Self-Organized Swelling of a Metal-Capped Polymer Thin Bilayer
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Self-Organized Swelling of a Metal-Capped Polymer Thin Bilayer S. Joon Kwon, and Jae-Gwan Park Nano Science and Technology Division, Korea Institute of Science and Technology, Hawolkok-Dong, Seongbuk-Gu, Seoul, 130-650, Korea, Republic of ABSTRACT Self-organized swelling of a metal-polymer bilayer directed by a corrugated mold was reported. The corrugated pattern by the elastomeric mold was observed from the earlier stages of swelling. The temporal evolution of the self-organized pattern was analyzed theoretically, and the experimental data were well matched with the analysis. The maximum harmonic number for the corrugated wave number was also analyzed. With a relatively large line width, irregular self-organized patterns were observed. INTRODUCTION The use of external confinement to control the intrinsic patterns of a thin film has interesting effect on micro- and nano-patterning. In a metal-polymer thin bilayer, wrinkle can be controlled to form regular micro patterns.[1] The swelling can be self-organized by the external confinement. The periodicity and morphological dynamics of the self-organized swelling wave depends on the geometry of the external confinement and dynamics of the wavelength of the intrinsic swelling wave. In the present study, we report on the swellinginduced self-organized patterns in a metal-polymer thin bilayer. EXPERIMENTAL DETAILS The bilayer was composed of aluminum (Al)-capped novolak (NV) epoxy resin with a curing agent. The NV-curing agent mixture was dissolved in ethanol and spin coated to prepare NV thin film on a Si substrate, followed by the thermal evaporation of the Al. The polymer layer was annealed at 60o C for 30 min prior to the thermal evaporation of the metal film. The bilayer was placed on a pedestal in a sealed reactor whose atmosphere was saturated with ethanol vapor at room temperature. Prior to the sealing, a patterned polydimethylsiloxane (PDMS) mold was placed on the metal film. The resulting surface patterns were examined by atomic force microscope (AFM). Schematic experimental procedure was illustrated in Figure 1(a) and 1(b).
DISCUSSION The pattern replication and the first self-organized swelling patterns An intrinsic wrinkled morphology without PDMS mold is observed (Figure 1(c)). Anisotropic swelling patterns with clear directionality and periodicity can be obtained by conformal contact of the corrugated PDMS mold, and could be directed into 1D and 2D patterns (Figure 1(c)). The replication giving rise to the 1D anisotropic pattern forms according to two sequential processes in the course of the swelling. Prior to the selforganization corrugated patterns form in the earlier times of the swelling. The periodic corrugated pattern (the first self-organization) had the same periodicity as the PDMS mold, and the shape of the corrugation is sinusoidal. These wrinkles have considerable regularity and periodicity and form on the ridge of the corrugated pattern. The wave vector of the wrinkles was perpendicular to that of the corrugated pattern, and thei
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