Optical and structural properties of thin films of ZnO at elevated temperature
Introduction
ZnO is an important multifunctional material with actual and potential applications in display devices, solar cells, electro-chromic devices, transistors, LEDs and lasers. Simultaneous presence of both high optical transmittance in the visible range, and low resistivity make it an important material in the production of heat mirrors used in gas stoves, conducting coatings in aircrafts glass avoiding surface icing, and thin film electrodes in amorphous silicon solar cells.
The sol–gel process is a wet-chemical technique widely used in the fields of materials science and engineering. Such methods are used primarily for the fabrication of materials (typically metal oxides) and deposition of thin films. In sol–gel technique the films are produced with the application of three methods: Spin coating method, dip-coating method and spray coating method. In the present studies dip-coating method was applied. Several researchers have deposited thin films of ZnO by dip-coating method [1]. This work was performed to investigate the dip-coating method and study the properties of ZnO thin films including crystallization of material deposited, its transparency in ultraviolet region and band gap energy. These parameters are studied as a function of withdrawal speed.
Section snippets
Materials and methods
The sol was prepared by dissolution of zinc acetate dehydrate (99.5%) in ethanol followed by de-ionized water. The thin films were deposited on soda-lime-glass substrates by dip-coating technique with different withdrawal speed in the range 100–250 mm/s, at room temperature (RT) and room humidity (RH) conditions. Films were dried in air for ten minutes. The procedure was repeated 3 times. The films were then annealed for 1 h in air at 650 °C.
The crystal structure of thin films was evaluated by
FTIR
The FTIR spectrum in Fig. 1 of ZnO showed main absorption bands due to OH stretching of hydroxyl group at 4907 cm−1, asymmetric and symmetric CO stretching of Zinc acetate at 1385 cm−1, The ZnO peak that appears on the 403, 493 and 702 cm−1 shows that the transformation of Zn(OH)2 to ZnO was completed.
Structural studies
The XRD pattern of Fig. 2 clearly shows the characteristic peaks of ZnO for the thin film prepared at different withdrawal speed of dip-coater. The intensity of the peaks decreases with the increase
Conclusions
Thin films of ZnO are successfully prepared on glass substrates using dip-coating. The films are characterized by means of FTIR, UV–Vis spectrophotometer, scanning electron microscopy and X-ray diffraction. The X-ray diffraction analysis showed that films are amorphous in nature. Optical measurements show that the film possesses high transmittance over 90% in the visible region. The transmission decreased with increased withdrawal speed. Envelope method was employed to calculate the refractive
Acknowledgments
Authors want to thank Centre of Excellence in Solid State Physics, University of the Punjab, Lahore for providing facilities for SEM analysis.
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