Inhomogenous Deposition of Vertical MoS 2 Grown by Chemical Vapor Deposition

Vertical Mos 2 flakes have potentials in various electronics and catalysis applications. Field emission scanning electron microscopy (FESEM) and Raman spectroscopy were used to study the morphology and uniformity of vertical MoS 2 flakes prepared by chemical vapor deposition. By understanding the morphology and uniformity of the flakes, we can obtain large and high density of vertical flakes. The MoS 2 samples were grown by using MoO 3 and sulfur precursors at 850 °C for 10 minutes at atmospheric pressure. The distance between MoO 3 and substrate was varied at 1 (sample A) and 6 cm (sample B). Little to no deposition was observed on sample B. For sample A, inhomogenous deposition was observed and was divided to three regions. At region 1, the vertical flakes of MoS 2 were the largest (~770 nm) and further reduced to ~140 and ~85 nm at region 2 and 3, respectively. The $\mathbf{E}^{1}2\mathbf{g}$ and $\mathbf{A}_{1\mathbf{g}}$ vibration modes of MoS 2 were observed in all regions. Raman mapping of the vibration modes ( $\mathbf{E}^{1}{2\mathbf{g}}$ and $\mathbf{A}_{1\mathbf{g}}$ ) at their respective peak positions and their intensity ratio showed region 1 may consist of region with horizontal flakes.