Sub-50nm nanopore membrane based on patterned self-assembly monolayer of nanospheres

In this paper, we report a simple method to fabricate a patterned ultrathin metal membrane with hexagonally arrayed sub-50 nm nanopores based on hydrophilicity-templated self-assembly of polystyrene nanospheres. The formation of patterned self-assembly monolayer (SAM) and the nanosphere lithography (NSL) process are two main steps in this approach. The different parts of substrate surface, defined by conventional photolithography, are firstly modified to be hydrophilic or hydrophobic. Via evaporation-induced self-assembly, the hexagonally close-packed SAM of polystyrene nanospheres is deposited in the hydrophilic area. Afterward, the arrayed nanopores are transferred from SAM to the metal membrane in the defined area by NSL. In the end, parylene is deposited conformally to reduce the pore size further. The membrane thickness, depending on the physical vapor deposition process and the metal robustness, is as thin as tens of nanometers. The spatial periods of nanopores are changeable and can vary from hundreds of nanometers to several micrometers, determined by the original particle diameters. Above all, the nanopore size, which can be decreased to sub-50 nm, depends to a great extent on the diameter of shrunk nanospheres and can be reduced further by uniform coating of parylene. All these crucial parameters in practical applications are controllable in this method.