Interface Stability-Controlled Growth of FexGe on Ge (100), (110), and (111) Substrates

Abstract

The electronic and magnetic properties of materials are strongly influenced by their surface and interface structures and configurations. In this work, we have grown FexGe single crystalline islands on the Ge substrate with three different surfaces, (001) (110), and (111), and investigated the interface structures between FexGe crystals and Ge substrates. The FexGe crystals result in two distinct phases on all three Ge substrates, namely, monoclinic and hexagonal. Using TEM/HRTEM, 3D rotational electron diffraction, and DFT simulation approaches, we carefully studied the facet orientation at the interface and explained the coexistence and formation mechanism of the monoclinic-FeGe and hexagonal-Fe13Ge8. Although Ge substrates with different orientations were used in the study, our findings suggest a unique facet preference that all the FexGe crystals tend to grow with Ge {111} epitaxially or endotaxially. Combining simulation of energy difference on selected facets, lattice mismatch, and the dangling bond density, we derive the mechanism of such a phenomenon as an interfacial equilibrium driven by the difference of interface energy. Our study provides valuable information in the FexGe/Ge system and will potentially benefit the future development of FexGe-related electronic/magnetic devices.