Tapering is the increasing or decreasing of the nanopore diameter with depth. In this work a reduction of nanopore diameter with length, positive tapering, was much more common than negative tapering. This is due to our desire to have high aspect ratio pores. The longer the nanopores become, the greater the risk of positive tapering. Due to loss of ions through image force, the number of ions reaching the bottom of the pore to etch is reduced To mitigate positive tapering it is necessary to increase parameters to increase the isotropy at the end of the etch. This is achieved by increasing by increasing the amount of reactive species later in the etch process via the pressure or by increasing the etch cycle time. By definition, to remove the positive taper any change will increase the isotropy of the etch and contribute to side wall erosion as in Figure when the end etch cycle time was increased to t f 4 seconds.