Room-temperature ammonia sensors, from doped ZnO thin films to carbon-nanotube networks, with a focus on selectivity, response time, and long-term stability.
Optimized spray pyrolysis conditions grow c-axis oriented boron-doped ZnO films instead of the usual crystallinity loss, with 10 mol% boron giving the strongest, most selective room-temperature ammonia response.
Magnesium doping tunes spray-pyrolysis ZnO crystallite size and band gap, with the lowest-doping film reaching a room-temperature ammonia response of 796 at 100 ppm.
Manganese doping shrinks ZnO crystallite size from 28 to 7 nm while keeping films selective to ammonia, with the best-performing film giving roughly 5x the undoped response and 60-day stability.
Raising the spray-pyrolysis substrate temperature shifts ZnO grain shape from spherical to pebble-like and strengthens the room-temperature ammonia response, peaking at 623 K.
Ultrasonically treated, annealed carbon-nanotube networks show a striking dual response to ammonia: resistance rises with concentration, then drops three orders of magnitude above 2500 ppm.
A nanopebble-textured ZnO film made by high-temperature spray pyrolysis selectively senses ammonia at room temperature down to 1 ppm.
