| dc.description.abstract | A distinct feature of secondary ion mass spectrometry, SMIS, with large projectiles, e.g. C60, Au400, Ar2000, is abundant secondary ion, SI, emission. Thus it is feasible to run experiments in the event-by-event bombardment detection regime, where SI’s from each individual projectile impact are recorded separately. A sequence of impacts amounts to probing a set of nanospots, as the ejecta originate each time from an area of 10-15 nm in diameter. To date we have developed nano analysis with Au4004+ viz. n/q=100, produced with a liquid metal ion source, LMIS. The purpose of this study, was to pursue this approach with still more massive projectiles. We found that the LMIS can produce projectiles measured to have n/q values of 200 to 350. A first task was to characterize the novel projectile by identifying the number of constituent atoms and the charge of each projectile. This was accomplished by implanting the projectile into highly oriented pyrolytic graphite (HOPG) and performing Neutron Activation Analysis (NAA). By NAA, it was determined that the number of constituent atoms corresponding to n/q=100 and n/q=350 where 400 and 2800 respectively. A second objective was to determine if the more massive projectiles can produce more analyte specific secondary ions without increasing fragmentation. A library of mass spectra corresponding to different size gold clusters (n/q=100,200,350), was created for various samples (glycine, cysteine, Gramicidin S, etc.). When bombarding each sample with n/q=100 and n/q=350, the number of analyte specific secondary ions roughly doubled showing a promising future for these massive projectiles. For glycine we measured an increase from 1 to 2.6 molecular ions per impact when increasing the size of the projectile from n/q=100 to n/q=350. These massive projectiles show a promising enhancement in the performance of SIMS. | en |
