Influence of instrument conditions on the evaporation behavior of uranium dioxide with UV laser-assisted atom probe tomography

Abstract

2016-11-02T18:49:00

Investigation of material property influenced stoichiometric deviations as evidenced during UV laser-assisted atom probe tomography in fluorite oxides

“…Laser energies greater than 10 pJ did not affect the O/U ratio, maintaining an O/U near 2.00. The optimization of run parameters for UO 2 in UV-APT are discussed in detail elsewhere [23]. For CeO 2 , the following atom probe run parameters were investigated: 20-50 K, 100-250 kHz, 2.5-120 pJ, and detection rate 0.01-0.03 atoms/pulse.…”

“…At laser energies below 5 pJ, correct stoichiometry will be measured in CeO 2 [22]. However for UO 2 , the laser energy is not sufficient to achieve laser-assisted evaporation since at 5 pJ, the evaporation of ions is primarily controlled by the DC electric field, which produces an oxygen deficient composition measurement [23]. For these reasons, a moderate laser energy of 120 pJ was selected for this comparative study.…”

“…6. Effect of laser energy on the O/M ratio in CeO 2 [22] and UO 2 [23]. Constant conditions for UO 2 : 50 K, 100 kHz, and a detection rate of 0.003 atoms/pulse.…”

“…Systematic studies of the evaporation behavior for both CeO 2 [22] and UO 2 [23] will also be used to further elucidate the findings in this study. Although it is generally presumed that the macroscopic behavior of CeO 2 is similar to UO 2 , fundamental differences in the electronic structure, optical properties, heat transfer properties, and thermodynamic stability can contribute to dissimilar ionization characteristics.…”

“…The results from Kirchhofer et al [22] indicate that the optimal evaporation behavior of CeO 2 for analysis with APT are obtained using a 1 pJ laser energy, specimen base temperature of 20 K, and a pulse repetition rate of 100 kHz. For UO 2 , it was determined that the optimal conditions for evaporation are a 10 pJ laser energy, specimen base temperature of 50 K, and a pulse repetition rate of 100 kHz [23]. Studies of CeO 2 [22], MgO [24], and Al 2 O 3 [24] with APT indicate that correct stoichiometry is only possible at low laser energies for oxides, primarily due to an increase in temperature associated with high laser energies, however, UO 2 differs in this behavior.…”