Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session P43: Focus Session: Thin Film Block Copolymers III |
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Sponsoring Units: DPOLY Chair: Mark Stoykovich, University of Colorado at Boulder Room: A306/307 |
Wednesday, March 23, 2011 8:00AM - 8:12AM |
P43.00001: Effect of Well-defined Roughness on the Microdomain Orientation of Block Copolymer Thin Films Kookheon Char, Youngwoo Choo, Hyo Seon Suh, Taehee Kim It is well known that the perpendicular orientation of block copolymer (BCP) films is preferred over the parallel orientation when the BCP films are placed on rough surfaces due to the unfavorable elastic deformation of BCP chains in the parallel oriented microdomains. More recently, the approach to utilize the rough substrate for BCP domains in long range order has been reported. However, the quantitative analysis to explore the effect of each individual roughness factors, such as lateral or vertical displacement, on the microdomain orientation of BCP films has not been thoroughly studied yet. In order to examine the roughness effect systematically, we prepared substrates with well-defined roughness utilizing either nanoparticle monolayers or line patterns generated by e-beam lithographic technique. Based on the detailed observation of the orientational change of BCP films on the well-defined surface roughness, we analyzed the dependence of BCP domain orientation on each roughness parameter. Furthermore, we found that the BCP film thickness, coated on the substrate, is another important parameter determining the orientation of microphase-separated domains of BCP thin films in addition to the surface roughness. [Preview Abstract] |
Wednesday, March 23, 2011 8:12AM - 8:24AM |
P43.00002: Multiple Replicas of Block Copolymer Thin Films from a Brushless Organosilicate Substrate Hyo Seon Suh, Hyunsik Yoon, Kookheon Char The chain end-grafted polymer brushes or cross-linked polymer mats have typically been utilized as the surface modification layers to induce the perpendicular orientation of block copolymer (BCP) thin films. Instead of such polymer-based approaches, we have recently introduced a new concept to control the BCP orientation using the brushless organosilicate (OS) substrates, whose surface energy can be finely tuned with thermal treatment. In this brushless case, the BCP chains do not penetrate into the underlying hard OS substrates during thermal annealing of BCP films, therefore, the BCP chains at the interface have no entangled structure with fairly weak adhesion of BCP films against the substrate. Owing to such weak adhesion of BCP films against the OS substrate, the perpendicularly oriented BCP film on a neutral OS substrate could be easily peeled off and transferred to a UV-curable resin applied onto the BCP film. The OS substrate after the peel-off process of a BCP film could regenerate the perpendicularly oriented BCP films since the surface energy of the OS substrate remains intact during the peel-off process. Furthermore, the direct-assembled BCP films on chemically patterned OS substrates could also be peeled off and transferred on to a UV-curable resin, allowing us to produce multiple replicas of direct-assembled BCP thin films from a single chemically patterned OS substrate. [Preview Abstract] |
Wednesday, March 23, 2011 8:24AM - 8:36AM |
P43.00003: Rational design of block copolymer morphologies via control of the film thickness and substrate patterning: A self consistent field study Xianggui Ye, Brian J. Edwards, Bamin Khomami Chemically patterned substrates can direct the assembly of adsorbed layers or thin films of block copolymers. In this study we have examined the self-assembly of a lamella-forming diblock copolymer on periodically stripe-patterned substrates, and a cylinder-forming diblock copolymer on periodically doted-patterned substrates for various film thicknesses. In general, we have shown that for thin films the morphology of the block copolymer follows the chemical pattern at the substrate; however, with an increase degree of mismatch between the spacing of the pattern and the natural spacing of bulk block copolymer, a host of novel morphologies can been created, which have not to date been experimentally realized. Our studies clearly demonstrate that the film thickness and the pattern of substrate can be judiciously manipulated to rationally design morphologies for various applications such as filtration, conduction, and high-surface area membranes. Overall, these results demonstrate a promising strategy for fabrication of complex interfacial nanostructures from chemically patterned templates. [Preview Abstract] |
Wednesday, March 23, 2011 8:36AM - 8:48AM |
