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 C60þ ion source. Experiments were conducted on a ToF-SIMS instrument equipped with C60þand Gaþ ion sources. A focused dc C60þ 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 C60þ 20 keV and Gaþ 15 keV ion beams at field-of-views smaller than the sputter area. PMMA fragment ion at m/z ¼ 69 and substrate Au m/z ¼ 197 were monitored with respect to primary ion doses of up to 1014 ions/cm2. Depth resolution as determined by the interfacial region is found to be about 14 nm. A >10-fold increase in sputter yield for C60þ ion bombardment over Gaþ ions under similar conditions is observed from quartz crystal microbalance (QCM) measurements and our findings compare to enhanced SF5þ cluster bombardment yields of organic species. # 2004 Elsevier B.V. All rights reserved.