Time-Resolved Analysis of Domain Growth and Alignment of Cylinder-Forming Block Copolymers Confined within Nanopatterned Substrates

Abstract

In this Letter, we elucidate the microstructure evolution of asymmetric poly(styrene-b-methyl methacrylate), PS-b-PMMA, block copolymer confined within nanoscale linear channels on silicon nitride substrates. We have directly observed the mechanism for cylinder alignment within the nanochannels using time-resolved AFM imaging and computerized image analysis. The overall alignment occurs via the coarsening of grains that have preferred cylinder orientation along the channel direction and is energetically driven by the interface energies of adjacent diblock domains of differing orientation. Grain coarsening is strongly affected by the annealing temperature and the geometry of the grain boundary itself. Grain coarsening promptly occurs when a domain is bordered by adjacent high-angle grain boundaries. The energetic term that drives this process arises from the fact that high-angle grain boundaries with larger excess energy migrate faster than other lower-angle grain boundaries. The velocity of grain boundary migration is proportional to the boundary tilt angle, while the activation energy depends weakly on this angle.