Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session T34: Thin Films of Block Copolymers and Hybrid Materials: Directed Assembly II |
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Sponsoring Units: DPOLY Chair: Gila Stein, University of Houston Room: 342 |
Thursday, March 21, 2013 8:00AM - 8:12AM |
T34.00001: Coupling Dynamic Thermal Shear Field to Block Copolymer Molecular Ordering for Highly Oriented and Hierarchically Patternable Nanostructures Gurpreet Singh, Kevin Yager, Ho-Cheol Kim, Alamgir Karim Dynamic thermal field processing of block copolymer (BCP) thin film is a highly attractive roll-to-roll directed self-assembly method for molecular level organization of BCP nanostructures over large areas without requiring physical or chemical guiding templates. Previously, we discovered that a sharp temperature gradient \textgreater 30 $^{\mathrm{o}}$C/mm flips BCP cylinders from horizontal to vertical orientation with respect to the substrate such that tuning the dynamic thermal sweep rate to the BCP's terminal relaxation time is critical for optimal hexagonally-packed vertical order. We now exploit the dynamic thermal field to induce a directional gradient soft-shear field via a thermally expanding elastomeric overlayer that yields highly oriented and hierarchically patternable horizontal BCP cylinders. BCP thin films confined under a flat or patterned elastomeric overlayer and translated across the dynamic thermal field experience directional elastomer expansion-contraction in the heating-cooling zone as a single oscillatory shear cycle that aligns the BCP films. We successfully characterize the molecular level ordering mechanism and create unidirectionally aligned single crystal cylindrical BCP thin films over a wide range of thicknesses and processing speeds. Excitingly, the BCP cylinder alignment is fully decoupled from the PDMS mold pattern direction and dimensions. [Preview Abstract] |
Thursday, March 21, 2013 8:12AM - 8:24AM |
T34.00002: Strongly segregated polydisperse block copolymer near the order-disorder transition Adam Schmitt, Mahesh Mahanthappa Newer polymerization techniques afford polydisperse block polymers comprised of functional monomers with interesting potential applications as membranes for selective transport applications. As a result of their molecular chain length dispersity, the melt-phase behavior of these polymeric materials differs from that of well-studied monodisperse block copolymers. Extending our previous work dealing with weakly segregated poly(styrene-b-1,4-butadiene-b-styrene) (SBS) copolymers with a polydisperse middle block, we have examined the morphological consequences of increasing the segmental incompatibility between the copolymer segments. We will specifically outline recent studies of the melt phase behavior of highly segregated poly(lactide-b-1,4-butadiene-b-lactide) (LBL) triblock copolymers with a polydisperse center segment near the order-disorder transition. Comparison of the thermodynamics of SBS \& LBL copolymer self-assembly suggests additional order parameters that characterize the phase behavior of these complex polymer mixtures. [Preview Abstract] |
Thursday, March 21, 2013 8:24AM - 8:36AM |
T34.00003: Shear-alignment of metal-containing block copolymer thin films for nanofabrication So Youn Kim, Richard Register, Jessica Gwyther, Ian Manners, Paul Chaikin Cylinder-forming block copolymers can be used as etch masks for the fabrication of nanowire grids, with both fine resolution and scalability. However, achieving a high aspect ratio in these nanostructures, where reactive ion etching is employed for pattern transfer, requires strong etch contrast between two blocks of the copolymer. We achieve this strong contrast by using metal-containing block copolymers: materials which either contain metal as synthesized, or which can be selectively metallized after deposition as thin films. In the first case, iron-containing polystyrene-b-poly(ferrocenylisopropylmethylsilane) (PS-PFS) forming PFS cylinders was employed, and a spin-coated film was aligned by shearing with a polydimethylsiloxane pad. In the second case, polystyrene-b-poly-2-vinylpyridine (PS-P2VP) was deposited as a film, shear-aligned, and then platinum was selectively sequestered within the P2VP cylinders by brief soaking in an aqueous solution of a Pt salt. In both cases, shear stress produced alignment over centimeter-scale areas; this alignment was retained for PS-P2VP during the selective metallization. The line pattern in these aligned block copolymer thin films is then transferred via reactive ion etching into amorphous silicon deposited onto a quartz wafer to fabricate silicon nanowire grid polarizers which can operate at deep ultraviolet wavelengths. [Preview Abstract] |
Thursday, March 21, 2013 8:36AM - 8:48AM |
