (BCP) films as directed templates for advanced lithography or nanoporous membranes for energy storage is the prohibitively long times required for thermally directed self-assembly. We explore the use of zone annealing as a method to control both the kinetics of ordering as well as the resulting morphology in thin block copolymer films. Inspired by earlier results of Hashimoto and co-workers, films are processed by a moving hot-cold temperature gradient zone, hot being below the order-disorder transition temperature but above the glass transition temperature. A significant increase in the ordering kinetics of the BCP was observed, where morphologies characteristic of anneal times approaching a day using isothermal annealing are created in minutes using a moving thermal front. Surface topology persists even when sample velocities are ca. 500 micrometers/second. The mechanisms driving such rapid morphological evolution and the resulting low concentration of defects are explored through a combination of temperature gradients, zone velocity, and surface chemistry. Results from tomographic small angle neutron scattering and scanning probe microscopy demonstrate the relationship of zone velocity and thermal gradient on the formation mechanisms in BCP films. [Preview Abstract] |
Wednesday, March 7, 2007 3:54PM - 4:06PM |
S25.00008: Orientation of Microdomains of Block Copolymers by Zone casting Chuanbing Tang, Krzysztof Matyjaszewski, Tomasz Kowalewski As a ``bottom up'' method, the self-assembly of block copolymers plays a vital role in the development of soft lithography for the fabrication of microelectronic devices. A variety of methods have been developed toward better and more precise controlled patterns on solid substrates. This presentation will describe a novel solution casting technique, ``zone casting'', to induce orientation of cylindrical and lamellar microphase-separated domains of various block copolymers. [Preview Abstract] |
Wednesday, March 7, 2007 4:06PM - 4:18PM |
S25.00009: The Effect of Humidity on the Ordering of Triblock Copolymer Thin Films Joona Bang, Bumjoon J. Kim, Gila E. Stein, Edward J. Kramer, Craig J. Hawker, Thomas P. Russell Solvent cast diblock/triblock copolymer films of poly(styrene-$b$-ethylene oxide) (PS-PEO) and poly(styrene-$b$-methyl methacrylate-$b$-ethylene oxide) (PS-PMMA-PEO), with cylindrical microdomains of PEO or PMMA-PEO, have a high degree of long-range lateral order after solvent annealing. Relative humidity of the vapor during the solvent annealing has been shown to play an important role in achieving this order. Here, it was found that a PS-PMMA-PEO triblock copolymer having a lamellar morphology in bulk, develops a hexagonal array of depressed PEO domains on the film surface after solvent annealing under high humidity, while the film surface remains flat under less humid conditions. Cross-sectional TEM and GISAXS show that the film annealed under high humidity conditions exhibits a well-defined hexagonally-perforated lamellar (HPL) structure throughout its thickness, whereas a stack of lamellae aligned parallel to the surface is evident for the film annealed at lower humidity. These results strongly suggest that water vapor induces the morphological transition from lamellar to HPL by swelling the PEO. [Preview Abstract] |
Wednesday, March 7, 2007 4:18PM - 4:30PM |
S25.00010: Directing the Assembly of Patterns with Complex Geometries using Block Copolymers and Chemically Nanopatterned Substrates SangMin Park, Prabu Ravindran, Young-Hye La, Nicola Ferrier, Paul Nealey A combinatorial methodology was developed to explore the ultimate complexity of the patterns over which the domain structure of thin films of block copolymer can be directed to assemble. Films of lamellae-forming materials self-assemble into complex ``fingerprint'' patterns with the domains oriented normal to the plane of the film upon annealing on a surface exhibiting neutral wetting behavior towards the two blocks of the copolymer. Here we transfer the fingerprint pattern into a pattern of different chemical functionality (with little topography) through a series of processing steps. The chemical pattern is subsequently recoated with a block copolymer film and annealed, resulting in replication of the original fingerprint template. Using this methodology we demonstrated that the domains of the block copolymer film can be simultaneously directed to assembly into extraordinarily complex structures including dots, circles, ovals, and a variety of connected structures with very high degrees of curvature. The perfection with which the geometries on the nanopatterned substrates assemble is analyzed statistically using an automatic image processing system that can identify and track the changes of reassembled structures. [Preview Abstract] |
Wednesday, March 7, 2007 4:30PM - 4:42PM |
