To reduce positive tapering which would result from the decreased number of reactive species, we decided to increase the pressure at end of the whole etch process. In Figure the beginnings of a negative taper, widening at the bottom of the pore, is apparent, indicating that 26 mtorr is more than required to eliminate positive tapering. This negative tapering suggests that end pressure is an effective way to control both the tapering of the nanopore as well as the initial scallops.