Comparison of fullerene and large argon clusters for the molecular depth profiling of amino acid multilayers

N. Wehbe, T. Mouhib, A. Delcorte, P. Bertrand, R. Moellers, E. Niehuis, L. Houssiau

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Abstract

A major challenge regarding the characterization of multilayer films is to perform high-resolution molecular depth profiling of, in particular, organic materials. This experimental work compares the performance of C 60 + and Ar1700 + for the depth profiling of model multilayer organic films. In particular, the conditions under which the original interface widths (depth resolution) were preserved were investigated as a function of the sputtering energy. The multilayer samples consisted of three thin d-layers (̃8 nm) of the amino acid tyrosine embedded between four thicker layers (̃93 nm) of the amino acid phenylalanine, all evaporated on to a silicon substrate under high vacuum.When C60 + was used for sputtering, the interface quality degraded with depth through an increase of the apparent width and a decay of the signal intensity. Due to the continuous sputtering yield decline with increasing the C60 + dose, the second and third d-layers were shifted with respect to the first one; this deterioration wasmore pronounced at 10 keV, when the third d-layer, and a fortiori the silicon substrate, could not be reached even after prolonged sputtering. When large argon clusters, Ar1700 +, were used for sputtering, a stable molecular signal and constant sputtering yield were achieved throughout the erosion process. The depth resolution parameters calculated for all d-layers were very similar irrespective of the impact energy. The experimental interface widths of approximately 10 nm were barely larger than the theoretical thickness of 8 nm for the evaporated d-layers.

Original languageEnglish
Pages (from-to)201-211
Number of pages11
JournalAnalytical and Bioanalytical Chemistry
Volume406
Issue number1
DOIs
Publication statusPublished - 1 Jan 2014

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Keywords

  • Argon clusters
  • C
  • Depth resolution
  • Multilayer organic films
  • SIMSdepth profiling
  • Sputtering yield

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