Each measurement in this work was performed on a freshly-prepared Au POSC, shown in an SEM image in Fig. . A detailed description of the preparation procedure, verification of the quality, and the size of the crystals can be found in the experimental section. From Laue X-ray diffraction (XRD) measurements, we determined the position of the low-index facets, i.e., Au(111), Au(110), and Au(100). Typical Laue XRD patterns of all three low-index facets of a Au POSC can be found in the SI (Section S1). Once these regions were characterized, the Au(111) and the Au(100) facets can also be discerned by visual inspection of the POSC. Other facets, such as the Au(110), can then be inferred from their relative position to the other low-index facets. A magnification of the Au(111) and Au(100) facets is shown in the SEM images in Figs. and. The images in Figs. and show the region vicinal to the Au(111) and the Au(100) facets, which are referred to as Au(111*) and Au(100*) regions throughout this work. These regions have a significant amount of steps. We suggest that the crystallographic orientation in these regions is, however, predominately that of the adjacent low-index facet.