*2.3. Micro-Pillar Production*

The chosen GBs were cut out at the sample edge in order to facilitate the FIB cutting. During the FIB process, the top surface should indeed be polished from two sides in order to ensure that it is perpendicular to the upper surface. Only in that case is it a pure compression test. If not, there are some bending stresses. In the present study, it was crucial to have a pure compression in order to get accurate loading stresses, which were used in the simulations. Finally, the pre-prepared sample was cut into a micro-pillar by FIB with FEI Versa 3D Dual Beam system (Hillsboro, OR, USA) using ion beam currents of 15 nA for rough cutting and 1 nA at 30 kV for fine polishing as shown in Figure 1b,d for Ni and *α*-Brass, respectively. In the present paper, the grain at the edge side of the macrosample is named crystal I and the other one is named crystal II. For the Ni sample, the average length of the micro-pillar was about 15.46 μm and the average width was about 8.03 μm with 4.30 μm for crystal I and 3.73 μm for crystal II. While for the *α*-Brass sample, the average length of the micro-pillar was about 15.37 μm and the average width was about 9.02 μm with 3.97 μm for crystal I and 5.05 μm for crystal II. Then, the orientations of the bi-crystal were acquired again by EBSD with a spatial step resolution of 0.1 μm. Data processing was performed by AZtec software (2.0, Oxford Instruments, Abingdon, UK) with an indexing rate greater than 99%. The microstructures of the micro-pillars are presented by IPF in Figure 1a for Ni and in Figure 1c for *α*-Brass. Meanwhile, the slip analysis configuration is presented in Figure 1e. The inclination angle of GB are *ε* = 0◦ for the Ni micro-pillar and *ε* = 6.4◦ for the *α*-Brass micro-pillar (see Figure 1e).

**Figure 1.** The crystallographic orientations of both crystals, Cry\_I and Cry\_II, are given in the standard IPF in the direction of the *y*-axis which is parallel to GB and is also the loading direction of the compression test for (**a**) Ni micro-pillar and (**c**) *α*-Brass micro-pillar. SEM micrograph of a micro-pillar containing GB cut by FIB for (**b**) Ni sample and (**d**) *α*-Brass sample; (**e**) schematic figure of slip line analyses: The sample coordinates are set as *y* perpendicular to GB line on the upper surface pointing towards crystal II, *z* perpendicular to the upper surface and *x* = *y* × *z* parallel to the GB line. The angle between the slip line and the GB line in a positive *x*-direction on the upper surface is noted as *θ*Up. The angle between the slip line and the upper edge of sample in a positive *x*-direction on the side surface is noted as *θ*Side. The inclination angle of GB is noted as *ε*.
