C60 molecular depth profiling of a model polymer

The bombardment of a 26 nm poly(methyl methacrylate) (PMMA) film has been studied as a model for depth profiling of polymeric samples using a newly developed C-60(+) ion source. Experiments were conducted on a ToF-SIMS instrument equipped with C-60(+) and Ga. ion sources. A focused dc C-60(+) ion beam was used to etch through the polymer sample at specified time intervals. Subsequent spectra were recorded after each individual etching cycle using both C-60(+) 20 keV and Ga+ 15 keV ion beams at field-of-views smaller than the sputter area. PMMA fragment ion at m/z = 69 and substrate Au m/z = 197 were monitored with respect to primary ion doses of up to 10(14) ion S/cm(2). Depth resolution as determined by the interfacial region is found to be about 14 nm. A >10-fold increase in sputter yield for C-60(+) ion bombardment over Ga+ ions under similar conditions is observed from quartz crystal microbalance (QCM) measurements and our findings compare to enhanced SF5+ cluster bombardment yields of organic species. (C) 2004 Elsevier B.V. All rights reserved.