Dewetting and Layer Inversion of Inverted PVP/PS Bilayer Films

This work was supported by the National Research Laboratory fund (Grant M1-0104-00-0191) from the Ministry of Science and Technology (MOST), the Ministry of Education through the Brain Korea 21 Program at Seoul National University, and the National R&D Project for Nano Science and Technology from MOST

Novel Amphiphilic Styrene-Based Block Copolymers for Induced Surface Reconstruction

This paper describes the synthesis of amphiphilic block copolymers by living radical polymerization (NMP) of new styrene-like monomers. The polar monomers (ethylene oxide side chains and free hydroxyl- or amino-groups after deprotection) were polymerized in a protected form to adjust the solubility of the monomers. In this way high molar mass polymers with a narrow polydispersity (around or below 1.2) were accessible. In the bulk state hydrophobic and hydrophilic domains demix. By exposing thin films of these polymers to vacuum (air) or alternatively to water or a hydrophilic surface it becomes possible to switch the surface polarity reversibly between contact angles of about 105° and 83° as a result of surface reconstruction. Through side chains of different length and with different functionalities, it was possible to adjust the glass transition temperatures to values between -2 °C to 140 °C for the hydrophilic blocks and -30 °C to 100 °C for the hydrophobic block. The wide range of the glass temperatures allowed it to find a block copolymer system with a slow kinetic concerning the surface reconstruction process, so that a mechanistic examination of the process by AFM was possible. It got, thereby, possible to detect the break-up of the hydrophobic surface lamella and the upfold of the hydrophilic lamella in contact with water.A grant from the DAAD-KOSEF Summer Institute Program FY 2004 for L. Funk and also a grant from the IRTG Mainz-Seoul are highly appreciated. KC acknowledges the financial support from the Korea Science and Engineering Foundation (KOSEF) grant funded by the Ministry of Science and Technology R17-2007-059-01000-0]

Hierarchical Surface Topography in Block Copolymer Thin Films Induced by Residual Solvent

We have investigated the hierarchical surface topography in block copolymer thin films induced by residual solvent using optical microscopy and atomic force microscopy. A polystyrene−poly(2-vinylpyridine) (PS−P2VP) block copolymer forming lamellar morphology was spun-cast from N,N-dimethylformamide (DMF) solution onto a silicon wafer with a native oxide layer. Thin films with various thicknesses between 2.0L0 and 3.5L0, where L0 is the equilibrium lamellar period, were prepared. Typical multilayered lamellae having either islands or holes with quantized thicknesses were observed after annealing at 180 °C due to the strong affinity of the P2VP blocks toward the Si substrate and the preferential wetting of the PS blocks at the free surface. Further annealing, however, resulted in the formation of hierarchical surface topography such as hole-in-hole and/or island-on-island morphology. In addition, holes adjacent to the brush layer with L0/2 thickness tightly bound to the substrate were found to be fractal having a fractal dimension of 1.65. A small amount of residual solvent still remains in the film after spin-casting due to the high boiling temperature of DMF. This induces the lateral strain within the films during the annealing process, which further triggers the formation of the intriguing surface patterns. Autophobic dewetting is also believed to play an important role in the growth of the pattern.This work was funded in part by the National Research Laboratory program (Grant M1-0104-00-0191). Financial support from the Korean Ministry of Education through the Brain Korea 21 Program and from the Korean Ministry of Science and Technology (MOST) under Grant 99-07 is also greatly acknowledged. SAXS experiments performed at PLS were supported in part by MOST and POSCO. We thank Dr. S.-H. Chu for helping us with the ellipsometric measurement of film thickness

Dual Morphology of Islands and Fractal Holes in Block Copolymer Thin Films

This work was funded in part by the National Research Laboratory program. Financial supports from the Korean Ministry of Education through the Brain Korea 21 Program and from the Korean Ministry of Science and Technology (MOST) under Grant 99-07 as well as through the National Program for Tera-level Nano-devices as one of the 21 century Frontier Programs are also greatly appreciated. SAXS experiments performed at PLS were supported in part by MOST and POSCO. We thank Dr. S.-H. Chu for helping us with the ellipsometry

Interfacial Roughening Induced by the Reaction of End-Functionalized Polymers at a PS/P2VP Interface: Quantitative Analysis by DSIMS

