Non-equilibrium laser annealing derived mesostructured silicon templated in mesoporous thin film network structures from block copolymer self-assembly*

Block copolymer self-assembly derived network structures are combined with non-equilibrium transient laser heating to serve as nanotemplates for directing structures of inorganic materials, which otherwise are difficult to achieve mesoscale order. Amphiphilic block copolymers swelled by carbon precursors self-assemble into equilibrium bicontinuous gyroid phases via solvent vapor annealing. After pyrolysis in nitrogen, the resulting mesoporous 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 an enormous challenge in preparing crystalline mesostructured Si in the carbon templates. The carbon templates' stability is significantly enhanced, however, using nanosecond laser heating. Melting and recrystallization of Si (a-Si melts at ~1250 °C) during this ultrafast, highly non-equilibrium process allow conformal template backfilling so that crystallized Si inherits the templates' mesostructural order. Such non-equilibrium nanostructure formation approaches in conjunction with equilibrium self-assembly process open up opportunities for novel materials in catalysis and photonics.