Advanced nanomechanics in the TEM: effects of thermal annealing on FIB prepared Cu samples

Abstract

The effect of focused ion beam (FIB) fabrication on the mechanical properties of miniaturized mechanical tests has recently been realized, but is not well documented. In this study, the effect of post thermal annealing on the plastic properties of FIB fabricated micro- and nanometer-sized Cu samples was studied by means of advanced analytic and in situ transmission electron microscopy. In situ heating experiments on thin films and pillars revealed a reduction of the initially high dislocation density, but never a recovery of the bulk dislocation density. Aberration-corrected atomic imaging documented the recovery of a pristine crystalline surface structure upon annealing, while electron energy-loss spectroscopy showed that the remaining contamination layer consisted of amorphous carbon. These structural observations were combined with the mechanical data from in situ tests of annealed micro- and nanometer-sized tensile and compression samples. The thermal annealing in the micron regime mainly influences the initial yield point, as it reduces the number of suited dislocation sources, while the flow behavior is mostly unaffected. For the submicron samples, the annealed material sustains significantly higher stresses throughout the deformation. This is explained by the high stresses required for surfacemediated dislocation nucleation of the annealed material at the nanoscale. In the present case, the FIB affected the surface near defects and facilitated dislocation nucleation, thereby lowering the material strength

In Situ TEM Microcompression of Single and Bicrystalline Samples: Insights and Limitations

“…All samples were heated in situ in the TEM to 480°C for 25 min at 2 9 10 À7 mbar using a Gatan heating holder in order to reduce FIB damage (Fig. 2) as suggested by Kiener et al 30 After annealing, the samples were compressed with a Bdoped diamond flat punch in a Hysitron PI 95 PicoIndenter Ò using the displacement controlled mode with a 78-kHz feedback loop inside a Jeol 2100F TEM operated at 200 kV. A displacement rate of 1 nm/s, leading to a strain rate of $2 9 10 À3 s À1 was used while observing the samples in either TEM or scanning transmission electron microscopy (STEM) mode.…”

“…As suggested in Ref. 30, an in situ heat treatment was performed to reduce the FIB-induced damage. If this is done with an in situ heating stage, annealing times and temperature can be systematically changed to obtain high-quality specimens.…”

A Novel Approach for Preparation and In Situ Tensile Testing of Silica Glass Membranes in the Transmission Electron Microscope

“…Even though FIB instruments nowadays have excellent imaging and micro-/nanomachining capabilities, one wellknown issue is the ion irradiation-induced damage and change of the specimen material (Volkert and Minor, 2007). Most reports are based on experiences from FIB preparation and its impact on the structure and mechanical properties of crystalline materials (Uchic et al, 2004;Biener et al, 2006;Volkert and Lilleodden, 2006;Kiener et al, 2012). As for instance emphasized by Kiener et al (2007), Ga + irradiation-induced damage can significantly influence the mechanical behavior of submicron-sized Cu.…”

In-Situ Measurements of Free-Standing, Ultra-Thin Film Cracking in Bending

“…It is duly noted that FIB preparation results in residual damage from Gallium implantation and is a concern here. However, rapidly varying contrast, typical for local lattice damage, was not significant compared to other materials FIB prepared for in-situ mechanical testing as in [32].…”