Reactive growth of NiO ultrathin films on Pd(100): a multitechnique approach

Reactive growth of NiO ultrathin films on Pd(1 0 0) has been performed by evaporating metallic Ni in an oxygen atmosphere. The evolution of the ultrathin film is followed by means of low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), X-ray photoelectron diffraction (XPD) and scanning tunnelling microscopy (STM). The first monolayer (ML) of the deposited oxide develops as a completely wetting 2D overlayer with a c(4 x 2) periodicity, as shown by sharp LEED patterns and atomically resolved STM images. Further NiO deposition results in 3D NiO(1 00) islands formation on-top the c(4 x 2) superstructure, as shown by STM images and XPD data. Two layers thick islands are shown to be pseudomorphic to the substrate, i.e. characterised by in-plane compressive strain and interlayer expansion. LEED, XPD and STM give independent yet converging evidence that partial strain relaxation occurs within the third monolayer. (c) 2005 Elsevier B.V. All rights reserved.