Dose-dependent cesium ion beam damage effects on chemically modified poly(methyl methacrylate) films using secondary ion mass spectrometry and x-ray photoelectron spectroscopy

The Cameca IMS-3f ion microscope was used to obtain negative SIMS spectra of poly(methyl methacrylate) (PMMA) and chemically modified PMMA films to assess its ability to provide surface structural information from organic samples. Negative ion spectra generated by Cs+ bombardment produced structurally specific fragment ions, particularly for Cs+ doses of < 1 X 1015 ions/cm2. At larger doses, the progressive degradation of the native polymer structure was reflected by an increasing hydrocarbon-like fragmentation pattern. The primary ion dose dependence of various secondary ion intensities, as influenced by beam damage effects, was established. Small-area X-ray photoelectron spectroscopy (XPS) was used to confirm these results. The PMMA was chemically modified with pentafluorobenzaldehyde (PFBA) and dissolved in a solvent in which the polymer was insoluble, to provide tag molecules at the polymer's surface. Although XPS indicated that only 6% of the near-surface ester side chains were labeled with PFBA, tag-related molecular fragment ions such as C6F5- exhibited strong intensities in the immediate surface region. 24 references, 7 figures, 5 tables