  We propose a direct self-assembly mechanism towards obtaining defect-free
perpendicular lamellar phases of diblock copolymer (BCP) thin films. In our
numerical study, a thin BCP film having a flat top surface is casted on a
uni-directional corrugated solid substrate. The substrate is treated chemically
and has a weak preference toward one of the two BCP components. Employing
self-consistent field theory (SCFT), we find that there is an enhanced synergy
between two substrate characteristics: its topography (geometrical roughness)
combined with a weak surface preference. This synergy produces the desired
perpendicular lamellar phase with perfect inplane ordering. Defect-free BCP
lamellar phases are reproducible for several random initial states, and are
obtained for a range of substrate roughness and chemical characteristics, even
for a uni-directional multi-mode substrate roughness. Our theoretical study
suggests possible experiments that will explore the interplay between
uni-directional substrate corrugation and chemical surface treatment. It may
lead to viable and economical ways of obtaining BCP films with defect-free
lateral alignment.
