Figure 8.
Controlling the structure and phase of Sn monochalcogenides through epitaxy. (a) Top view showing the in-plane unit cell in dashed lines, orientation of the polar bonds, and the net in-plane polarization within a single sheet. (b, c) Visualizing the in-plane armchair and zigzag directions. (d) The coordination polyhedron. Reproduced with permission from ref 134. Copyright 2022 American Chemical Society. (e-h) Demonstrations of structure and phase control through epitaxy: (e) eliminating twin domains. Reproduced with permission from ref 134. Copyright 2022 American Chemical Society. (f) realizing ferroelectricity in monolayers. Reproduced with permission from ref 135. Copyright 2020 American Chemical Society. (g) making a multilayer, polar crystal with metastable layer stacking. Reproduced with permission under a Creative Commons CC-BY 4.0 License from ref 136. Copyright 2020 Springer Nature. (h) Making a topological crystalline insulator by stabilizing the rock-salt phase. Reproduced with permission under a Creative Commons Attribution 4.0 International license from ref 137. Copyright 2017 American Physical Society. (i) Reported lattice constants ordered from smallest to largest along the armchair direction and separated into results reported by theory (left) and experiments (right). Gray arrows give more information on the simulated/measured samples. (j, k) Cross-section and plan-view images of SnSe simulated by DFT for the case of (j) bulk and (k) monolayer. The armchair lattice constants are visualized using gray dashed lines, and the reduced in-plane anisotropy in the monolayer case is highlighted using blue ovals. Note that there is no consensus in the literature on crystal indexing.