Initial stages of growth and electronic properties of epitaxial SrF2 thin films on Ag(111)

[Display omitted] •Strontium fluoride forms weakly-interacting interfaces with Ag(111).•Almost ideal and continuous dielectric layer is formed when growth is carried out at room temperature.•A valence band offset of 6.7 eV between Ag and SrF2 is obtained for 5 nm of dielectric film.•High temperature growth causes the formation of 3D fluoride structures. Molecular beam epitaxy (MBE) is used to grow ultrathin SrF2 layers at different temperatures on Ag(111) epitaxial films prepared on mica. The electronic properties, structure and morphology of the films are probed by ultraviolet and x-ray photoelectron spectroscopies (UPS and XPS) supported by ab-initio calculations, reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM). The SrF2 films are composed of crystallites with their [111] direction parallel to the substrate normal, thereby reproducing the symmetry of the substrate. Twinned domains are also observed. At the Ag/SrF2 interface, fluoride molecules do not dissociate and the interaction with the substrate is weak. At room temperature, fluoride crystallites merge together, resulting in a continuous film covering the entire substrate when it reaches a nominal thickness of 5 nm. Growth at higher temperature induces the formation of triangular 3D islands, leaving sizable portions of the Ag substrate uncovered. At 400 °C, also a small fraction of SrF2(001)-oriented crystallites are observed, with their [1 −1 0] axis rotated by about 30° with respect to the [1 −1 0] substrate direction.