Highlights
- Spraying more precursor solution (15 to 45 mL) at a fixed concentration produced thicker ZnO films, from 225 nm up to 781 nm.
- Film crystallite size, electrical conductivity, and water contact angle all increased with precursor volume.
- The 30 mL film had the best crystallinity and lowest strain, ideal for optical applications.
- The thicker 45 mL film had a more open, void-containing morphology and lower band gap, better suited to gas sensing.
Abstract
This study investigated how the volume of precursor solution used in spray pyrolysis affects the properties of nanostructured zinc oxide (ZnO) thin films. Three precursor volumes (15, 30, and 45 mL of a fixed-concentration zinc nitrate solution) were sprayed onto heated glass substrates under otherwise identical conditions. Increasing the precursor volume increased film thickness, crystallite size, and electrical conductivity, while decreasing optical transmittance and band gap. Contact-angle measurements showed all films were hydrophobic, with the water contact angle increasing alongside film thickness. The 30 mL film had the best crystallinity and lowest strain, while the thicker 45 mL film had a more open, void-containing structure that the authors identified as favorable for gas-sensing applications.
Research summary
Film thickness is one of the most important variables in determining how a zinc oxide (ZnO) thin film performs in sensors, solar cells, and other devices. This study looked specifically at how the volume of precursor solution sprayed during deposition — rather than its chemical concentration — changes the thickness and resulting properties of spray-pyrolysis ZnO films.
What the study examined
- ZnO thin films spray-deposited on glass using three precursor volumes (15, 30, and 45 mL) of the same zinc nitrate solution, with all other deposition parameters held fixed
- Crystal structure, crystallite size, and strain across the three film thicknesses
- Surface morphology, optical transmittance, band gap, and electrical resistance as a function of precursor volume
- Water contact angle to assess how film thickness affects surface wettability
Main findings
Film thickness increased substantially with precursor volume, from 225 nm at 15 mL to 781 nm at 45 mL, and crystallite size increased alongside it. The film deposited with 30 mL of precursor had the most densely packed grain structure, the strongest crystallinity, and the lowest strain, while the 15 mL and 45 mL films both showed more voids in their grain structure.
Electrical resistance decreased and optical band gap narrowed as precursor volume — and film thickness — increased, while the water contact angle increased, indicating all films were hydrophobic and became modestly more water-repelling as they grew thicker. Based on these trends, the authors identified the 30 mL film as best suited for optical applications and the thicker, more porous 45 mL film as more promising for gas sensing.
Why it matters
The findings show that precursor volume alone, independent of its chemical concentration, is a practical and simple parameter for tuning ZnO film thickness and, through it, a whole set of structural, optical, electrical, and surface properties. That gives researchers a lower-effort way to target a specific film thickness for a specific application — denser, more crystalline films for optics, or thicker, more porous films for gas sensing — without changing the deposition chemistry itself.
Citation
S. Balaji, G. K. Mani, Prabakaran Shankar, J. B. B. Rayappan. Effect of Precursor Volume on Spray Pyrolysis Deposited Nanostructured ZnO Thin Films. Journal of Nanoelectronics and Optoelectronics 9 (2014) 529-533.
