TiO₂-modified MoS₂ monolayer films enable sensitive NH₃ sensing at room temperature

The research and development of high-performance NH₃ sensors are of great significance for environment monitoring and disease diagnosis applications. Two-dimensional (2D) MoS₂ nanomaterials have exhibited great potential for building room-temperature (RT) NH₃ sensors but still suffer from relatively low sensitivity. Herein, the TiO₂-modified monolayer MoS₂ films with controllable TiO₂ loading contents are fabricated by a facile approach. A remarkable enhancement in the RT NH₃ sensing performance is achieved after the n-n hetero-compositing of the TiO₂/MoS₂ system. The device with 95% surface coverage of TiO₂ 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 TiO₂ modification not only improved the surface reactivity of the sensing layers but also contributed to the NH₃ sensing performance by serving as the "gas-gating" layers that modulated the electron depletion layer and the conductivity of the MoS₂ films. Such an n-n hetero-compositing strategy can provide a simple and cost-effective approach for developing high-performance NH₃ sensors based on 2D semiconductors.