Sample film-thickness influence on fast heavy-ion induced desorption yields of biomolecular ions

Abstract

Fast ion induced desorption yields for positive and negative secondary ions of biomolecules have been studied as a function of sample film thickness. The films were prepared with the spin-coating technique and the film thicknesses were measured with ellipsometry. The secondary ions were mass analyzed with a time-of-flight technique. The sample thickness dependence was investigated for three different biomolecules; the aminoacid valine (MW = 117), the peptides LHRH (MW = 1182) and bovine insulin (MW = 5733). It was found that the yield increases with thickness in all three cases up to a thickness of 80–200 Å and then saturates. The shape of the ion yield curves were found to be independent of the electronic stopping power of the primary ion in the range of stopping powers investigated. The type of backing used was found to influence the yield vs film thickness dependence.