Atomic and electronic structure of V/MgO interface

Thin films of vanadium were deposited on the (001) surface of a MgO substrate by molecular beam epitaxy (MBE) and the V/MgO interface was investigated by cross-sectional high resolution electron microscopy (HREM) and electron energy loss spectroscopy (EELS). In order to determine the location of atoms at the interface, computer simulations were performed for four possible models, and best matching between the experimental and simulated images was obtained for the model where the V atoms are located directly on top of the Mg atoms at the interface. Interface bonding mechanism was investigated by a first principles molecular-orbital (MO) calculation using the discrete-variational (DV)-X alpha method for a model cluster of the interface, i.e., (Mg9O9V5) The V-3d band was located in between the band-gap of MgO, and nearly empty Mg-3sp orbitals were found to overlap with the V-3d band. The Mg-Ssp and V-3d hybridized in a bonding manner, thereby generates strong covalent bonding between V and Mg. Nearly filled O-2p orbitals were also found to hybridize with the V-3d orbitals in an antibonding manner. The bond overlap population of the V-O bond was approximately four times smaller than that of the V-Mg bond when the bond-length was the same. The near edge structure of EELS specific to the interface was obtained using a V/MgO multilayer specimen at both Mg-K and O-K edges. Comparison between the experimental and theoretical spectra by the present MO calculation clearly found the presence of hybridized orbitals of V-3d with Mg-3p.