Perforated, freely suspended layer-by-layer nanoscale membranes.

Ultrathin, perforated, and freely suspended membranes with uniform nanopores in the range of tens of nanometers have been fabricated using a fast, simple method of spin-assisted layer-by-layer assembly on hydrophobic substrates. Membranes with thicknesses down to 20 nm were robust enough to be released from the sacrificial substrates, transferred onto various surfaces, and suspended over microscopic openings. The nanopore size can be controlled by tuning the number of polyelectrolyte bilayers, spinning speed, and a proper selection of hydrophobic substrates. We demonstrate that the formation of nanopores is caused by the partial dewetting of polyelectrolyte layers in the course of their deposition on the underlying hydrophobic surfaces. The nanoscale thickness of perforated membranes with relatively uniform size and a high concentration of nanopores provides perspectives for higher rates of transport through freely suspended LbL membranes. The highly perforated LbL membranes introduced here can serve as a novel platform for ultrafine separation considering an intriguing combination of nanopores, nanoscale membrane thickness, and easy functionalization.