Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session D28: Block Copolymer Thin Films |
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Sponsoring Units: DPOLY Chair: Travis Bailey, Colorado State University Room: Baltimore Convention Center 325 |
Monday, March 13, 2006 2:30PM - 2:42PM |
D28.00001: Tuning Surface Interactions to Control Thin Film Block Copolymer Orientation Alamgir Karim, Ronald Jones, Duangrut Julthongpiput, Michael Fasolka, Eric Amis, Sushil Satija We tune polymer-substrate surface interactions in order to control the orientation and ordering of diblock copolymers of polystyrene -- polymethylmethacrylate (PS-b-PMMA) ultrathin films. To this end we utilize UV to alter the surface energy of a SAM coated substrate and anneal spin coated thin films of high molecular weight (approx. 50kDa) PS-b-PMMA. We have previously utilized a combinatorial approach of substrate surface energy vs. diblock film thickness to map out the distribution of surface topography measured by optical microscopy (such as island and hole formation regions), and observed a switch in symmetry of topography with surface energy variation across a ``neutral'' region. In the present work, we report results pertaining to the neutral surface energy substrate conditions. We utilize AFM, neutron reflection, SEM and TEM to characterize the morphology of ordered structures on the controlled surface energy substrates. The advantage of the present work is the relative ease of surface energy control with UV and the tunability of surface energy to potentially match neutral boundary conditions for a broad set of block copolymers with different chemical blocks components. [Preview Abstract] |
Monday, March 13, 2006 2:42PM - 2:54PM |
D28.00002: Internal and Interface Structure in Diblock Copolymer Brushes Mark D. Foster, Bulent Akgun, Gokce Ugur, William J. Brittain, Xuefa Li, Dong Ryeol Lee, Jin Wang Internal and surface structure of polystyrene-$b$-polyacrylate diblock copolymer brushes have been studied using grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM). Polystyrene-$b$-polyacrylate or polyacrylate-$b$-polystyrene brushes were synthesized using atom transfer radical polymerization. Poly (methylacrylate) or poly($n$-butyl acrylate) is used as the acrylate block. Each as-deposited diblock brush show an internal lateral structure with a spacing comparable to the thickness of the top layer of the brush on the order of 10 nm. After a brush is treated with a selective solvent which is a good or theta solvent for the bottom block and poor solvent for the top block, Bragg rods appear in GISAXS pattern. The lateral spacing corresponding to the Bragg rods is on the order of the total thicknesses of the brushes. This lateral correlation is also detected by the power spectral density analysis of the AFM measurements of the samples' surfaces using tapping mode imaging. The Bragg rods disappear upon heating to 80 \r{ }C and this behavior does not depend on which polyacrylate block was used. [Preview Abstract] |
Monday, March 13, 2006 2:54PM - 3:06PM |
D28.00003: Internal Morphology of Diblock Copolymer Brushes Determined by Neutron Reflectivity. Bulent Akgun, William J. Brittain, Mark D. Foster, Charles F. Majkrzak Although diblock copolymer brushes (BCB) have been extensively studied in recent years, their internal structure is still unknown. To elucidate the interface width and internal structure of BCBs, neutron reflectivity (NR) has been used. BCBs of deuterated polystyrene (dPS) and poly(methyl acrylate) (PMA) with dPS adjacent to the surface (d-PS-$b$-PMA) or with PMA adjacent to the surface (PMA-$b$-dPS) and having different thicknesses were synthesized using atom transfer radical polymerization. In ultrathin BCBs a gradient in composition perpendicular to the surface extends essentially through the entire thickness of the brush. The interface width, defined as the full-width at half-maximum of a Gaussian function needed to represent the broadening of the step interface profile, is found to be smaller for PMA-$b$-dPS than for dPS-$b$-PMA brushes. The interface width for a film spun from untethered chains of dPS-b-PMA has been measured and the results compared with those for the BCBs. BCBs have been measured in both good solvent and poor solvent vapors with NR and the concentration profiles and extent of swelling determined. [Preview Abstract] |
Monday, March 13, 2006 3:06PM - 3:18PM |
