Fabrication of nanopores in polymer foils with surfactant-controlled longitudinal profiles

We present a surfactant-controlled etching method which allows the production of asymmetric track-etched nanopore membranes with diode-like ionic conductivity. The asymmetry of the pores is provided by self-assembly of amphiphilic molecules at the pore entrances on one side of the membrane during chemical etching while this process is excluded on the other side. By varying the alkali concentration in the etchant, control over the pore profile is achieved. The pore geometry is characterized in detail using field-emission scanning electron microscopy. The method is equally applicable to membranes with many and with single pores and may constitute an alternative to existing methods of production of resistive-pulse sensors.