Effect of Ion Irradiation Introduced by Focused Ion-Beam Milling on the Mechanical Behaviour of Sub-Micron-Sized Samples
Jinqiao Liu, Ranming Niu, Ji Gu, Matthew Cabral, Min Song & Xiaozhou Liao
Scientific Reports volume 10, Article number: 10324 (2020) Cite this article
[
Abstract]
The development of xenon plasma focused ion-beam (Xe+ PFIB) milling technique enables site-specific sample preparation with milling rates several times larger than the conventional gallium focused ion-beam (Ga+ FIB) technique. As such, the effect of higher beam currents and the heavier ions utilized in the Xe+ PFIB system is of particular importance when investigating material properties. To investigate potential artifacts resulting from these new parameters, a comparative study is performed on transmission electron microscopy (TEM) samples prepared via Xe+ PFIB and Ga+ FIB systems. Utilizing samples prepared with each system, the mechanical properties of CrMnFeCoNi high-entropy alloy (HEA) samples are evaluated with in situ tensile straining TEM studies. The results show that HEA samples prepared by Xe+ PFIB present better ductility but lower strength than those prepared by Ga+ FIB. This is due to the small ion-irradiated volumes and the insignificant alloying effect brought by Xe irradiation. Overall, these results demonstrate that Xe+ PFIB systems allow for a more efficient material removal rate while imparting less damage to HEAs than conventional Ga+ FIB systems.
[Introduction]
The rapid development of micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS), which utilize materials at the micron scale and below, has resulted in a growing number of potential applications in electronic devices1. Mechanical properties are of particular importance for applications in M/NEMS as efforts seek to improve the functionality and reliability of advanced electronic devices. Continuing efforts have focused on understanding how the mechanical properties of these materials change with decreasing dimensions2,3,4,5,6. To facilitate this understanding, in situ straining transmission electron microscopy (TEM) is commonly used to test the mechanical properties7,8,9,10 and observe deformation mechanisms11,12,13,14,15,16,17 of small-sized samples. In situ straining TEM allows for simultaneous structural characterisation and mechanical property testing13,15,18, providing opportunities for building direct relationships between microstructure, deformation mechanisms, and mechanical properties of small-sized materials.
Sample preparation is of particular importance when studying small-sized materials in the TEM19. Traditionally, these TEM samples are prepared using a focused ion-beam (FIB) with a gallium ion (Ga+) source to thin samples from bulk to ~100?nm20,21,22,23,24,25,26. Despite technological advances, the material removal rates of Ga+ FIB systems have remained too low for researchers hoping to increase sample preparation efficiency27. To help facilitate more efficient sample preparation, researchers have developed FIB systems with alternative ion sources such as the Xe+ plasma FIB (Xe+ PFIB)27. As an alternative to Ga+ ions, Xe+ PFIB systems utilize inert Xe gas as the milling media resulting in material removal rates around six times larger than for Ga+ mills27, which enables the preparation of samples with larger dimensions. On the other hand, Xe+ PFIB induces a thinner amorphous layer on the sample surface compared to the Ga+ source20,27,28. Further, the low reactivity of the chemically inert Xe gas has enabled sample preparation of materials that are sensitive to many other types of ions20,28.
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