3D APT sample volume of the interface region between the ion-bombardment InP surface of a nanodot and the deposited Cr layer (upper panel). The analysis direction is from top to bottom. The colored dots represent different atoms in this sample volume: Cr (magenta), In (purple), P (orange), P3 (red), and P4 (green). In addition, an isoconcentration surface is depicted for Cr (the continuous magenta feature) which defines a volume with a Cr concentration >50% and separates the InP specimen proper and the deposited Cr layer. Also shown is a cylindrical region-of-interest (the cyan feature) which was used to derive a local concentration profile in this region (lower panel).