The reaction of end-functionalized polymer chains at the melt interface between the immiscible polymers, polystyrene (PS) and poly(2-vinylpyridine) (P2VP), has been investigated experimentally. Diblock copolymers were formed at the interface by the reaction of amine end-functionalized deuterated PS with anhydride end-functionalized P2VP. The normalized interfacial excess (ξ = z*PS/Rg,PS) of the deuterium-labeled block copolymer was determined using dynamic secondary ion mass spectrometry (DSIMS). As ξ increases, the interfacial tension decreases to zero, at which point the interface becomes unstable, inducing interfacial roughening by hydrodynamic flow of the homopolymers. Roughening was detected using scanning force microscopy (SFM) after removing the polystyrene with a selective solvent. Evidence of the interfacial instability was also observed by cross-sectional transmission electron microscopy (TEM). The length scale of the corrugation was around 15 nm, which was comparable to the diameter of diblock copolymer emulsified droplets found near the interface. For a short symmetric block copolymer (PS (4K)−P2VP (4K)), we observed that the interfacial roughening takes place above ξ = 0.9, in good agreement with the predictions of self-consistent mean-field theory.We acknowledge the support of the UCSB Materials Research Lab. (NSF-DMR-MRSEC Grant DMR00-80034). The skillful help of Dr. Tom Mates and Dr. Krystyna Brzezinska of this facility as well as useful discussions with Dr. Ryan Hayward and Dr. Seung-Heon Lee is greatly appreciated

Quantitative analysis on the adsorbed amount and structural characteristics of spin self-assembled multilayer films

In this study, we demonstrate that the adsorbed amount of respective layers in spin self-assembled multilayer films can be controlled and predictable using an empirical power-law equation in terms of spin speed and initial solution concentration. The amount of a pair of polyelectrolytes deposited per bilayer rapidly increases with increasing polyelectrolyte concentration up to 12.5 mM while the solution concentration above 16 mM has no appreciable effect on the adsorbed amount. The adsorbed film thickness per bilayer is shown to be easily controlled from about 5 to 40 Å and proportional to constant power exponents of −0.34 and 0.78 with respect to the spinning speed (Ω) and the mole concentration of polyelectrolytes, respectively. We also demonstrate with synchrotron X-ray reflectivity measurement that the alternating organic/inorganic ultrathin films fabricated by the spin self-assembly process contain highly ordered internal structure and retain unique optical characteristics determined by the boundary condition at both the substrate/multilayer film interface as well as the multilayer/air interface.This work was supported by the National Research Laboratory fund (Grant M1-0104-00-0191) from the Ministry of Science and Technology (MOST), the Ministry of Education through the Brain Korea 21 Program at Seoul National University and the National R&D Project for Nano Science and Technology. X-ray reflectivity experiments performed at the Pohang Light Source (PLS) were also supported in part by MOST and POSCO

Directed Self-Assembly of Block Copolymers for Nanolithography: Fabrication of Isolated Features and Essential Integrated Circuit Geometries

Self-assembling block copolymers are of interest for nanomanufacturing due to the ability to realize sub-100 nm dimensions, thermodynamic control over the size and uniformity and density of features, and inexpensive processing. The insertion point of these materials in the production of integrated circuits, however, is often conceptualized in the short term for niche applications using the dense periodic arrays of spots or lines that characterize bulk block copolymer morphologies, or in the long term for device layouts completely redesigned into periodic arrays. Here we show that the domain structure of block copolymers in thin films can be directed to assemble into nearly the complete set of essential dense and isolated patterns as currently defined by the semiconductor industry. These results suggest that block copolymer materials, with their intrinsically advantageous self-assembling properties, may be amenable for broad application in advanced lithography, including device layouts used in existing nanomanufacturing processes

Chemical Patterns for Directed Self-Assembly of Lamellae-Forming Block Copolymers with Density Multiplication of Features

Lamellae-forming polystyrene-<i>block</i>-poly­(methyl methacrylate) (PS-<i>b</i>-PMMA) films, with bulk period <i>L</i>₀, were directed to assemble on lithographically nanopatterned surfaces. The chemical pattern was comprised of “guiding” stripes of cross-linked polystyrene (X-PS) or poly­(methyl methacrylate) (X-PMMA) mats, with width <i>W</i>, and interspatial “background” regions of a random copolymer brush of styrene and methyl methacrylate (P­(S-<i>r</i>-MMA)). The fraction of styrene (<i>f</i>) in the brush was varied to control the chemistry of the background regions. The period of the pattern was <i>L</i>_s. After assembly, the density of the features (domains) in the block copolymer film was an integer multiple (<i>n</i>) of the density of features of the chemical pattern, where <i>n</i> = <i>L</i>_s/<i>L</i>₀. The quality of the assembled PS-<i>b</i>-PMMA films into patterns of dense lines as a function of <i>n</i>, <i>W</i>/<i>L</i>₀, and <i>f</i> was analyzed with top-down scanning electron microscopy. The most effective background chemistry for directed assembly with density multiplication corresponded to a brush chemistry (<i>f</i>) that minimized the interfacial energy between the background regions and the composition of the film overlying the background regions. The three-dimensional structure of the domains within the film was investigated using cross-sectional SEM and Monte Carlo simulations of a coarse-grained model and was found most closely to resemble perpendicularly oriented lamellae when <i>W</i>/<i>L</i>₀ ∼ 0.5–0.6. Directed self-assembly with density multiplication (<i>n</i> = 4) and <i>W</i>/<i>L</i>₀ = 1 or 1.5 yields pattern of high quality, parallel linear structures on the top surface of the assembled films, but complex, three-dimensional structures within the film