Paper NM-TuP10
Synthesis and Application of Large-Area Transition Metal Dichalcogenides by Chemical Vapor Deposition

Tuesday, December 9, 2014, 4:00 pm, Room Mauka

Transition metal dichalcogenides (MoS₂, WS₂, Wse₂, MoSe₂, NbS₂, NbSe₂, etc.) are layered materials that would exhibit semiconducting, metallic and even superconducting behavior. In the bulk, it is semiconducting and has an indirect band gap. Recently, these layered systems have attracted a great deal of attention mainly due to their complementary electronic properties when compared to other two-dimensional materials, such as graphene (a semimetal) and boron nitride (an insulator). However, these bulk properties could be significantly modified when the system becomes mono-layered; the indirect band gap becomes direct. Such changes in the band structure when reducing the thickness of a MoS₂ and WS₂ films has important implications for the development of novel applications, such as valleytronics. In this work, we report for the controlled synthesis of large-area (~cm²) single-, bi-, and few-layer MoS₂ and WS₂ using a two-step process. MoO_x and WO_x thin films were deposited onto a Si/SiO₂ substrate, and these films were then sulfurized under vacuum in a second step occurring at high temperatures (750 °C). The synthesized MoS₂ and WS₂ atomic thin films were analyzed by optical microscopy, Raman spectroscopy and TEM, and their photoluminescence properties were evaluated.