Nanoimprinting-induced molecular orientation in poly(3-hexylthiophene) nanogratings and its extraordinary retention after thermal annealing
Nanoimprinting has been widely explored not only to simply fabricate topographical nanostructures, but also to induce preferential molecule orientations of conjugated polymer films. We demonstrate here that poly(3-hexylthiophene) (P3HT) film with a nanograting topography can be fabricated very readily by a simple and cost-effective solvent-assisted room-temperature nanoimprinting lithography (SART-NIL) method. Grazing incidence wide angle X-ray diffraction (GIWAXD) is employed to determine the molecular orientation transition from edge-on to face-on alignment in the nanograting P3HT film. Furthermore, variation of the thermal annealing temperature from 23 °C to 150 °C verifies that the highly ordered nanostructure morphology of the nanograting film nearly vanishes at elevated annealing temperatures; however, the nanoimprint-induced face-on molecule orientation is remarkably well retained within the distorted nanograting film. Surprisingly, the crystallization degree of the face-on alignment increases steadily and independently after thermal annealing.