Metal-Assisted Secondary Ion Mass Spectrometry:  Influence of Ag and Au Deposition on Molecular Ion Yields

A series of organic dyes and a pharmaceutical are used to study secondary ion yield enhancement by metal deposition. The molecules were dissolved in methanol and spin-casted on silicon substrates. Subsequently, silver or gold was evaporated onto the samples to produce a very thin coating. The coated samples, when measured with TOF-SIMS, showed a considerable increase in characteristic secondary ion intensity. Gold evaporated samples appeared to exhibit the highest signal enhancement. A major advantage of the metallization technique is that it can be used on real world samples. In particular, additive containing organic crystals could be studied; however, the observed signal increase does not occur at any given moment. The time between metal deposition on the sample surface and the measurement of the sample with TOf-SIMS appears to have an important influence on the enhancement of the secondary ion intensities. Therefore, the metal-coated samples were measured at different times after sample preparation. The results show that, depending on the sample and the metal deposited, the secondary ion signals reach their maximum at different times. Further study will be necessary to reveal the mechanism responsible for the observed enhancement effect.