[en] The surface chemistry of silicon bombarded at low temperature with a beam extracted from a SF₆ microwave plasma has been studied using quasi in situ X-ray photoemission spectroscopy. At 123 K and when no ions strike the surface, strong adsorption of neutral SF_x species generated in the plasma is observed. In these conditions, physisorbed SF₃ and SF₄ species are detected but the presence of SF₆ molecules is not observed. Increasing the ion energy to 360 eV and the ion current density to 650 μA cm^-2 allows to desorb the adsorbed species and to maintain the adsorbed layer well below 75 Angstroms. At room temperature, the presence of chemisorbed sulfur, chemisorbed SF₃ radicals and physisorbed SF₄ species is observed for 60 eV and 5 μA cm^-2 ion bombardment conditions. Physisorbed SF species and chemisorbed sulfur are detected after ion bombardment at 360 eV and 650 μA cm^-2. During these different experiments, the presence of Fe and Cr due to the contamination of the beam is also observed. Results of this XPS analysis are correlated with etch rates measurements presented in a previous work. The role of ion-stimulated desorption and ion-induced reaction mechanisms on the silicon surface chemistry is discussed

[en] X-ray Photoelectron Spectroscopy (XPS) is commonly used to study the chemical composition of TiC/C nanocomposite films. Nevertheless, XPS remains a surface analysis technique and the obtained chemical information can be strongly affected by the surface oxidation and carbon contamination of the nanocomposite samples due to their exposure to air. Generally, an erosion stage is performed before XPS analysis using argon ion bombardment to remove the surface contamination. Since ion bombardment is likely to modify the surface chemical composition of the films, the question of whether XPS results are really representative of the bulk nanocomposite material can be addressed. Therefore, this study is devoted to the effect of ion bombardment on the surface chemical composition of nanocomposite films. TiC_x and TiC_xO_y films were grown by a hybrid plasma process combining Physical Vapor Deposition and Plasma Enhanced Chemical Vapor Deposition. Then, the samples were transferred to the XPS system where an in situ study of the modification of the surface chemical composition under argon ion bombardment was performed. XPS results are compared to Energy Dispersive X-ray analysis.

[en] Transparent C, Au and Pt films with thickness in the 5–10 nm range have been deposited by a DC magnetron sputtering system on commercial ITO (indium tin oxide) coated glass substrate for evaluation as electrode of spectro-electrochemical transducer. The transmission, over the investigated spectral range, is superior to 55% with the best transmission values obtained for C films (higher than 80%). The deposited films have been characterized by AFM, XPS and electrochemical methods. Results showed a low roughness, improved in comparison with uncoated electrodes. Electrochemical properties of the Au and Pt films evidenced a metallic behavior, which allowed qualifying them as conductive optically transparent electrodes for spectro-electrochemical devices.

[en] Amorphous carbon nitride (a-CN _x) thin films have been synthesized by rf reactive magnetron sputtering of a graphite target in an Ar/N₂ gas mixture. The total discharge pressure was 1.3 Pa and an N₂ fraction in plasma was between 0 and 0.5. The electrical resistivity of films was studied as a function of temperature between 80 and 360 K. At very low nitrogen contents in films, the resistivity decreases with increasing nitrogen content, whereas there is a strong increase in ρ at nitrogen content higher than 13 at.%. Chemical composition and C-N bonds was investigated by X-ray Photoelectron Spectroscopy (XPS). The results, related to the core level C1s and N1s, show the structural change. The temperature dependence evolutions was thermally activated and suggest the presence of two types of conduction associated with two different activation energies. The conductivity variation was interpreted within the limits of the band structure model of the π electrons in a disordered carbon with the presence of localized states

[en] An electrochemical transducer based on vertically aligned carbon nanotubes (CNT) was prepared as a platform for biosensor development. Prior to enzyme immobilization, the CNT were treated using a microwave plasma system (CO₂ and N₂/H₂) in order to functionalize the CNT surface with oxygenated and aminated groups. The morphological aspect of the electrode surface was examined by SEM and its chemical structure was also elucidated by XPS analysis. It was found out that microwave plasma system (CO₂ and N₂/H₂) not only functionalizes the CNT but also permits to avoid the collapse phenomena retaining thus the alignment structure of the electrode surface. The electrochemical properties of the resulting new material based on CNT were carried out by cyclic voltammetry and were found suitable to develop high sensitive enzyme (HRP) biosensors operating on direct electron transfer process.

