M. Jacquet

Characterization of zirconia films deposited by r.f. magnetron sputtering

Thin films of zirconium oxide were prepared by r.f. magnetron sputtering from a ZrO2 target. A systematic study has been made on the influence of the sputtering parameters (total pressure, oxygen partial pressure and r.f. power) on the film composition and on their structural and optical properties. The zirconia films crystallize either in the cubic or in the monoclinic phases depending on the sputtering gas. The crystallinity and the compactness of the films were found to increase with the kinetic energy of the sputtered particles. The stresses are compressive and become very important in thick films deposited at a high power density. Films are generally substoichiometric and their O/Zr atomic ratio was found to increase with the oxygen partial pressure. On the contrary, films deposited at high sputtering pressures (more than 5 Pa) contain an oxygen excess. This overstoichiometry results, as it was revealed by F. T. I. R. analyses, from the incorporation of water and hydroxyl groups into the ZrO2 structure. The optical constants (refractive index and extinction coefficient) vary also in a wide range with the deposition conditions. These variations were correlated mainly to structural properties.

Structural and optical studies of ZnO thin films deposited by r.f. magnetron sputtering: influence of annealing

Abstract Zinc oxide thin films were deposited on various substrates by sputtering from a ZnO target. The sputtering gas was obtained from an argon–oxygen mixture (95–5%), at 1 Pa pressure and using a r.f. power density of 0.89 W cm −2 . The structural and optical properties of ZnO deposits, submitted to an annealing treatment in the 373–673 K ranges are studied by X-ray diffraction (XRD) and UV-visible spectrometry. XRD measurements show that all the films are crystallised in the wurtzite phase and present a preferential orientation along the c -axis. Only one peak, corresponding to the (002) phase (2 θ≈ 34.4°), appears on the diffractograms. The crystallite size, the density and the O/Zn atomic ratio increases with the treatment temperature. These modifications influence the optical properties. The refractive index n , the absorption coefficient α and the optical gap E g , increase with the treatment temperature, and are sensitive to the oxygen incorporation.

Structural and optical properties of sputtered Titania films

Abstract Titania thin films have been deposited by the magnetron sputtering method. This process has been used to give improved optical and structural properties such as high refractive index and low defect density. A detailed investigation has been made to study the influence of the combined effect of both deposition conditions (sputtering pressure and r.f. power) and post deposition annealing up to 600°C on the composition, structural and optical properties of the titanium oxide films. The as-deposited films are found to be amorphous. The cristallinity sets by post deposition annealing. The variation in microstructural properties is explained according to the basis of the enhanced mobility of the sputtered particles at high r.f. power and low sputtering pressure. The changes in the stoichiometry are attributed to the preferential sputtering and microstructural evolution. The stresses determined by the bending beam method are found to be compressive, the highest values are obtained in the coatings exhibiting the most dense structure. Both, those structure variations and the deviations from stoichiometry result in a variation in the optical constants of the sputtered films.

X-ray photoelectron spectroscopy studies of plasma-modified PET surface and alumina/PET interface

Abstract X-ray photoelectron spectroscopy was used to study the chemical effects of a reactive plasma treatment on the PET surface and to investigate the chemical interactions involved at the alumina/PET interface. The treatment of the PET by a carbon dooxide plasma introduces new oxygen reactive species on the polymer surface. Evidence of this chemical modification is given by the appearance of additional carbonyl bonds. The interfacial study reveals a reaction of alumina with the oxygen atoms of the carbonyl bonds of PET (plasma-induced carbonyl bonds and carbonyl bonds of the ester groups). This chemical interaction results in the formation of AlOC interfacial bonds in the early stages of deposition.

XPS characterisation of plasma-treated and alumina-coated PMMA

Abstract The present study is entirely devoted to an XPS analysis of (i) the surface of as received and plasma (argon, CO2) treated poly(methyl–methacrylate) (PMMA) and (ii) the interface between PMMA and alumina thin films, deposited by r.f. magnetron sputtering respectively on untreated and CO2 plasma-treated polymer films. As expected, important chemical modifications of PMMA surface are observed when this polymer is plasma-treated. Such modifications increase the level of interactions between alumina and the substrate. However, if the formation of aluminium carboxylate is observed at the interface, no covalent bonds between the alumina film and the polymer are evidenced.

