TOF-SIMS depth profiling of multilayer amino-acid films using large Argon cluster Arn+, C60+ and Cs+ sputtering ions: A comparative study

The performance of Cs, C and Ar (with n ≈ 1700) sputtering ions have been compared for depth profiling multilayer films made from three evaporated phenylalanine layers sandwiched between four thicker evaporated tyrosine layers. Using Cs , the ion signals and depth resolution degrade with depth and were significantly affected beyond a 200-nm depth. The depth profiling quality was more successful using C. However, in this case, the depth resolution and the layer width values still degrade with the sputtered depth and are particularly poor after reaching a depth of about 400 nm. When Ar clusters were used, a depth resolution as low as 6 nm was obtained, and this value never exceeds 9 nm. Moreover, the experimental layer width is found to be of the same order of magnitude as the real value.