Etude des propriétés physiques de couches minces TiO2 élaborées par différentes techniques

Abstract

we have undertaken, the main objective optimization of parameters inherent to both chemical (sol-gel) and physical (Pulsed Laser Deposition) used for the preparation of TiO2 thin films on different substrates. Structural, optical and electrical properties of these films were studied by mean of X-ray diffraction (XRD), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), UV-Visible spectroscopy, and resistivity (conductivity) measurements. Undoped and Cu-doped TiO2 (Cu:TiO2) thin films were deposited by sol-gel method on glass substrates. Structural, optical and electrical properties of undoped doped copper doped TiO2 films. XRD spectra show that the non-annealed sample is amorphous and crystallized anatase phase from 400 °C. The obtained films are polycrystalline of anatase structure with (1 0 1) plan as preferential orientation. The surfaces of Cu-doped TiO2 films are smoother than undoped TiO2 films. The optical transmittance of simples is about 75 % in the visible region. The optical band gap undergoes a blue shift from 3.3 to 2.97 eV for undoped and 7at. % Cu doped TiO2 respectively. The values of the refractive index and the packing density increases, with increasing copper doping. The electrical characterization shows a maximum electrical conductivity of 1.29 (Ω cm)-1 obtained for the film doped with 7 at.% Cu. Al-doped TiO2 (TiO2:Al) thin films were deposited at 450ºC onto glass substrates using pulsed laser deposition method. The used source was a Nd:YAG laser (λ = 335 nm, ν = 5 Hz, Φ = 2 J/cm2 and τ = 8 ns pulse duration). X-rays diffraction spectra showed that the obtained films are polycrystalline of anatase structure with preferential orientation of (101) direction. AFM images, nanoparticles size and surface roughness mean square values showed that the surfaces of TiO2:Al films are smoother than that of undoped TiO2 films. A blue shift in the absorption edge of TiO2 with increasing Al concentration in the film is noteworthy as it leads to increase in the width of the optical transmission. The optical waveguiding performances of the TiO2:Al films were demonstrated by using the m-lines spectroscopy technique and the results were correlated to the structural properties. Spectroscopic ellipsometry was used to extract the optical constants of the films. The determined band gap of undoped and Al doped films varies from 3.43 to 3.61 eV,which is in accordance to Burstein-Moss shift.