Structural elements in the oxidation process of a single cobalt layer on Ir(100)-(1 × 1)

The ordered phases developing in sequence by oxidation of a single monolayer of cobalt deposited on Ir(100)-(1 × 1) were investigated by low-energy electron diffraction (LEED), scanning tunneling microscopy, and thermal desorption spectroscopy. It turns out that the structural elements of the different phases observed for increasing oxygen content and analyzed by quantitative LEED are pyramids based on squares or triangles made up by cobalt species and oxygen on top. The Co-O bond lengths are smaller than in the bulk of cobalt oxide owing to the reduced coordination of oxygen. For O:Co ratios of r = 1/4, 1/2, and 5/8, the bonding of the oxide to the iridium substrate is merely by the cobalt species, and at r = 1 it is via both Co and O

Interface Chemistry and Molecular Bonding of Functional Ethoxysilane-Based Self-Assembled Monolayers on Magnesium Surfaces

The modification of magnesium implants with functional organic molecules is important for increasing the biological acceptance and for reducing the corrosion rate of the implant. In this work, we evaluated by a combined experimental and theoretical approach the adsorption strength and geometry of a functional self-assembled monolayer (SAM) of hydrolyzed (3-aminopropyl)­triethoxysilane (APTES) molecules on a model magnesium implant surface. In time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS), only a minor amount of reverse attachment was observed. Substrate–O–Si signals could be detected, as well as other characteristic APTES fragments. The stability of the SAM upon heating in UHV was investigated additionally. Density-functional theory (DFT) calculations were used to explore the preferred binding mode and the most favorable binding configuration of the hydrolyzed APTES molecules on the hydroxylated magnesium substrate. Attachment of the molecules via hydrogen bonding or covalent bond formation via single or multiple condensation reactions were considered. The impact of the experimental conditions and the water concentration in the solvent on the thermodynamic stability of possible APTES binding modes is analyzed as a function of the water chemical potential of the environment. Finally, the influence of van der Waals contributions to the adsorption energy will be discussed