T34.00004: High Aspect Ratio Sub-15 nm Silicon Trenches From Block Copolymer Templates Xiaodan Gu, Zuwei Liu, Ilja Gunkel, Deirdre Olynick, Thomas Russell High-aspect-ratio sub-15 nm silicon trenches are fabricated directly from plasma etching of a block copolymer (BCP) mask. Polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP) 40k-b-18k was spin coated and solvent annealed to form cylindrical structures parallel to the silicon substrate. The BCP thin film was reconstructed by immersion in ethanol and then subjected to an oxygen and argon reactive ion etching to fabricate the polymer mask. A low temperature ion coupled plasma with sulfur hexafluoride and oxygen was used to pattern transfer block copolymer structure to silicon with high selectivity (8:1) and fidelity. The silicon pattern was characterized by scanning electron microscopy and grazing incidence x-ray scattering. We also demonstrated fabrication of silicon nano-holes using polystyrene-b-polyethylene oxide (PS-b-PEO) using same methodology described above for PS-b-P2VP. Finally, we show such silicon nano-strucutre serves as excellent nano-imprint master template to pattern various functional materials like poly 3-hexylthiophene (P3HT). [Preview Abstract] |
Thursday, March 21, 2013 8:48AM - 9:00AM |
T34.00005: Fabrication of 3 Dimensional SERS substrate using block copolymer confined AAO template Jin Kon Kim, Duesik Bae We fabricated alternatively stacked lamellar microdomains of polystyrene (PS) and poly(methyl methacrylate) (PMMA) by confining PS-b-PMMA copolymer within anodic aluminum oxide (AAO) template modified by neutral brush. The size of stacked lamellar microdomains was easily controlled by changing the molecular weights of the block copolymers. We also deposited silver with 10 nm height selectively on the PS microdomains. The distance of neighboring silver was changed by microdomain size, height and diameter of the AAO template. The fabricated surface enhanced Raman scattering (SERS) substrates showed high sensitivity and reliablity. [Preview Abstract] |
Thursday, March 21, 2013 9:00AM - 9:12AM |
T34.00006: Silver based SERS substrates fabricated from block copolymer thin film Xin Zhang, Wonjoo Lee, Seung Yong Lee, Zhenghan Gao, Oded Rabin, R.M. Briber Poly (styrene-block-4-vinyl pyridine) (PS-b-P4VP, Mw $=$ 47-b-10 kDa, PDI$=$1.10) thin films were used to form large-scale long range ordered self-assembled hexagonal patterns of vertically P4VP oriented cylinders in a PS matrix on Si substrates. The P4VP cylindrical domains were crosslinked and quaternized using 1,4-dibromobutane. Negatively charged 15nm gold nanoparticles were attached to the quaternized P4VP domains through Coulombic interactions. Silver was then grown on the gold seeds to create nanometer scale gaps between the nanoparticles. The gap between the nanoparticles was fine tuned by controlling the silver growth time. The substrates showed large enhancement factors in the Raman scattering signal for a broad range of incident wavelengths. [Preview Abstract] |
Thursday, March 21, 2013 9:12AM - 9:24AM |
T34.00007: 3D Nanoparticle Assemblies in Thin Films of Supramolecular Nanocomposites Joseph Kao, Peter Bai, Vivian Chuang, Zhang Jiang, Peter Ercius, Ting Xu Nanocomposite thin films containing hierarchically-ordered nanoparticle assemblies are highly desirable to modulate the collective properties of nanoparticles to meet material requirements for nanodevice fabrication. Block copolymer-based supramolecules have shown great potential in directing the assembly of ordered nanoparticle arrays for a wide range of nanoparticles in bulk. Here, I will describe systematic studies on the phase behavior of supramolecular nanocomposites in thin films using a model system that forms parallel cylindrical morphology. By tailoring the conformational entropy of the comb block of the supramolecule, a rich library of nanoparticle assemblies including 1D chains, 2D lattices, 3D arrays and networks with precisely controlled inter-particle ordering can be obtained. Furthermore, the entropic contributions in the assembly process can be tuned by varying nanoparticle size. This enables one to achieve 3D hybrid arrays of metallic and semiconductor nanoparticles in thin films. The comprehensive studies on the thermodynamics and kinetics of the nanoparticle assemblies in supramolecular nanocomposite thin films opens up a new avenue for the fabrication of next-generation nanoparticle-based devices. [Preview Abstract] |
Thursday, March 21, 2013 9:24AM - 9:36AM |
T34.00008: Interfacial roughness of self-assembled lamellae in cross-linkable block copolymer thin films Chunlin He, Mark Stoykovich Although diblock copolymers are attractive for fabricating structures with 5-50 nm dimensions, the ability of such materials to self-correct or ``heal'' nanoscale defects is of equal importance for future lithographic applications. Reduced interfacial roughness and enhanced dimensional control have been demonstrated to occur at the molecular-level when the block copolymers are directed to self-assemble on chemically patterned surfaces or in topographic structures. Here we demonstrate that cross-linking in self-assembled block copolymer domains can also significantly reduce interfacial roughness caused by thermal fluctuations. Lamellar-forming block copolymer/homopolymer blends, with and without cross-linkable components, were directed to self-assemble on chemically patterned substrates and processed by solvent-annealing at room temperature. The lamellae were subsequently thermally-processed or exposed to UV light to perform a cross-linking reaction in a step distinct from the self-assembly process. Spectral analysis of the interfacial roughness was compared between the cross-linkable and uncross-linkable block copolymer materials, and the cross-linked system was quantified to have lower interfacial roughness due to a tighter coupling between neighboring interfaces. [Preview Abstract] |
