Chemical vapor deposition of ultra-thin molybdenum dioxide nanosheets

• MoO2 nanosheets with thickness down to 5.5 nm were achieved through chemical vapor deposition.
• The ultrathin MoO2 nanosheets exhibit high electrical conductivity.
• The MoO2 nanosheets possess atomic smooth surfaces and could be oxidized into rough α-MoO3 nanosheets via heat treatment.

We report the growth of ultra-thin molybdenum dioxide nanosheets on SiO2/Si substrate via chemical vapor deposition using molybdenum trioxide and sublimated sulfur as precursors. The thicknesses of the obtained MoO2 nanosheets show notable dependence on the baking temperature of the sulfur precursor. At sulfur temperature of 90 °C, the obtained nanosheets can be 5.5 nm thin, more than one order of magnitude thinner than that previously reported, in a narrow scatter ranging from 5.5 to 11.5 nm. Two-probe electrical measurements show that the as-prepared ultrathin MoO2 nanosheets preserve a high electrical conductivity of 3600 S/cm with thermal stability up to 200 °C. Above 250 °C, metallic MoO2 nanosheets are oxidized into insulating MoO3 flakes in air.