Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session D28: Block Copolymer Thin Films |
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Sponsoring Units: DPOLY Chair: Michael Fasolka, NIST Room: LACC 506 |
Monday, March 21, 2005 2:30PM - 2:42PM |
D28.00001: Competing Surface Fields on the Ordering Transition of Block Copolymer Films Peter Green, Abraham Arceo The ordering temperatures of \textit{polystryene-b- polymethylmthacrylate} (PS-$b$-PMMA) thin film diblock copolymers of thickness h$\le $2$L$, supported by \textit{SiO}$_{x}$\textit {/Si} substrates, were examined in compressed CO2 fluid and vacuum environments. The substrate is shown to induce ordering into the film as temperatures above the bulk order-disorder transition. This ordering temperature is estimated to be about 200 degrees above the bulk ODT. We also show that in compressed CO$_{2}$ environments, these films are ordered at temperatures above which they would be ordered in vacuum! This latter observation is of particular significance since compressed CO$_{2}$ is a known plasticizer for both polymers and low molecular weight diluents generally have the effect of lowering the \textit{ODT}, not increasing it. [Preview Abstract] |
Monday, March 21, 2005 2:42PM - 2:54PM |
D28.00002: Substrate Surface Energy Effects in Triply-Periodic Block Copolymer Thin Films Thomas Epps, Michael Fasolka The effect of substrate surface energy on the thin film structure of ABC triblocks exhibiting triply-periodic bulk morphologies was investigated. Several films, with various polymer compositions and film thicknesses near the bulk triblock domain spacings (d), were studied by atomic force microscopy (AFM) on gradient substrates. Surface energy gradient libraries were generated on silicon wafers coated with a chlorosilane SAM, accelerated under a UV/ozone lamp. Using this approach, surface energies ranging from 25 mJ/m2 to 72 mJ/m2 were probed on a single wafer. Surface energy and composition influenced the polymer nanostructures and the film's terrace structures. Terrace heights typically corresponded to 1/2 d and 3/2 d, and terrace structures varied with surface energy. Additionally, at least three distinct polymer morphologies were identified, including a hexagonally-packed structure, a network-like structure, and a disorganized microphase-separated structure. For several triblock films, the morphologies were surface energy dependent, and polymer morphologies often varied from the 1/2 d terrace to the 3/2 d terrace. [Preview Abstract] |
Monday, March 21, 2005 2:54PM - 3:06PM |
D28.00003: Investigating the Morphology and Dynamics of Thin Films of Diblock Copolymers on Chemically Nanopatterned Substrates of Varying Interfacial Energy and Pattern Quality Erik W. Edwards, M.P. Stoykovich, Paul F. Nealey, H.H. Solak, C.J. Hawker The convergence of technologies to tailor interfacial interactions between polymer films and surfaces and to precisely pattern at the nanoscale has resulted in a wealth of important information about the physics of block copolymer thin films. We patterned stripes of SiOx and polymer brushes of varying styrene and methyl methacrylate compositions with periods, Ls using EUV interferometric lithography and investigated the morphology and dynamics of ordering in PS-b-MMA films with a bulk lamellar period Lo. Perfect epitaxial ordering, pattern registration and the range of periods, L$_{S}$ where perfect ordering occurs has been found to depend on the contrast in interfacial energy of the chemical patterns and the ratio of the widths of the SiOx/brush stripes. The final morphologies were captured by a phenomenological model that predicts equilibrated structures based on chain stretching, interfacial interactions and copolymer/substrate interactions. The dynamics of ordering occurs as follows: a hexagonally close packed morphology forms which transitions to lamellar structures. The dynamics of perfect microdomain ordering has been found to depend on the interfacial energy contrast of the patterns and the commensurability of Ls and Lo. [Preview Abstract] |
Monday, March 21, 2005 3:06PM - 3:18PM |
D28.00004: Self-assembly of block-copolymers on binary chemical nanopatterns Gabriel Baralia, Bernard Nysten, Alain M. Jonas Thin films of block-copolymers have received great attention as they can self-assemble in ordered periodic structures at the molecular scale [1]. There are different ways by which ordering can be obtain over large areas [2-4]. One such way consists of the local tailoring of the substrate by placing chemical moieties at regularly repeated locations [5]. Here we present another versatile way to control the ordering of block-copolymers over micrometer-scale areas. Fabrication process and examples of chemically nanopatterned substrates will be first shown. The substrates are created by combining the ability of the e-beam lithography to create nanometer-scale regions with self-assembly of alkanethiols. In a second part, the study of self-assembly of symmetric and asymmetric block-copolymers on such nanopatterns will be presented. References [1] F. S. Bates, Science, \textbf{251}, 898 (1991). [2] T. L. Morkved \textit{et al.}, Science \textbf{273}, 931 (1996). [3] M. D. Morariu, N. E. Voicu, E. Schaffer, Z. Lin, T. P. Russell, U. Steiner, Nature Materials \textbf{2}, 48 (2003). [4] C. Park \textit{et al.}, Appl. Phys. Lett. \textbf{79}, 848 (1996). [5] S. O. Kim, H. H. Solak, M.P. Stoykovich, N. J. Ferrier, J. J. de Pablo, P. F. Nealey, Nature \textbf{424}, 411 (2003). [Preview Abstract] |
