Highly sensitive, selective and stable NO₂ gas sensors with a ppb-level detection limit on 2D-platinum diselenide films

Unlike common TMDCs such as MoS₂, PtSe₂ can be fabricated at temperatures below 600 °C, or even as low as 300 °C, while still maintaining high quality. By varying the selenization temperature from 300 °C to 600 °C, the electrical properties were changed significantly, resulting in superior gas sensing performance. Through comprehensive material analysis, an interesting phenomenon was found, namely that strain along the [001] direction existed in films grown at a low temperature rather than at a high temperature. Moreover, due to the layer-dependent property of PtSe₂, a phase transition from metal-to-semiconductor occurs as the thickness is reduced. Hybridization of phase engineering and thermal strain engineering significantly enhances the gas sensing performance, resulting in PtSe₂ with a dramatic increase in the response to 1 ppm NO₂ from 25% to 550% once the thickness was reduced from 10 to 5 layers. In addition, PtSe₂ showed good stability during exposure to not only 1 ppm but also 50 ppb NO₂ for more than 5 cycles with responses of over 550% and 60%, respectively.