Surface Structure of Polar Silver Iodide (0001) in Various Liquids: No Indication for a Surface Reconstruction

Silver iodide (AgI) has long been known as a material that induces precipitation in clouds. The superior ice nucleation ability is commonly explained by the close lattice match between β-AgI(0001) and the basal plane of ice. However, this surface is polar, indicating that a stabilization mechanism should be present. Here, we investigate the Ag-terminated β-AgI(0001) and the I-terminated β-AgI(000-1) surfaces in water and compare the results with images recorded in n-dodecane, 0.1 M NaCl, and 0.1 M KI aqueous solutions. Strikingly, high-resolution images consistently reveal a bulk-truncated structure. These findings and observations at a larger scale indicate the absence of any periodic or triangular surface reconstruction. Although the observed structures reveal a variety of features and depend on the surface termination, some general conclusions can be drawn. First, in solvents with poor AgI solubility, only minor changes are observed. Second, the images taken in KI solution exhibit patterns that are characteristic of mineral dissolution and growth. Thus, even in a situation where AgI can and does dissolve, no indication for a surface reconstruction can be found. These results shed new light onto the surface structure of β-AgI(0001), challenging the expectation that a surface reconstruction is present under ambient conditions.