Monday, March 21, 2005 3:18PM - 3:30PM |
D28.00005: Lateral Confinement Effects in Block Copolymer Thin Films August Bosse, Scott Sides, Carlos Garcia-Cervera, Glenn Fredrickson In recent years there has been increased interest in using microphase separated block copolymer thin films as sub-micron masks in the fabrication of semiconductor devices and high-density magnetic storage media. However, if these techniques are to evolve into a practical lithography scheme, one must have an understanding of and control over in-plane defects within the block copolymer microstructure. The topic of defects in block copolymer thin films has garnered significant attention in the experimental sector. However, little theoretical work has appeared on this subject. In this talk, we discuss a technique for field-based modeling of thin films of block copolymer melts subject to lateral confinement. We apply pseudo-spectral, large-cell self-consistent field theory (SCFT) simulations with confining boundary conditions based of the work of Matsen. Our investigations are aimed at elucidating the role of the following factors on defect populations: the shape and size of the confining boundaries, the nature of the interactions between the copolymer segments and the boundaries, copolymer architecture, and annealing procedure applied. [Preview Abstract] |
Monday, March 21, 2005 3:30PM - 3:42PM |
D28.00006: Shear alignment of spherical microdomain block copolymer thin films via a viscous fluid layer. M.W. Wu, D.E. Angelescu, D.H. Adamson, X. Guo, R.K. Prud'homme, P.M. Chaikin, R.A. Register Shearing block copolymer thin films has recently been shown to be a simple method to produce macroscopic orientation and order of the microdomain patterns. We study the alignment of thin films (two or three layers) of a sphere-forming polystyrene-\emph{b}-poly(ethylene-\emph{alt}-propylene) polymer under steady shear flows. With the diblock film as the bottom plate of a rotating plate-plate rheometer and PDMS oil to transmit the shear viscously while annealing above the glass transition and below the order-disorder temperatures, we produce long range order without applying a normal force. This geometry also allows the evaluation of the alignment as a function of stress on a single sample. We observe a temperature-dependent threshold stress for alignment, and propose a possible mechanism for alignment of spheres. [Preview Abstract] |
Monday, March 21, 2005 3:42PM - 3:54PM |
D28.00007: Alignment of Cylindrical Diblock Copolymer Thin Films Using Flow Stress Vincent Pelletier, Mingshaw Wu, Douglas Adamson, Richard Register, Paul Chaikin Producing macroscopic alignment of diblock copolymer thin film microdomains is of great interest in industry, as it can be used as pattern masks, especially when the alignment direction can be controlled. Our previous studies of the alignment of monolayer films of cylindrical phase diblock copolymers used shear applied through contact with an elastomer pad to obtain macroscopic order. Here we extend these studies with quantitative measurements using stress applied via a fluid, high viscosity polydimethylsiloxane. The shear stress is provided by a rotating disk on the viscous layer, or by Poiseuille flow of the fluid through a channel cut out of an elastomer sheet and placed on the diblock film. There is a minimum stress required for alignment of the microdomains. We can give the channels any shape we want, offering the possibility to pattern the nanometer scale cylindrical microdomain alignment on the micrometer-to-millimeter scale. [Preview Abstract] |
Monday, March 21, 2005 3:54PM - 4:06PM |
D28.00008: Long-Range Order in Cylindrical Block Copolymer Thin Films using Graphoepitaxy Mark Dadmun, Scott Fontana, Doug Lowndes A block copolymer thin film of polystyrene and methyl methacrylate on a neutral surface forms cylinders that are removed by UV exposure and rinsing, creating a template for the deposition of nickel nanodots, which are subsequently used to grow carbon nanofibers. Additionally, graphoepitaxy is used to successfully induce long-range order in hexagonally packed cylinders. The kinetics of the ordering process, limitations on this technique, and specific sample preparation conditions for successful transfer of the porous template to the deposited nanodots will also be discussed [Preview Abstract] |
