Since the isolation of graphene, various two-dimensional (2D) materials have been extensively investigated. Nevertheless, only few 2D oxides have been reported to date due to difficulties in their synthesis. However, it is expected that the layered transition-metal oxides (TMOs) could be missing blocks for van der Waals heterostructures and essential elements for 2D electronics. Herein, the crystal structure and band structure of van der Waals epitaxially grown α-MoO3 nanosheets on various 2D growth templates are characterized. Monolayer and multilayer α-MoO3 nanosheets are successfully grown on a 2D substrate by simply evaporating amorphous molybdenum oxide thin film in ambient conditions. A single-crystal α-MoO3 nanosheet without grain boundary is epitaxially grown on various 2D substrates despite a large lattice mismatch. During growth, the quasi-stable monolayer α-MoO3 first covers the 2D substrate, then additional layers are continuously grown on the first monolayer α-MoO3. The band gap of the α-MoO3 increases from 2.9 to 3.2 eV as the thickness decreases. Furthermore, due to oxygen vacancies and surface adsorbates, the synthesized α-MoO3 is highly n-doped with a small work function. Therefore, α-MoO3 field-effect transistors (FETs) exhibit a typical n-type conductance. This work shows the great potential of ultra-thin α-MoO3 in 2D-material-based electronics.
Bibliographical noteFunding Information:
This work was supported by the Samsung Research Funding Center of Samsung Electronics under Project Number SRFC-MA1502-12. J D and C H acknowledge support by the Korea Research Fellowship Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and Future Planning (2016H1D3A1938061 and NRF-2016R1D1A1B01011181).
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering