Direct Imaging of Interfacial Fluctuations in Confined Block Copolymer with <i>in Situ</i> Slow-Scan-Disabled Atomic Force Microscopy.

Abstract

Using environmentally controlled, high-speed atomic force microscopy (AFM), we examine dynamic fluctuations of topographically confined poly(styrene-<i>block</i>-methyl methacrylate) (PS-<i>b</i>-PMMA) cylinders. During thermal annealing, fluctuations drive perturbations of the block copolymer (BCP) interface between polymer domains, leading to pattern roughness. Whereas previous investigations have examined roughness in room-temperature and kinetically quenched samples, we directly visualize the dynamics of PS/PMMA interfaces in real space and time at <i>in situ</i> temperatures above the glass transition temperature, <i>T</i>_g. Imaging under these experimentally challenging thermal annealing conditions is critical to understanding the inherent connection between thermal fluctuations and BCP pattern assembly. Through the use of slow-scan-disabled AFM, we dramatically improve the imaging time resolution for tracking polymer dynamics. Fluctuations increase in intensity with temperature and, at high temperatures, become spatially coherent across their confining potential. Additionally, we observe that topographic confinement suppresses fluctuations and correlations in the proximity of the guiding field. <i>In situ</i> imaging at annealing temperatures represents a significant step in capturing the dynamics of chain mobility at BCP interfaces.