Monday, March 21, 2005 4:06PM - 4:18PM |
D28.00009: Experimental studies of symmetric block copolymer blends in thin films. Easan Sivaniah, Shinya Matsubara, Yue Zhao, Takeji Hashimoto, Tom Mates, Edward J. Kramer Microdomain size control in thin films of blended symmetric poly(styrene-\textit{block-}methyl methacrylate) [PS-$b$-PMMA] was examined. Rough substrates and high temperatures were used to prepare perpendicularly oriented PS-$b$-PMMA lamellae. A large block copolymer [BCP], (with $N_{\mbox{large}} $ monomer units) and a small BCP (with N$_{small}$ monomer units) were mixed in a range of composition using a set of symmetric PS-$b$-PMMA BCPs (where $\chi N$ ranged from 20$\sim $100). Thus the blend was characterized by; blend composition, the ratio $\alpha =N_{\mbox{large}} /N_{\mbox{small}} $ and $\chi N_{\mbox{large}} $. AFM studies of the perpendicular surface structure determined the effect of blend composition on lamella periodicity, $D_{mix}$. Depth profile analysis and x-ray scattering studies determined the copolymer distribution in the film and the bulk lamellar period, respectively. The effect of composition on $D_{mix}$ was compared to an analytic mean field theory in the strong segregation limit. Whilst good agreement was observed when both $\chi N_{\mbox{large}} $ and $\chi N_{\mbox{s}mall} $ were large ($\sim $70-100), there were significant deviations from the theory when $\chi N_{\mbox{s}mall} \sim $ 20-60. However in agreement with bulk blend studies, block copolymer macrophase separation was observed at the polymer air surface when the relative size of the block copolymer pairs exceeded $\alpha \sim $5. [Preview Abstract] |
Monday, March 21, 2005 4:18PM - 4:30PM |
D28.00010: Nanoporous Thin Films Using Benzocyclobutene-Containing Diblock Copolymers Julie Leiston-Belanger, Thomas Russell, Eric Drockenmuller, Craig Hawker Microphase separated diblock copolymer thin films are important in the fields of nano-templating and data storage. Diblock copolymers containing vinyl benzocyclobutene (BCB) moieties were thermally cross-linked to afford chemically and thermally robust nanoporous thin films with hydroxy-functionalized nanopores. The ability for the morphology to resist solvation allows for a wider array of chemical modifications inside the nanoporous channels. Poly[(styrene-r-BCB)-b-lactic acid] (PSBCBLA) was synthesized by a combination of living free radical polymerization and ring-opening polymerization. The PSBCBPLA copolymer used was shown to phase separate into a cylindrical morphology, confirmed by SAXS, with cylinders oriented perpendicular to the substrate, as suggested by AFM and TEM studies. The PSBCB block can be thermally cross-linked at temperatures from 200 C -- 250 C and the PLA block can be easily removed with weak base to give accessible hydroxyl-functionalized nanopores. [Preview Abstract] |
Monday, March 21, 2005 4:30PM - 4:42PM |
D28.00011: Helix morphology forced by confinement upon bulk cylinder-forming block copolymers Hongqi Xiang, Kyusoon Shin, Taehyung Kim, Sung In Moon, Thomas J. McCarthy, Thomas P. Russell Confinement can break the symmetry of a structure, forcing a change from bulk equilibrium behavior. This effect is examined here by placing asymmetric diblock copolymers into nanoscopic cylindrical pores, i.e., a two-dimensional confinement. In the bulk the copolymers self-assemble into hexagonally packed cylinders with an equilibrium cylinder-to-cylinder period. Within the pores, the cylinder microdomains were oriented along the pore axis when the pore diameter is large in comparison to the equilibrium period. Their period and packing differed from that observed in the bulk, due to an incommensurability between the pore geometry and the natural period and hexagonal packing of the copolymer. However, as the pore diameter decreases, a helical morphology is found to form under certain conditions. This nanostructured material is interesting for its potential applications in fabricating unique nanostructured materials from diblock copolymers, expanding the types of morphology accessible from these simple molecules. [Preview Abstract] |
Monday, March 21, 2005 4:42PM - 4:54PM |