S25.00011: Order and disorder in cylindrical block copolymers on a surface with positive and negative Gaussian curvature A. Hexemer, E. J. Kramer, V. Vitelli, C. D. Santangelo, R. D. Kamien We present a novel approach of creating surfaces with Gaussian curvature gradients by using commercially available colloidal particles and standard processing techniques. We also demonstrate that these non-flat surfaces can induce regions of both high order, as well as disorder in cylindrical block copolymer films depending on the Gaussian curvature of the surface. On a flat surface the ground state has no preferential direction and a high density of disclinations is observed. A Gaussian curvature destroys the isotropy in alignment and induces a preferential alignment. For small bumps the cylinders wrap around the top of the bump with a constant density of disclinations and dislocations as a function of distance from the top. Higher bumps show a disordered phase in a region on the top of the bump. The disorder is induced by the migration of disclinations towards the top of the bump. Present address of AH is LBNL. [Preview Abstract] |
Wednesday, March 7, 2007 4:42PM - 4:54PM |
S25.00012: Rod-Coil Block Copolymer Self-Assembly in Thin Films B.D. Olsen, X. Li, J. Wang, R.A. Segalman Rod-coil block copolymers demonstrate self-assembly behavior distinct from traditional block copolymers due to liquid crystalline interactions between rod blocks and the geometric mismatch between the rigid rod and flexible coil. In thin films, surface segregation and confinement of the block copolymer in one dimension create novel self-assembly effects. Films of a model rod-coil block copolymer less than a few lamellar layers thick demonstrate lamellae oriented primarily parallel to the surface of the film due to a preference for one block to segregate to the interface. Increasing thickness results in a reorientation of lamellae at the free interface to a perpendicular orientation, although parallel orientation persists near the supported interface. While parallel lamellae show a domain spacing similar to the bulk value, the domain spacing of perpendicular lamellae varies with changing film thickness, approaching the bulk value for thicker films. We suggest that this distortion of domain spacing in thin films results from the dilation of block copolymer domains to accommodate defects. [Preview Abstract] |
Wednesday, March 7, 2007 4:54PM - 5:06PM |
S25.00013: Self-consistent field theory simulations of block copolymer assembly on a sphere T.L. Chantawansri, A.W. Bosse, A. Hexemer, H.D. Ceniceros, C.J. Garcia-Cervera, E.J. Kramer, G.H. Fredrickson Using a self-consistent field theory (SCFT) framework, we explore the topic of self-assembly in a thin AB diblock copolymer melt confined to the surface of the sphere. This model is numerically simulated by spectral collocation with a spherical harmonic basis. The method allows us to investigate the lamellar and cylindrical phases on the surface of a sphere as a function of sphere radius. For thin cylinder-forming films, with uniform radial composition, we have found that the number of microdomains in the ground state configuration is determined by a delicate competition between chain stretching and topological constraints. Notably, our SCFT simulations have shown the absence of configurations with 11 and 13 domains in the ground state. For thin lamellar films, we examined the stability of three lamellar configurations: spiral, hedgehog, and quasi-baseball phases. The spiral and hedgehog morphologies are found to alternate in stability over a range of sphere radii. [Preview Abstract] |
Wednesday, March 7, 2007 5:06PM - 5:18PM |
S25.00014: Freestanding nanowire arrays from soft-etch block copolymer templates. E. Crossland, S. Ludwigs, M. Hillmyer, U. Steiner We describe the preparation of highly ordered arrays of freestanding nanowires using block copolymer templates. The procedure consists of the alignment of the copolymer microphase morphology in a 150V$\mu $m$^{-1}$ electric field, removal of the minority phase and the electrodeposition of a metal or a metal-oxide. This results in 12 nm wide and $\sim $300 nm long isolated wires. In difference to earlier work by Russell, we use a polylactide as sacrificial block, enabling its degradation in a dilute aqueous base. Template formation by polylactide degradation is useful because it avoids aggressive degradation steps, which also alters the remaining template. The template-based manufacture of hybrid materials with a well defined structure on the 10-nm scale can this way be extended to composites, in which the detailed molecular structure of all components is important. In particular we envisage application in patterning semiconductors for bulk heterojunction hybrid solar cells. In addition to the successful alignment and replication of cylindrical micro domains we report the application of this method to the more complex gyroid morphology. In the presence of an applied electric field, we observe a transition from gyroid topology to a mix of standing cylinders and lamellae. [Preview Abstract] |
Wednesday, March 7, 2007 5:18PM - 5:30PM |
