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 MoO 2 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 MoO 2 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 MoO 2 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 MoO 2 flakes in a MoS 2 field-effect transistor (FET) by introducing MoO 2 flakes as a van der Waals contact. High carrier mobility combined with an optimized Schottky barrier height was achieved in the designed MoS 2 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.