Anouar Hajjaji

Structure and photoluminescence of ultrathin films of SnO2 nanoparticles synthesized by means of pulsed laser deposition

Tin oxide (SnO2) ultrathin films were deposited by pulsed laser deposition (PLD) onto SiO2/Si and quartz substrates, at various nominal thicknesses ranging from isolated nanoparticles (NPs) to ∼300 nm-thick films, under an oxygen background pressure of 10 mTorr. The microstructural and surface morphologies of the NP-based SnO2 films were characterized by x-ray diffraction and atomic force microscopy, as a function of their nominal film thickness. The PLD-SnO2 films were found to be composed of NPs (in the 1–6 nm range), whose size increases with the film thickness. The energy band gap, as determined from the absorption edge, was found to shift to higher values with decreasing the film thickness (i.e., decreasing the NPs size). It was found that an annealing at 700 °C under O2 ambient is a prerequisite to get a photoluminescence (PL) emission from the PLD-SnO2 films. The PL of the annealed SnO2 films was found to consist of two broad emission bands, regardless of the SnO2 film thickness. The first band is ...

Optical Properties Tuning of SnO2 Films by Metal Incorporation (Pt,Pd): Correlation with Microstructure Change

In this work, we report on the effect of noble metal doping (namely Pd or Pt) on the optical properties of SnO2 thin films. The optical constants (n and k) of the films, as a function of noble metal nature and content, were obtained using variable angle spectroscopic ellipsometry in the ultraviolet–visible–near infrared (UV–vis–NIR) regions. Ellipsometry analysis showed that we can tune the optical constants of SnO2 films by changing Pt or Pd doping concentration. In particular, their refractive index increases from 1.6 to ~2 while varying Pt content from 3 to 12 at. %. The origin of this optical behaviour was correlated to the microstructure change induced by metal doping. X-ray diffraction (XRD) was used to investigate the effect of doping on SnO2 lattice parameter, on crystallite size and on film preferential orientation. Atomic force microscopy (AFM) was used to estimate the surface roughness of the films. A metal concentration of ~3 at. % (for both Pt and Pd), which is known to yield the highest SnO2 gas sensing response, was found to correspond to the highest contraction of the lattice parameter of the films. Finally, the energy band gap of undoped SnO2 thin films (estimated to 4 eV) was found to shift to lower value while increasing doping concentrations.

Enhancing the photoelectrochemical response of TiO2 nanotubes through their nanodecoration by pulsed-laser-deposited Ag nanoparticles

We report on the pulsed laser deposition (PLD) based nanodecoration of titanium dioxide (TiO2) nanotube arrays (NTAs) by Ag nanoparticles (NPs). We focus here on the investigation of the effect of the number of laser ablation pulses (NLP) of the silver target on both the average size of the Ag-NPs and the photoelectrochemical conversion efficiency of the Ag-NP decorated TiO2-NT based photoanodes. By varying the NLP, we were able to not only control the size of the PLD-deposited Ag nanoparticles from 20 to ∼50 nm, but also to increase concomitantly the surface coverage of the TiO2 NTAs by Ag-NPs. The red-shifting of the surface plasmon resonance peak of the PLD-deposited Ag-NPs deposited onto quartz substrates confirmed the increase of their size as the NLP is increased from 500 to 10 000. By investigating the photo-electrochemical properties of Ag-NP decorated TiO2-NTAs, by means of linear sweep cyclic voltammetry under UV-Vis illumination, we found that the generated photocurrent is sensitive to the size...

TiO 2 Photocatalysis

This work is completed with a summary and a brief outlook for the further improvement of the photocatalytic performance when this chromium element is incorporated into TiO2 oxide growing on quartz and porous multicrystalline silicon substrates. These photosensitivity tests emerged as a new way to show the important role of the structural modification and microstructure of such Cr doped TiO2 sputtered thin films.

Microstructure and Optical Properties of Pure and Cr-Doped TiO2 Thin Films

This chapter describes the structural, optical and electrical properties of TiO2 layers grown on various substrates such as quartz, intrinsic silicon and both P and N types silicon. This chapter starts with a brief description of the deposition parameters. In particular, the influence of chromium content as well as the growth and mechanism conditions on the structure, morphology and optical proprieties (size of crystallites, mesh parameter, morphology, chemical composition, optical index, bandgap energy, reflectivity, etc.) of the final prepared films are described.

TiO 2 Properties and Deposition Techniques

This chapter deals with some physical properties of TiO2 used in various physical applications. Indeed, a brief review of the structural, optical and electronic properties of TiO2 films is presented; then some technical methods as well as fundaments and experimental features of this oxide are provided. Particular attention is paid to the effect of the microstructure and the incorporation of doping elements on the optoelectronic and sensing properties of TiO2 films.

Gas Sensors and Photo-Conversion Applications

First, this chapter investigates the electrical behavior as well as stability and reproducibility of Cr doped TiO2 thin films against ethanol gas. Second the TiO2-Cr/SP/Si structures are studied using different techniques such as AFM, SEM, photoluminescence, lifetime and laser-induced current (LBIC). Finally, the optoelectronic and photosensibility properties of such structures based on Cr doped TiO2 revealed potential applications in photovoltaic solar cells.

Synthesis and Characterization of TiO2–Cr Thin Films

Details of the important experimental conditions of the synthesis of Cr doped TiO2 thin films by means of co-deposition by magnetron sputtering process are presented. Furthermore, a brief description of the structural, electrical and optical characterizations set-up is provided. These physical characterizations are based on X-ray diffraction, atomic force and scanning electronic microscopy, LBIC… techniques.