All etching experiments were performed using a SPTS Pegasus reactive ion etcher in the MESA + Nanolab using C 4 F 8 as the protection gas, SF 6 as the etching gas and O 2 for plasma cleaning to remove leftover fluorocarbon from the sample surface after etching. In the protection step, a layer of insulation fluorocarbon is deposited on the substrate. In the etch step, the fluorocarbon layer is removed from the bottom of the nanopore and the silicon is etched. The steps are repeated until the desired pore length is achieved.