Long-range order of cylinders in diblock copolymer thin films using graphoepitaxy

Abstract

Topographically patterned substrates are known to induce long-range lateral order in spherical diblock copolymers, but it is not clear that similar confinement will also order cylindrical diblock copolymers across the whole surface. The role of graphoepitaxial parameters including trough width and mesa height on the ordering process of cylindrical domains in diblock copolymers thin films is monitored in this study. The quantification of order was achieved by the calculation of an order parameter of the hexagonally packed cylinders. These results demonstrate that graphoepitaxy is an effective method to induce long-range order in cylindrical domain diblock copolymer systems. An increase in order was observed in samples prepared on the mesas and in troughs of widths up to 20 μm, and mesa heights greater than 1.0 but less than 5.0 L 0 The role of molecular weight on the kinetics of the ordering process of cylindrical domains in diblock copolymers thin films is also monitored in this study, where ordering is readily observed for lower molecular weight copolymers (number average molecular weight, M n = 63,000), but not for larger copolymers ( M n = 230,000). The reduction of the rate of formation of long-range order is attributed to the impeded diffusion of higher molecular weight polymers. These results demonstrate that there will exist upper limits on the molecular weights of diblock copolymers that can be used to create nanoscale templates with long-range order, which also translates to an upper limit in pore size and spacing in these templates.