Issue |
Eur. Phys. J. AP
Volume 14, Number 3, June 2001
|
|
---|---|---|
Page(s) | 199 - 231 | |
Section | Instrumentation and Metrology | |
DOI | https://doi.org/10.1051/epjap:2001160 | |
Published online | 15 June 2001 |
https://doi.org/10.1051/epjap:2001160
Precise in situ measurements of isotopic abundances with pulse counting of sputtered ions
Laboratoire de Physique des Solides, Bât. 510, Université Paris-Sud, 91405 Orsay, France
Corresponding author: slodzian@lps.u-psud.fr
Received:
12
October
2000
Accepted:
26
March
2001
Published online: 15 June 2001
Ion counting with an electron multiplier (EM) is necessary when sputtered ions are
used for in situ and precise isotopic abundance measurements (10−4
)
on small sample volume (about 100 μm3 for pure silicon). Measurements were performed
on silicon samples bombarded with Cs+ ions by extracting negative secondary monatomic
Si− ions. Pulse-height distributions (PHD) and isotopic ratios were used as diagnostic
tools for repeatability studies. Repeatability could be greatly improved by determining the
optimal position of the impact area on the conversion dynode and by addressing each isotopic
beam properly focused on this area (adaptive optics). A simplified model based on Poisson's
laws was developed to fit PHDs and allowed us to calculate quantum detection efficiencies
versus thresholds. EM isotopic discriminations were determined with the resulting semiempirical algorithm so as to reconstruct the lost information and get data independent of threshold setting. To reach consistent results, quasi-simultaneous arrivals (QSA) on the conversion dynode had to be assumed and modelled using direct ionisation yields Si−/ Cs+ at different collection efficiencies. The QSA corrected data fitted well on the terrestrial isotopic fractionation line. Dead time uncertainties and possible emission non-linear isotopic fractionation processes were examined. PHDs from other elements and polyatomic ions were also discussed.
PACS: 07.77.Ka – Charged-particle beam sources and detectors / 79.20.Hx – Electron impact: secondary emission / 91.65.Dt – Isotopic composition/chemistry
© EDP Sciences, 2001
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.