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 C60 þ ion source. Experiments were conducted on a ToF-SIMS instrument equipped with C60 þand Gaþ ion sources. A focused dc C60 þ 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 C60 þ 20 keV and Gaþ 15 keV ion beams at field-of-views smaller than the sputter area. PMMA fragment ion at m/z 1⁄4 69 and substrate Au m/z 1⁄4 197 were monitored with respect to primary ion doses of up to 10 ions/cm. Depth resolution as determined by the interfacial region is found to be about 14 nm. A >10-fold increase in sputter yield for C60 þ ion bombardment over Gaþ ions under similar conditions is observed from quartz crystal microbalance (QCM) measurements and our findings compare to enhanced SF5 þ cluster bombardment yields of organic species. # 2004 Elsevier B.V. All rights reserved.