P43.00004: Utilizing low surface energy moieties to control surface composition of a polystyrene-b-poly(2-vinylpyridine) block copolymer Michael Dimitriou, Daniel Fischer, Craig Hawker, Edward Kramer During processing the interaction of a block copolymer film with a free surface affects its final orientation and surface composition. A strategy to control this interaction and hence tailor the final structure of a polymer film is to introduce low surface energy moieties to the system. A lamellar forming polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer was synthesized with varying amounts of 1-[(3-butenyloxy)methyl]-4-vinylbenzene copolymerized with the 2VP block. Utilizing thiol-ene chemistry the pendant alkene of 1-[(3-butenyloxy)methyl]-4-vinylbenzene was functionalized with 1H,1H,2H,2H-perfluorooctanethiol to efficiently and selectively incorporate fluorinated hydrocarbons into the 2VP block. Near edge X-ray absorption fine structure spectroscopy (NEXAFS) and X-ray photoelectron spectroscopy were used to characterize the polymer surface as a function of 1H,1H,2H,2H-perfluorooctanethiol incorporation. At molar incorporations of the fluorinated monomer in P2VP greater than 4{\%} dynamic secondary ion mass spectrometry and NEXAFS indicate a P2VP rich surface. [Preview Abstract] |
Wednesday, March 23, 2011 8:48AM - 9:00AM |
P43.00005: Flexible Confinement of Block Copolymer Films Between Tunable Surface Energy Elastomeric Films and Xerogel Substrates Manish Kulkarni, Gurpreet Singh, Sushil Satija, Alamgir Karim Orientation control of block copolymer (BCP) films is important for advanced technological applications such as nanoscale lithography. Here we present a different strategy whereby both interfaces of the poly(styrene)-block-poly(methylmethacrylate) BCP films are tunably controlled. The BCP films were coated on a roughness and surface energy tunable xerogel substrates and the top surface of the polymer film was conformally covered by crosslinked PDMS elastomer. The surface energies of xerogel substrate and crosslinked PDMS is tunable from 28 and 18 mJ/m$^{2}$ to 45 and 55 mJ/m$^{2 }$resp. via UV-Ozone treatment. The confined BCP film was then thermally annealed to induce ordering. Such a unique approach allowed the BCP films to respond in its orientation of cylinders and lamellae from parallel to perpendicular. The morphology of these micro-phase separated BCP films was studied by tapping mode atomic force microscopy and neutron reflectivity. [Preview Abstract] |
Wednesday, March 23, 2011 9:00AM - 9:12AM |
P43.00006: Directed Assembly of Block Copolymer on Tunable Surface Energy Flexible Substrate Arzu Hayirlioglu, Alamgir Karim We examine the ordering properties of micro-phase separated block copolymer (BCP) films on flexible substrates. In particular, we investigated the wettability characteristics and morphology of the BCP films before and after annealing on tunable surface energy PDMS substrates. The surface energy of PDMS substrates was modified to vary from 20 to 68 mJ/m$^{2}$ by exposing them to UV-ozone (UVO). Two types of block copolymer systems were examined on these UVO exposed PDMS substrates. Our experiments were carried out with surface energy above 42 mJ/m$^{2}$ because the BCP dewets on the PDMS substrate below that surface energy. Atomic Force Microscope (AFM) and Optical Microscope (OM) were used to study of the surface morphology of the BCP films. It was observed that the BCP morphology exhibits perpendicular orientation on PDMS substrate with surface energy in the range of 42 to 66 mJ/m$^{2} $ and parallel orientation above 67 mJ/m$^{2}$. BCP film morphology on other types of soft substrates and different BCP systems as a function of annealing temperatures and film thickness will be presented. [Preview Abstract] |
Wednesday, March 23, 2011 9:12AM - 9:24AM |
P43.00007: The effect of Surface Neutrality on ODT of PS-b-PMMA films Eunhye Kim, Seunghoon Choi, Rui Guo, Du Yeol Ryu, Craig J. Hawker, Thomas P. Russell The film transitions, the order-to-disorder transition (ODT), has been investigated in a symmetric polystyrene- b-poly(methyl methacrylate) (PS-b-PMMA) on a random copolymer (P(S-r-MMA)) grafted substrate where the interfacial interactions are balanced. With decreasing film thickness less than 25L0, the ODT significantly decreases, because the interfacial interactions by a random copolymer grafted to the substrate provide a surface-induced compatibilization toward two block components. However, a plateau of the ODT for films thicker than 25L0 was observed above the bulk value. The elevation of this ODT indicates a suppression of compositional fluctuations normal to the film surface, more than likely because the dominant orientation of the lamellar microdomains was found to be parallel to the film surface. [Preview Abstract] |
Wednesday, March 23, 2011 9:24AM - 9:36AM |
