Field ion microscopy, often referred to as FIM, provides atomic-resolution imaging of the surface of a specimen. A rare gas, called the imaging-gas, is introduced in the vicinity of a positively charged sharp needle. The electric field at the apex of the specimen is of the order of 1010 V m–1. Gas atoms are ionised very close to the tip surface and subsequently accelerated away by the intense electric field. The image that is formed by the impact of these gas ions onto a phosphor screen maps the distribution of the electric field at the surface, which is intrinsically related to the local topography of the tip [1, 2]. The specimen is maintained at an extremely low temperature (5–80 K) to optimise the spatial resolution, which is high enough to provide direct imaging of individual surface atoms.
