Directed Assembly of Lamellae Forming Block Copolymer Thin Films near the Order-Disorder Transition*

The impact of thin film confinement on the ordering of a lamellar morphology was investigated using partially epoxidized poly(styrene-$b$-isoprene) diblock copolymers bound by non-preferential wetting interfaces. Even in the 2-dimensional limit (\textless L\textgreater $\to $ L$_{0}$, where \textless L\textgreater and L$_{0}$ denote the average film thickness and the periodicity, respectively), the composition fluctuations are observed at the crossover from the ordered to the disordered states, establishing the order-disorder transition temperature (T$_{ODT})$ in thin films. While the minimum feature size of block copolymers achievable for nanolithography is set effectively by the T$_{ODT}$, the dimensionality reduction leaves the T$_{ODT}$ unaffected compared to the bulk limit within experimental error. Directed self-assembly with the half pitch (L$_{0}$/2) \textless 8 nm has been accomplished using chemical patterning near T$_{ODT}$.