Jacques Perriere

Nanoparticle formation by femtosecond laser ablation

Ultra short femtosecond (fs) pulses for the laser ablation of materials lead to deposited films which are very different from those obtained by the well-known classical nanosecond (ns) pulsed laser deposition (PLD). In very specific cases, epitaxial thin films can be obtained, whereas in the majority of materials, the films formed by fs PLD are constituted by the random stacking of nanoparticles (Nps) in the 10–100 nm size range. As a result, fs PLD has been rapidly considered as a viable and efficient method for the synthesis of Nps of a wide range of materials presenting interesting physical properties and potential applications. The Np synthesis by fs laser ablation has been studied, and theoretical investigations have been reported to establish their formation mechanisms. Two possibilities can be assumed to explain the Np synthesis: direct cluster ejection from the target or collisional sticking and aggregation in the ablated plume flow.

Laser‐induced forward transfer of high‐Tc YBaCuO and BiSrCaCuO superconducting thin films

For the first time, the deposition of YBaCuO and BiSrCaCuO thin films has been performed by the single‐laser pulse‐induced forward transfer technique. In addition, the BiSrCaCuO films were successfully converted into the superconducting phase, with an onset critical temperature of about 90 K and a zero resistance at 80 K, by a subsequent thermal anneal in oxygen atmosphere in the 850–900 °C temperature range.

Metal-semiconductor transition in epitaxial ZnO thin films

We report on the formation and transport properties of ZnO thin films which are grown by pulsed-electron beam deposition under a low residual oxygen pressure (10(-5) mbar). ZnO films presenting metallic conductivity at room temperature, and a metal-semiconductor transition at low temperature, were epitaxially grown on Al(2)O(3) single crystal substrates for growth temperatures in the 300-450 degrees C range. These results have been interpreted through the quantum corrections to conductivity in a disordered oxide conductor, implying first a high density of carriers leading to degenerate semiconductor ZnO films, and then a sufficient disorder in these films. These characteristics could be related to the nature of the ZnO films formed by pulsed-electron deposition: a high density of carriers related to an oxygen deficiency in the films and a high density of defects related to the high deposition rate of the pulsed-electron beam deposition method

Zirconium nitrides deposited by dual ion beam sputtering : physical properties and growth modelling

Abstract Zirconium nitrides reveal interesting optical and electrical properties which highly depend on the nitrogen stoichiometry. Indeed, the material exhibits a transition from the stable metallic ZrN (optical index for bulk at 633 nm: N=0.5−i3.2) to the metastable semi-transparent insulating Zr3N4 (N=3.2−i0.4). This work deals with the elaboration of homogeneous ZrN-like and Zr3N4-like coatings. These have been prepared using reactive Dual Ion Beam Sputtering (DIBS) using a Zr target and N2 or N2+Ar reactive gas. The influence of different elaboration parameters (ion energy, gas composition of the reactive beam and substrate temperature) on the nitrides composition and on their optical and electrical properties was particularly studied. A model was proposed to explain the influence of energy and temperature on the nitrogen composition. The nitrogen stoichiometry was shown to be controlled by a competitive mechanism between implantation of excess nitrogen amount in the subsurface and their elimination by exodiffusion. The first phenomenon is mainly controlled by the ion energy whereas the second one is enhanced by a high temperature and a high irradiation defects density. Therefore, the Zr3N4-like nitrides were obtained with low temperature and high energy (200 eV) conditions whereas high temperature and low energy led to ZrN-like materials.

Structural and optical properties of rare-earth-doped Y2O3 waveguides grown by pulsed-laser deposition

Crystalline rare-earth-doped yttrium oxide thin films were grown by pulsed-laser deposition (PLD) on SiO2/Si substrates. The structural and morphological features of these films were studied, as a function of the growth conditions (temperature from 200 to 800 °C and oxygen pressure from 10−6 to 0.5 mbar), by using Rutherford backscattering spectroscopy, x-ray diffraction, and atomic force microscopy. The related optical properties were investigated by m-lines spectroscopy at 633 nm and 1.3 μm. The optimal conditions were found to be a temperature and a pressure of 700 °C and 10−6 mbar, respectively. In that case, the Y2O3 films are stoichiometric with controlled erbium and europium rates, and present a well-crystallized, (111) textured cubic phase and a low surface roughness of about 10 A. Moreover, the PLD films show good waveguiding properties with a high refractive index (1.92 at 633 nm), a step-index structure, and low optical losses around 1 dB/cm in the near infrared region, promising for a planar a...

