Ordered Block Copolymer Thin Films Studied by Guided-Wave Depolarized Light Scattering

Polytechnic University Of New York, Brooklyn NY

Investigators

Abstract

TECHNICAL EXPLANATION This proposal seeks funds to continue the development of a novel analytical technique for characterizing the organization of anisotropic nanostructures (e.g. lamellae and cylinders) in optically transparent block copolymer thin films. Quantitative measurement of organization is critical for many proposed applications of nanotechnology, ranging from fuel cells to optoelectronic devices. GWDLS allows the low-cost, non-destructive, realtime measurement of order formation and defect density in optically transparent thin films. Among methods for thin-film characterization, GWDLS is unique in that it provides an average measure of defect density over macroscopic length scales (~1 cm) in a film. Position-space methods for studying defect structure, such as atomic force microscopy (AFM) and scanning electron microscopy (SEM), can measure local defect structure, but are impractical for obtaining statistical averages over macroscopic regions. The GWDLS technique involves the coupling of a laser beam into a guided mode of a planar optical waveguide consisting of a block copolymer film deposited on a low refractive index substrate. Light coupled into a guided mode propagates through the film by total internal reflection. As the light interacts with anisotropic grains in the film, it generates depolarized scattered light which propagates in guided modes with orthogonal polarization. This scattered light is coupled out of the film and detected. In the proposed work, we will (1) Modify the current GWDLS apparatus to study the propagation of polarized light in a symmetric silica-polymer-silica sample environment using a grating coupler. (2) Develop a theoretical model for quantifying the relationship between the GWDLS signal and statistical properties of randomly oriented and partially oriented grains in thin films. (3) Use GWDLS to determine the order-disorder transition temperature of block copolymer thin films with both lamellar and cylindrical order. (4) Measure the kinetics of order formation in thin films after quenching from the disordered to the ordered state. (5) Obtain a quantitative measure of the average grain size by comparing the measured signal with theoretical predictions. All of the polymers and substrates required for the project will be prepared by the students. Complete characterization of the films using complementary techniques such as AFM, SEM, and SIMS will be carried out. NON-TECHNICAL EXPLANATION Balsara will serve as a faculty instructor in the Math and Science Summer Academy which brings approximately 60 students from local high schools to the University campus to participate in a six-week enrichment program in math and science. Typically half of the participants are African American, one quarter Chicano, and the remaining quarter Asian, Caucasian, Filipino and Latino. Garetz will continue his 7-year involvement with Polytechnic University's David Packard Center for Technology and Educational Alliances. His activities include conducting workshops at the New York City Science/Technology Forum where 500 students from New York City public schools come to Poly for a full-day program where they meet outstanding engineers and technologists representing centers of higher education, hospitals, and corporations. The graduate students working on this project will receive multidisciplinary scientific training encompassing synthesis and characterization of polymers, optics, lithography, and nonequilibrium thermodynamics. Their background in characterization and manipulating nanostructured thin films is relevant for current and future technologies.