Evaluating the effects of pillar shape and gallium ion beam damage on the mechanical properties of single crystal aluminum nanopillars

In situ TEM nanopillar compression experiments are widely used to study the mechanical behavior of nanoscale materials. Often, the pillars are fabricated using gallium-focused ion beam (FIB) milling from a bulk sample. During the FIB process, the choice of the pillar shape and the energy of the Ga ions can significantly impact the mechanical performance of samples with electron-transparent dimensions. Here, we systematically explore the effects of various pillar fabrication parameters in a single crystal aluminum (Al) system with a well-controlled crystal orientation. A novel method is proposed to fabricate square pillars to minimize FIB artifacts such as tapering, high pillar base compliance, and preferential deformation at the pillar tip. These square pillars enable more uniform deformation and accurate measurement of the engineering strain. Lastly, we show an intriguing in situ TEM laser irradiation experiment, which has enabled direct visualization of the surface oxide layer in FIB-fabricated Al pillars.