Gyroidal Thin Films from Block Copolymer Self-Assembly as Structural Directing Templates for Fabrication of Mesostructured Crystalline Inorganic Materials*

Amphiphilic block copolymers swelled by carbon precursors self-assemble into bicontinuous gyroid mesophases (space group 214) compressed along <110> on Si wafers upon quenching after solvent vapor annealing. After pyrolysis in inert atmosphere, the resulting textured, mesoporous, and gyroidal carbon thin films are backfilled with amorphous Si (a-Si). The poor tolerance of carbon toward high temperature in air and the high melting points of inorganic materials present a seemingly insurmountable challenge in preparing crystalline mesostructured Si in the carbon templates. The stability of the carbon templates is significantly enhanced, however, when employing nanosecond transient laser heating. Melting and recrystallization of Si (a-Si melting point ~1250 °C) during this ultrafast, highly non-equilibrium process allow conformal template backfilling so that the templates' mesostructural order is inherited by the crystalized Si, which otherwise has little access to mesoscale ordering. Non-equilibrium transient laser technology in conjunction with block copolymer self-assembly in thin films opens up opportunities in fabricating materials for applications in catalysis, photonics, and beyond.