The directed self-assembly of block copolymers offers a highly promising approach for fabricating large-scale-ordered nanopatterns. How to design guiding patterns with facile processability has been a core issue for a long time. Line trenches have been demonstrated to effectively guide asymmetric diblock copolymers to form long-range-ordered hexagonal cylinders, yet few studies have focused on determining the parameter window for achieving defect-free hexagonal patterns. This is not only a thermodynamic equilibrium problem but also closely related to the ordering kinetics of block copolymers, posing a great challenge for both experiments and simulations. In this work, we employed large-scale dissipative particle dynamics (DPD) simulations to investigate the self-assembly of asymmetric diblock copolymers into hexagonal cylinders under the direction of line trenches, focusing on the effect of the trench width on the formation of ordered patterns. The results obtained from DPD simulations within a relatively short simulation time demonstrate that perfect hexagonal patterns can be achieved at any trench width, provided that the cylinder rows within the trenches do not exceed 5. When the rows are between 6 and 13, a small number of defects emerge at the window boundaries of adjacent rows, which can be very likely eliminated by prolonging the ordering time. In contrast, as the rows become more than 13, cylindrical grains with different orientations start to form, and the defects at grain boundaries become increasingly difficult to eliminate. It is found that the mismatched trench width together with the periodic boundary condition along the trench is a primary cause of defects. Accordingly, we added periodic inward-protruding geometries onto the trench boundaries to break the translational symmetry of the boundaries. Our simulations further demonstrate that such trench patterns can effectively lead to the formation of defect-free hexagonal patterns. Even for the pattern with 17 rows (containing 134 cylinders per period), a considerable trench width window (approximately 5–8 nm) still exists. Therefore, the periodic trenches are expected to serve as useful guiding templates for the fabrication of perfect hexagonal patterns.
Li et al. (Fri,) studied this question.