Interstellar dust laser explorer: A new instrument for elemental and isotopic analysis and imaging of interstellar and interplanetary dust

Abstract

We present the performance characteristics of a time-of-flight secondary ion mass spectrometer designed for 157 nm laser postionization of sputtered neutrals for high sensitivity elemental and isotopic analyses. The instrument was built with the aim of analyzing rare element abundances in micron to submicron samples such as interstellar grains and cometary dust. Relative sensitivity factors have been determined for secondary ion mass spectrometry which show an exponential dependency against the first ionization potential. This allows elemental abundances to be measured with errors below 25% for most major elements. The accuracy for isotope ratios, where isotopes can be resolved from isobaric interferences, is usually limited only by counting statistics. In laser secondary neutral mass spectrometry, the spatial and temporal overlaps between the laser and sputtered neutral atoms are modeled and predictions of total detection efficiency and isotopic and elemental fractionation are compared with experimental data. Relative sensitivity factors for laser-ionized secondary neutrals from a stainless steel standard are found to vary less than 3% above saturation laser pulse energy enabling more accurate quantification.

Reactions of the feldspar surface with metal ions: Sorption of Pb(II), U(VI) and Np(V), and surface analytical studies of reaction with Pb(II) and U(VI)

“…6 as a function of estimated depth in nm (Jochum et al, 2000;Henkel et al, 2007). At pH 2, the U concentration relative to Si decreased steadily with depth.…”

“…A custom-built TOF-SIMS instrument was used (Henkel et al, 2006(Henkel et al, , 2007based upon Braun et al, 1998). Twenty-five kilo electron volt Ga + ions were used to sputter the surface and secondary ions were accepted from an area of $30 lm · 30 lm from within the sputtered area to avoid crater edge effects.…”

“…Secondary ions were mass analysed with sufficient mass resolution (m/Dm $ 2000 at 50% peak height) to detect 238 U + and 238 UO + unambiguously using a set of prepared silicate glass standards (Jochum et al, 2000). Sputtering depths were estimated from known sputtering rates of similar materials (Henkel et al, 2007) and the depth resolution provided by the high energy Ga + primary ion beam was $10 nm since the high energy Ga + ions implant up to this depth and mix the surface layers, and any forward sputtering will also occur only over a comparable depth range.…”

Trace element depth profiles in presolar silicon carbide grains

“…These instruments are based upon the designs of Braun et al. (1998) and previous versions have been described elsewhere by Henkel et al. (2006, 2007b).…”

“…2007). Isotopic ratios were corrected for instrumental mass fractionation using an average of multiple analyses of silicate standards made by Henkel et al. (2007b).…”