Evaluation of neon focused ion beam milling for TEM sample preparation

Gallium-based focused ion beams generated from liquid-metal sources are widely used in micromachining and sample preparation for transmission electron microscopy, with well-known drawbacks such as sample damage and contamination. In this work, an alternative (neon) focused ion beam generated by a gas field-ionization source is evaluated for the preparation of electron-transparent specimens. To do so, electron-transparent sections of Si and an Al alloy are prepared with both Ga and Ne ion beams for direct comparison. Diffraction-contrast imaging and energy dispersive x-ray spectroscopy are used to evaluate the relative damage induced by the two beams, and cross-sections of milled trenches are examined to compare the implantation depth with theoretical predictions from Monte Carlo simulations. Our results show that for the beam voltages and materials systems investigated, Ne ion beam milling does not significantly reduce the focused ion beam induced artefacts. However, the Ne ion beam does enable more precise milling and may be of interest in cases where Ga contamination cannot be tolerated.