Step Edge Induced Reconstructions of NaCl(100) Bilayers on Ag(111): A Route To Alter the Properties of Nanoscale Insulators

The electrical and optical properties of insulators are largely determined by defects. In view of the increasing importance of nanoscale insulating structures, it is not only crucial to develop strategies to form defects in insulating structures but also inevitable to understand them on the nanoscale. We use fast-Fourier transform scanning tunneling microscopy to investigate reconstructions of bilayer-high NaCl(100) islands, grown at or across intrinsic step edges of Ag(111). Such islands show deviations from a bulklike structure. The reconstructions consist of dipoles that relax perpendicular to the (100) plane of the bilayer-high islands in a concerted manner. We propose that the reconstruction is induced by the intrinsic dipole of the Ag step edges. We thus demonstrate that NaCl bilayers show a remarkable flexibility in adapting to surface defects besides being a hard and brittle material in its bulk phase. The large-scale reconstructions provide a possibility to alter the structure of the nanoscale islands with the long-term goal to tune their properties.