Micron-Scale Deformation 1079


Figure 2. Detail of the second, final step of the micropillar fabrication procedure with an ion current of 5 nA. a: After the first step, described in Figure 1, the sample is tilted by 45° resulting in a tilted ion beam direction. Then, two rec- tangular focused ion beam (FIB) patterns are used to obtain the surface marked in red. b: Next, the sample is rotated by 180° and the two rectangular FIB patterns are used again for the surface marked in yellow. By rotating 90° and repeating the previous two steps, the surfaces marked by (c) green and (d) blue are obtained. Finally, a rectangular- shaped pillar is obtained. To craft a pillar with smooth surfaces and practically no tapering, the entire procedure is repeated with ion currents of 1 nA and 100 pA. The final pillar is shown in the inset (e).


AE MEASUREMENTS


Figure 3. Schematic view of the in situ device for the NanoTest. AE, acoustic emission.


chamber. To suppress this disturbing effect, strong perma- nent magnets were placed near the lamellae of the force measuring spring, thus providing the necessary damping from the eddy currents.


An AE measuring system was employed to study the dynamic processes during the plastic deformation of micropillars. AEs are transient elastic waves generated by the rapid release of energy from localized sources within the material. Therefore, AE signals can be detected when sudden localized structural changes, such as collective dislocation motion or twinning, occur. Consequently, the AE technique provides information about the dynamic phenomena involved in plastic deformation (Heiple & Carpenter, 1987). In bulk materials, a direct correlation of the AE para-


meters with the stress–strain curves reveals the activation of different deformation mechanisms (Bohlen et al., 2004;


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