Couches minces d'oxynitrure de tantale déposées par pulvérisation réactive. Étude du système Ta-Ar-O2-N2 et caractérisation des films

Le but de ce travail de thèse est d étudier les propriétés d un plasma réactif ainsi que les caractéristiques structurales, optiques et électriques de couches minces d oxynitrure de tantale (TaOxNy) élaborées par pulvérisation cathodique radiofréquence. L élaboration de ce matériau ternaire par pulvérisation d une cible de tantale au moyen d un plasma contenant à la fois de l argon, de l oxygène et de l azote est complexe en raison de phénomènes d empoisonnement de la cible. L analyse de la composition du plasma par spectroscopie d émission optique et le suivi de l évolution de certaines raies représentatives d espèces excitées dans le milieu, nous ont permis de déterminer les conditions optimales au dépôt de films de types TaOxNy sur une large gamme de compositions. Grâce à une étude par diffraction des rayons X et spectroscopie de photoélectrons X, nous avons suivi les évolutions structurales de couches ayant subi ou non un recuit thermique. Nous avons montré de quoi étaient constituées les parties amorphes et cristallisées de ces films et déterminé la taille des domaines de cohérence. Enfin, les propriétés optiques (indice de réfraction, gap optique, paramètre d Urbach) et diélectriques ont été corrélées à la structure des matériaux.The aim of this thesis is to study the properties of a reactive plasma as well as the structural, optical and electrical properties of tantalum oxynitride thin films (TaOxNy) prepared by radiofrequency sputtering. The elaboration of this ternary material by sputtering a pure tantalum target using plasma containing both of argon, oxygen and nitrogen is complex due to the target-poisoning phenomenon. The analysis of the composition of the plasma by optical emission spectroscopy and monitoring the evolution of some representative line of excited species in this environment, allow us to determine the optimal conditions to deposit TaOxNy films over a wide range of composition. Thanks to a study by X-ray diffraction and X-ray photoelectron spectroscopy, we followed the structural evolution of the films subjected or not to a rapid thermal annealing. We showed by what were constituted the amorphous and crystalline parts of the films and determined the size of the crystalline domains. Finally, the optical properties (refractive index, optical gap, Urbach parameter) and dielectric behavior have been correlated with the structure of materials.CLERMONT FD-Bib.électronique (631139902) / SudocSudocFranceF

Characterization of Sol-Gel derived scintillating LuBO3 films doped with rare earth ions.

Rare earth doped LuBO3 thin films have been prepared by combining sol-gel process and coatings techniques such as spin coating and spray pyrolysis. Annealing treatment results in the crystallization of the film as vaterite phase and incorporation of the doping ions in solid solution. XPS and RBS spectrocopies showed that the composition of the films is close to the nominal one. Adventitious carbon has been observed and attributed to incomplete pyrolysis of metal-organic precursors. XPS concentrations profiles show a good homogeneity for the films. RBS demonstrated some inter-diffusion between amorphous carbon substrate and borate films resulting in a gradient of carbon at the interface between the substrate and the film itself. Finally scintillation spectra have been recorded and demonstrate the potentiality of these films to be used as X-ray intensifying screens

Prediction of water retention of soils from the humid tropics by the nonparametric k-nearest neighbor approach

Nonparametric approaches such as the k-nearest neighbor (k-NN) approach are considered attractive for pedotransfer modeling in hydrology; however, they have not been applied to predict water retention of highly weathered soils in the humid tropics. Therefore, the objectives of this study were: to apply the k-NN approach to predict soil water retention in a humid tropical region; to test its ability to predict soil water content at eight different matric potentials; to test the benefit of using more input attributes than most previous studies and their combinations; to discuss the importance of particular input attributes in the prediction of soil water retention at low, intermediate, and high matric potentials; and to compare this approach with two published tropical pedotransfer functions (PTFs) based on multiple linear regression (MLR). The overall estimation error ranges generated by the k-NN approach were statistically different but comparable to the two examined MLR PTFs. When the best combination of input variables (sand + silt + clay + bulk density + cation exchange capacity) was used, the overall error was remarkably low: 0.0360 to 0.0390 m(3) m(-3) in the dry and very wet ranges and 0.0490 to 0.0510 m(3) m(-3) in the intermediate range (i.e., -3 to -50 kPa) of the soil water retention curve. This k-NN variant can be considered as a competitive alternative to more classical, equation-based PTFs due to the accuracy of the water retention estimation and, as an added benefit, its flexibility to incorporate new data without the need to redevelop new equations. This is highly beneficial in developing countries where soil databases for agricultural planning are at present sparse, though slowly developing

Surface characterization of sol-gel derived scintillating rare-earth doped Lu2SiO5 thin films

