Atom Probe Tomography: 3D Imaging at the Atomic Level

Atom probe tomography (APT) is the only approach able to map out the 3D distribution of chemical species in a material at the atomic-scale. The instrument provides quantitative measurements of local chemical composition in a small selected volume at the nm scale. The in-depth spatial resolution reaches a few tens of picometres enabling atomic layers to be imaged. The lateral resolution is however limited to a fraction of a nanometre, precluding therefore the crystal lattice to be fully reconstructed in the general case. APT has been applied to number of issues in physical metallurgy including precipitation, segregation of impurities to lattice defects, ordering, magnetic multilayers. Up to the beginning of this century, APT has been mainly limited to metals. The implementation of ultrafast laser pulses instead of high-voltage pulses to field evaporate surface atoms has now opened APT to the analysis of semi-conductors or oxides that are key materials in microelectronics. With the introduction of ion milling using Focussed Ion Beam (FIB), the instrument has now gained a key place in nanosciences. Salient results were hence recently produced on tunnel junctions, nanowires, oxides, dopant distribution in semiconductors and nano-transistors. The potential of APT as well as both limitations and future prospects will be discussed on the basis of some selected illustrations.