Phase formation in intermixed Ni–Ge thin films: Influence of Ge content and low-temperature nucleation of hexagonal nickel germanides

•We study phase formation in the Ni–Ge thin film system using in situ XRD and TEM.•We deposited Ni films with different Ge concentrations using combinatorial sputtering.•A metastable germanide was observed when adding between 36 and 48 at.‰Ge.•When adding between 36 and 42 at.% Ge, this phase is already present as-deposited.

In this study, we focus on phase formation in intermixed Ni–Ge thin films as they represent a simplified model of the small intermixed interface layer that is believed to form upon deposition of Ni on Ge and where initial phase formation happens. A combinatorial sputter deposition technique was used to co-deposit a range of intermixed Ni–Ge thin films with Ge concentrations varying between 0 and 50 at.%Ge in a single deposition on both Ge (100) and inert SiO2 substrates. In situ X-ray diffraction and transmission electron microscopy where used to study phase formation. In almost the entire composition range under investigation, crystalline phases where found to be present in the as-deposited films. Between 36 and 48 at.%Ge, high-temperature hexagonal nickel germanides were found to occur metastabily below 300 °C, both on SiO2 and Ge (100) substrates. For Ge concentrations in the range between 36 and 42 at.%, this hexagonal germanide phase was even found to be present at room temperature in the as-deposited films. The results obtained in this work could provide more insight in the phase sequence of a pure Ni film on Ge.

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