Laurent Roux

Bio: Laurent Roux is an academic researcher from Centre national de la recherche scientifique. The author has contributed to research in topics: Plasma-immersion ion implantation & Ion implantation. The author has an hindex of 9, co-authored 85 publications receiving 447 citations.

Vacancy effects in the x-ray photoelectron spectra of Ti N x

Abstract: The electronic structures of titanium nitrides $\mathrm{Ti}{\mathrm{N}}_{x}$ have been investigated by x-ray photoelectron spectroscopy over the entire composition range of the rocksalt structure ($0.5\ensuremath{\lesssim}x\ensuremath{\lesssim}1$). The valence-region spectrum of stoichiometric TiN is consistent with results of band-structure calculations. The filling of a defect state at about 2-eV binding energy with decreasing $x$ is explicitly demonstrated. Experimental results are compared with different models for calculation of the electronic structure of anion-deficient rocksalt transition-metal compounds. Variation of the core-level binding energies indicates a decrease of the ionicity in $\mathrm{Ti}{\mathrm{N}}_{x}$ with decreasing $x$. The Ti $2p$ satellite structure found for nearly stoichiometric samples is discussed in terms of screening of the core hole by the conduction electrons.

Fluorescence of Ta 2 O 5 thin films doped by kilo-electron-volt Er implantation: application to microcavities

Abstract: Luminescent layers are prepared by the implantation of kilo-electron-volt Er ions into tantalum pentoxide (Ta(2)O(5)) thin films made by ion plating. The implantation fluences range from 3.3 × 10(14) to 2 × 10(15) ions/cm(2), and the energies range from 190 to 380 keV. Refractive index, extinction coefficient, and losses on guided propagation are investigated. We show that these Er-implanted layers present an absorption as low as that of the nonimplanted films. When optically pumped with an Ar(+) laser (λ = 0.488 μm) beam, implanted films show peaked fluorescence spectra centered near 1.53 and 0.532 μm. We show that the fluorescence intensity is correlated with the intensity of the pump beam in the region where Er ions are implanted. Radiation patterns of Er ions located inside a single layer or inside a Ta(2)O(5)/SiO(2) dielectric stack made by ion plating are also investigated. We show that, in any case, spontaneous emission of Er ions can be spatially controlled.

Titanium implantation in bulk and thin film amorphous silica

Abstract: Both bulk and thin film amorphous silica implanted with titanium were investigated We studied the induced modifications of the microstructure and the consequences on the optical properties We determined the refractive index profile of implanted materials from guided wave measurements and we show that it matches the distribution of titanium An increase in refractive index of up to 09 can be obtained by high dose implantation A study of thermal annealing in air shows that the implanted materials exhibit low optical losses

Titanium nitride oxidation chemistry: An x‐ray photoelectron spectroscopy study

Abstract: We report a study of the oxidation of TiN. In previous work, the oxidation kinetics for 350–450 °C were reported and an initiation time prior to fast oxidation was identified. In this study, x‐ray photoelectron spectroscopy was used to investigate the oxidation mechanisms at 350 °C during this initiation time period. The oxide thickness increases slowly with oxidation time and the film appears to change from an amorphous TiO2 layer to a crystalline TiO2 layer. Spectral features which are intermediate between TiO2 and TiN are reported and a model involving grain boundary oxidation is proposed. One of the thicker oxides studied was annealed in vacuum to 700 °C. Following oxidation, some of the capping oxide and much of the intermediate material is no longer in the analysis volume and we suggest that the oxygen and nitrogen is being dissolved into the bulk in much the same way that nonevaporable getters are activated before use.

Highly Efficient Formation of Visible Light Tunable TiO2-xNx Photocatalysts and Their Transformation at the Nanoscale

Abstract: Using a simple nanoscale exclusive synthesis route, TiO2-xNx photocatalysts that can be tuned to absorb across the visible region are produced in seconds at room temperature. The photocatalysts are formed by employing the direct nitridation of anatase TiO2 nanostructures with alkylammonium salts. Depending on the degree of TiO2 nanoparticle agglomeration, catalytically active TiO2-xNx anatase structured particles are obtained whose absorption onset extends well into the visible region at λ ∼ 550 nm. The introduction of a small quantity of palladium in the form of the chloride or nitrate facilitates further nitrogen uptake, appears to lead to a partial phase transformation, displays a counterion effect when compared also to the acetate, and produces a material absorbing well into the near-infrared. The introduction of palladium via the chloride also facilitates the formation of small tetrahedral and octahedral palladium-based crystallites throughout the TiO2-xNx lattice. Surprisingly, no organics appear to...

Simulation of light emission from thin-film microcavities

Abstract: In light-emitting devices based on thin-film technology, light waves that are partially or totally reflected at interfaces between different materials interfere and influence the angular distribution of the emitted light. For an electrical dipole transition, the radiation pattern is equivalent to that of an electrical dipole antenna. New theoretical expressions are provided for the radiation, discriminating for polarization, emission angle, absorption, and transmission; and the numerical calculation of discrete modes, narrow modes, and evanescent waves near absorbing media is discussed.

Characterization of nitride coatings by XPS

Abstract: Nitride coatings have been used in numerous applications to increase the hardness and improve the wear and corrosion resistance of structural materials, as well as in various high-tech areas, where their functional rather than mechanical properties are of prime importance. Performance of these coatings is equally dependent on their chemical composition and long-range crystalline structure, as well as on the nature and amount of impurities and intergranular interactions. Significant improvement in the mechanical properties has recently been achieved with multi-component superlattice and nanocomposite nitride coatings. In the case of such multi-component systems, not only is close control of the elemental composition (stoichiometry) necessary to optimize the properties of the coatings, but the influence of chemical bond formation between the components is also of prime importance. Special care needs to be taken when non-equilibrium preparation conditions, activation of CVD and PVD by plasmas or energetic particle beams are applied, occasionally leading to unpredicted deviations, both in composition and structure. As is highlighted in this paper, nitride coatings or nitrided surfaces can be analyzed in detail by X-ray photoelectron spectroscopy (XPS) due to its excellent element selectivity, quantitative character and high surface sensitivity. More importantly, XPS reflects the atomic scale chemical interactions, i.e. the bonds between neighboring atoms, and thus it also provides reliable structural characteristics for amorphous or nano-crystalline coatings of complex composition, for which application of diffraction techniques is not straightforward. A number of examples of the application of XPS are given for various types of nitride coatings, including interstitial compounds, such as TiN, CrNx, etc., as well as compounds with predominantly covalent bonding, such as AlN, GaN, Si3N4 and CNx. Special emphasis is placed on ion beam-induced compositional and structural changes and to the formation of ‘superstoichiometric’ TiN1+x, ZrN1+x compounds.