Real-Time Atomic Force Microscopy Imaging of Block Copolymer Directed Self Assembly

Area of Science:

• Materials Science
• Polymer Science
• Nanotechnology

Background:

• Directed self-assembly (DSA) of block copolymers is key for creating ordered nanostructures.
• Chemically patterned templates guide self-assembly but kinetic control remains challenging for applications.

Purpose of the Study:

• To investigate the kinetics and mechanisms of directed self-assembly of symmetric PS-b-PMMA diblock copolymers on chemically patterned substrates.
• To understand the role of a unique metastable morphology in pattern evolution and alignment.

Main Methods:

• In situ thermal annealing combined with high-speed, environmentally controlled atomic force microscopy (AFM).
• Real-time tracking of microdomain evolution and defect healing mechanisms.

Main Results:

• A novel metastable "stitch" morphology was identified, mediating pattern alignment.
• Anisotropic conversion mechanisms from the stitch morphology to equilibrium lamellar stripes were observed.
• The process followed exponential kinetics with a high energetic barrier (360 ± 80 kJ/mol), enhanced compared to unpatterned substrates.
• Morphological ordering and lamellar alignment were found to be irreversible under the chemical guiding field.

Conclusions:

• The "stitch" morphology is critical for achieving well-aligned patterns in directed self-assembly on chemical templates.
• Understanding these kinetic pathways allows for optimization of defect-free nanostructures for advanced applications.
• The irreversible nature of the ordering highlights the effectiveness of chemical guiding fields in controlling block copolymer self-assembly.