Understanding nanoscale effects in oxide/metal heteroepitaxy

Abstract

The growth mode of strained epitaxial films relies on the interaction strength, the lattice matching and the mechanical response of the system. The present work focuses on the basic physics of supported nano-islands by examining the characteristics of MgO/Ag(100) taken as a case study. The combination of experiments and simulations highlights the existence of a small size regime in which, despite the largest adhesion and the smallest mismatch, the islands are the least distorted by the substrate. We assign this unexpected behavior to the enhanced island stiffness which makes the cost of elastic distortion prohibitive compared to the associated gain of MgO-Ag interaction energy. The analysis provides a general framework to predict and/or understand nanoscale effects on interfacial pseudomorphism. These are likely to hold whatever the nature of the deposit and substrate under consideration. It may have far reaching consequences on many properties of supported nano-objects.

Chromium Adsorption Reveals a Persistent Hydroxylation of Vacuum-Annealed α-Al2O3(0001)

“…Experiments have been performed on the LUCIA beamline at synchrotron SOLEIL (St Aubin, France) in a UHV apparatus that involves the preparation and main chambers already described. , The surfaces of the α-Al 2 O 3 (0001) single crystals were annealed in the first chamber at ∼1500 K in front of a gas doser under a stationary oxygen partial pressure of ∼1 × 10 –6 mbar. The cleanliness of the surface was controlled by Auger spectroscopy, and low-energy electron diffraction (LEED) revealed a (1 × 1)-termination.…”

“…Experiments have been performed on the LUCIA beamline at synchrotron SOLEIL (St Aubin, France) in a UHV apparatus that involves the preparation and main chambers already described. 46,47 The surfaces of the α-Al 2 O 3 (0001) single crystals were annealed in the first chamber at ∼1500 K in front of a gas doser under a stationary oxygen partial pressure of ∼1 × 10 −6 mbar. The cleanliness of the surface was controlled by Auger spectroscopy, and low-energy electron diffraction (LEED) revealed a (1 × 1)-termination.…”

“…The Cr/alumina film is studied by a combination of X-ray absorption spectroscopy (Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES)), laboratory X-ray photoemission (XPS) and numerical simulations relying on DFT. The EXAFS technique proved efficient in studying submonolayer coverage of adatoms [44][45][46][47] . The possible presence of non-periodically arranged 34 residual OH groups maintains a persistent blur on the nature of the non-polar Al-terminated α-Al 2 O 3 (0001) surface (Fig.…”

“…The Cr/alumina film is studied by a combination of X-ray absorption spectroscopy (XAS) (the extended X-ray absorption fine structure (EXAFS) and the X-ray absorption near-edge structure (XANES)), laboratory X-ray photoemission (XPS), and numerical simulations relying on DFT. The EXAFS technique proved efficient in studying the submonolayer coverage of adatoms. − The possible presence of nonperiodically arranged residual OH groups maintains a persistent blur on the nature of the nonpolar Al-terminated α-Al 2 O 3 (0001) surface. The objective is both to determine the site and chemistry of chromium atoms at the α-Al 2 O 3 (0001) surface and to examine whether there are interactions of metal adatoms with surface hydroxyl groups.…”

Interface Oxygen Induced Internal Structures of Ultrathin MgO Islands Grown on Ag(100)

“…In the ultrathin limit, the properties of MgO layers are known to depend critically on growth parameters. Indeed, when the film is produced by reactive deposition its stoichiometry is influenced by the O 2 partial pressure and Mg evaporation rate, as well as by growth temperature ( T g ), post annealing treatment, and, as some of us recently demonstrated, cooling rate of the sample after film preparation. , A recent paper addresses the dependence of the MgO lattice parameter on island size, while an additional factor of complexity is the mobility of the Ag atoms, which allows for the formation of MgO islands partially embedded in the Ag terrace. − Finally, islands were found to present a bias dependence under nontopographic conditions and to undergo an aging effect, which implies the accumulation of oxygen containing species attributed to hydroxyls. ,, The importance of such effect depends on the growth protocol of the islands as well.…”