Thursday, March 21, 2013 9:36AM - 9:48AM |
T34.00009: Ordered Deposition of Block Copolymer Thin Films and Its Continuous Growth by Electrospray Hanqiong Hu, Chinedum Osuji Ordering of block copolymer thin films have been studied extensively using different approaches primarily as a post-deposition step. Here we show that well-ordered block copolymer thin films can be continuously deposited through electrospray. Under appropriate conditions, fine particles are generated and sub-attoliter quantities of material is delivered and equilibrated with heated substrate in the presence of solvent-mediated interface. Ordered film formation is predicated on fast thermal equilibration relative to the rate of deposition. We investigate the effects of process parameters that underpin film morphology including solvent selectivity, substrate temperature, flow rate of electrospray feed solution and wetting conditions in a couple of material systems, such as PS-b-PEO, PS-b-PMMA and PS-b-P4VP. We've demonstrated that at relative fast deposition rate ($\sim$ 5nm/min), solvent assists ordering of the film and its selectivity plays an important role in determining the film morphology as it mediates the interface preference regardless of the wetting conditions. We also observe wide temperature and flow rate windows for the film to be ordered. Cylinders were found to align with their long axes perpendicular to the film-air interface at optimal spray conditions. When the material is delivered free of solvent at relative slow deposition rate ($\sim$ 10nm/h), templated substrate or neutral wetting conditions becomes key to ordering of the film and continuity of perpendicular growth is expected under such. [Preview Abstract] |
Thursday, March 21, 2013 9:48AM - 10:00AM |
T34.00010: Process-dependent Nanostructure and Crystallinity Competition in All-Conjugated Poly(3-hexylthiophene) Block Copolymers Yen-Hao Lin, Rafael Verduzco The nanostructure of active layer in organic photovoltaic (OPV) is critical to charge transfer and power conversion efficiency (PCE). This study elucidates a model example of crystallinity competition and process-dependent nanostructures in various composition of an all-conjugated block copolymer, poly(3-hexylthiophene)-$b$-poly(9$^{\prime}$,9$^{\prime}$-dioctylfluorene) (P3HT-$b$-PF) synthesized from a combination of Grignard metathesis and Suzuki-Miyaura polycondensation. In contrast to previous studies of P3HT-based all-conjugated block copolymer where P3HT typically dominates the final morphology through crystallization. Grazing-incidence X-ray scattering (GIXS) measurements verify that thermally annealed P3HT-b-PF spun-cast films show a morphology dominated by crystallization of P3HT or PF, depending on the size of block ratios. However, all solvent annealed films show primarily an out-of-plane stacking ($q$ $\sim$ 0.15n {\AA}$^{-1}$ where n $=$1,2,3,4,5,6,7) on the substrate and with strong (020) $\pi $-stacking parallel to substrate surface. This expanded small lamellar domain is about 4 nm which is designated to alkyl-chain stacking within block copolymer. Subsequent thermal annealing at high temperatures results in loss of the expanded spacing, indicating that the observed orientation and structure of P3HT-$b$-PF is in non-equilibrium status so that proper processing condition is important in determining final nanostructure and potentially enhanced PCE in all-polymer OPVs. [Preview Abstract] |
Thursday, March 21, 2013 10:00AM - 10:12AM |
T34.00011: Evaporation-induced ordering in solution-cast block copolymer thin films Sean Paradiso, Kris Delaney, Hector Ceniceros, Carlos Garcia-Cervera, Glenn Fredrickson Block copolymer thin films are currently being investigated for a wide variety of applications, ranging from separation membranes to organic photovoltaics and lithographic masks. Over the last decade or so, there has been mounting interest in using solvent casting techniques to control morphology selection in thin films either through spin coating, drop casting, or simple annealing under a mixture of solvent vapors. While these added degrees of freedom and process variables offer the promise of enhanced morphology control, they necessarily add extra dimensions and inter-dependencies between parameters that must be sorted out before this control can be effectively exercised. To this end, we have adapted a dynamical extension of Self-Consistent Field Theory to study the dynamics of ordering from a dilute copolymer solution to a dry, ordered thin film. This talk will offer a visual summary of the range in behavior available to a single copolymer $+$ neutral solvent system in both 2D (lamella-forming) and 3D (cylinder-forming) environments. In addition, a brief analysis will be presented on the competing time scales, equilibrium, and non-equilibrium effects that appear to govern the initiation event and propagation of evaporation-induced ordering fronts. [Preview Abstract] |
