Revealing buckling of an apparently flat monolayer of NaCl on Pt(111)

Platinum is relatively reactive, compared to silver and copper, which prompted us study the growth structure of a thin insulating layer on Pt(111). We grew monolayer islands NaCl studied them with scanning tunneling microscopy (STM) atomic force (AFM). STM images revealed square lattice we confirmed, via density functional theory (DFT) calculations, be Cl anions, similar other surfaces. Surprisingly, however, AFM appeared only resolve approximately two-thirds ions. DFT calculations showed that adsorption heights anions above surface have bimodal distribution in they are either 60 pm Na ionic plane or 40 lower. An electrostatic model shows this reproduces observations.