A mold developed by Cornell University researchers can shape liquid silicon out of organic polymer materials. The self-assembling organic polymers create a template dotted with precisely sized and shaped nanopores. The development could lead to exact single-crystal silicon nanostructures.
To help the polymer mold maintain its shape, the researchers heated the silicon with nanosecond-long laser pulses. At such short time scales, the silicon can be heated to a liquid; the melt duration, however, is so short that the polymer does not have time to oxidize and decompose. When the mold was etched away, the Cornell team created the well-defined silicon.
The engineers previously learned to self-assemble highly ordered, porous nanomaterials using specially structured molecules called block copolymers. A carbon dioxide laser was used to “write” the nanoporous materials onto a silicon wafer. A film, spin-coated on the wafer, contained a block copolymer, which directed the assembly of a polymer resin. Writing lines in the film with the laser, the block copolymer decomposed, acting like a positive-tone resist, while the negative-tone resin was left behind to form the porous nanostructure.
The organic templates have been used to create structures as complex as a gyroid, a periodically ordered cubic network structure.