Highlights
- Fe-dopant concentration (0.002-0.010 M) was varied in spray-deposited ZnO thin films to study morphology and property changes.
- Increasing Fe doping drove a clear shape transition from rounded nanospheres toward elongated nanorods.
- Crystallite size increased and optical band gap decreased with increasing Fe-dopant concentration.
- Electrical conductivity increased with Fe doping, consistent with Fe acting as a shallow donor in ZnO.
Abstract
Undoped and iron-doped ZnO thin films were spray-deposited on glass, with Fe-dopant concentration varied from 0.002 to 0.010 M, and post-annealed to raise crystallinity. X-ray diffraction confirmed a polycrystalline hexagonal wurtzite structure throughout, with no separate iron-oxide phase, and both crystallinity and crystallite size increased with Fe-dopant concentration. Increasing Fe doping also drove a clear change in surface morphology, from rounded nanospheres toward elongated nanorods, together with a decrease in optical band gap and an increase in electrical conductivity.
Research summary
Doping is a well-established tool for tuning a semiconductor’s electronic and optical properties, but its effect on the physical shape, or morphology, of a nanostructured film is less commonly studied in a systematic way. This work looks specifically at whether varying the concentration of iron dopant in spray-deposited ZnO thin films can be used to deliberately reshape the film, from rounded nanosphere grains toward elongated nanorods.
What the study examined
- Undoped and Fe-doped ZnO thin films deposited on glass by spray pyrolysis, with Fe-dopant concentration varied from 0.002 to 0.010 M
- Post-annealing of the films at 723 K to increase crystallinity
- Crystal structure and preferred growth orientation across the doping series, using X-ray diffraction and texture-coefficient analysis
- Surface morphology of undoped and Fe-doped films, using field-emission electron microscopy
- Optical absorbance, band gap, and electrical conductivity across the Fe-dopant concentration range
Main findings
Across the entire doping range, the films stayed polycrystalline ZnO with a hexagonal wurtzite structure and no detectable separate iron-oxide phase, indicating the Fe atoms substituted into the ZnO lattice rather than forming their own compound. Both crystallinity and crystallite size increased as Fe-dopant concentration rose, and the preferred crystal growth orientation shifted from largely random at low doping toward a specific crystal plane at higher Fe concentrations.
That structural shift was accompanied by a clear change in surface morphology: films moved from rounded nanospheres at low Fe concentration toward more elongated, nanorod-shaped grains as doping increased. Alongside this morphology transition, the optical absorption edge shifted to longer wavelengths and the optical band gap decreased with increasing Fe concentration, while electrical conductivity increased, consistent with iron acting as a shallow donor within the ZnO lattice.
Why it matters
The findings show that Fe-dopant concentration is not just a lever for adjusting ZnO’s electronic and optical properties, it can also be used to deliberately reshape the film’s morphology from nanospheres to nanorods. That gives materials designers a single, simple synthesis variable, dopant concentration, for jointly tuning shape, band gap, and conductivity in spray-deposited ZnO thin films.
Citation
P. Karthika, G. K. Mani, Prabakaran Shankar, J. B. B. Rayappan. ZnO Nanospheres to Nanorods: Morphology Transition via Fe-Doping. Superlattices and Microstructures 62 (2013) 39-46.
