Controlled synthesis of ultrathin metallic MoO2 nanosheets for van der Waals contact

Van der Waals contact through assembly of two-dimensional (2D) semiconductors with metallic materials by van der Waals force is considered as one of the most promising methods to solve the contact problem in 2D-material-based electronics. However, the previous studies mostly focused on semiconductor materials, while the preparation and properties of metallic materials have been less studied. In this paper, we reported a controlled synthesis of metallic layered MoO2 flakes with thicknesses of 3.5 to 106.8 nm using the chemical vapor deposition method. X-ray diffraction, scanning tunneling microscopy, and transmission electron microscopy were used to characterize the fabricated MoO2 nanoplates. The results indicate that the samples have a monoclinic crystal structure with high crystal quality and stability. The electrical characterization reveals an excellent conduction behavior of thin MoO2 flakes with a conductivity exceeding 10(6) S m(-)(1), which is comparable to those of graphene and some metals. In addition, we explored the contact applications of thin MoO2 flakes in a MoS2 field-effect transistor (FET) by introducing MoO2 flakes as a van der Waals contact. High carrier mobility combined with an optimized Schottky barrier height was achieved in the designed MoS2 FET. This study provides new insights into the preparation as well as application of metallic materials and is expected to promote the development of 2D-material-based electronics.