Julien Petersen

Structural and photoluminescence properties of ZnO thin films prepared by sol-gel process

The present study focuses on the structural and optical properties of ZnO thin films fabricated by sol-gel process and spin coated onto Si (100) and quartz substrates. The ZnO films have a hexagonal wurtzite structure with a grain size of about 50 nm. The x-ray photoelectron spectroscopy measurements reveal the presence of Zn2+ and of zinc hydroxyl groups at the film. Optical properties were studied by photoluminescence (PL) and absorption spectroscopy at low and room temperatures. The absorption spectrum is dominated by a sharp excitonic peak at room and low temperatures. At room temperature, PL observations show two transitions: one near the absorption edge in the ultraviolet (UV) region and the second centered at 640 nm, characteristic of the deep electronic levels in the bandgap. The spectrum at 6 K is dominated by donor bound exciton lines and donor-acceptor pair transitions. LO-phonon replica and two-electron satellite transitions are also observed. These optical characteristics are a signature of g...

Optical properties of ZnO thin films prepared by sol-gel process

The present study focused on ZnO thin films fabricated by sol-gel process and spin coated onto Si (100) and quartz substrates. ZnO thin films have a hexagonal wurtzite structure with a grain diameter about 50nm. Optical properties were determined by photoluminescence (PL) and absorption spectroscopy. The absorption spectrum is dominated by a sharp excitonic peak at room and low temperatures. At room temperature, two transitions were observed by PL. One near to the prohibited energy band in ultraviolet (UV) region and the other centered at 640nm, characteristic of the electronic defects in the band-gap. The spectrum at 6K is dominated by donor-bound exciton lines and donor-acceptor pair transition. LO-phonon replica and two-electron satellite transitions are also observed. These optical characteristics are a signature of high-quality thin films.

Correlation of structural properties with energy transfer of Eu-doped ZnO thin films prepared by sol-gel process and magnetron reactive sputtering.

We investigated the structural and optical properties of Eu-doped ZnO thin films made by sol-gel technique and magnetron reactive sputtering on Si (100) substrate. The films elaborated by sol-gel process are polycrystalline while the films made by sputtering show a strongly textured growth along the c-axis. X-ray diffraction patterns and transmission electron microscopy analysis show that all samples are free of spurious phases. The presence of Eu(2+) and Eu(3+) into the ZnO matrix has been confirmed by x-ray photoemission spectroscopy. This means that a small fraction of Europium substitutes Zn(2+) as Eu(2+) into the ZnO matrix; the rest of Eu being in the trivalent state. This is probably due to the formation of Eu(2)O(3) oxide at the surface of ZnO particles. This is at the origin of the strong photoluminescence band observed at 2 eV, which is characteristic of the (5)D(0)-->(7)F(2) Eu(3+) transition. In addition the photoluminescence excitonic spectra showed efficient energy transfer from the ZnO matrix to the Eu(3+) ion, which is qualitatively similar for both films although the sputtered films have a better structural quality compared to the sol-gel process grown films.

Enhanced Adhesion over Aluminum Solid Substrates by Controlled Atmospheric Plasma Deposition of Amine-Rich Primers

Controlled chemical modification of aluminum surface is carried by atmospheric plasma polymerization of allylamine. The amine-rich coatings are characterized and tested for their behavior as adhesion promoter. The adhesion strength of aluminum-epoxy assemblies is shown to increase according to primary amino group content and coating thickness, which in turn can be regulated by plasma power parameters, allowing tailoring the coating chemical properties. The increase in adherence can be correlated to the total and primary amino group contents in the film, indicating covalent bonding of epoxy groups to the primer as the basis of the mechanical improvement.

Organosilicon coatings deposited in atmospheric pressure townsend discharge for gas barrier purpose: effect of substrate temperature on structure and properties.

