Sulfur Vacancies Enable Reversible NH 3 Chemisorption on Monolayer MoS 2 for Ultrasensitive Room Temperature Sensing

ABSTRACT Sensitive ammonia (NH 3 ) detection at room temperature (RT) is essential for environmental monitoring, industrial safety, and emerging energy technologies. However, developed semiconductor sensors often suffer from insufficient NH 3 response magnitude, slow response kinetics, and a requirement for elevated temperatures. In this work, we propose a controllable surface Sulfur‐vacancy (V S ) induced physisorption to reversible RT‐chemisorption transition for NH 3 on monolayer molybdenum disulfide (MoS 2 ). This transition facilitates the extensive formation of N─Mo bonds, narrows the band gap of MoS 2 substantially, and achieves highly sensitive NH 3 detection accordingly. Consequently, an optimized vacancy density of 8.0 at.% enables RT‐NH 3 sensing with a theoretical detection limit of 2.2 ppb, a wide dynamic range up to 10000 ppm, a minimum response time less than 2 s, and a remarkable selectivity ratio of 12. Benefiting from large surface and enhanced charge transfer, our RT‐ NH 3 prototype portable detector can deliver a prominent response of 23.7 with response time of 12 s toward 50 ppm NH 3 , and reversible recovery under 40% relative humidity (RH). These results establish rational RT‐chemisorption enabled molecular recognition as a route to superior performance RT‐NH 3 sensing in two‐dimensional monolayered materials.