TiO 2 -modified MoS 2 monolayer films enable sensitive NH 3 sensing at room temperature.

The research and development of high-performance NH ₃ sensors are of great significance for environment monitoring and disease diagnosis applications. Two-dimensional (2D) MoS ₂ nanomaterials have exhibited great potential for building room-temperature (RT) NH ₃ sensors but still suffer from relatively low sensitivity. Herein, the TiO ₂ -modified monolayer MoS ₂ films with controllable TiO ₂ loading contents are fabricated by a facile approach. A remarkable enhancement in the RT NH ₃ sensing performance is achieved after the n - n hetero-compositing of the TiO ₂ /MoS ₂ system. The device with 95% surface coverage of TiO ₂ shows enhanced sensor response, low detection limit (0.5 ppm), wide detection range (0.5-1000 ppm), good repeatability, and superior selectivity against other gases. In situ Kelvin potential force microscopy results revealed that the TiO ₂ modification not only improved the surface reactivity of the sensing layers but also contributed to the NH ₃ sensing performance by serving as the "gas-gating" layers that modulated the electron depletion layer and the conductivity of the MoS ₂ films. Such an n - n hetero-compositing strategy can provide a simple and cost-effective approach for developing high-performance NH ₃ sensors based on 2D semiconductors.