Highlights
- Mg-doped ZnO thin films (0.002-0.01 M Mg) were deposited by spray pyrolysis and evaluated for room-temperature ammonia sensing.
- Crystallite size and optical band gap increased with Mg doping up to an intermediate level, then declined at the highest doping.
- All films, doped and undoped, responded most strongly to ammonia among six vapors tested.
- The lowest-doping film reached a response of 796 toward 100 ppm ammonia with 34 s/28 s response/recovery times, ahead of several other doped-ZnO ammonia sensors in the literature.
Abstract
This study examined how doping zinc oxide (ZnO) thin films with magnesium affects their structural, optical, electrical, and ammonia-sensing properties. Undoped and Mg-doped ZnO films, with Mg-precursor concentration varied from 0.002 to 0.01 M, were deposited on glass by spray pyrolysis. Crystallite size and the optical band gap both increased with Mg doping up to a point before declining at the highest doping levels, and electrical resistance followed a similar trend. All films responded most strongly to ammonia among several tested vapors, and the film with the lowest Mg-doping level gave the best sensing performance, reaching a room-temperature response of 796 toward 100 ppm ammonia with response and recovery times of 34 and 28 seconds — better than several previously reported doped ZnO ammonia sensors.
Research summary
Ammonia is a widely produced industrial gas that is hazardous at high concentrations, making low-cost, room-temperature sensors valuable for safety monitoring. This study examined how doping zinc oxide (ZnO) thin films with magnesium, at several different concentrations, affects the film’s structure and its ability to detect ammonia gas without heating.
What the study examined
- Undoped and Mg-doped ZnO thin films deposited on glass by spray pyrolysis, with Mg-precursor concentration varied from 0.002 to 0.01 M
- Crystal structure, grain morphology, and optical band gap across the doping range
- Electrical resistance trends linked to crystallite size and doping level
- Room-temperature sensing response and selectivity toward ammonia compared with acetaldehyde, acetone, ethanol, formaldehyde, and toluene vapors
Main findings
Increasing Mg doping first increased crystallite size and optical band gap, up to an intermediate doping level, then reversed at the highest doping concentrations as more defects formed in the film. Electrical resistance tracked the same pattern, dropping to a minimum at the intermediate doping level before rising again.
All of the films, doped and undoped, responded most strongly to ammonia among the six vapors tested, which the authors linked to ammonia’s small molecular size and low ionization energy. The film with the lowest Mg-doping concentration gave the best overall sensing performance, reaching a room-temperature response of 796 toward 100 ppm ammonia with response and recovery times of 34 and 28 seconds, ahead of several other doped-ZnO ammonia sensors reported in earlier work.
Why it matters
The results show that Mg doping is not a simple “more is better” lever — moderate doping levels changed the crystal structure most, but the lowest doping level actually gave the strongest gas response because of its larger surface-to-volume ratio. That distinction matters for anyone designing doped metal-oxide sensors: the doping level that best controls the material’s structure is not necessarily the one that best controls its sensing performance, and both need to be optimized for a room-temperature, low-power ammonia sensor.
Citation
K. Arockia Jayalatha, J. R. Reddy, S. Parthasarathy, K. Jayanth Babu, G. K. Mani, Prabakaran Shankar, J. B. B. Rayappan. Room Temperature Ammonia Sensing Properties of ZnO Thin Films Grown by Spray Pyrolysis: Effect of Mg Doping. Journal of Alloys and Compounds 688 (2016) 422-429.