Elaboration and characterization of titania coatings

Abstract The titania coatings have been deposited on polyethylene terephtalate (PET) by r.f. magnetron sputtering in an oxygen-argon plasma from a pure titanium target. The titania films always consist of a mixture of amorphous and crystallized phases of the anatase structure. The composition (O/Ti atomic ratio) established by Rutherford backscattering spectrometry depends on the deposition parameters and mainly on the oxygen partial pressure. The crystallinity, the compactness, the stresses and the gas barrier effect of the titania coalings increase with the kinetic energy of the sputtered particles. This varies in the same way as the r.f. power and in the opposite manner to the oxygen partial pressure. The refractive index increases ail along with the compactness of the titania film; the extinction coefficient decreases and the optical bandgap values increase when the O/Ti atomic ratio increases. Good adhesion of a titania coating on a TET film needs at the same time activation of the surface of the PET by a CO2 plasma treatment and optimization of the sputtering parameters.

Alumina coating on polyethylene terephthalate

The adhesion of an alumina coating from 10 to 200 nm thick deposited by r.f. magnetron sputtering on polyethylene terephthalate (bi-stretched; 12 microm thick) has been characterized. Modification of the surface energy of the polymer by a cold CO2 plasma was found to be an excellent method to increase adhesion as characterized by a fragmentation test. Various parameters were studied for the plasma treatment: r.f. power; duration; pressure. X-ray photoelectron spectroscopy analysis revealed the formation of a superficial carbonyl function which involves an increase in the polar component of the surface energy. The presence of these carbonyl groups promotes AlOC or AlC type of bond formation which may be responsible for the good level of adhesion observed.

Characterization and adhesion study of thin alumina coatings sputtered on PET

Abstract Thin amorphous alumina coatings have been deposited on polyethylene terephthalate (PET) by rf magnetron sputtering in a pure argon plasma. Their microstructure, composition, stresses and adhesion to the PET films have been studied. SEM microstructure study showed a good agreement with Thorntons structure zone model, i.e. a progression from a dense structure to a columnar structure was observed as the pressure was increased. The composition of deposits, determined by RBS, showed that oxygen-rich alumina was obtained when high plasma pressures (more than 1 Pa) were used. FTIR spectra of alumina indicate that the excess oxygen was essentially due to the presence of hydroxyl groups in the coatings. The stress evolution in alumina deposits, determined by the bending beam method, was correlated with the microstructural change. Adhesion of alumina on PET has been studied by a peel test. Best results were obtained when sputtering parameters combined moderate power (1 W cm−2) and pressure of about 1 Pa. XPS analysis of the alumina PET interface showed that bonding between the ceramic and the polymer occurred primarily via Al-O-C bonds.

Surface Free Energy Modification of PET by Plasma Treatment—Influence on Adhesion

Abstract Different cold plasmas have been used to treat the surface of polyethylene terephtalate (PET) in order to improve the adhesion of alumina thin films deposited by RF sputtering. The influence of these treatments on the surface free energy of the polymer is shown by a study of wettability. ESCA analysis of the PET surface suggests that chemical changes occur as the polymer is plasma treated. The adhesion of alumina films on PET is studied by using tensile testing. The results show that the surface treatment of the PET by a slightly oxidizing plasma, such as carbon dioxide, increases by a factor of 1.7 the adhesion of alumina coatings.

Photoprotective zinc oxide coatings on polyethylene terephthalate films

Abstract Zinc oxide coatings have been deposited on polyethylene terephthalate by r.f. magnetron sputtering from a ceramic target in different argon–oxygen mixtures. The influence of the sputtering parameters on the properties of the coatings was studied. It was found that ZnO deposits crystallize in the wurtzite phase and that the crystallinity decreased when the oxygen partial pressure increased. The composition and the optical constants (refractive index, extinction coefficient, optical band gap) of the ZnO films were varied over a wide range depending on sputtering parameters. In addition, the ZnO films grow under a state of compression, which is mainly due to the internal defects. The stress increased with the sputtered particles energy. The better adhesion between the coating and the polymer induced by cold plasma treatments and the influence of the sputtering conditions were also studied. The permeability to oxygen was limited and the PET photo-oxidation rate was strongly reduced once the polymer had been coated with ZnO layers prepared under optimal conditions.