A Pathway Toward Sub-10 nm Surface Nanostructures Utilizing Block Copolymer Crystallization Control

It is elucidated how crystallization can be used to create lateral surface nanostructures in a size regime toward sub-10 nm using molecular self-assembly of short chain crystallizable block copolymers (BCP) and assist in overcoming the high-χ barrier for microphase separation. In this work, an amphiphilic double-crystalline polyethylene-b-polyethylene oxide (PE-b-PEO) block co-oligomer is used. A crystallization mechanism of the short-chain BCP in combination with neutral wetting of the functionalized substrate surface that permits to form edge-on, extended chain crystal lamellae with enhanced thermodynamic stability. In situ atomic force microscopy (AFM) analysis along with surface energy considerations suggest that upon cooling from the polymer melt, the PE-b-PEO first forms a segregated horizontal lamellar morphology. AFM analysis indicates that the PEO crystallization triggers a morphological transition involving a rotation of the forming extended chain crystals in edge-on orientation. Exposing their crystal side facets to the top surface permits to minimize their interfacial energy and form vertical nanostructures. Moreover, the edge-on lamellae can be macroscopically aligned by directed self-assembly (DSA), one necessity for various nanotechnological applications. It is believed that the observed mechanism to form stable edge-on lamellae can be transferred to other crystallizable short chain BCPs, providing potential pathways for sub-10 nm nanotechnology.