Biomolecular & Analytical Mass Spectrometry

Surface analysis: imaging

TOF-S-SIMS can visualise the chemical composition of a surface in a secondary ion (SI) image. The spectral information of each point is stored. The color of the pixels is dependent of the measured SI yield, where black represents very low intensity and white the highest intensity.

A lateral resolution of 150 nm can be obtained in the so called “extreme crossover mode”.

Molecular characterisation of fibres to be used in high-tech textile and fibre-reinforced composites requires the analysis of curved surfaces with S-SIMS. The application is challenging because the detected SI intensity depends not only on the analyte and its concentration but also on the local angle of incidence and the ion extraction yield.

The figure below shows an SI image of a PET fibre (diameter 100 µm) homogeneously coated with cetyl trimethyl ammonium bromide (CTAB), obtained by using standard SIMS operating parameters. The distribution of the detected SI intensity in the fibre image is uneven. Two zones with high SI yield are separated by a zone with very low SI intensity. A more homogeneous ion distribution (figure below, right) is obtained by adjusting the extractor’s voltage and/or distance to the sample. However, empiric optimisation is still required to improve the homogeneity of the intensity distribution.