Synthesis of large-area MoS₂films by plasma-enhanced chemical film conversion of solution-processed ammonium tetrathiomolybdate

The synthesis of large-area molybdenum disulfide (MoS2) films is desired for many emerging electronic and optical applications. A typical approach is to deposit films from vapor-phase precursors either by thermal- or plasma-activated chemistry. Here, we show that MoS2 films exhibiting excellent crystallinity and smooth surfaces are produced by plasma conversion of solution-deposited precursor films. Films containing a single-source precursor for MoS2, ammonium tetrathiomolybdate, were spin coated and converted by an atmospheric-pressure dielectric barrier discharge with substrate heating at 500 °C. X-ray diffraction and micro-Raman spectroscopy show that the plasma is necessary to successfully convert the precursor to MoS2. Further enhancements in the crystallinity and surface roughness were obtained by annealing the films, as revealed by high-resolution transmission electron microscopy and atomic force microscopy (AFM). Insights into the role of the plasma were provided by AFM characterization and a "plasma-trigger"experiment, which suggest that a nanocone surface morphology facilitates the growth of the films.