Fabrication of Gas Field Ion Emitter by Field Induced Oxygen Etching Method

Abstract

Focused ion beam system with a liquid metal ion source has a serious problem which is the pollution of samples due to irradiated ion species. To solve the problem, we have developed a noble gas field ion source which scarcely gives rise to the pollution. In this case, a key issue for the field-ion emitter is the shape of tip-apex to obtain a higher angular current density. Better performance is expected for a shape of tip-apex having a nanoscale-protrusion on the emitter tip with large radius of curvature. For realization of such a shape of tip-apex, field-induced oxygen etching method, which was reported by Onoda et al., was modified and applied to a sharpened tungsten wire which was electrolitically polished. Observation of formed emitter tips by transmission electron microscopy revealed that a nanoprotrusion having a shape of truncated cone with ∼5 nm in diameter and ∼4 nm in height was formed at the center of an emitter tip with ∼90 nm in radius of curvature. [DOI: 10.1380/ejssnt.2011.344]