In an aperture for use in an ion beam optical system having its surface coated with a liquid metal, instability of an ion source attributable to sputtering and re-deposition of an aperture base material is prevented. An embodiment of the invention automatically generates configuration files from an input data flow diagram defining the ETL system. The longitudinal spacing between opposing tips of adjacent hooks of adjacent rows is greater in a first portion of the array than the longitudinal spacing between opposing tips of adjacent hooks of adjacent rows in a second portion of the array, such that the crooks of the hooks of the first portion are more exposed for engaging loops than the crooks of the hooks of the second portion.