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New constraints on electron-beam induced halogen migration in apatite

Stock, M.J.; Humphreys, M.C.S.; Smith, V.C.; Johnson, R.D.; Pyle, D.M.; EIMF

New constraints on electron-beam induced halogen migration in apatite Thumbnail


M.J. Stock

V.C. Smith

R.D. Johnson

D.M. Pyle



Fluorine and chlorine X-ray count rates are known to vary significantly during electron probe microanalysis (EPMA) of apatite. Since the rate, timing, and magnitude of this variation are a function of apatite orientation and composition, as well as EPMA operating conditions, this represents a significant problem for volatile element analysis in apatite. Although the effect is thought to be an intrinsic crystallographic response to electron-beam exposure, the mechanisms and causes of the count rate variability remain unclear. We tackle this by examining directly the effects of electron-beam exposure on apatite, by performing secondary ion mass spectrometry (SIMS) depth profiles of points previously subject to electron-beam irradiation. During irradiation of fluorapatite, oriented with the c-axis parallel to the electron beam, halogens become progressively concentrated at the sample surface, even under a relatively low power (15 nA, 10–15 kV) beam. This surface enrichment corresponds to an observed increase in EPMA FKα X-ray count rates. After prolonged irradiation, the surface region starts to lose halogens and becomes progressively depleted, corresponding with a drop in EPMA count rates. Under normal EPMA operating conditions there is no halogen redistribution in fluorapatite oriented with the c-axis perpendicular to the electron beam, or in chlorapatite. We infer that anionic enrichment results from the migration of halogens away from a center of charge build-up caused by the implantation of electrons from the EPMA beam, assisted by the thermal gradient induced by electron-matter interactions. The process of surface enrichment is best explained by halogen migration through interstitial crystallographic sites in the c-axis channel. This suggests that once the thermal and electric fields are removed, halogens may relax back to their original positions on very long timescales or with sample heating.


Stock, M., Humphreys, M., Smith, V., Johnson, R., Pyle, D., & EIMF. (2015). New constraints on electron-beam induced halogen migration in apatite. American Mineralogist, 100(1), 281-293.

Journal Article Type Article
Acceptance Date Jul 15, 2014
Online Publication Date Dec 23, 2014
Publication Date Jan 1, 2015
Deposit Date Jul 16, 2014
Publicly Available Date Dec 1, 2014
Journal American Mineralogist
Print ISSN 0003-004X
Publisher Mineralogical Society of America
Peer Reviewed Peer Reviewed
Volume 100
Issue 1
Pages 281-293
Keywords Apatite, Electron-probe microanalysis, Secondary ion mass spectrometry, Halogen migration, Beam damage.


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