MoS2 films from few layers to monolayer: Scalable synthesis and their band alignments with Al2O3 interfaces

Large-area MoS2 thin films, ranging from few layers to monolayers, were successfully synthesized on sapphire (Al2O3) substrates using e-beam deposition followed by sulfurization. The synthesized MoS2 films correspond to the 2H phase, as confirmed by grazing incidence x-ray diffraction and high-resolution transmission electron microscopy measurements. Monolayer and few layers of MoS2 thin film formation on Al2O3 was established by Raman spectroscopy and corroborated by photoluminescence (PL) spectroscopy and atomic force microscopy (AFM) measurements. Energy band alignments at the MoS2/Al2O3 interfaces for the films were studied non-destructively using hard x-ray photoelectron spectroscopy measurements. The valence band offset (VBO) at the monolayer MoS2/Al2O3 interface was measured to be 3.41 eV, and the conduction band offset (CBO) was 3.24 eV, within the measurement accuracy. Both VBO and CBO values increased with the number of MoS2 layers. The results contribute to the understanding of MoS2-based nano-electronic and optoelectronic devices, highlighting the importance of precise control over film thickness and interface engineering.