J.A. Maurer, S.F. Bartolucci
U.S. Army RDECOM-ARDEC,
Keywords: 2D molybdenum disulfide, molybdenum trioxide, chemical vapor deposition
Summary:Two-dimensional materials, such as graphene and transition metal dichalcogenides, are a promising class of nanomaterials for next generation electronics, photovoltaics, electrocatalysts, sensors, and optoelectronic devices. Molybdenum disulfide (MoS2) is of particular interest due to its direct bandgap in the visible spectrum, high electron mobility, and chemical stability. In this work, we demonstrate that alterations in the density of surface hydroxyl groups on silicon dioxide substrates can control nucleation and growth in molybdenum disulfide thin films produced by atmospheric-pressure chemical vapor deposition. We have shown that the surface density of hydroxyl groups on silicon dioxide (SiO2) can be easily controlled using conventional gallium focused ion beam (FIB) patterning. After implantation into the silicon dioxide substrate, gallium ions undergo a charge transfer reaction with silicon atoms, which generates surface hydroxyl groups upon exposure of the substrate to atmospheric water. We have demonstrated that the number of hydroxyl groups generated on the surface is directly proportional to the ion dosage. Additionally, the extent of MoS2 nucleation is linearly correlated to the density of surface hydroxyl groups. Thus, controlling the density of surface hydroxyl groups on the initial substrate provides a method of growing patterned molybdenum disulfide. In addition, we show a two-step growth method, where molybdenum trioxide is first vaporized and nucleated on the SiO2 substrate, including preferentially in the FIB-hydroxylated regions. A second sulfurization step results in large-area monolayer MoS2, as confirmed by Raman spectroscopy and photoluminescence. Our two-step approach to MoS2 synthesis provides robust control over the parameters in chemical vaporization, which greatly increase reliability and reproducibility of this widely used method for monolayer synthesis. This work establishes a means of patterning large-area monolayer MoS2 on silicon dioxide substrates, which is a critical step for realizing applications in imaging, catalysis, biosensing, chemical detection, electronics and optoelectronics.