D28.00004: Resonant X-Ray Scattering in Block Copolymer Thin Films Justin Virgili, Jeffrey Kortright, Nitash Balsara, Rachel Segalman Resonant x-ray scattering in a transmission geometry is reported in block copolymer films for the first time. By tuning soft x-rays to the carbon $\pi $*-$\pi $* bonds in a poly(styrene-b-isoprene) (PS-PI) diblock copolymer thin film, the scattering intensity is enhanced, thereby overcoming the small scattering volume inherent to a thin film geometry. This technique provides an alternative polymer thin film characterization technique to GISAXS that shares the same benefit of averaging over large sample areas (100's $\mu $m x 100's $\mu $m). The characterization of large sample areas is not readily accessible via real-space characterization techniques, such as TEM and AFM, and is of growing importance to applications such as optoelectronic devices. We will demonstrate the use of the resonant x-ray scattering technique in thin films of PS-PI and will demonstrate the effects block copolymer composition and film thickness on the observed scattering profiles. We will also compare our results from resonant x-ray scattering to TEM and AFM data. [Preview Abstract] |
Monday, March 13, 2006 3:18PM - 3:30PM |
D28.00005: The development of order in ultra-thin PS-PMMA diblock copolymer films. Ward Lopes, Hai Qian, Gene Mazenko, Heinrich Jaeger Knowledge of how two dimensional systems order is important for techniques like hierarchical self-assembly or diblock copolymer lithography. The applicability of these techniques can be limited by the defects which influence the late stage of ordering. Further, one would like to know whether or not the qualitative features of ordering depend only on the symmetry of the system. We address these concerns by studying the growth of order in weakly-segregated, cylindrical-phase, PS-PMMA diblock copolymer films. Our samples have smectic (striped) symmetry and form a single layer of half-cylinders with more than 10$^{5}$ repeat spacings. We have found qualitative differences between our results and results reported on strongly segregated cylindrical-phase diblock copolymer films(1) . We find, for example, that the number of dislocations and disclinations are approximately equal and that grain boundaries persist for long times. We are using time lapse atomic force microscopy to track disclination dipole, tripole, and quadrupole annihilations and will report on the relative frequency of each. We will compare our results with numerical simulations of the Swift-Hohenberg Model. (1) Harrison et. al. Science, \textbf{290}, 1558 (2000); Harrison et. al. Phys. Rev. E, \textbf{66}, 11706 (2002). [Preview Abstract] |
Monday, March 13, 2006 3:30PM - 3:42PM |
D28.00006: Thickness Dependent Packing Symmetries of Spherical-Domain Block Copolymer Multilayers G.E. Stein, E. Cochran, G.H. Fredrickson, E.J. Kramer, X. Li, J. Wang The packing of spherical block copolymer domains confined to a thin film is investigated with grazing-incidence small angle x-ray scattering. Whereas the equilibrium structure of a monolayer is hexagonal (HEX), and that of the bulk is body-centered cubic (BCC), we find a remarkably complex transition from 2D to 3D packing as a function of film thickness. Films 1-3 layers of spheres thick have close-packed hexagonal symmetry. At four layers the hexagonal symmetry breaks to form an orthorhombic phase, characterized by a second-to-first nearest-neighbor distance ratio $a_1/a_2 = 1.08$ with an angle $\phi=57^{\circ}$ between $\vec{a}_1$ and $\vec{a}_2$. As the number of layers is increased from 4 to 23, $a_1/a_2$ increases monotonically to 1.17, and $\phi$ decreases monotonically to $54.2^{\circ}$, a structure similar to the stacking of BCC (110) planes. From measurements above and below the polymer critical angle, we determine that all phases are uniform throughout the depth of the film. These results are interpreted in the context of a Landau-type theory, using SCFT calculations to demonstrate the competition between the packing preferred in the bulk with that at the interfaces. [Preview Abstract] |
Monday, March 13, 2006 3:42PM - 3:54PM |
D28.00007: Effect of chain architecture and surface energies on the microdomain orientation in block copolymer films V. Khanna, E. J. Kramer, E. W. Cochran, G. H. Fredrickson, X. Li, J. Wang, S. F. Hahn We investigate the effect of surface energy and chain architecture on the orientation of microdomains in relatively thick films (~ 600nm) of lamellar and cylindrical block copolymers of poly(vinylcyclohexane)(C) and poly(ethylene)(E). The E block has 26 ethyl branches per 1000 backbone carbon atoms. Melt surface energies of the C and E blocks are 22.3 and 20.9 mJ/m$^{2}$, respectively. GISAXS, SFM and cross sectional TEM show that cylindrical and lamellar CEC triblock copolymers orient their microdomains normal to the surface through the film thickness. However, a lamellar CE diblock prefers a parallel orientation of the sheets with an E surface. Moreover, a cylindrical CEBC triblock copolymer where the EB block has 125 ethyl branches per 1000 backbone carbon atoms leads to EB cylinders that always orient parallel to the surface. In this case the lower surface energy EB block dominates the surface. Self-consistent field theory calculations allow us to interpret the experimental results in terms of the entropic cost of forming a wetting layer comprised entirely of looping blocks. Thus in triblock copolymers, parallel orientations are only stabilized when the surface energy of the midblock is low enough to compensate for this conformational penalty, which is absent in diblock copolymers. [Preview Abstract] |
