A simultaneous dual-polarity mass spectrometer with electron start for MeV-SIMS

Klaus-Ulrich Miltenberger,Max Döbeli,Christof Vockenhuber,Hans-Arno Synal

doi:10.1016/j.nimb.2021.09.010

Klaus-Ulrich Miltenberger, Max Döbeli + Show 2 more

Open Access

https://doi.org/10.1016/j.nimb.2021.09.010

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Abstract

The Capillary Heavy Ion MeV-SIMS Probe (CHIMP) at ETH Zürich has been redesigned with a second mass spectrometer and symmetric extraction to enable simultaneous analysis of positive and negative secondary ions. Secondary electrons are deflected within the negative spectrometer and detected independently. The fast secondary electron signal is used as a start signal for both Time-of-Flight mass spectrometers.The new setup enables the simultaneous acquisition and analysis of both secondary ion polarities emitted under identical conditions from the same sample location. This allows to study correlations between secondary ions of different polarities emitted from a single primary ion impact. Measurements with small primary Cn cluster ions show the influence of cluster size on the multiplicity of secondary ion emission. Furthermore, a cluster effect in the ratio between positive and negative ion yields of corresponding secondary ion species is identified, with the ratio approaching parity for larger cluster sizes n.

Highlights

MeV-SIMS (Secondary Ion Mass Spectrometry) achieves high yields of large molecular secondary ions by bombarding a sample surface with primary ions in the MeV energy range
The existing Capillary Heavy Ion MeV-SIMS Probe (CHIMP) setup at ETH Zurich was upgraded to a new simultaneous dual polarity MeV-SIMS instrument
The new instrument demonstrates the feasibility of independent detection of secondary electrons as well as negative and positive secondary ions emitted from the sample after a single primary ion impact

Summary

Introduction

MeV-SIMS (Secondary Ion Mass Spectrometry) achieves high yields of large molecular secondary ions by bombarding a sample surface with primary ions in the MeV energy range. This has been demonstrated in several studies so far [1,2] and is generally attributed to the enormous electronic stopping power of the primary ions in this energy regime prevailing over their much smaller nuclear stopping power. The underlying desorption and ionization processes are not well under stood yet. More in-depth overviews of the proposed theoretical models were compiled [3,4] but the theoretical approaches mostly focus on the desorption effect and largely neglect the ionization process

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