Direct Imaging of Interfacial Fluctuations in Confined Block Copolymer with in Situ 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-block-methyl methacrylate) (PS-b-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 in situ temperatures above the glass transition temperature, T 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. In situ imaging at annealing temperatures represents a significant step in capturing the dynamics of chain mobility at BCP interfaces.

Nanomechanical mapping of soft materials with the atomic force microscope: methods, theory and applications

“…320,321 Several viscoelastic processes on polymer blends and polymer nanocomposites have been studied by AFM phase contrast images. 322,323 The sensitivity of the phase shift signal has enabled to detect interfacial fluctuations on PS-b-PMMA, 324 to perform in situ studies of crystallization of polymers as a function of the temperature 325 or to image in realtime selfassembly processes. 326 The compatibility of AFM phaseimaging and high-speed AFM was demonstrated by imaging membrane vesicles isolated from different bacterial strains at 2 s per frame (200 Â 200 pixels).…”

Correlating polymer structure, dynamics, and function with atomic force microscopy

“…In these systems, scan rates are limited by the potential for sample damage of the heated polymer melts rather than the AFM imaging capabilities. In addition to measuring morphological evolution, high‐speed, temperature‐controlled AFM has been used to track fluctuations of the PS/PMMA interface of confined BCP cylinders in real time, shown in Figure 6 115 . Disabling of the AFM slow‐scan axis allowed for rapid sampling of one‐dimensional phase profiles to monitor equilibrium fluctuations of the interfacial boundary, sacrificing one spatial dimension for a dramatic increase in time resolution.…”

“…(C) Pearson correlation coefficient plots showing coherence in cylinder fluctuations, propagating throughout the channel for edge and placement fluctuations, and anticorrelation for width fluctuations, extending only to adjacent cylinders. Reproduced with permission from Reference 115. Copyright 2019, American Chemical Society [Color figure can be viewed at wileyonlinelibrary.com]…”

“…In addition to measuring morphological evolution, highspeed, temperature-controlled AFM has been used to track fluctuations of the PS/PMMA interface of confined BCP cylinders in real time, shown in Figure 6. 115 Disabling of the AFM slow-scan axis allowed for rapid sampling of one-dimensional phase profiles to monitor equilibrium fluctuations of the interfacial boundary, sacrificing one spatial dimension for a dramatic increase in time resolution. Fluctuations of the cylinder edges, placements, and widths were found to be spatially coherent over multiple domains due to the chain connectivity and incompressibility of the blocks and were enhanced with increasing measurement temperatures.…”

From Lab to Fab: Enabling Enhanced Control of Block Polymer Thin-Film Nanostructures

“…These approaches often combine an environment that increases chain mobility (e.g., heat or solvent) with a topological pattern, a chemical pattern, or a field. ,,− DSA has additional tunable handles for optimization, such as field strength, and the self-assembly pathways that BPs undergo may differ on the basis of the type of DSA used. As such, gradient and in situ investigations are critical to understand the underlying mechanisms of these methods and to improve their efficiency in manufacturing-related applications. , …”