Process optimization of broad ion beam milling for preparation of coating cross-sections

The application of Argon ion based broad ion beam milling in the preparation of coating cross-sections is systematically evaluated in this work. In order to reduce and eliminate defects and artefacts from the prepared sectional surface, the substrate side of the sample is found to be best facing the ion beams, and the milling time needs to be optimized to be not too long to introduce scratching of the obtained surface, while not too short to result in particle deposition. Further, the energy of the ion beams is found to have great effect on the etch rate of the sample, thus having a large impact on the process time and quality depending on the materials nature of the samples. It is found that by introducing a second low-energy polishing step after the high-energy milling step, the quality of the cross-section is greatly improved with the measured surface roughness down to the nanometer scale. The capability of broad ion beam milling method to provide smooth cross-sections for the subsequent microscopic investigations by e.g. scanning electron microscopy or atomic force microscopy is important to reveal morphological information of the coating systems with high level of details without distortions due to sample preparation.