Tahar Touam

Effects of Low Ag Doping on Physical and Optical Waveguide Properties of Highly Oriented Sol-Gel ZnO Thin Films

A sol-gel dip-coating process was used to deposit almost stress-free highly c-axis oriented zinc oxide (ZnO) thin films onto glass substrates. The effects of low silver doping concentration (Ag/Zn < 1%) on the structural, morphological, optical, and waveguide properties of such films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy, UV-Visible spectrophotometry, and M-lines spectroscopy (MLS). XRD analysis revealed that all the films were in single phase and had a hexagonal wurtzite structure. The grain size values were calculated and found to be about 24–29 nm. SEM micrographs and AFM images have shown that film morphology and surface roughness were influenced by Ag doping concentration. According to UV-Vis. measurements all the films were highly transparent with average visible transmission values ranging from 80% to 86%. It was found that the Ag contents lead to widening of the band gap. MLS measurements at 632.8 nm wavelength put into evidence that all thin film planar waveguides demonstrate a well-guided fundamental mode for both transverse electric and transverse magnetic polarized light. Moreover, the refractive index of ZnO thin films was found to increase by Ag doping levels.

Post-annealing effects on the physical and optical waveguiding properties of RF sputtered ZnO thin films

ZnO thin films were deposited at room temperature onto glass substrate by RF sputtering technique. Effects of the post-annealing at 300–500°C on the structural, morphological, optical and waveguiding properties were investigated using different characterization techniques. X-ray diffraction (XRD) analyses have shown that all thin films have a hexagonal wurtzite structure with higher c-axis preferred orientation (002), better crystallinity and larger crystallite size as post-annealing temperature increases. Fourier transform infrared (FTIR) spectra of annealed samples confirmed that the ZnO stretching vibration bond was found to be stable at 419 cm−1. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images have revealed that film morphology and surface roughness were influenced by heat treatment temperatures. The UV-Vis-NIR spectrophotometry characterisations have indicated that all the films were highly transparent with average transmittance exceeding 81% within the visible region, and the bandgap energy of the as-deposited film was increased with increasing of the annealing temperature.The obtained results from m-lines spectroscopy (MLS) measurements at 632.8 nm wavelength have demonstrated that all ZnO thin film optical waveguides were single mode and the ordinary and extraordinary refractive index values of the film annealed at 500°C were very close to the corresponding ZnO single-crystal values.

Physical and optical waveguiding properties of sol-gel deposited nano-structured TiO2 thin films: a study on the effect of synthesis parameters

In this paper, amorphous and polycrystalline nano-structured TiO2 thin films were prepared by sol-gel dip-coating process. The effects of different fabrication parameters (e.g., withdrawal speed, annealing temperature) on the structural, morphological and optical properties of the synthesised films were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and UV-visible Spectrophotometry. Waveguiding properties such as propagating modes and optical loss were measured at 632.8 nm by M-lines spectroscopy (MLS). The results indicate that all thin films annealed at 500oC exhibit XRD patterns and FTIR data consistent with the TiO2 anatase phase. AFM images have revealed that morphology and surface roughness of deposited thin films depend on withdrawal speed and heat treatment temperature. The UV-visible transmittance results show that all thin films were transparent with an average transmittance higher than 70% in the visible region. The results have also demonstrated from MLS measurements that TiO2 thin film slab waveguides deposited at withdrawal speed of 2 cm/min and annealed at 500°C exhibit not only better light confinement but also lower optical loss than those dip-coated at the speed of 1 and 3 cm/min.