Microjunction-Modulated Selective Ammonia Sensor with P-Type Oxides-Decorated WS 2 Microflakes.

In this study, p-type oxides including NiO, Co 3 O 4 , and CuO had been heterostructured with WS 2 microflakes for chemiresistive-type gas sensors at room temperature. Microjunctions formed between p-type oxides and WS 2 microflakes effectively modulated the sensitivities of the sensors to ammonia. In comparison to Co 3 O 4 - or CuO-decorated WS 2 -based sensors in which "deep energy puddles" were formed at the microjunctions between the oxides and WS 2 , the fabricated NiO/WS 2 heterostructure-based sensor without the formed energy puddles exhibited a better sensing performance with improved sensitivity and a faster response to gaseous 1-10 ppm of NH 3 . It also processes a good selectivity to some volatile organic compounds including HCHO, toluene, CH 3 OH, C 2 H 5 OH, CH 3 COCH 3 , and trimethylamine (TMA). The underlying mechanisms for the enhanced responses were examined by employing in situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory computation. The oxidization of NH 3 on NiO/WS 2 was much more intensified compared to those occurred on Co 3 O 4 /WS 2 and CuO/WS 2 . NiO/WS 2 has a stronger adsorption to NH 3 and gains more effective charges transferred from NH 3 which significantly contributes to the enhanced sensing properties.