Dissociation of GaN 2+ and AlN 2+ in APT: Analysis of experimental measurements

• Published in: The Journal of chemical physics 2018-10, Vol.149 (13), p.134311
• Main Authors: Zanuttini, D, Blum, I, di Russo, E, Rigutti, L, Vurpillot, F, Douady, J, Jacquet, E, Anglade, P-M, Gervais, B
• Format: Article
• Language: English
• Subjects: Physics
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.5037010

The use of a tip-shaped sample for the atom probe tomography technique offers the unique opportunity to analyze the dynamics of molecular ions in strong DC fields. We investigate here the stability of AlN and GaN dications emitted from an Al Ga N sample in a joint theoretical and experimental study. Despite the strong chemical resemblance of these two molecules, we observe only stable AlN , while GaN can only be observed as a transient species. We simulate the emission dynamics of these ions on field-perturbed potential energy surfaces obtained from quantum chemical calculations. We show that the dissociation is governed by two independent processes. For all bound states, a mechanical dissociation is induced by the distortion of the potential energy surface in the close vicinity of the emitting tip. In the specific case of GaN , the relatively small electric dipole of the dication in its ground 1 Σ and excited 1 Δ states induces a weak coupling with the electric field so that the mechanical dissociation into Ga + N lasts for sufficient time to be observed. By contrast, the AlN mechanical dissociation leads to Al + N which cannot be observed as a correlated event. For some deeply bound singlet excited states, the spin-orbit coupling with lower energy triplet states gives another chance of dissociation by system inter-system crossing with specific patterns observed experimentally in a correlated time of flight map.