Electron-beam (5–10 keV) damage in triplite-group phosphates: Consequences for electron-microprobe analysis of fluorine
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Michel Fialin
Abstract
The FKα emission in samples of triplite-group phosphates (TGP) submitted to electron beams routinely used for electron-probe microanalysis of light elements (5-10 keV, 30 nA, 5 μm in diameter) evolves anisotropically with time. The intensity variations consist of an initial rise of the signal (time constants on the order of few tens of seconds), by up to 20.30% of the zero-time value, followed by a longer-time-constant increase or decrease. The initial signal rise is interpreted as an enhancement of the fluorescence yield of the F ions due to bond breaking. Halogen-formed lattices are known to be sensitive to radiolysis, i.e., destabilization of the atomic arrangement due to perturbations of the electronic structure induced by particle irradiation, leading often to bond breakage and lattice-ion displacements. In strongly ionic structures (alkali halides and alkaline-earth fluorides, notably), bond breakage results from the decay of metastable states in which transient molecular ions (e.g., F2- ) are formed. Molecular ions preexisting within ionic lattices under the form of halogen-halogen bonds (e.g., F0-F- bonds) are likely involved in the degradation processes under irradiation of materials such as fluoro-phosphates. High-resolution studies of the FKα emission band in TGPs reveal that lattice F ions may have an average fractional charge of .x (0.5 < x < 1, instead of x = 1 for ideally ionic lattices) consistent with the presence of F0-F- bonds.
Other longer-time-constant processes are attributed to the production of F- interstitials beneath the specimen surface that can accumulate (increasing signal) or desorb (decreasing signal) when they have enough energy to overcome the surface potential barrier. The role of the energy stored within the lattice by charging is critical to the understanding of both the anisotropy of the FKα intensity and the accumulation-desorption processes of the produced F- interstitials. Owing to the differences between specimens in (1) the effective charge of the F ions and (2) the electron-stimulated desorption (ESD) mechanisms leading to the emission of F- and F+ ions, it is concluded that standards with structural properties close to those of unknowns should be selected for accurate analysis of F in beam-sensitive minerals or glasses.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Structural model for the biogenic Mn oxide produced by Pseudomonas putida
- Electron-beam (5–10 keV) damage in triplite-group phosphates: Consequences for electron-microprobe analysis of fluorine
- Vacancy defects in MgO at high pressure
- Plastic flow of pyrope at mantle pressure and temperature
- Parvo-mangano-edenite, parvo-manganotremolite, and the solid solution between Ca and Mn2+ at the M4 site in amphiboles
- Reinvestigation of the MgSiO3 perovskite structure at high pressure
- The mechanism and kinetics of α-NiS oxidation in the temperature range 670–700°C
- Influence of charge location on 29Si NMR chemical shift of 2:1 phyllosilicates
- The size distribution of exsolution lamellae in iron-free clinopyroxene
- The high-pressure phase transformation and breakdown of MgFe2O4
- Elastic behavior, phase transition, and pressure induced structural evolution of analcime
- A new chemical etching technique for peridotites using molten anhydrous borax
- Poppiite, the V3+ end-member of the pumpellyite group: Description and crystal structure
- Cation redistribution in the octahedral sheet during diagenesis of illite-smectites from Jurassic and Cambrian oil source rock shales
- A shock-induced polymorph of anatase and rutile from the Chesapeake Bay impact structure, Virginia, U.S.A.
- Water in the interlayer region of birnessite: Importance in cation exchange and structural stability
- In situ HAFM study of the thermal dehydration on gypsum (010) surfaces
- Influence of dehydration kinetics on T-O-T bridge breaking in zeolites with framework type STI: The case of stellerite
- Estimation of volume fractions of liquid and vapor phases in fluid inclusions, and definition of inclusion shapes
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- SIMS investigation of electron-beam damage to hydrous, rhyolitic glasses: Implications for melt inclusion analysis
- Synthetic Ag-rich tourmaline: Structure and chemistry
- Genesis and compositional heterogeneity of smectites. Part III: Alteration of basic pyroclastic rocksA case study from the Troodos Ophiolite Complex, Cyprus
- Ganterite, the barium mica Ba0.5K0.5Al2(Al1.5Si2.5)O10(OH)2, from Oreana, Nevada
- Letter. Transformation of pentlandite to violarite under mild hydrothermal conditions