P43.00008: Surface Affinity Effects On Confined Thin Film Block Copolymers Using Self Consistent Field Theory Modeling Adam Hannon, Alfredo Alexander-Katz, Caroline Ross Self consistent field theory (SCFT) applied to inhomogeneous thin film block copolymer systems allows for the exploration of a wide array of potential equilibrium ordered morphologies at the nanoscale through varying parameters such as $\chi $, the segmental Flory-Huggins parameter, N, the polymer degree of polymerization, and $f$, the volume fraction of the minority polymer component. In addition, boundary conditions of the chemical potential fields in the field theory can be specified to model surface features such as polymer brush layers and topological templating features from lithography that enrich the possible morphologies observed [Macromolecules 2010, 43, 8290--8295]. In this presentation, we show how the orientation and surface morphology of diblock copolymers with large $\chi $N varies with surface affinity, surface shape, and $f $for confined thin film systems. Surfaces neutral to both polymer species are examined, as well as surfaces preferential to both the minority and majority polymer components with fine variances in the magnitude of the surface affinity. Commensurability of the ordered structures is examined as well by varying simulation cell size. The results of the study will be applied to the generation of complex features for nanolithography applications. [Preview Abstract] |
Wednesday, March 23, 2011 9:36AM - 9:48AM |
P43.00009: Stress induced topographic patterning in thin diblock copolymer films Andrew Croll, Alfred Crosby When a thin rigid polymer film is attached to a soft elastic substrate and placed in a state of compressive stress, the system wrinkles as a critical stress is surpassed. This simple deformation pattern contains information about the mechanical state of both the polymer film and substrate. Although classical mechanics can be used to relate the global deformation of the film/substrate to the local wrinkle geometry as a function of materials properties, relatively little is known about how the thin capping film material accommodates the localized bending (and therefore localized stress). Here we conduct wrinkling experiments using a model diblock copolymer/elastomer composite. Wrinkling a homogeneous, disordered block copolymer film places the film in a well-defined initial stress state. When heated above its glass transition, the wrinkled film flows, microphase separates, and relaxes from the stress imposed by local wrinkle deformations. The periodic stress relaxation leads to the emergence of a new pattern in the microphase separated surface structure, thus providing new insight into how block copolymers react to stress. [Preview Abstract] |
Wednesday, March 23, 2011 9:48AM - 10:00AM |
P43.00010: Shear-induced sphere-to-cylinder transition in thin films of diblock copolymers and the role of wetting layers Alexandros Chremos, Richard Register, Paul Chaikin, Athanassios Panagiotopoulos The shear-induced sphere-to-cylinder transition in diblock copolymer thin films has been studied using large-scale coarse- grained Langevin dynamics simulations. At zero-shear conditions and below the order-disorder transition temperature the thin film forms a monolayer or bilayer of spheres given the thickness of the film. Mimicking the experimental setup the minority block has an affinity to be adsorbed on the confining surfaces forming brushes which interpenetrate the rest of the film. Once a shear field is applied and above a critical shear rate, the spheres elongate and merge with their neighbors to form cylinders. We find that the mechanism with which the spheres merge is closely related with the stretching of individual diblock chains. In particular, we find that in monolayer thin films it is more difficult to achieve the sphere-to-cylinder transition, which is also an experimental observation, because the brushes restrict the stretching of diblock chains. The simulations were performed with the use of Graphical Processing Units allowing large-scale simulations with long polymer chains to studied. [Preview Abstract] |
Wednesday, March 23, 2011 10:00AM - 10:12AM |
P43.00011: Shear alignment of standing block copolymer lamellae in thin films Saswati Pujari, Michael Keaton, Paul Chaikin, Richard Register While thin films of cylinder-forming block copolymers (BCPs) can be effective templates for striped patterns (leading to parallel nanowires), a drawback is the modest aspect ratio of the final structures, because of limited etch contrast between the two polymer blocks. Using thin films of lamellar BCPs, with the lamellae standing perpendicular to the substrate, could yield structures with larger aspect ratio. To generate parallel stripes of controlled direction, the in-plane orientation needs to be guided while preserving the out-of-plane perpendicular orientation. In this study, we have produced thin films of standing lamellae of a polystyrene/polymethylmethacrylate BCP of thicknesses up to 1.5 times the domain spacing, by neutralizing the Si substrate with a random terpolymer brush layer. To date, films less than one domain spacing thick have been aligned by shear, while shearing thicker films causes the perpendicular lamellae to switch to parallel orientation. We are currently investigating the alignment as a function of stress, film thickness, terpolymer composition and domain spacing. [Preview Abstract] |
