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Composition of uranium oxide particles related to TOF‐SIMS ion distributions
Author(s) -
Hocking Hannah E.,
Burggraf Larry W.,
Duan Xiaofeng F.,
Gardella Joseph A.,
Yatzor Brett P.,
Schuler Wesley A.
Publication year - 2013
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.5114
Subject(s) - chemistry , protonation , secondary ion mass spectrometry , ion , analytical chemistry (journal) , valence (chemistry) , uranium , oxide , mass spectrum , uranium oxide , materials science , organic chemistry , metallurgy , chromatography
Uranium oxide particles tens of micrometers in size, including natural and depleted UO 2 , U 3 O 8 , and UO 3 were analyzed using an IONTOF V time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) V. Particulate samples were mounted on gold substrates made using a novel technique that reduced hydrocarbon contamination and volatile outgassing as well as provided an internal standard of Au x ion peaks to calibrate high masses. For UO 2 surfaces, the dominant U 3 O x and U 4 O y cations were U 3 O 6 + and U 4 O 8 + , whereas for both U 3 O 8 and UO 3 surfaces, they were U 3 O 7 + and U 4 O 9 + . Secondary ion abundance ratios contained additional information about the chemical composition of the sample related to the relative stability of the cluster ions. Relative stabilities of the most stable cation isomers corresponding to masses observed in SIMS spectra were calculated using high‐level density functional theory in order to compare ion stabilities to TOF‐SIMS intensity distributions. Cation isomers having high oxygen content were doublets, and those having low oxygen content were quartet spin states. Depth profile trends for ‘protonation’ ratio and ‘lattice valence’, as defined by Plog, Wiedmann, and Benninghoven, were used to distinguish U 3 O 8 from UO 3 . Cations containing a greater number of uranium atoms were also found to have a lower protonation ratio. UO 2 and U 3 O 8 surfaces show a steeper reduction in protonation ratio compared to UO 3 surfaces which exhibit a nearly constant near‐surface protonation ratio followed by a more gradual smaller decline with depth. We interpret secondary ion distribution results using density functional quantum mechanics calculations comparing the relative stability of cations and anions for different oxygen atom environments. Copyright © 2012 John Wiley & Sons, Ltd.