Investigation of a Reversible Apex Topography in Core/Shell Field Emitters

In atom probe tomography, nonhemispherical specimen apex topographies lead to a varying local magnification. This induces the distorted imaging of features and potential errors in the measured composition. In this paper, we systematically investigate the local magnification in Si-core and VOx-shell specimens: the magnification of the core increases with increasing DC-voltage and a decreasing laser pulse energy, which was shown to be reversible. Here, both the DC-voltage and the laser pulse energy were shown to contribute independently to the change in local magnification. Using atomic force microscopy, the changing magnification of the core was attributed to a change in the apex topography from a protrusion to a concavity in the center of the specimen. Two-dimensional field evaporation simulations were used to establish a link between the apex topography, the local magnification and (local) fields of evaporation. The observed apex topographies could be explained by silicon behaving as a low-field material for one experimental condition while behaving as a high-field material for another experimental condition.