Ellipsometric thickness as a probe for temperature-driven nanocrystallinity evolution in MoS2 films grown from Mo seed layers

The controlled synthesis of large-area molybdenum disulfide (MoS 2 ) films is critical for advancing optoelectronic applications, yet achieving uniform thickness and crystallinity remains a challenge. This study investigates the sulfurization of molybdenum seed layers (1, 5, and 10 nm) on SiO 2 /Si substrates across a wide temperature range of 400–900 °C, using spectroscopic ellipsometry to probe the interplay between morphological evolution and MoS 2 film thickness. We demonstrate that sulfurization temperature drives significant morphological changes that directly influence film thickness, contradicting the assumption that thickness depends solely on the Mo precursor. For the 1 nm Mo precursor, initial dewetting forms vertically oriented flakes in the MoS 2 film, which flatten at higher temperatures, resulting in a monotonic thickness decrease. In contrast, MoS 2 films from the 10 nm Mo precursor exhibit a smooth morphology at lower temperatures, transitioning to a granular structure with vertically oriented platelets above 600 °C, accompanied by a stepped thickness increase from 23.3 nm to 28.9 nm at 700 °C. MoS 2 films grown from the 5 nm precursor show a similar granular transition, with thickness peaking at 17.1 nm at 700 °C before declining at higher temperatures. These variations in thickness reflect temperature-driven nanocrystallinity changes, validated by SEM, AFM, Raman, and dielectric function analyses. The MoS 2 thickness profiles from the 5 and 10 nm precursors at elevated temperatures are compatible with strain relaxation models, where the vertical reorientation of MoS 2 layers helps to release strain energy. • MoS 2 film thickness and dielectric function from sulfurization of Mo precursors at 400–900 °C were studied by ellipsometry. • MoS 2 thickness varies not only with Mo precursor thickness but also with temperature-driven morphological changes. • MoS 2 films (10 nm Mo precursor) shift from smooth to granular morphology, with thickness rising from 23.3 to 28.9 nm. • MoS 2 thickness (10 nm Mo) rises at high T, aligning with strain relaxation models as layer reorientation lowers strain energy.