Modeling nucleation and insulating properties of oxide surfaces and ultra-thin films

The deposition of calcium ions is the first and most crucial step of apatite nucleation on ceramic supports from ionic solution. This process is believed to initiate the growth of bone-like material on the surface of biocompatibile implants. We have investigated the adsorption of Ca2+ from water solution on the rutile TiO2 (110) surface by means of first principles techniques. The preferential binding site of the calcium ion on the hydrated oxide surface was determined through a series of static calculations. Molecular dynamics simulations were then performed to elucidate the deposition pathway. The driving force for adsorption is identified in the electrostatic interaction between the Ca2+ complexes and negatively charged deprotonated sites present on the hydrated TiO2 (110) surface. In a separate set of simulations and experiments, the electronic structure and morphology of ultrathin MgO films epitaxially grown on Ag(001) was investigated using low temperature scanning tunneling spectroscopy (STS) and scanning tunneling microscopy (STM). Layer-resolved differential conductance (dI/dU) measurements reveal that, already at a film thickness of three monolayers, a band gap of about 6 eV is formed corresponding to that of the MgO(001) single crystal surface. This finding is confirmed by a series of layer-resolved calculations of the local density of states (LDOS) based on density functional theory (DFT).