Growth, structure and stability of sputter-deposited MoS₂ thin films

Molybdenum disulphide (MoS₂) thin films have received increasing interest as device-active layers in low-dimensional electronics and also as novel catalysts in electrochemical processes such as the hydrogen evolution reaction (HER) in electrochemical water splitting. For both types of applications, industrially scalable fabrication methods with good control over the MoS₂ film properties are crucial. Here, we investigate scalable physical vapour deposition (PVD) of MoS₂ films by magnetron sputtering. MoS₂ films with thicknesses from ≈10 to ≈1000 nm were deposited on SiO₂/Si and reticulated vitreous carbon (RVC) substrates. Samples deposited at room temperature (RT) and at 400 °C were compared. The deposited MoS₂ was characterized by macro- and microscopic X-ray, electron beam and light scattering, scanning and spectroscopic methods as well as electrical device characterization. We find that room-temperature-deposited MoS₂ films are amorphous, of smooth surface morphology and easily degraded upon moderate laser-induced annealing in ambient conditions. In contrast, films deposited at 400 °C are nano-crystalline, show a nano-grained surface morphology and are comparatively stable against laser-induced degradation. Interestingly, results from electrical transport measurements indicate an unexpected metallic-like conduction character of the studied PVD MoS₂ films, independent of deposition temperature. Possible reasons for these unusual electrical properties of our PVD MoS₂ thin films are discussed. A potential application for such conductive nanostructured MoS₂ films could be as catalytically active electrodes in (photo-)electrocatalysis and initial electrochemical measurements suggest directions for future work on our PVD MoS₂ films.