Characterisation of human hair surfaces by means of static ToF-SIMS: A comparison between Ga+ and C60+ primary ions

This study deals with the secondary ion yield improvement induced by using C60+ primary ions instead of Ga+ ones to characterize human hair surfaces by ToF-SIMS. For that purpose, a bunch of hair fibres has been analysed with both ion sources. A high improvement is observed for the detection of amino acids with C60+ primary ions as compared to Ga+ ions. As an example, a yield enhancement factor greater than 3000 is found for the CNO− peak. A similar gain is observed for the positive secondary ions characteristic of the amino acids. Most of the atomic ions, such as Ca+, O− and S−, constitute minor peaks with C60+ ions while they often dominate the spectrum in the case of Ga+ ions. However, with the C60+ source, a series of inorganic combination peaks with the elements Ca, S and O are observed in the positive spectra (i.e. HCaSO4+), while they are marginal with the Ga+ source. For the mass range beyond 100 m/z and in both polarities, the hair fingerprints are similar with both sources. In average, for a comparable number of primary ions per spectrum, the C60+ ion source gives intensities between two and three orders of magnitude higher than the Ga+ one.