Ion yield enhancement at the organic/inorganic interface in SIMS analysis using Ar-GCIB

V. Cristaudo, C. Poleunis, P. Laha, P. Eloy, T. Hauffman, H. Terryn, A. Delcorte

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Abstract

Argon gas cluster ion beams (Ar-GCIBs) provide new opportunities for molecular depth profiling and imaging of organic materials and biological samples, thanks to recent technological developments that have led to the construction of new SIMS spectrometers where the traditional issues related to their low lateral resolution along with poor mass resolution and mass accuracy are overcome. The present fundamental contribution on SIMS molecular depth profiling investigates the variations of the secondary ion signals observed at the organic–inorganic hybrid interface when using Ar-GCIB as the analytical beam. With this in mind, depth profiling experiments were performed with a ToF-SIMS spectrometer using different analysis beams: 30-keV Bi5+ versus 10-keV Arn+ with a cluster size (n) of 800, 1500, 3000 and 5000 atoms, respectively. A 10-keV Ar3000+ beam was used for sputtering in all the experiments. Irganox 1010 and model polymers such as polystyrene (PS) and poly (methyl methacrylate) (PMMA) oligomers were chosen. Silicon wafer and a polymer-based substrates were employed to test materials with different stiffness, which is directly related to their Young's moduli, an important parameter in this study. Ar-GCIB depth profiles systematically show ion signal enhancement of the characteristic fragments of PS and Irganox 1010 when approaching the interface with the silicon substrate, that can reach up to 60% for [M1010-H] in Irganox films deposited onto silicon wafers. This enhancement increases with increasing n in both ion polarities. These results point out some ionization effects on the observed signal enhancement at the interface. The experimental observations will be explained on the basis of the physics of the impact of large argon clusters on different target materials and the energy confinement of the ion projectile in the organic overlayers. Finally, the thickness of organic films on rigid substrates in the nanoscale appears to be a crucial parameter to dramatically improve the sensitivity to molecular fragments when using large Ar cluster ions as analysis beams.

Original languageEnglish
Article number147716
JournalApplied Surface Science
Volume536
DOIs
Publication statusPublished - 4 Sep 2020

Bibliographical note

Funding Information:
A.D. is a Research Director of the Fonds National de la Recherche Scientifique (FNRS) of Belgium. This work was supported by the Fédération Wallonie Bruxelles , through the project “iBEAM” funded by its research program “Actions de Recherche Concertées” (Convention n° 18/23-090 ). The authors also acknowledge the FNRS for financial support to purchase the ToF-SIMS instrument. V. Cristaudo thanks Dr. Delphine Magnin and Dr. Naïma Sallem for useful discussion concerning the ellipsometry measurements.

Publisher Copyright:
© 2020 Elsevier B.V.

Keywords

  • Fragmentation
  • Ion signal enhancement factor
  • Irganox 1010
  • Polystyrene
  • Sputtering yield volume
  • ToF-SIMS

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