Abstract:
In this work, effect of zinc acetate concentration on ZnO thin films dip-coated on glass substrates has been investigated. As a starting material, zinc acetate dehydrate was dissolved in a mixture of ethanol and monoethanolamine solution with a sol concentration of 0.5, 0.6, 0.7, and 0.8 mol. L–1. The samples were characterized by X-Ray Diffraction (XRD) and the results clearly demonstrate that all the obtained films display a ZnO hexagonal wurtzite structure with a strong preferential orientation of the (002) direction. The thickness of the all samples was measured to be about of 350 nm by a Profilometer. The Roughness Mean Square (RMS) extracted from the Atomic Force Microscopy (AFM) images of the ZnO thin films surfaces show a small roughness value. It was estimated about of 6 nm for the thin film synthesised with a sol concentration of 0.7M . The optical transmission spectra in the UV-Visible domains indicate transmission values greater than 70% for all of the deposited layers . They also show that increasing the concentration, the maximum transmission exceeds 90% for all layers and moves towards longer wavelengths. For concentrations of 0.5 and 0.6 M, the best transmission is in the visible region, while for concentration of 0.7 to 0.8 M, it is maximal in the IR one. We also find that the optical gap is dependent on the concentration. It has a maximum value for a concentration of 0.7M.
MOTS-CLEFS : Sol-gel ; ZnO thin films; Optical properties; Photonic applications
M. Tazerout1, A. Chelouche 1, S. Khodja2, D. Djouadi1, A. Aksas1, T. Touam2
1 Laboratoire de Génie de l’Environnement, Université A. Mira de Béjaia, Route de Targua Ouzemmour Béjaia 06600
2 Laboratoire des Semi-conducteurs, Université Badji Mokhtar-Annaba, BP 12 Annaba 23000, Algérie.
EFFECT OF SOL CONCENTRATION ON OPTICAL PROPOERTIES OF SOL-GEL THIN FILMS FOR PHOTONIC APPLICATIONS
Optical properties
Thin films preparation by Sol-Gel:
Conclusion
Films display polycrystalline ZnO hexagonal wurtzite structure . Strong preferential orientation of the (002) direction. Increasing concentration increase (002) peak intensity.
Optical transmission greater than 70% for all layers . Increasing concentration, the maximum transmission moves towards longer wavelengths. For 0.5 and 0.6 M best transmission is in the visible region, for 0.7 to 0.8 M maximal transmission in IR region.
Optical gap dependents on the concentration. Maximum value for 0.7M . Importance of the sol-gel ZnO elaboration conditions .
The morphology of films dependents on elaboration conditions.
Structural properties
Figure 3. Transmission spectra of the ZnO films as a function of the sol concentration M. Figure 5: Optical band gap as a function of sol concentration
Figure 1: XRD spectra of the ZnO films as a function of the sol concentration
Figure 6: SEM image of ZnO thin film surface with a sol concentration of 0.5 ,0.6 , 0.7 and 0.8M. Figure 7: AFM image of ZnO thin film surface with a sol concentration of 0.7M.
Morphology
Ethanol
Zn(CH3COO)2. 2H2O
MEA/ZnO =1(mole ratio) Monoethanolamine (MEA)
Stairring at 60°C for 1h
Clear and homogneous solutions
C= 0.5 -0.8
Dip coating (v= 3mn/s
Preheating at 200°C for 15 mn Annealing at 500°C for 1h
Repeating 5 times
ZnO thin films
0.5M 0.6M 0.7M 0.8M
Figure 4: First derivative plot of the transmittance spectra of the ZnO thin films
Figure 2: relative Intensity of (002) peak as a function of sol concentration
