Angélique Bousquet

Investigation of O-atom kinetics in O2, CO2, H2O and O2/HMDSO low pressure radiofrequency pulsed plasmas by time-resolved optical emission spectroscopy

In the present paper, O-atom kinetics is investigated in low pressure (around 0.7?Pa) O2/hexamethyldisiloxane pulsed plasmas by time-resolved optical emission spectroscopy. In order to distinguish direct O-atom excitation by electron impact from dissociative excitation of O2, CO, CO2 and H2O molecules formed in O2/HMDSO plasmas, measurements were first carried out in pure O2, CO2 and H2O plasmas. From these measurements it was concluded that direct O-atom excitation by electron impact was the dominant mechanism and that actinometry could be used to monitor O-atom kinetics provided molecular oxygen dissociative excitation is taken into account. Second, the surface O-atom loss coefficient measured in oxygen pulsed plasmas is in agreement with the literature (10?1) and is five times higher than the one measured in CO2 pulsed plasma (2 ? 10?2). This latter result is attributed to competition effect at surface sites between CO and O. Finally, we point out the influence of water molecule wall adsorption on O-atom kinetics in H2O and O2/HMDSO pulsed plasmas. During the post-discharge, H2O and/or OH molecules adsorbed at the reactor walls strongly reduce the O-atom loss coefficient. During the discharge, ion bombardment enhances desorption of molecules leading to an increase in the O-atom loss coefficient.

Structural and ellipsometric study on tailored optical properties of tantalum oxynitride films deposited by reactive sputtering

Oxynitride materials, which offer the possibility of merging oxide and nitride properties, are increasingly studied for this reason. This paper focuses on assessing the optical properties of tantalum oxynitride thin films deposited by pure tantalum target sputtering in an Ar/O2/N2 reactive atmosphere. First, by changing the oxygen to reactive gas flow rate ratio, and using thermal post-treatment, we deposited films with elemental compositions studied by Rutherford backscattering spectroscopy, ranging from a nitride (close to Ta3N5) to an oxide (close to Ta2O5) with various structures analyzed by x-ray diffraction. Their optical properties were investigated in depth by spectroscopic ellipsometry and UV-visible spectroscopy. For the ellipsometry investigation, we propose a model combining the Tauc–Lorentz law and additional Lorentz oscillator: the first contribution is linked to a semi-conductor or insulator film matrix, and the second one to the presence of conductive TaN crystals. Ellipsometry thus appears as a powerful tool to investigate complex materials such as tantalum oxynitrides. Moreover, we demonstrated that using this deposition method we were able to finely tune the film refractive index from 3.4 to 2.0 (at 1.96 eV) and the optical band gap, specifically from 1.3 to 2.7 eV.

Preparation and characterization of a red luminescent composite composed of an EVA copolymer and a Y3BO6:Eu3+ phosphor

This work describes the preparation of red luminescent composites based on an ethylene/vinyl acetate (EVA) copolymer filled with a Y3BO6:Eu3+ phosphor powder. Luminescent powders were synthesized using a method derived from the Pechini synthesis method. The powders were then homogeneously dispersed in an EVA copolymer solution to achieve luminescent composite films. The structural, morphological and optical properties of the red luminescent composite films were investigated. The dispersion of phosphor particles in an EVA copolymer did not globally modify their optical features. However, the presence of an Eu3+–O2− charge transfer excitation band was observed and attributed to the effect of the refractive index of the EVA copolymer. Finally, the optical studies of these films evidenced their compatibility with commercial ultra-violet light emitting diodes (LEDs).

In-Situ Cu(In,Ga)Se 2 composition control by Optical Emission Spectroscopy during hybrid co-sputtering/evaporation process

In this work, we have developed a hybrid one-step co-sputtering/evaporation Cu(In,Ga)Se2 process, where Cu, In and Ga are sputtered simultaneously with the thermal evaporation of selenium, thus avoiding the use of H2Se. An appropriate control of the selenium flux is very important to prevent the target poisoning and hence some material flux variations. Indeed, the control of the CIGS composition must be rigorous to ensure reproducible solar cell properties. In this regard, a study of the correlations between plasma species, thin film composition and morphology has been performed by varying Se evaporation temperature in the 170 to 230 °C range.

Potential of TaOXNY Thin Films Deposited by Reactive Sputtering as Antireflective Coatings: Composition and Optical Properties

Tantalum oxynitride thin films are deposited by radio-frequency magnetron sputtering using a pure tantalum target under argon/oxygen/nitrogen gas mixture. The argon flow is kept constant while the oxygen and nitrogen flows are changed simultaneously in a way to keep constant the total flow of these reactive gases. We succeed to deposit TaOxNy films with stoichiometry ranging between those of TaN and Ta2O5. All films are deposited at room temperature and are amorphous. Spectroscopic ellipsometry and UV-visible spectrometry investigations show a direct relation between the optical properties and the stoichiometry of the films. In particular, the results show a variation of the refractive index from pure tantalum nitride-like films (3.76) to tantalum pentoxyde-like films (2.1), which confirms the possibility to deposit graded antireflective coatings with tantalum oxynitride.

Reactive gas pulsing sputtering process, a promising technique to elaborate silicon oxynitride multilayer nanometric antireflective coatings

The oxynitride materials present a high versatility, which enables their properties to be controlled by tuning their elemental composition. This is the case for silicon oxynitrides used for multilayer antireflective coatings (ARCs), where several thin films with various refractive indexes are needed. Different techniques allow for the modification of the thin film composition. In this paper, we investigate the reactive gas pulsing sputtering process to easily tune the thin film composition, from an oxide to a nitride, by controlling the averaged oxygen flow rate, without reducing the deposition rate, compared to a conventional reactive process (CP). We then demonstrated that the refractive indexes of films deposited by this pulsing process (PP) can be varied in the same range compared to films obtained by CP (from 1.83 to 1.45 at 1.95 eV), whereas their extinction coefficients remain low. Finally, the multilayer ARC has been simulated and optimized by a genetic algorithm for wavelength at 600 nm and for the silicon substrate. Various optimized multilayer (mono-, bi- and tri-layers) structures have been deposited by the PP technique and characterized. They are presented in good agreement with the simulated reflectivity. Hence, the PP allows for an easy depositing tri-layer system with a reasonable deposition rate and low reflectivity (8.1% averaged on 400–750 nm visible light range).