[en] Recent papers have demonstrated that the growth of carbon nanotubes (CNTs) by plasma enhanced chemical vapor deposition (PECVD) was possible using nanocomposite nickel/carbon (nc-Ni/C) thin films as catalysts. In this study, the growth of CNTs by PECVD in H₂/C₂H₄ atmosphere was achieved using nc-Ni/C thin films deposited by a hybrid plasma process combining the sputtering of a nickel target and the deposition of hydrocarbon by PECVD using Ar/CH₄ atmosphere. In order to identify the most favorable conditions to obtain dense CNTs arrays using nc-Ni/C thin films, the Ni content in the catalyst as well as the growth conditions of the CNTs were varied. Films containing 40, 55 and 65 at.% of Ni were selected for this study. The growth temperature of the CNTs was varied between 500 and 700 °C whereas the electrical power applied to the PECVD source was tuned from 30 to 50 W. Scanning electron microscopy and Raman spectroscopy were employed to probe the morphology and the structure of the CNT's. Depending on the chemical composition of the nc-Ni/C thin films, different trends were observed. No CNTs were obtained neither for the highest nickel content (i.e. %Ni = 65 at.%) nor for the lowest growth temperature (i.e. 500 °C). On the other hand, for temperatures exceeding 500 °C, while a high power on the PECVD source (i.e. 50 W) was found to be necessary to obtain CNTs in the case of films with a moderate Ni content (i.e. %Ni = 55 at.%), a lower power (i.e. 30 W) was sufficient for the film with the lowest Ni content (i.e. %Ni = 40 at.%). This difference in behavior was attributed to the differences in microstructure of nc-Ni/C thin films which is directly related to their chemical composition. - Highlights: • The growth of carbon nanotubes using nickel/carbon thin films as catalyst is studied. • Best conditions depending on Ni/C composition for CNT growth are identified. • Growth mechanisms including Ni diffusion in the Ni/C film are discussed.

[en] To evaluate the mechanical behaviour of CN _x thin films deposited on a Ti₆Al₄V titanium alloy by RF magnetron sputtering, in situ tensile tests in a scanning electron microscope were performed. Sputtered films were deposited on one side of Ti₆Al₄V samples using a conventional magnetron sputtering system with a graphite target and Ar/N₂ plasma. The amount of nitrogen in film was about 30 at.%. Three film thicknesses (100, 300, and 800 nm) were tested, and different surface pretreatments before deposition were applied in order to improve film adhesion: inductive plasma generated by an additional RF antenna (ionized magnetron sputtering, or IMS) and plasma immersion ion implantation (PIII). A very low tensile strain rate was chosen (0.05 mm/min) in order to follow in situ the deformation and damaging phenomena that could appear during the test. The films revealed a brittle behaviour: straight lines of fracture perpendicular to the loading axis systematically appeared. However, the total strain amplitude at which the earlier traces of damage in the film were detected greatly differed according to its thickness, or to the surface pretreatment. The characteristics of the fracture process were also highly influenced by these parameters: length and distribution of cracks, average spacing between cracks at saturation, relationship with the local plasticity activity in the substrate, etc. Blistering and peeling off the film quasi-systematically followed the early stage of cracking often for the highest strain amplitudes. Finally, it was shown that the fracture resistance is better for thinnest films and that the nitriding of the upper surface layers of the substrate by PIII improves the adherence of films

[en] Bi_4-xLa _xTi₃O₁₂ (BLT _x) (x = 0 to 1) thin films were grown on silicon (100) and platinized substrates Pt/TiO₂/SiO₂/Si using RF diode sputtering, magnetron sputtering and pulsed laser deposition (PLD). Stoichiometric home-synthesized targets were used. Reactive sputtering was investigated in argon/oxygen gas mixture, with a pressure ranging from 0.33 to 10 Pa without heating the substrate. PLD was investigated in pure oxygen, at a chamber pressure of 20 Pa for a substrate temperature of 400-440 deg. C. Comparative structural, chemical, optical and morphological characterizations of BLT thin films have been performed by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Photoelectron Spectroscopy (XPS), Spectro-ellipsometric measurements (SE) and Atomic Force Microscopy (AFM). Both sputtering techniques allow to obtain uniform films with thickness ranging from 200 to 1000 nm and chemical composition varying from (Bi,La)₂ Ti₃ O₁₂ to (Bi,La)_4.5Ti₃O₁₂, depending on deposition pressure and RF power. In addition, BLT films deposited by magnetron sputtering, at a pressure deposition ranging from 1.1 to 5 Pa, were well-crystallized after a post-deposition annealing at 650 deg. C in oxygen. They exhibit a refractive index and optical band gap of 2.7 and 3.15 eV, respectively. Regarding PLD, single phase and well-crystallized, 100-200 nm thick BLT films with a stoichiometric (Bi,La)₄Ti₃O₁₂ chemical composition were obtained, exhibiting in addition a preferential orientation along (200). It is worth noting that BLT films deposited by magnetron sputtering are as well-crystallized than PLD ones