Initial stage growth mechanisms of metal adsorbates – Ti, Zr, Fe, Ni, Ge, and Ag – on MgO(001) surface

Abstract

The initial stage growth mechanisms of metal adsorbates (Ti, Zr, Fe, Ni, Ge, and Ag) on MgO(001) surfaces are investigated using coaxial impact-collision ion scattering spectroscopy and reflection high-energy electron diffraction. It is found that Ti adatoms diffuse into the MgO bulk via Mg substitutional sites even at room temperature. This interdiffusion of Ti is activated by heat treatment. Some of the deposited Ti atoms remain on the outermost MgO surface after annealing at 1270 K to form a 2×2 superstructure. A model of the superstructure is proposed in the present study. Zr is also revealed to be incorporated into the MgO substrate, following the same process as that for the Ti/MgO system. By contrast, there is no interfacial reaction in the systems of Fe, Ni, Ge, and Ag on MgO. The difference in the growth morphology among these nonreactive systems is found, and the wetting ability of the metal adsorbates is as follows: Ge>Fe and Ni>Ag. The interfacial reaction and growth morphology of the metal overlayers are interpreted in terms of the reactivity of the metal adsorbates toward oxygen and the stability of the metal adsorbates in the MgO lattice, which is estimated by comparing the ion size between Mg 2+ and the adsorbates.