Variations of the lamellar period in thin films of diblock copolymers by selective staining agents

Abstract

We investigated variations of the domain period of block copolymers by selective staining agents that are used for contrast enhancement in transmission electron microscopy. Employing thin films of symmetric diblock copolymers, homogeneous but selective staining was obtained throughout the film. Moreover, the thin film had a multilayered structure of parallel lamellae with the total film thickness quantized in terms of the lamellar period so that increments of the lamellar period by staining were conveniently and quantitatively evaluated as a function of staining time. In the case of a chemisorbed staining agent of osmium tetroxide for polybutadiene, the lamellar period in thin films of polystyrene-block-polybutadiene was gradually increased with staining time and had 22% increase at the saturation. Similar results were also obtained in the case of thin films of polystyrene-block-poly(methyl methacrylate) by ruthenium tetroxide and polystyrene-block-polyvinylpyridine by iodine. Cross-sectional TEM image of a thin film of symmetric diblock copolymers: 4.0L0-thick PS-PB stained by OsO4 for 3 h.