International audienceRare earth doped Lu2SiO5 thin films have been prepared by combining sol-gel process and spin coating. Annealing treatment results in the crystallization of the film and efficient incorporation of rare earth doping ions. XPS and RBS spectrocopies showed that the composition of the films is close to the nominal one. Adventitious carbon has been observed and attributed to incomplete pyrolysis of metal-organic precursors. XPS concentrations profiles show a good homogeneity for the films. RBS demonstrated some inter-diffusion between amorphous carbon substrate and silicate films resulting in a gradient of carbon at the interface between the substrate and the film itself

a-C:H thin films deposited by radio-frequency plasma: influence of gas composition on structure, optical properties and stress levels

a-C:H thin films are deposited by plasma-enhanced chemical vapor deposition PE-CVD at 13.56 MHz at room temperature. Ž . Three different precursor gas mixtures are used CH , CH He, CH Ar . Structure, optical properties and stress levels are 4 4 4 Ž . evaluated by elastic recoil detection analysis ERDA , IR absorption, UVvis spectrometry, Raman spectroscopy. We observe a Ž . 2 Ž . loss of hydrogen content bonded and not bonded from 38 to 24 at.%, as well as an increasing of sp content from 14 to 29% with the increase of self-bias voltage for all mixtures. Argon and helium addition to methane induce a greater graphitization of a-C:H thin films. These modifications induce a decrease of the optical gap which is set between 1.4 and 1.1 eV and an increase of the Urbach gap from 0.6 to 0.8 eV. The internal stresses are controlled by subplantation model and decrease from 4 to 1 GPa with the increase of the bias voltage. The use of argon and helium as carrier gas induce lower stress in the films

Structural and mechanical properties of a-C:H thin films grown by RF-PECVD

a-C:H thin films have been deposited by plasma enhanced chemical vapor deposition at 13.56 MHz in a large bias voltage range (200–600 V). Their mechanical properties have been studied through different techniques such as nanoindentation, profilometry and finally X-ray reflectometry in order to determine their hardness, elastic modulus, stress level, interfacial fracture energy and density.We show that the hardness, the Young modulus, the density and the stress level decrease with increasing bias voltage contrary to the interfacial fracture energy, hence the adhesion of the deposits. To understand this behavior, films microstructure has been characterized through the determination of hydrogen and sp3 hybridized carbon contents by ERDA, FTIR, Raman diffusion and ESR. We have demonstrated that a graphitization and a loss of hydrogen occur when the bias increases. Such evolutions are explained in terms of the subplantation model proposed by Lifshitz. Finally, hard and dense coatings can be grown at low bias as the sp3 carbon content is high, but their corresponding adhesion is low

X-Ray reflectometry study of diamond-like carbon films obtained by plasma-assisted chemical vapor deposition

X-Ray reflectivity is used to determine the electron density profiles normal to the surface of diamond-like carbon DLC films Ž . prepared by plasma-enhanced chemical vapor deposition PE-CVD . Average values of the scattering lengths obtained from the Ž . specular reflection data and elastic recoil detection analysis ERDA hydrogen measurements are used to calculate the average mass density of the films. The density is shown to be strongly dependent on the hydrogen content. This depends on the plasma parameters. Argon diluted methane plasma produces homogeneous DLC films but generally with a lower density than the films prepared from pure or He diluted plasmas. These later plasmas produce films with a high density contrast and higher densities

Characterization by electron spin resonance of defects in a-C:H thin films. Correlation between structural evolutions and optical properties

The structural evolutions of a-C:H thin films prepared by r.f. plasma-enhanced chemical vapor deposition from a CH yAr or 4 CH yHe gas mixture have been investigated. Elastic recoil detection analysis, infrared and Raman spectroscopies have been used 4 to quantify, respectively, hydrogen content, the bonding and sp proportion carbon of thin films. The variations of electron spin 2 resonance parameters, the peak-to-peak linewidth DH , g-factor and the spin density, as a function of the film preparation are pp discussed on the basis of the complete physico-chemical characterization. The type of defects do not change drastically when the conditions of the film preparation vary contrary to the spin–spin interaction: a stronger exchange resulting from the greater delocalization of the p-electron occurs when the bias voltage increases. Moreover, the hyperfine interaction of the spins with the hydrogen atoms decreases. We have found that the optical band gap E of these films decreases with the loss of hydrogen g (bonded and unbonded) and the increasing of sp content while E gap increases. These results have been related to the spin densities

Multiphase Structure of Tantalum Oxynitride TaOxNy Thin Films Deposited by Reactive Magnetron Sputtering

International audienceThis work deals with the structure and the microstructure of tantalum oxynitride thin films deposited by reactive magnetron sputtering. The local structures of amorphous as-prepared thin films are investigated using the pair distribution function (PDF) technique based on total X-ray scattering experiments. The corresponding annealed thin films are analyzed using conventional θ–θ X-ray diffraction technique and full-pattern fitting methods. Rutherford backscattering and X-ray photoelectron spectrometries are used in conjunction with X-ray techniques. As-prepared thin films are nanostructured. The PDF signal is coming from small structural units below 10 Å in diameter, which only maintain nearest-neighbor order and with a composition changing gradually from TaN to δ-TaON and Ta2O5 as the oxygen content in the reactive gas increases. On the other hand, the annealed thin films consist of a mixture of separate crystalline phases with refined cell parameters consistent with the formation of TaN (Fm–3m), β-TaON (P21/c), and Ta2O5 (C2mm) more or less successively as the oxygen content in the reactive gas increases. Information on the size of the coherent domains and the preferential growth orientation are obtained from analysis of anisotropic diffraction line broadening effects in the XRD patterns. The results are in favor of a random bonding model (RBM) in the case of as prepared thin film and random mixture model (RMM) for annealed samples