Wednesday, March 23, 2011 10:12AM - 10:24AM |
P43.00012: Defect generation in thin films of block copolymer cylinders: the effect of cylinder spacing and film thickness Vindhya Mishra, Edward Kramer Understanding the fundamental physics of disordering and defect generation in block copolymer (BCP) films is important for directed assembly based block copolymer lithography. We investigate the defect generation in, and smectic-nematic-isotropic transition temperature T$_{m}$ of, monolayers and bilayers of poly (styrene-b-2vinyl pyridine) diblock copolymer cylinders aligned parallel to the substrate in 2 micron wide channels. Quantitative AFM studies were supplemented with grazing incidence small angle X-ray diffraction line-shape analysis to quantify the decay of translational and orientational correlation functions with increasing temperature. We find that T$_{m}$ decreases, and the dislocation density $n$ below T$_{m}$ increases, if either the number of layers or the cylinder spacing $a$ decreases. These results are expected since $n\sim $ exp(-E$_{d}$/kT) and E$_{d}$, the dislocation formation energy, scales as $a^{2}h$, where $h$ is film thickness. Since only a 10{\%} decrease in $a$ produces a dramatic increase in $n$, these results suggest that using 2D smectic structures such as BCP cylinders aligned parallel to, or BCP lamellae normal to, a substrate to produce more closely spaced features will result in patterns with more and more defects. [Preview Abstract] |
Wednesday, March 23, 2011 10:24AM - 10:36AM |
P43.00013: Micelle Formation of Diblock Copolymer in a Thin Film Homopolymer: a Comparison with Polymer Brush-Coated Nanoparticles Hengxi Yang, Chelsea Chen, Peter Green We investigated micelle formation of a diblock copolymer polystyrene-$b$-poly(2-vinylpyridine) (PS-$b$-P2VP) of degree of polymerization $N$, in thin films of homopolymer polystyrenes (PS) of different degrees of polymerization $P$, supported on substrates, and compared the results with the phase behavior of PS brush-coated Au nanoparticles in homopolymer PS matrix. PS-$b$-P2VP copolymer chains aggregated to form micelles, composed of an inner P2VP core and an outer PS corona. The size of the micelle cores, $D_{core}$, increased with increasing $P$, and reached a plateau at very large $P$. The transition occurred at a larger $P$/$N$ than expected from brush-melt interaction theories. The organization of micelles at large $P$ regimes suggested attractions between micelles. P2VP block also adsorbed onto the substrate to form a brush layer and the surface adsorption process was affected by micellization of copolymers. We compared the micelle formation of PS-$b$-P2VP in PS with the phase behavior of PS coated Au nanoparticle/PS mixtures: the host chains penetrate into the corona of the micelles more easily than into the PS brush grafted on the particle due to low ``grafting density;'' what's more, micelles can self-adjust their aggregation number as the interaction between host chains and the corona changes. [Preview Abstract] |
Wednesday, March 23, 2011 10:36AM - 10:48AM |
P43.00014: Bicontinuous nanoporous block copolymer films prepared from a spherical-phase architecture Easan Sivaniah, Paul Zavala, Kevin Channon, Sanna Nataraj, Shaheen Al-Muhtaseb In a recent discovery, we have found a way to make a bicontinuous nanoporous polymer network and subsequently transform this into interconnected mesoporous inorganic oxide sheets. Notably, these structures arise from a spherical block copolymer template. Nanoporous materials of such architecture, both polymeric and inorganic, are rare and also extremely useful.~ Importantly, the process is not restricted to a single block copolymer system or a narrow range of molecular weights or compositions. All of the process steps are scaleable, fast enough to be appropriate to continuous production methods, do not require vacuum technology, and can be achieved by solution processing. We discuss the process and its use to make PLEDs, photovoltaics and filtration membranes. [Preview Abstract] |
Wednesday, March 23, 2011 10:48AM - 11:00AM |
P43.00015: Arrangement of the Microdomains of Block Copolymers Confined at Hemi-sphere Walls Du Sik Bae, Jin Kon Kim The arrangement of the microdomains of polystyrene-\textit{block}-poly(methyl methacrylate) copolymer (PS-$b$-PMMA) confined at hemi-sphere walls was investigated by scanning and transmission electron microscopy. The hemi-spherical constraint was introduced by using anodic aluminum oxide template.. The wall surface was modified by thin layers grafted by PS, PMMA, and PS-\textit{ran}-PMMA copolymer. We observed interesting morphologies which have not been observed. The observed microdomain arrangement was compared with theoretical predictions. [Preview Abstract] |
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