AVS 60th International Symposium and Exhibition
    Atom Probe Tomography Focus Topic Tuesday Sessions
       Session AP+AS+SS-TuA

Paper AP+AS+SS-TuA10
Space Charge Effects in Atom Probe tomography

Tuesday, October 29, 2013, 5:00 pm, Room 203 A

Session: Microstructural and Interface Analysis of Metals Subjected to Various Conditions
Presenter: I. Blum, Groupe de Physique des Matériaux, France
Authors: I. Blum, Groupe de Physique des Matériaux, France
F. Vurpillot, Groupe de Physique des Matériaux, France
L. Rigutti, Groupe de Physique des Matériaux, France
A. Gaillard, Groupe de Physique des Matériaux, France
D. Shinde, Groupe de Physique des Matériaux, France
J. Houard, Groupe de Physique des Matériaux, France
A. Vella, Groupe de Physique des Matériaux, France
B. Deconihout, Groupe de Physique des Matériaux, France
Correspondent: Click to Email
Because of the relatively low ion currents observed during an APT analysis (0.1 to 0.0001 atom/pulse), it is generally assumed that the evaporated ions do not interact with each other during the field evaporation of the sample. It was shown recently, however, that ion-ion interactions do occur after dissociation of molecular ions [1], which can be observed during the analysis of compound semiconductors [1-2]. Indeed, coulomb repulsion between the dissociation products modifies their trajectory in a manner similar to space charge effects in high intensity beams of charged particles.

In this work, we combine the information on the time-of-flight and impact positions on the detector of multiple events to study this phenomenon. Experimental results on GaN and ZnO samples are explained by taking into account the orientation of the molecule during dissociation, the shape of the electric field around the tip and the dissociation potential. We show that the coulomb repulsion between the dissociation products occurs in a direction of space that depends on the orientation of the molecule during dissociation. Therefore, the coulomb interactions can have a significant effect on their impact positions on the detector but can also have an effect on the time-of-flight of the particles. The times-of-flight and impact positions of the dissociation products are correlated and contain potential information about the physics of the dissociation of the original molecule in high electric field. These results are compared to simple simulations of the ions trajectories in the electric field. We also discuss the potential effect of this phenomenon on the quality of APT data and provide simple methods for its identification.

[1] M. Müller, B. Gault, G. D. W. Smith, and C. R. M. Grovenor, “Accuracy of pulsed laser atom probe tomography for compound semiconductor analysis,” Journal of Physics: Conference Series, vol. 326, p. 012031, Nov. 2011.

[2] D. W. Saxey, “Correlated ion analysis and the interpretation of atom probe mass spectra.,” Ultramicroscopy, vol. 111, no. 6, pp. 473–479, May 2011.