Alignment and Structural Evolution of Cylinder-Forming Diblock Copolymer Thin Films in Patterned Tapered-Width Nanochannels

Abstract

Control over the orientation of cylindrical block copolymer microdomains and the position of dislocations using tapered nanochannels is herein demonstrated. Dislocations are introduced periodically as the channels become progressively wider. Our high-temperature atomic force microscopy (AFM) enables us to probe real-time and real-space dislocation movement directly. Upon annealing, dislocations are observed to move to their equilibrium positions, where the average free energy of the polymer chains reaches a minimum. Smaller confinement widths impose a powerful guiding field for templating domain alignment, as the deviations of the dislocations at the narrower end of the channel from their equilibrium positions are minimal. Finally, the fluctuations of dislocations across the wedge are studied under different temperatures, and the perpendicular diffusion coefficients and activation energy are determined. These experiments demonstrate the ability to control the placement of periodically located dislocations along tapered nanochannels, offering an efficacious route to placing defects at predetermined locations in such hierarchically assembled nanostructures. This also suggests the possibility of transporting and concentrating defect-seeking species such as nanoparticle additives into intentionally selected locations along the tapered channel.

Engineering the Kinetics of Directed Self-Assembly of Block Copolymers toward Fast and Defect-Free Assembly

“…We investigated the evolution of BCP structures during the DSA process through arrested annealing studies. Previous experimental studies on BCP kinetics used either ex situ arrested annealing , or more recently in situ high speed AFM. ,, The in situ AFM was capable of closely tracking the evolution of specific defects at a fixed location during the annealing process. However, it was difficult for the in situ AFM to capture the early stages of annealing, as the instrument required several minutes to stabilize before imaging could begin.…”

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

“…Dislocations form at regularly spaced sites where the channel width does not accommodate an integral pattern spacing, shown in Figure 4C. With in situ AFM imaging, tracking the motion of individual dislocations allows for controlled measurements of defect energetics and diffusivity 95 …”

“…Dislocations, indicated with white arrows in the AFM phase image, occur at regular intervals along the length of the channel, as shown in the plot of number of cylinder domains, N , versus the confinement width, W , in terms of equilibrium periodicity, d 0 ; the black dots represent the dislocation positions. Adapted with permission from Reference 95. Copyright 2014, American Chemical Society [Color figure can be viewed at wileyonlinelibrary.com]…”

“…With in situ AFM imaging, tracking the motion of individual dislocations allows for controlled measurements of defect energetics and diffusivity. 95 The intricate patterns produced by BCPs have inspired AFM imaging from early in its development. 96 Real-space images of BCP morphology served as direct confirmation of its structure as predicted theoretically and measured in reciprocal space through X-ray and neutron scattering experiments.…”

Sub‐5 nm Patterning by Directed Self‐Assembly of Oligo(Dimethylsiloxane) Liquid Crystal Thin Films

“…However, the lithographic processes used to produce the trenches are imperfect which results in local variations of the trench width on the order of several nanometers . Apparent defects result from confinement of the LC by trench walls with nonzero roughness, which causes bending of the line structures, in addition to a few disclinations; however, these largely limited to the edge of each channel . Given the low density of nonequilibrium defects in samples with no directing features (≈2 defects μm −2 , based on Figure and similar images), it is unlikely that such defects are present within the trenches.…”