Morphology, Work Function, and Silver Ad-Structures of High-Temperature Grown Ultrathin MgO Films on Ag(001)

Abstract

We characterized the high-temperature growth of ultrathin MgO films on Ag(001) at 783 K through analyzing the film’s morphology and work function by noncontact atomic force microscopy (nc-AFM), scanning tunneling microscopy (STM), Kelvin probe force microscopy (KPFM) and assisting low-energy electron diffraction (LEED). At submonolayer coverage, one-atomic-plane-high MgO islands are formed, which are preferentially embedded into the silver surface and which are larger and more regular than the islands of those films normally grown between 500 and 600 K. KPFM shows that embedded MgO islands decrease the silver work function (WF) by ΔϕMgO–Ag = −50 ± 20 meV, whereas a small amount of supported islands increase the WF by ΔϕMgO–Ag = +50 ± 20 meV. When the MgO film starts to cover entirely the silver surface, ad-islands, nanoparticles (NPs), and much larger particles of silver are formed, which is due to the high mobility of silver and the embedding of the MgO islands into the silver surface. Our work opens the...