S25.00015: Investigation of polystyrene-b-polyferrocenyl silane diblock copolymer thin films via conducting probe atomic force microscopy James Li, Shan Zou, David Rider, Ian Manners, Gilbert Walker Conducting probe atomic force microscopy (CP-AFM) was used to investigate the electronic properties of polystyrene-b-polyferrocenyl silane (PS-b-PFS) diblock copolymer thin films. In this system, cylindrical domains of polyferrocenyl silane, a weak semiconductor, is surrounded by polystyrene, an insulating material. Mapping the electrical current response of the film to an applied voltage bias showed a correlation with the location of PS and PFS domains as evidenced by concurrent topographical and lateral friction imaging. The higher conductivity in the PFS region is believed to arise from localized oxidation rather than through-chain electron tunneling. Polyferrocenyl silane was additionally observed to exhibit diode-like behavior. Experiments were performed using contact mode AFM operation under ambient conditions and also in low-oxygen environments. The electronic properties of PFS in addition to the locally ordered configuration afforded by the self-assembly process provide a system which may have possible device applications. [Preview Abstract] |
Wednesday, March 7, 2007 5:30PM - 5:42PM |
S25.00016: Directed Assembly of Block Copolymers to Pattern Isolated Features and Essential Integrated Circuit Geometries M. P. Stoykovich, H. Kang, G. Liu, K. Ch. Daoulas, J. J. de Pablo, M. Mueller, P. F. Nealey Block copolymers are being explored for fabricating highly ordered lamellar, cylindrical, and spherical geometries with dimensions of 5-50 nm. The Semiconductor Industry Association's member companies have indicated, however, that successful insertion of self-assembling materials into the lithographic process requires the ability to pattern more complex geometries including long lines, short segments, sharp bends, jogs, T-junctions, periodic arrays of contact openings, and combinations thereof, e.g. the gate layer of integrated circuits. Here we show that this essential set of dense and isolated geometries can be achieved using the directed assembly of block copolymers on chemically patterned surfaces. Dense structures were fabricated by block copolymer domains oriented perpendicular to the substrate, while isolated structures were assembled with neighboring domains oriented parallel and perpendicular to the substrate. The line edge roughness of the block copolymer structures was also considered with respect to imperfections in the surface pattern. [Preview Abstract] |
Wednesday, March 7, 2007 5:42PM - 5:54PM |
S25.00017: Reversible reordering of a sphere-forming diblock at the substrate interface: surface directed sphere to lamellar transition Jessica L. Carvalho, Michael V. Massa, Kari Dalnoki-Veress We present our results on the use of ellipsometry to probe thin films of a diblock-copolymer. Ellipsometry uses the ellipticity induced upon reflection of light from a film covered substrate to allow calculation of the refractive index and thickness of the film. By studying the temperature dependence of these quantities one can measure phase transitions. The samples used are thin films of a polybutadiene-poly(ethylene oxide) diblock that micro phase-separates into PEO minority spheres in a PB matrix. We will discuss a transition that takes place which is the result of a reordering of the diblock morphology at the substrate. As the samples are cooled there is a reversible transition from a partially wetting layer of PEO spheres to a wetting lamella of PEO on the substrate. We will discuss the experimental results as well as the physical mechanism which drives the sphere to lamella transition. [Preview Abstract] |
Wednesday, March 7, 2007 5:54PM - 6:06PM |
S25.00018: Lamellar nanostructures of diblock copolymers confined in submicro-patterns Sehee Kim, Kookheon Char, Byeong-Hyeok Sohn Diblock copolymers consisting of two immiscible polymers covalently bonded together spontaneously form periodic nanostructures such as spheres, cylinders, and lamellae. In bulk, however, these periodic nanostructures of copolymers tend to orient randomly if no external forces are applied. To obtain periodic nanostructures over large areas, copolymers can be confined into topographic patterns. When block copolymers are physically confined, structural frustration and interfacial interaction can influence molecular organizations of copolymers, leading to hierarchically ordered nanostructures. In this presentation, the lithographic method and self-assembly of lamellae-forming diblock copolymers were combined to induce hierarchical nanostructures. Confined nanostructures of copolymers were investigated by transmission electron microscopy. Diblock copolymers confined in the submicro-pattern exhibited the unique orientation of lamellar nanostructures depending on the preparation conditions of the film before the confinement. [Preview Abstract] |
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