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

Abstract : 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 AlN2+ and GaN2+ dications emitted from an Al0.25Ga0.75N sample in a joint theoretical and experimental study. Despite the strong chemical resemblance of these two molecules, we observe only stable AlN2+, while GaN2+ 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 GaN2+, the relatively small electric dipole of the dication in its ground 13Σ− and excited 11Δ 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 AlN2+ mechanical dissociation leads to Al2+ + 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. See also: The Journal of Chemical Physics 149 (13), 134310 (2018)
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https://hal.archives-ouvertes.fr/hal-02061762
Contributor : Etienne Talbot <>
Submitted on : Friday, March 8, 2019 - 12:36:48 PM
Last modification on : Monday, May 20, 2019 - 3:50:04 PM

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D. Zanuttini, I. Blum, E. Di Russo, L. Rigutti, F. Vurpillot, et al.. Dissociation of GaN 2+ and AlN 2+ in APT: Analysis of experimental measurements. Journal of Chemical Physics, American Institute of Physics, 2018, 149 (13), pp.134311. ⟨10.1063/1.5037010⟩. ⟨hal-02061762⟩

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