Enhancement of the static SIMS secondary ion yields of lipid moieties by ultrathin gold coating of aged oil paint surfaces
Surf. Interface Anal. , Volume 36 p. 1620- 1628
Static secondary ion mass spectrometry (SIMS) is a powerful technique for identification and localization of pigments and binding media present in traditional paintings. Coating the surface of a cross-section with a 20 Ã… thick gold layer improves the yields of secondary ions from the fatty acids and diacids. A chalk tablet containing 1% stearic acid, which was partially covered during gold deposition, is used as a test system to investigate the increase of the organic secondary ion yields upon gold deposition in SIMS imaging. A comparative study of a native and gold-coated aged surface of a lead white-containing linseed oil paint demonstrates the enhancement of the organic ion yields on a sample relevant for painting studies. The yields of oil paint-derived negative ions increase by a factor of 3 whereas the yields of positive ions increase by a factor of 2-4. The different types of charged functional groups determine the degree of improvement in yield. Gold coating improves the ionization process of the fatty acids and does not influence their fragmentation. The dissociation of the lead white by the primary ion beam is reduced due to the gold coating.