Impact of slow gold clusters on various solids: nonlinear effects in secondary ion emission

A liquid metal ion source (LMIS) has been installed on a pulsed ion gun built at the IPN. The time of flight (TOF) spectra of the pulsed beam were recorded. With the gold source several cluster ions (up to 10 atoms in the cluster) and doubly charged ions were identified in the ion beam TOF spectra. With a second pulsation, single cluster ions can be selected as projectiles for secondary ion TOF mass spectrometry. We have studied the secondary ion emission (SIE) induced by cluster impact from a variety of targets: organic, CsI, metallic. A large enhancement of yield is observed by comparison to single atomic ion impact (e.g. factor of 30 between Au3+ and Au+). The secondary ion yields increase strongly with the number of constituents in the cluster. This effect is not linear. A comparison with other types of clusters and also fission fragments of 252Cf has been performed. The rate of secondary emission stimulated by cluster is similar to SI yield induced by fission fragments.