C_(60) molecular depth profiling of a model polymer

摘要

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) ions/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 SF_5~+ cluster bombardment yields of organic species.