Figure 1

(a) $p(3\times 3)$ “kagome” phase ($16\mathrm{nm}\times 16\mathrm{nm}$). (b) ($\surd 7\times \surd 7$) “hex” phase ($13.5\mathrm{nm}\times 13.5\mathrm{nm}$). (c) ($2\surd 3\times 2\surd 3$) pinwheel phase ($12.5\mathrm{nm}\times 12.5\mathrm{nm}$). In each image, the unit cell and a Co-Co close-packed direction are labeled. (d) A line profile shows alternating Na-Na distances. (e) An interstitial Na atom ($\mathbf{A}$) is shown. (f) Triangle-like pinwheel segments with discernible atomic resolution. (g) Coexisting kagome and hex phases ($17\times 17{\mathrm{nm}}^2$). (h) Coexisting pinwheel and hex phases ($35\times 35{\mathrm{nm}}^2$) and mirrored hex domains (squares). Both phases are overlaid on a $p(6\times 1)$ stripe phase that will be discussed in a separate publication. Imaging condition: (a), (d) sample bias $V_s=-1.85\mathrm{V}$, tunneling current $I_t=70\mathrm{pA}$; (b), (e) ($-2.05\mathrm{V}$, 56 pA); (c), (f) ($-1.78\mathrm{V}$, 51 pA); (g) ($-2.05\mathrm{V}$, 91 pA); (h) ($-1.78\mathrm{V}$, 55 pA).Reuse & Permissions

Figure 2

Proposed structure models of the (a) kagome ($x_s=1/3$), (b) hex ($x_s=3/7$), and (c) pinwheel ($x_s=1/2$) phases, which consist of ordered superlattices of Co-, O-, Co-centered Na(2) trimers, respectively. In the 2(b) legend, Na(1), Na(2), oxygen sites are denoted. A 3D model is shown in (d) (see also, e.g., 24, 25). All arrows denote the allowed $\mathrm{Na}(2)\leftrightarrow \mathrm{Na}(1)$ site switching paths. In (b), the dashed circles denote concerted rotation of the Na trimers (triangles). One substrate mirror plane ($\mathbf{M}$), two mirror domains intersected at 21.8°, and an interstitial Na atom ($\mathbf{A}$) at a Na(2) site are also shown. In (c), each pinwheel segment (trimer) can also “rotate” (see dotted triangles) and renders itself triangle-like [see Fig. 1f]. For details of each model, see text.Reuse & Permissions