High-χ Poly(fluorinated methacrylate)-<i>block</i>-Poly(acetoxystyrene) Block Copolymers for Sub-5 nm Nanopatterning

Poly(pentadecafluorooctyl methacrylate)-<i>block</i>-poly(4-acetoxystyrene) (PPDFMA-<i>b</i>-P4AS) and disubstituted PPDFMA-<i>block</i>-poly(3,4-diacetoxystyrene) (PPDFMA-<i>b</i>-PDAS) were synthesized by reversible addition-fragmentation chain-transfer polymerization initiated from a PPDFMA chain-transfer agent. The strong interaction between the fluorinated block and the poly(acetoxystyrene) block resulted in minimum cylindrical domain sizes of 5.0 and 4.8 nm for PPDFMA-<i>b</i>-P4AS and PPDFMA-<i>b</i>-PDAS, with χ values of 0.34 and 0.37, respectively. Both hexagonal and lamellar domain sizes increased along with molecular weight. Thermal annealing at 160 °C led to the formation of cylindrical domains in both thin-film and bulk samples, as confirmed by scanning electron microscopy, atomic force microscopy, and small-angle X-ray scattering. When the film thickness increased from 20 to 50 nm, the parallel cylindrical domains were oriented perpendicular to the substrate. Such patterns formed directly on a silicon substrate could be used in sub-5 nm lithographic patterning. Additionally, a self-assembled thin film (could be wafer level production) of boron-doped PPDFMA-<i>b</i>-P4AS was employed as a patterned nanocomposite with 5 nm lines in a charge-storage layer in an organic field-effect transistor device, exhibiting an <i>I</i>_on/<i>I</i>_off ratio of 10⁵ and a hysteresis window of 34 V.