Figure shows a schematic of a nanopore in cross section, highlighting the important features and measurements that are made. The running depth is denoted by x, and the full depth of the nanopore from mask to bottom is denoted by x max . The diameter of the mask d mask is measured from cross-sectional SEM images. The mask undercut is how far under the mask the first etch step etches, determining the diameter of the nanopore. The initial scallops are defined as the first 10 scallops of the nanopore formed in the first 10 etch cycles.