Use of STIM for morphological studies of microstructured polymer foils

In this work, morphological characterization of microstructures produced by focused 3 MeV H+ beams and chemical etching on poly(ethylene terephthalate) foils was investigated by on- and off-axis scanning transmission ion microscopy (STIM). STIM images were obtained from different energy regions of the transmitted energy spectra. STIM performance was compared to scanning electron microscopy (SEM) used as a reference. STIM and SEM images provided similar morphological information. The deviations observed between the measured dimensions obtained from both techniques were within the uncertainties of the experiment. Moreover, the scaling of the structures' size versus etching time (i.e. the etching rates) extracted from STIM and SEM data were equivalent. Prolonged etching times of up to 60 min were performed to check the effect of the irradiation on the non-bombarded vicinity of the structured lines. STIM images clearly revealed a distribution of cavities and porosity along the structured walls for etching times above 20 min. This is attributed to thermal effects and outgassing during the proton beam writing, which probably create voids that are enlarged by the long exposure to the etching solution.