Electronic structure and stability of the SiO2+ dications produced in tomographic atom probe experiments

Abstract

The molecular electronic states of the SiO dication have been investigated in a joint theoretical and experimental analysis. The use of a tip-shaped sample for tomographic atom probe analysis offers the unique opportunity to produce and to analyze the lifetime of some excited states of this dication. The perturbation brought by the large electric field of the polarized tip along the ion trajectory is analyzed by means of molecular dynamics simulation. For the typical electric fields used in the experiment, the lowest energy triplet states spontaneously dissociate, while the lowest energy singlet states do not. We show that the emission process leads to the formation of some excited singlet state, which dissociates by means of spin-orbit coupling with lower-energy triplet states to produce specific patterns associated with Si + O and Si + O dissociation channels. These patterns are recorded and observed experimentally in a correlated time-of-flight map.

Absence of free carriers in silicon nanocrystals grown from phosphorus- and boron-doped silicon-rich oxide and oxynitride

“…Inevitably, this artefact also influences the exact values of the P-concentration, but since both samples are subject to the same LME the comparison discussed above is not influenced. Besides LME there are also other factors influencing the precision and resolution of APT such as inhomogeneous tip shape evolution during the measurement [ 31 ], delayed dissociation of molecules during the flight [ 32 ], and associated problems with the detection of neutral fragments [ 33 ]. Still, APT provides unique and very useful data inaccessible by any other method.…”

Compositional accuracy of atom probe tomography measurements in GaN: Impact of experimental parameters and multiple evaporation events

“…This angle is defined as the orientation of the GaN 2 + molecule axis with respect to the electric field upon dissociation. At α d = 0 °the N is toward the detector, while α d = 180 °corresponds to the Ga toward the detector [9,10] . The simulation has taken into account the conditions at which experimental data were collected: the tip geometry, the electric field conditions around the tip and the configuration of the analysis chamber.…”

“…In the case of GaN, the reactions GaN 2 + → Ga 2 + + N and GaN + → Ga + + N represent the most interesting candidates for a theoretical study. It must be underlined, in fact, that differently to the case of dissociation reactions producing neutral fragments in SiO x [10] , these specific reactions would not leave a trace in atom probe data, and their possible occurrence should be investigated with dedicated theoretical tools.…”

“…The mechanisms that promote both formation and dissociation of molecular ions are not well understood: experiments show at least that non-dissociated group-V molecular ions are more abundant at low field conditions [1,8] . Furthermore, theory shows that dissociation can be promoted by the high electric field surrounding the tip and/or by the fact that molecules can leave the tip in an excited state [9,10] . Moreover, dissociation processes and correlated evaporation can lead to intrinsic detection issues (pile-up effect), which reduce the probability of detecting certain ions [8,11] .…”

Potential sources of compositional inaccuracy in the atom probe tomography of InxGa1-xAs

“…This again may lead to quantification errors due to ion pile-up effects [15] at the detector. Dissociation may even result in neutral fragments [24], [26], [27], which are not always detected. Theoretically predicting whether the production of neutrals rather than charged fragments is more favorable during dissociation, in the presence of a high DC field, entails a dedicated study for each material/molecular-ion, which is a non-trivial process [27]- [29].…”