Roles of chemical pattern period and film thickness in directed self-assembly of diblock copolymers

Abstract

We develop a new numerical self-consistent field theory (SCFT) scheme for examining thin film nanostructures of cylinder-forming AB diblock copolymers on a chemically patterned substrate. Using this, we make a systematic analysis to achieve a fundamental understanding of the model system, and the conditions to create various novel film morphologies are scrutinized by varying the pattern period and film thickness. At a fixed pattern period, eight candidate phases which are divided into two groups according to the film thickness are found, and then their free energies are compared to identify the stable morphology. Among the thinner film morphologies, a crossed cylinder geometry is found to be stable with a comfortable margin. While for the thicker film morphologies, the stability of the phases depends strongly on both the pattern period and film thickness. In addition, we identify an unstable phase capable of thinning the films and consequently providing instability for the ordering of the thicker film nanostructures. A qualitative agreement is found between our theory and previously reported experimental results.

Directed self-assembly of cylinder-forming diblock copolymers on sparse chemical patterns

“…2 View Article Online target morphologies of the 1HnV phase (n = 1, 2, 3 and 4) at the parameter set which minimizes the free energy for the given morphology. 42 In the most preferable period, we get L 1H1V It is interesting that for each 1HnV phase, many similar morphologies are found which we may collectively call a 1HnV family, and the difference between each member of the family is mainly the relative position of vertical cylinders across the horizontal hemicylinder. This is in agreement with the experimental results, 40,44,47 and the case for 1H1V was intensely analyzed in the previous simulation.…”

“…For the actual evaluation of the modified diffusion equation, we use a real space SCFT method improved by Yang et al, 42 which is known to eliminate the material conservation problem found in most real space methods. Although Z i (x,y) can accommodate any two dimensional pattern, the stripe geometry treated in this work makes it only a function of x.…”

“…For these morphologies, on the A-preferable stripes, horizontal hemicylinders are always stuck to the stripe, while in the neutral region, the given number and shape of vertical cylinder arrays are formed. 42 where only 1H1V was studied and the A-preferable stripe covers 30% of the substrate). 42 In the most preferable period, we get L 1H1V It is interesting that for each 1HnV phase, many similar morphologies are found which we may collectively call a 1HnV family, and the difference between each member of the family is mainly the relative position of vertical cylinders across the horizontal hemicylinder.…”

“…For instance, combining self-consistent field theory (SCFT) and dissipative particle dynamics simulation, Kriksin et al 48 studied the thin films of cylinder-forming block copolymers deposited on various substrates including sparse hexagonal, rectangular and triangular patterns. Yang et al, 42 including two authors of this report, examined thin film nanostructures of cylinder-forming AB diblock copolymers on a chemically patterned substrate using a developed SCFT scheme. It was also shown that the surface control over the ordering and the orientation of the hexagonal phase was regulated by the degree of commensurability between polymers and substrate patterning as well as by the affinity between the minority domains and the pattern.…”

“…Yang et al, 42 including two authors of this report, examined thin film nanostructures of cylinder-forming AB diblock copolymers on a chemically patterned substrate using a developed SCFT scheme. 42 In this report, to proceed further, we report a systematic investigation of the complex nanostructures of cylinder-forming diblock copolymer films deposited on substrates with sparse chemical stripe patterns. These results provided a good explanation for the experiments in ref.…”