Highlights
- Fluorine doping concentration in spray-deposited ZnO thin films was varied to tune room-temperature acetaldehyde sensing.
- Average crystallite size decreased and micro-strain increased with increasing fluorine content.
- The 4 wt% fluorine-doped film gave the strongest, most selective acetaldehyde response, with a maximum response of 4.8 at 100 ppm.
- Response and recovery times for that film were about 18 and 25 seconds respectively.
Abstract
Undoped and fluorine-doped ZnO thin films were spray-deposited on glass, with fluorine-dopant concentration varied to study its effect on structure, morphology, and room-temperature gas sensing. All films kept a hexagonal wurtzite structure, but average crystallite size decreased and micro-strain increased as fluorine concentration rose. Among the tested concentrations, the film doped with 4 wt% fluorine showed the strongest and most selective response to acetaldehyde vapor at room temperature, with a maximum response of 4.8 toward 100 ppm and response/recovery times of about 18 and 25 seconds.
Research summary
Detecting acetaldehyde at low concentrations matters for food-spoilage monitoring and indoor air-quality applications, but building a sensor that is both selective and able to work at room temperature is a persistent challenge for metal-oxide gas sensors. This study investigates whether doping ZnO thin films with fluorine can produce a room-temperature acetaldehyde sensor with useful selectivity.
What the study examined
- Undoped and fluorine-doped ZnO thin films deposited on glass by spray pyrolysis, with fluorine concentration varied across several levels
- Crystal structure, crystallite size, and micro-strain across the doping series, using X-ray diffraction
- Surface morphology and optical and electrical properties of the doped films
- Room-temperature sensing response and selectivity toward acetaldehyde compared with other common vapors
- Response and recovery times of the best-performing film toward 100 ppm acetaldehyde
Main findings
All films retained the hexagonal wurtzite ZnO structure regardless of fluorine content, but increasing fluorine concentration produced a clear structural trend: average crystallite size decreased while micro-strain in the film increased. Among the concentrations tested, the film doped with 4 wt% fluorine stood out, giving the strongest and most selective response to acetaldehyde among the vapors tested at room temperature.
That film reached a maximum response of 4.8 toward 100 ppm acetaldehyde, with a response time of about 18 seconds and a recovery time of about 25 seconds. The authors link this doping-dependent performance to the structural changes fluorine introduces, particularly the combination of smaller crystallite size and increased strain at the optimal doping level.
Why it matters
The results identify fluorine doping concentration as a practical, tunable variable for building selective, room-temperature acetaldehyde sensors from a low-cost, spray-deposited ZnO platform. That combination of selectivity and room-temperature operation is attractive for real-world monitoring applications such as food-quality checks, where a low-power sensor that does not need a heating element has a clear practical advantage.
Citation
E. Gunasekaran, M. Ezhilan, G. K. Mani, Prabakaran Shankar, K. Arockia Jayalatha, J. B. B. Rayappan, K. J. Babu. Fluorine Doped ZnO Thin Film as Acetaldehyde Sensor. Semiconductor Science and Technology 33 (2018) 095005.