Transport number measurements during plasma anodization of Si, GaAs, and ZrSi2

In contrast to the thermal oxidation of Si where molecular oxygen is the sole moving species, the plasma anodization involves the movements of anions (oxygen or its compounds) or cations (Si or its compounds) or both. A similar situation is observed during the plasma anodization of refractory metal silicides (ZrSi2) or even GaAs. To get some insights on the mechanisms of plasma anodization, the transport number of cations t+ in oxides grown by anodization in oxygen plasma has been investigated using Xe atom markers. Rutherford backscattering techniques were used to determine the change in Xe marker position related to the change in oxide thickness. Results showed that t+≂0 for SiO2 growth indicating oxide formation solely by oxygen ion movement while for GaAs oxide, the t+ value obtained (t+≠0) evidences cation and oxygen anion migration during the growth. For ZrSi2 anodization, the position of the Xe markers remains unchanged during oxide formation yielding t+≂0, while the analysis of the backscattering ...

Non-stoichiometry in LiMn2O4 thin films by laser ablation

Abstract We have demonstrated that thin films of LiMn 2 O 4 deposited by laser ablation are stoichiometric when deposited in an oxygen pressure of 0.2 mbar on a substrate heated at 500°C. For higher oxygen pressures, the pure spinel structure is still obtained but non-stoichiometric. We show that the use of the unit cell volume determined by X-ray diffraction can be an accurate tool to determine the oxidation state of manganese in thin films. These results are confirmed by nuclear reaction analysis and X-ray absorption spectroscopy. Furthermore, we have tested the electrochemical properties of such films as a cathode in lithium batteries. The mobility of lithium within the structure determined by cyclic voltammetry depends on the quality of the films and is highest for the stoichiometric films.

Pulsed electron beam deposition of oxide thin films

In this work we studied the pulsed electron beam deposition (PED) method using a channel-spark discharge as the electron source. In order to estimate the potential of the PED method, thin films of zinc oxide, zirconium tin titanate, barium strontium titanate and biocompatible oxides were grown and investigated taking into account two important points: the Surface morphology and the film composition. We showed that PED leads to films free from micrometre size droplets and by a careful optimization of the beam parameters it is possible to drastically reduce the density and size of nanoparticulates. In fact, by studying the relationships between the discharge parameters, electron beam characteristics and surface morphology of films we evidenced that a decrease in the beam energy leads to a drastic reduction in the nanoparticulate density. The composition of the various oxide thin films investigated in this work is close to that of the target, as in the case of pulsed laser deposition, even in the case of complex oxide compounds. Hence, smooth and dense thin films preserving the composition of the bulk target can be obtained by the PIED method. The study by fast imaging of the expansion of the plasma plume produced by the pulsed electron beam interaction with the target indicates that the kinetic energy of the species emitted by the target is roughly in the 10-50eV range.

Nanocomposite indium tin oxide thin films: formation induced by a large oxygen deficiency and properties

We report on the formation and properties of nanocomposite indium tin oxide thin films which are grown by pulsed-electron beam deposition under a low oxygen pressure leading to the formation of highly non-stoichiometric indium tin oxide films. For growth at room temperature these films are amorphous and insulating, while at higher temperatures, the oxygen deficiency leads to a disproportionation reaction with the formation of metallic clusters (indium or indium tin clusters) embedded in a stoichiometric crystalline indium tin oxide. This matrix is well crystallized and even epitaxial for growth on c-cut sapphire single crystal substrates. The presence of the metallic clusters induces specific transport properties, i.e. a metallic conductivity at room temperature followed by a superconducting transition at low temperature (about 6 K). Moreover, the solid-liquid and liquid-solid phase transitions in the metallic clusters can be clearly seen from the resistivity curves as a function of temperature (in the room temperature to 450 K range), through specific changes in resistivity and the appearance of a hysteresis cycle.

Intrinsic defects and their influence on the chemical and optical properties of TiO2−x films

In this work, TiO2 films produced by rf sputtering of a TiO2 target in argon and argon–oxygen plasmas were studied. The oxygen content in the feed gas was varied in a range 3–20%. The chemical composition and structure of films were characterized by Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy (XPS) and x-ray diffraction. Important information about the intrinsic defects of the films and their effects on the optical properties as well as a scheme of the energy band structure of the films could be derived from a combined use of optical spectroscopy and XPS.