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Dynamic Thermal Field Induced Gradient Soft-Shear for Highly Oriented Block Copolymer Thin Films
ACS Nano
  • Gurpreet Singh, The University Of Akron
  • Kevin G. Yager
  • Brian Berry
  • Ho-Cheol Kim
  • Alamgir Karim
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As demand for smaller, more powerful, and energy-efficient devices continues, conventional patterning technologies are pushing up against fundamental limits. Block copolymers (BCPs) are considered prime candidates for a potential solution via directed self-assembly of nanostructures. We introduce here a facile directed self-assembly method to rapidly fabricate unidirectionally aligned BCP nanopatterns at large scale, on rigid or flexible template-free substrates via a thermally induced dynamic gradient soft-shear field. A localized differential thermal expansion at the interface between a BCP film and a confining polydimethylsiloxane (PDMS) layer due to a dynamic thermal field imposes the gradient soft-shear field. PDMS undergoes directional expansion (along the annealing direction) in the heating zone and contracts back in the cooling zone, thus setting up a single cycle of oscillatory shear (maximum lateral shear stress ∼12 × 10(4) Pa) in the system. We successfully apply this process to create unidirectional alignment of BCP thin films over a wide range of thicknesses (nm to μm) and processing speeds (μm/s to mm/s) using both a flat and patterned PDMS layer. Grazing incidence small-angle X-ray scattering measurements show absolutely no sign of isotropic population and reveal ≥99% aligned orientational order with an angular spread Δθ(fwhm) ≤ 5° (full width at half-maximum). This method may pave the way to practical industrial use of hierarchically patterned BCP nanostructures.
Citation Information
Gurpreet Singh, Kevin G. Yager, Brian Berry, Ho-Cheol Kim, et al.. "Dynamic Thermal Field Induced Gradient Soft-Shear for Highly Oriented Block Copolymer Thin Films" ACS Nano Vol. 6 Iss. 11 (2012) p. 10335 - 10342
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