Combining a SIMS with AMS: Super-SIMS at DREAMS - Status of this challenging initiative

At the DREAMS (DREsden AMS) facility [1,2] we are implementing a so-called Super-SIMS (SIMS =
Secondary Ion Mass Spectrometry) device [3] for specialized applications. The system combines the spatial
resolution capability of a commercial SIMS (CAMECA IMS 7f-auto) with AMS capability, which should
suppress molecular isobars in the ion beam allowing for the quantification of elemental abundances down to
~ E-9 - E-12. This would be more than an order of magnitude improvement over traditional dynamic SIMS
(e.g. [4,5]). We aim to use this for the highly sensitive analysis of geological samples in the context of
resource technology.
In the present setup, high efficiency transmission in the low-energy ion optics segment remains a challenge,
as the beam needs to traverse two existing magnet chambers without deflection, where no steering or lens
elements are available over a flight distance of 4 m. We have now improved the low-energy injection just
after the ion beam exits the 7f-auto, upgrading the steerers directly after the SIMS and by adding a beam
intensity attenuator. This provides both more stable conditions for instrument tuning and simplifies transition
between measurements of the beam intensity in Faraday cups and the gas ionization chamber. Regarding the
measurement of C, N and O in silicon, we found that a simple Wien-filter using permanent magnets for the
primary Cs-sputter beam significantly reduces the background at the detector, as the 7f-auto uses a Cs₂ CO₃
source – rather than metallic Cs – for the generation of the primary positive Cs beam.
Once the remaining issues associated with ion beam-path are fully addressed, we will still need to tackle the
issue of establishing suitable, well characterized reference materials needed for our first suite of resource and
geoscience applications (e.g., halides in naturally occurring sulphide minerals). We present ongoing
developments and results, as well as plans for extending to other matrices and isotope systems.
[1] S. Akhmadaliev et al., NIMB 294 (2013) 5. [2] G. Rugel et al. NIMB 370 (2016) 94. [3] J. M. Anthony,
D. J. Donahue, A. J. T. Jull, MRS Proceedings 69 (1986) 311-316. [4] C. Maden, PhD thesis, ETH Zurich
2003. [5] S. Matteson, Mass Spectrom. Rev., 27 (2008) 470.