Monday, March 13, 2006 3:54PM - 4:06PM |
D28.00008: Symmetry Breaking In Block Copolymer Thin Films Eric Cochran, Kirill Katsov, Gila Stein, Ed Kramer, Glenn Fredrickson Recent experiments by Stein and Kramer show that thin films of poly(styrene-b-vinylpyridine) diblock copolymer undergo a discontinuous transformation from hexagonally-close packed spheres to a Fmmm orthorhombic packing as the thickness of the film is increased; beyond the hcp-Fmmm transition, the unit cell deforms to asymptotically approach bcc symmetry, which is preferred in the bulk system. We use a Landau-type theory to construct various scenarios of symmetry-breaking in this system. High resolution SCFT calculations show the nature of the competition between the preferred packing in the bulk and that at the interface. We conclude that character of the transition from thin-film to bulk behavior may be either continuous or discontinuous, depending on the bulk properties of the block copolymer and the surface energy. [Preview Abstract] |
Monday, March 13, 2006 4:06PM - 4:18PM |
D28.00009: Ion Complexation in Salt Containing Block Copolymer Thin Films Matthew Misner, Seung Hyun Kim, Ling Yang, Thomas Russell Ion complexation within cylinder-forming PS-b-PEO thin films was investigated, where added salts bound the PEO block as the minor component. Small amounts of added salts, on the order a few ions per chain, show large effects on the ordering and orientation of the copolymer films during solvent annealing, a process where we have shown a large degree of long-range lateral order can be obtained. The orientation of the cylindrical microdomains was found to strongly depend on salt concentration and the nature of the counter ion. Furthermore, with the addition of relatively large amounts of salts, we observed that the copolymer microdomains remained ordered at a high degree of swelling and an extremely large amount of lateral spatial correlations of the cylindrical microdomains was found in the swollen state, as observed by grazing incidence small angle scattering. By using gold or cobalt salts, well-organized patterns of nanoparticles were generated in the copolymer microdomains after the reduction of the corresponding salts. [Preview Abstract] |
Monday, March 13, 2006 4:18PM - 4:30PM |
D28.00010: Homopolymer Penetration on Crosslinked Copolymer Mat Du Yeol Ryu, Jia-Yu Wang, Eric Drockenmuller, Kristopher Lavery, Craig Hawker, Thomas Russell Ultra-thin films of benzocyclobutene (BCB)-functionalized random copolymers of styrene and methyl methacrylate were thermally-crosslinked on a substrate, but applicable to other systems, with a controlled thickness. Contact angles measured in nano scale describe that over the critical minimum thickness (~ 5.5nm) interfacial interaction of crosslinked random copolymer is well balanced. Neutron Reflectivity has been used to investigate in terms of the penetration of the polymer into crosslinked random copolymer P(S-r-BCB-r-MMA). Thus, to evaluate the critical minimum thickness which is at least required to control over the microdomain orientation of the PS- PMMA block copolymer systematically, deuterated PMMA was spin coated on crosslinked random copolymer controlled with various thickness from 1 to 10 nm. The neutron scattering length densities (SLD) of crosslinked random copolymer are increased with decreasing thickness, which means that the SLD contribution of d-PMMA to BCB layer is getting bigger because thin BCB layer is not enough to cover the SiOx. [Preview Abstract] |
Monday, March 13, 2006 4:30PM - 4:42PM |
D28.00011: Enhanced order in thinfilms of Pluronic (A-B-A) and Brij (A-B) block copolymers blended with poly(acrylic acid) Vijay R. Tirumala, Bryan D. Vogt, Hae-jeong Lee, Eric K. Lin, James J. Watkins Pluronic (PEO$_{m}$-PPO$_{n}$-PEO$_{m})$ and Brij (PEO$_{m}$-PE$_{n})$ based block copolymer films have recently been used as sacrificial templates for the fabrication of mesoporous low-$k$ thinfilms. We have found that the addition of a low molecular weight third component homopolymer exhibiting strong interactions with one of the blocks enhances the local and long-range order of both Pluronic and Brij templates in the melt. In this work, small-angle neutron scattering and x-ray reflectivity were used to investigate the microstructure of block copolymer/poly(acrylic acid) blend templates. In templates where PEO serves as a majority phase, both scattering and reflectivity measurements show that addition of PAA decreases the interfacial width and strengthens domain segregation. In templates with PEO as the minority phase, addition of PAA can induce an order-order transition. Tuning the microphase morphology of block copolymer thinfilms using a low-molecular weight homopolymer additive has many implications for methods that use block copolymer melts as sacrificial templates. [Preview Abstract] |
