Characterization of Grain Structure in Block Copolymer Thin Films by Guided-wave Depolarized Light Scattering

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The proposal describes the development of guided-wave depolarized light scattering, a novel technique for characterizing the structure of ordered block copolymer thin films. This technique will enable cost-effective, nondestructive, real-time quantification of order formation and defect density in these two-dimensional systems. A planar optical waveguide will be fabricated by depositing the polymer film on a low refractive index substrate (fused silica). Standard optical waveguide elements such as prism couplers will be used to couple the laser beam into the film and the scattered light out of the film. The depolarized scattered beam will be guided through the film and detected using a CCD camera. Considerable effort will be devoted to the development of tractable models for relating the detected optical signal to the grain structure within the film. The models that have been established for the optical properties of bulk block copolymer samples will serve as a starting point for this development. Preliminary predictions indicate that the guided-wave geometry will lead to fundamental differences in the nature of the detected signal. The grain structure determined in reciprocal space by the guided-wave depolarized light scattering studies will compared with position space data obtained by scanning electron microscopy (SEM) and atomic force microscopy (AFM) experiments on the same samples.The proposed work builds on earlier work by the co-PIs on optical characterization of grain structure in three-dimensional block copolymer samples. This information is crucial for a number of recently proposed applications for block copolymer thin films such as information storage and photonics. The proposed research will also answer fundamental questions regarding the influence of substrates and interfaces on order formation and defect annihilation in thin block copolymer films.