D28.00012: Laterally Confined Block Copolymer Cylinder Monolayers: Smectic, Nematic, and Isotropic Ordering M.R. Hammond, E.J. Kramer We investigate the temperature dependence of nanodomain ordering in laterally confined, monolayer films of a cylinder-forming block copolymer. The lateral confinement (in channels up to 3 $\mu $m wide) aligns the cylinders, providing long range orientational order of the nanodomains over the entire channel width at annealing temperatures T well below the bulk ODT. As T is progressively increased, an increasing density of dislocations and disclinations is observed and the orientation correlation function g$_{2}$(r) decreases with r, eventually exponentially above a T$_{c} \quad <$ ODT. We compare these results to theory(1), which predicts that a 2-D smectic film at 0 K is, as T increases, transformed to a ``nematic'' phase, in which the local cylinder normal acts as the nematic director, by phonons and thermally generated dislocations. As the system is heated through T$_{c}$, we examine whether it is indeed the unbinding of disclinations that produces the observed isotropic (yet still microphase-separated) phase, as suggested by theory. (1) J. Toner and D. R. Nelson, Phys. Rev. B, \textbf{23}, 316, (1981) [Preview Abstract] |
Monday, March 21, 2005 4:54PM - 5:06PM |
D28.00013: Ordering in Salt Containing Block Copolymer Thin Films Seung Hyun Kim, Matthew J. Misner, Thomas P. Russell Polymer-salt complexes have been the subject of intense study due to the potential applications as the solid polymer electrolytes. Here the complexation of ionic salts with cylinder-forming P(S-$b$-EO) block copolymer in thin film was investigated, where added salts are expected to bind the PEO block as the minor component. Even small amounts of salt lead to large changes in the ordering behavior in the block copolymer thin films, inducing an ordering pathway different than without salt. The cylindrical microdomains were found to change from parallel to perpendicular orientation relative to the substrate. These results strongly depend on salt concentration and the counter ion. Combined with the solvent annealing, highly ordered arrays of cylinders with long-range lateral order were produced. Using this behavior, the well-organized patterns of inorganic materials such as gold and cobalt nanoparticles on the substrate are generated by solvent annealing. [Preview Abstract] |
Monday, March 21, 2005 5:06PM - 5:18PM |
D28.00014: Kinetics of Assembly of ``Looped'' Brushes at the Solid-Liquid Interface Jose Alonzo, S. Michael Kilbey II Dense layers of end-tethered polymers, often called polymer brushes, are of interest for their ability to modify interfacial properties. Along these lines, creating brushes comprised of loops by tethering the chains by both ends offers potential advantages in tailoring the adhesive or frictional properties of surfaces. Rigorously synthesized poly(2-vinylpyridine)-polystyrene-poly(2-vinylpyridine) triblock copolymers were used as a model system to examine the formation of looped brushes at the solid-liquid interface. In-situ phase modulated ellipsometry measurements were made to study the kinetics of assembly of these copolymers onto silicon surfaces. This technique allows the adsorbed amount and ellipsometric height of the layer to be sensitively measured as a function of time. These experiments provide evidence of loop formation: specifically, while the adsorbed amount increases asymptotically, the thickness shows an ``overshoot'' during the initial stages of adsorption followed by a slow reorganization. The final thickness of the looped brush is approximately one-half of that expected for a single-end tethered brush made from a diblock copolymer with a buoy block of similar molecular weight. The effect of triblock molecular weight and composition on layer assembly and structure will also be discussed. [Preview Abstract] |
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D28.00015: Two-dimensional order-disorder (melting) transition in a diblock copolymer cylinder-forming thin-film system. Weining Man, Dan E. Angelescu, Mingshaw W. Wu, Vincent Pelletier, Douglas H. Adamson, Richard A. Register, Paul M. Chaikin We have studied the phase diagram of a two dimensional smectic system, a monolayer film of di-block copolymer cylinders. Previous work was done on sphere-forming diblock polymer films. In this work we anneal PS-PEP 5-13 cylinder-forming diblock copolymer using a temperature gradient system, to investigate the orientational order-disorder (melting) transition. We find that on the high temperature side correlation lengths are very small, revealing complete lack of orientational order. This corresponds to annealing far above the order-disorder (or melting) transition. The disordered state in this case is a thermodynamic equilibrium state, continued annealing of the sample will not produce more ordering in this region of the sample. The order-disorder transition, ODT, occurred at $\approx $ 163 oC, higher than the bulk ODT of the same polymer (TODT =144 $^{o}$C). We present data on the temperature dependence of the correlation functions and the densities of topological defects. By lowing the temperature of the high T end of the gradient, we can also sweep the temperature gradient to study the effects of zone refining. [Preview Abstract] |
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