Structure and morphology of epitaxially grown Fe3O4/NiO bilayers on MgO(001)

TL;DR

This study investigates the structural and morphological properties of epitaxially grown Fe3O4/NiO bilayers on MgO(001), revealing insights into film relaxation, interface roughness, and epitaxial growth behavior using various advanced characterization techniques.

Contribution

It provides a detailed analysis of the growth, relaxation, and interface properties of Fe3O4/NiO bilayers on MgO(001), highlighting the pseudomorphic growth of NiO and relaxation of Fe3O4 films.

Findings

NiO films grow pseudomorphically up to 34nm thickness

Fe3O4 films relax continuously up to 50nm thickness

Interface roughness increases with NiO thickness

Abstract

Crystalline Fe3O4/NiO bilayers were grown on MgO(001) substrates using reactive molecular beam epitaxy to investigate their structural properties and their morphology. The film thickness either of the Fe3O4 film or of the NiO film has been varied to shed light on the relaxation of the bilayer system. The surface properties as studied by x-ray photo electron spectroscopy and low energy electron diffraction show clear evidence of stoichiometric well-ordered film surfaces. Based on the kinematic approach x-ray diffraction experiments were completely analyzed. As a result the NiO films grow pseudomorphic in the investigated thickness range (up to 34nm) while the Fe3O4 films relax continuously up to the thickness of 50nm. Although all diffraction data show well developed Laue fringes pointing to oxide films of very homogeneous thickness, the Fe3O4-NiO interface roughens continuously up to 1nm root-mean-square roughness with increasing NiO film thickness while the Fe3O4 surface is very smooth independent on the Fe3O4 film thickness. Finally, the Fe3O4-NiO interface spacing is similar to the interlayer spacing of the oxide films while the NiO-MgO interface is expanded.