Thursday, March 21, 2013 10:12AM - 10:24AM |
T34.00012: Coarse Grained Monte Carlo Simulations of Solvent Annealed Block Copolymer Thin Films Gurdaman Khaira, Su-Mi Hur, Juan de Pablo Solvent annealing has been shown to provide an effective means for controlling the self assembly of block copolymer thin films. However, the current theoretical understanding of solvent annealing processes is limited. We have developed a particle based coarse-grained model to study the solvent annealing and the effect of process variables on the self assembled structure of block copolymer thin films. For bulk materials, our model is shown to reproduce the phase behavior reported in experiments. In thin films, our approach enables us to mimic the experimental process, while accessing the large length and time scales relevant to applications in directed self assembly. In this presentation, we will discuss the effects of solvent-polymer interactions, solvent vapor pressure and solvent evaporation rate on the morphology of ordered domains. [Preview Abstract] |
Thursday, March 21, 2013 10:24AM - 10:36AM |
T34.00013: Morphology driven spinodal decomposition of film topography in symmetric diblock copolymer thin films Robert D. Peters, Pawel Stasiak, Mark W. Matsen, Kari Dalnoki-Veress At equilibrium, symmetric diblock copolymer thin films will microphase separate into lamellae oriented parallel to the substrate. If a film is not exactly commensurate, the free surface will form regions of two different film heights separated by one characteristic lamellar bilayer height. Though this equilibrium morphology has been well studied, the intermediate morphologies formed along the ordering pathway as the film transitions from a disordered melt to an equilibrated film with a terraced topography has received relatively little attention. Using atomic force microscopy we probe the topology and morphology evolution at the free surface of maximally incommensurate poly(styrene-b-methyl methacrylate) films during annealing. The film initially develops lamellae at the free surface with a perpendicular orientation, followed by the continuous growth in amplitude of fluctuations in film surface topography, indicating a spinodal process. Using self-consistent field theory we confirm that this spinodal decomposition of film topography is induced by an unstable mixed morphology intermediate state consisting of parallel lamellar domains at the substrate, and perpendicular lamellae at the free surface. [Preview Abstract] |
Thursday, March 21, 2013 10:36AM - 10:48AM |
T34.00014: Controlled Porous Nanostructure on Gold-Decorated Block Copolymer Microspheres Minsoo Kim, Kang Hee Ku, Hyeong Jun Kim, Gi-Ra Yi, Bumjoon Kim Hollow block copolymer microspheres (HPMs) with controlled porous nanostructures were simply prepared from gold decorated block copolymer microspheres (GPMs). First, the GPMs were fabricated by emulsifying polystyrene-$b$-poly(4-vinylpyridine) (PS-$b$-P4VP) micelle solution with gold precursors into surfactant solution. Then, the HPMs were prepared by adding cetyl trimethylammonium bromide (CTAB) into the GPMs suspension. Selective dissolution of gold precursors by CTAB resulted in the formation of porous nanostructures on the GPMs. The porous nanostructures can be controlled by molecular weight of block copolymers and the amounts of gold precursors incorporated to P4VP core in the micelle, of which both factors tuned sizes of the surface nanostructures in the HPMs. In addition, we demonstrated that increasing amounts of gold precursors resulted in increasing the pore depth. The detail pore morphology in the HPMs was investigated by SEM, AFM and cross-sectional TEM measurements. [Preview Abstract] |
Thursday, March 21, 2013 10:48AM - 11:00AM |
T34.00015: Microwave- assisted Rapid Self- Assembly of Lamellar Forming Poly (styrene-b- lactic acid) (PS-b-PLA) Block Copolymer for Fabrication of Silicon Nanowires Parvaneh Mokarian-Tabari, Cian Cummins, Sozaraj Rasappa, Justin D. Holmes, Michael M. Morris Photolithography has been a fundamental process in the production of integrated circuits, but it is reaching its physical limit for generating ultra-small feature sizes. Block copolymers have a great potential as mask templates for fabricating nano features. Although ordered sub 20 nm features utilising BCPs have been achieved, lengthy annealing times (hours to days) are currently employed. Here we use microwave annealing, a new emerging technique, to achieve lateral phase separation in a lamellar forming PS-b-PLA. Having optimised the microwave conditions such as power, temperature, anneal holding time, solvents etc, a long range order line pattern was formed in less than two minutes on Si, Ge and Al substrates. The etched pattern (PLA removed by Ar/O$_{2}$ RIE) was transferred to silicon substrate resulting in 18nm Si nanowires. [Preview Abstract] |
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