A C60 primary ion beam system for time of flight secondary ion mass spectrometry:: Its development and secondary ion yield characteristics

A buckminsterfullerene (C-60)-based primary ion beam system has been developed for routine application in TOF SIMS analysis of organic materials. The ion beam system is described, and its performance is characterized. Nano-amp beam currents Of C-60(+) are obtainable in continuous current mode. C-60(2+) can be obtained in pulsed mode. At 10 keV, the beam can be focused to less than 3 mum with 0.1 nA currents. TOF-SIMS studies of a series of molecular solids and a number of polymer systems in monolayer and thick film forms are reported. Very significant enhancement of secondary ion yields, particularly at higher mass, were observed using 10-keV C-60(+) for all samples other than PTFE, as compared to those observed from 10 keV Ga+ primary ions. Three materials (PS2000, Irganox 1010, PET) were studied in detail to investigate primary ion-induced disappearance (damage) cross sections to determine the increase in secondary ion formation efficiency. The C-60 disappearance cross sections observed from monolayer film PS2000 and self-supporting PET film are close to those observed from Ga+. The resulting C-60 efficiencies are 30-100 times those observed from gallium. The cross sections observed from C-60 bombardment of multilayer molecular solids are similar to100 times less, such that essentially zero damage sputtering is possible. The resulting efficiencies are >10(3) greater than from gallium. It is also shown that C-60 primary ions do not generate any more low-mass fragments than any other ion beam system does. C-60 is shown to be a very favorable ion beam system for TOF-SIMS, delivering high yield, close to 10% total yield, favoring high-mass ions, and on thick samples, offering the possibility of analysis well beyond the static limit.