Annealing-Driven Modifications in ZnO Nanorod Thin Films and Their Impact on NO2 Sensing Performance

Sandip M Nikam; Tanaji S Patil; Nilam A Nimbalkar; Raviraj S Kamble; Vandana R Patil; Uttam E Mote; Sadaf Jamal Gilani; Sagar M Mane; Jaewoong Lee; Ravindra D Mane

doi:10.3390/mi16070778

Annealing-Driven Modifications in ZnO Nanorod Thin Films and Their Impact on NO₂ Sensing Performance

Micromachines (Basel). 2025 Jun 30;16(7):778. doi: 10.3390/mi16070778.

Authors

Affiliations

¹ Department of Physics, Jaysingpur College, Jaysingpur, Shivaji University, Kolhapur 416101, Maharashtra, India.
² Department of Physics, Bhogawati Mahavidyalaya, Kurukali, Shivaji University, Kolhapur 416001, Maharashtra, India.
³ Sharad Institute of Technology, Polytechnic, Yadrav, Ichalkaranji 416121, Maharashtra, India.
⁴ Department of Chemistry, Bhogawati Mahavidyalaya, Kurukali, Shivaji University, Kolhapur 416001, Maharashtra, India.
⁵ Department of Physics, Shrimant Babasaheb Deshmukh Mahavidyalaya, Atpadi, Shivaji University, Kolhapur 415301, Maharashtra, India.
⁶ Department of Pharmaceutical Sciences, College of Pharmacy, Princess Nourah bint Abdulrahman University, P.O. Box 84428, Riyadh 11671, Saudi Arabia.
⁷ Department of Fiber System Engineering, Yeungnam University, Gyeongsan 38541, Gyeongbuk, Republic of Korea.

Abstract

This research examines the effect of annealing temperature on the growth orientation of zinc oxide (ZnO) nanorods and its subsequent influence on NO₂ gas sensing efficiency. Zinc oxide (ZnO) nanorods were synthesized using the chemical bath deposition method, followed by annealing at 300, 400, and 500 °C. Diffraction analysis confirmed that both non-annealed and annealed ZnO nanorods crystallize in a hexagonal wurtzite structure. However, increasing the annealing temperature shifts the growth orientation from the c-axis (002) toward the (100) and (101) directions. Microscopy images (FE-SEM) revealed a reduction in nanorod diameter as the annealing temperature increases. Optical characterization using UV-visible and photoluminescence spectroscopy indicated shifts in the band gap energy and emission properties. Contact angle measurements demonstrated the hydrophobic nature of the films. Gas sensing tests at 200 °C revealed that the ZnO thin film annealed at 400 °C achieved the highest NO₂ response of 5.88%. The study highlights the critical role of annealing in modifying the crystallinity, growth orientation, and defect states of ZnO thin films, ultimately enhancing their NO₂ detection capability.

Keywords: NO2 sensor; ZnO nanorod array; annealing temperature variation; growth orientation.