Vertically aligned carbon nanotubes (va-CNTs) in an array structure on a metallic surface have proved to be excellent field emission cathodes due to their high geometric field enhancement factor. In this study, coupling the experiment with numerical simulations, the authors revisited the field emission behavior and lifetime of these va-CNT based cathodes for two configurations, one is an array of individual va-CNTs and the other is an array of isolated tufts of va-CNTs. They conclude that arrays of isolated tufts are the most advantageous spatial configuration for field emission cathodes working in aggressive environment in particular, for the cathode field emission lifetime at increased by a factor of 5-10. (c) 2007 American Vacuum Society.