Effect of Nickel Doping on Structural, Optical, Electrical and Ethanol Sensing Properties of Spray Deposited Nanostructured ZnO Thin Films

Research summary

Metal oxide sensors that can detect ethanol vapor at room temperature, without a heater, are attractive for low-power gas sensing, but their performance depends heavily on how the sensing film is made. This study looks at whether doping zinc oxide (ZnO) thin films with nickel can improve their room-temperature ethanol response.

What the study examined

• Undoped and nickel-doped ZnO thin films spray-deposited on glass and annealed at 723 K
• Nickel precursor concentration varied from 0.002 to 0.010 M
• Crystal structure (XRD), surface morphology (FESEM), optical transmittance and band gap, and electrical resistivity
• Room-temperature response to 50 ppm ethanol vapor, including response and recovery times

Main findings

Nickel doping changed the film’s crystallite size (roughly 15 to 31 nm across the doping range) and reduced its optical band gap from about 3.21 to 3.09 eV as more nickel was added, consistent with additional defects forming in the doped films. The films stayed highly transparent throughout, with 70-80% average transmittance.

In room-temperature sensing tests against 50 ppm ethanol, the film doped with 0.008 M nickel gave the best response, with a response time of about 50 seconds and a recovery time of about 20 seconds — better than the undoped film or the other doping levels tested.

Why it matters

The results point to nickel doping as a workable route to improve ZnO’s room-temperature ethanol sensitivity, and show that there is an optimum doping level rather than a simple “more is better” trend. That is useful groundwork for later work aimed at practical, low-power ethanol sensors built on nickel-doped ZnO.