Organosilicon plasma polymer and silicalike layers are deposited at different temperatures in a dielectric barrier discharge at atmospheric pressure operating in the Townsend regime. Final properties of these two kinds of layers can be finely tuned by the plasma process conditions. In particular, influence of deposition temperature is investigated when hexamethyldisiloxane based monolayers are deposited on poly(ethylene naphtalate) substrate. Coating chemical structure is tested by means of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Their thickness, topography, and mechanical properties are evaluated by ellipsometry, scanning electron microscopy observation of coatings cross sections, atomic force microscopy, and nanoscratch testing. Permeability of coated polymer is measured for transparent silicalike layers, and the effect of coating structure on the oxygen gas permeability is discussed. The deposition temperature of coatings at 90 °C provides a strong improvement in barrier property compared to room temperature deposition, thanks to a densification of the SiO₂ matrix and to a decrease in the silanol group content.

Magnetic properties of Al-doped Zn0.95Co0.05O films: Experiment and theory

Al-doped ZnCoO films were grown by sol-gel process onto SiO2 and Si(100) substrates. Structural analysis shows that all samples have the hexagonal wurtzite structure with a slight preferential orientation along the c-axis. The insertion of Al and Co into the ZnO matrix has been experimentally evidenced by UV-visible spectroscopy and transmission electron microscopy. This is further supported by x-ray photoelectron spectroscopy which indicated that all Co is under ionic form and that the samples contain no metallic clusters. The creation of free carriers by Al doping was confirmed by Hall effect and resistance measurements. Although a weak ferromagnetism is observed in all films, no clear influence of Al doping on the magnetic properties is evidenced which is in agreement with electronic structure calculations. The calculations show clearly that there is almost no overlap between the Al and the Co states, suggesting no change in the magnetic properties of ZnCoO with the Al doping. The only major role of Al...

Extrinsic ferromagnetism in epitaxial Co-doped CeO2 pulsed laser deposited films

We report on the structural and magnetic properties of 5 at. % Co-doped CeO2 films grown on LaAlO3(001) substrates by pulsed laser deposition. A series of epitaxially grown samples made under different oxygen partial pressures ranging from 10−4 to 10−1 mbar showed a ferromagnetic signal at room temperature. This signal is independent on the oxygen partial pressure during deposition. X-ray photoelectron spectroscopy showed an increasing concentration of defects as the oxygen pressure during deposition decreases. Although x-ray diffraction and transmission electron microscopy observations could not prove the existence of spurious phases, the temperature dependent variation in the magnetization suggests the existence of small magnetic Co clusters with a large distribution of blocking temperatures.

Nano-ordered thin films achieved by soft atmospheric plasma polymerization

Plasma polymer thin films are of great interest in surface engineering in a wide range of applications. Herein, by using soft atmospheric plasma deposition parameters and by adapting these conditions to the used perfluorodecyl and dodecyl acrylates precursors, it is possible to get a high retention of monomer functionalities and a polymerization close to conventional methods. Molecular investigation revealed the presence of polymeric moieties and the mechanism of plasma polymerization has been mainly based on the polymerization by activation of the ethylenic groups. X-ray diffraction analyses have shown the presence of a smectic lamellar where the polyacrylate backbone was the amorphous phase and fluorinated and alkyl side chains were the hexagonal crystalline section. Wetting properties have been evaluated and finally showed hydrophobic surfaces

Atmospheric plasma polymer films as templates for inorganic synthesis to yield functional hybrid coatings

Plasma polymer films produced via dielectric barrier discharge under atmospheric conditions can simultaneously host charged segments and poly(dimethysiloxane)/silica like polymers. The former segments afford some anion exchange properties and the latter ones allow stabilization of the whole coating in the presence of water. The anion exchange capacity of the film can then be used to nucleate and to grow inorganic particles in the plasma polymer coating. In particular, we exploit the presence of allylamine oligomers in a plasma coating made from a mixture of allylamine and hexamethyldisiloxane to hydrolyse titanium(IV) (bisammonium lactato dihydroxyde) and to condense it in TiO2. As a second example, Prussian Blue is produced by the successive incubation of the coating in a solution of potassium hexacyanoferrate and iron(III) chloride. The distribution of TiO2 and of Prussian Blue across the film thickness is investigated, in a semi quantitative manner, by means of Rutherford backscattering. The functional properties of the hybrid coatings are then investigated and it is found that the TiO2 containing films display photoinduced hydrophilicity whereas the films with Prussian Blue display magnetic properties.