Monday, March 13, 2006 4:42PM - 4:54PM |
D28.00012: Ordering transition of block copolymer films under compressed CO2 Abraham Arceo, Peter F. Green It is well-known that a bulk, symmetric, A-b-B diblock copolymer forms a lamellar morphology, with period L, below an order- disorder transition temperature (TODT), for XN $<$ 10.5; X is the Flory-Huggins interaction parameter and N is the degree of polymerization of the copolymer. The ordering temperatures of poly(styrene-b-methyl methacrylate) (PS-b-PMMA) thin film diblock copolymers of thickness ca. 2L, supported by SiOx/Si substrates, in vacuum environments, are shown to increase beyond the bulk, having unusually large shifts of the transition temperature with small changes of XN. We find that in compressed CO$_2$ environments, these films are ordered at temperatures where the films are disordered in vacuum (or air) environments. This latter observation is of particular significance because small molecule diluents, including compressed CO$_2$, are known to decrease the TODT of the bulk (enhanced miscibility). We will discuss these results in light of the thin film compressibility and preferential sorption of the individual blocks at the experimental conditions. [Preview Abstract] |
Monday, March 13, 2006 4:54PM - 5:06PM |
D28.00013: Self-Organization of PS-b-PFOMA Block Copolymer Aggregates in Thin Films Yuan Li, Luciana Meli, Keith Johnston, Kwon Lim, Peter Green SFM, STEM and XPS were employed to study the morphologies of polystyrene-b-poly(1,1',2,2'-tetrahydroperflurooctyl methacrylate) (PS-b-PFOMA) films. The copolymer was dissolved in the co-solvent mixture of Freon 113 and toluene. Upon spin-casting on Si/SiOx substrate, PS-b-PFOMA was found to self-organize into spherical aggregates, where the cores of the spheres were composed primarily of PFOMA and the matrix was composed by PS. However, exposing the films to supercritical CO$_{2}$ led to a reversed morphology, where spheres of PS were embedded in the matrix of PFOMA. In addition, the degree of ordering was improved in sc-CO$_{2}$ and the domain size was tuned by adjusting sc-CO$_{2}$ density. The results were discussed based on the effects of sc-CO$_{2}$ on the interfacial tension and the relative PS-PFOMA interactions. [Preview Abstract] |
Monday, March 13, 2006 5:06PM - 5:18PM |
D28.00014: Scaling of Domain Spacing of Block Copolymers Dilated by High-Pressure Carbon Dioxide Timothy Francis, Bryan Vogt, Xiaohui Wang, James Watkins The dependence of the interdomain spacing on the sorbed solvent volume fraction of microphase separated poly(styrene-$b$-dimethyl siloxane) in the high concentration limit was probed using high-pressure carbon dioxide as the diluent. Domain spacing was measured using \textit{in situ} small angle neutron scattering, both isothermally and at constant polymer volume fraction. The results indicate that high-pressure CO$_{2}$ behaves similarly to a selective liquid solvent and that d-spacing is strongly influenced by solvent selectivity, which is a function of temperature for this system. The data also show that the d-spacing as a function of solvent volume fraction cannot be described by the traditional power law scaling that does not account for solvent selectivity, but collapse to a line when scaled by a swelling asymmetry factor. Data measured at constant polymer volume fraction are in good agreement with previously reported findings, and show that the interdomain spacing exhibits power law scaling with the temperature dependent interaction parameter. [Preview Abstract] |
Monday, March 13, 2006 5:18PM - 5:30PM |
D28.00015: Amphiphilic Block Copolymers in Condensed Carbon Dioxide William Edmonds, Timothy Lodge, Marc Hillmyer Condensed carbon dioxide represents a promising ``green'' solvent alternative on the basis of its abundance and modest critical conditions. Amphiphilic block copolymers offer the potential of enhancing the versatility and usefulness of this solvent through the formation of micelles. Our goal is to understand and define the parameters that control aggregate shape and dimensions in solution; these parameters include copolymer volume fraction and solvent density. We will present dynamic light scattering and solubility data for a series of polybutadiene-$b$-poly(hexafluoropropylene oxide) and polylactide-$b$-poly(hexafluoropropylene oxide) copolymers. At modest pressures ($<$ 500 bar), these materials are readily soluble. In addition, initial measurements suggest the formation of non-spherical micelles in solution. [Preview Abstract] |
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