Développements instrumentaux mis en place sur la plateforme SAFIR : Système d’Analyse par Faisceau d’Ions Rapides

International audienc

Method for determining the polymer content in non soluble polydiacetylene films – application to pentacosadiynoic acid

International audienceThe absorptivities of polydiacetylenes (PDA) used in Langmuir films or vesicles for the development of PDA sensors films or other applications such as in non linear optics or for field-effect transistors are not known, so polymer contents cannot be deduced from experimental spectra. Here we introduce a novel method, using Nuclear Reaction Analysis (NRA) that allows quantitative determination of the polymer content X proportion of monomers that have been incorporated into PDA chains. We apply it to pentacosadiynoic acid (PCDA) evaporated microcrystalline films. A calibration curve giving X as a function of the area under an absorption spectrum normalized to the monomer areal density is obtained for blue and red PCDA. The method is applicable to all kinds of films, and to other PDA, provided films with known molecular areal density are available. An example of application to a PCDA Langmuir film is given

Radiation damage in zirconia investigated by positively charged particles

19th International Conference on Application of Accelerators in Research and Industry, Ft Worth, TX, AUG 20-25, 2006International audiencePositrons, positive muons and deuterons were used - when applicable - to probe the production and thermal stability of defects induced at room temperature either by electron irradiation or He-ion implantation in zirconia stabilized by yttria in the cubic phase. No change in the positron lifetime or in the muon spin relaxation occurs after electron irradiation, indicating a positron saturation trapping in the annealed state, owing to the presence of structural defects inherent to phase stabilization. In contrast, after helium implantation, even at low fluence (similar to 10(14) cm(-2)), Slow positron implantation spectroscopy reveals the presence of a new type of defect (being more trapping effective than the native ones), whereas neither positronium nor muonium are detected. The diffusion of helium was followed after He-3-ion implantation and subsequent annealing using the He-3(d,p)(4) He nuclear reaction. A two-Gaussian distribution fit indicates that a part of the helium atoms is trapped at the projection range location, most likely in gas bubbles, while the other part diffuses and out-gasses after heat treatment already at around 1/5 of the melting temperature. In spite of differences in depths and concentrations probed by the present techniques, a fairly good correlation is observed between the various results. (c) 2007 Elsevier B.V. All rights reserved

Ageing of V2O5 thin films induced by Li intercalation multi-cycling

International audienceCyclic voltammetry, XPS, RBS and AFM have been combined to study the ageing mechanism of Li intercalation in V2O5 thin films prepared by thermal oxidation of vanadium metal. Multi-cycling tests were performed in 1 M LiClO4-PC in the potential range E epsilon [3.8, 2.8 V] versus Li/Li+, corresponding to the alpha-to-delta phase transition. XPS and AFM were performed using direct anaerobic and anhydrous transfer. Capacity fading remains inferior to 20% during similar to 2500 cycles. XPS shows slight modifications of the oxide composition with a V4+ concentration increasing from similar to 5% prior to cycling to similar to 16-27% after cycling, due to Li trapped in the oxide film and to the loss of V2O5 active material. The presence of lithium carbonate and lithium-alkyl carbonate species evidences the formation of the so-called SEI layer. AFM evidences the loss of crystalline material by grain exfoliation from the outer V2O5 layer of the oxide film. By further exfoliation, the inner VO2 layer of the oxide film is reached and pits are formed, occupying similar to 9-13% of the surface. This de-cohesion at grain boundaries is attributed to the strain generated by repeated lattice distortions. After 3300 cycles, the disappearance of lithium carbonates, whereas Li-alkyl carbonates and/or Li-alkoxides remain on the surface, indicates the dissolution and/or conversion of the SEI layer. After 4500 cycles, the oxide film became very labile and could be stripped away by rinsing to reveal the vanadium metal substrate. (C) 2007 Elsevier B.V. All rights reserved

Li-ion intercalation in thermal oxide thin films of MoO3 as studied by XPS, RBS, and NRA

International audienceXPS, RBS, and NRA have been combined to study the mechanisms of Li-ion electrochemical intercalation in MoO3 thin films prepared by thermal oxidation of molybdenum metal. A direct anaerobic and anhydrous transfer was used from a glovebox (O-2 and H2O < 1 ppm), where the samples were electrochemically treated at selected potentials between 1.7 and 3.2 V versus Li+/Li, to the XPS analysis chamber. The thermal oxide film grown at T = 450 +/- 10 degrees C and P(O-2) = 100 +/- 10 mbar for t = 5 min consisted of a 20 nm thick MoO3 outer layer overlying a 13 nm thick inner layer of lower oxides (Mo2O5 and MoO2). Combined RBS/NRA analysis allowed the dosing of intercalated lithium and the determination of the composition of the lithiated phases. Li0.50MoO3, Li1.20MoO3, and Li0.21MoO3 were obtained after intercalation at 2.58 and 1.73 V and deintercalation at 3.2 V, respectively, showing that similar to 1.2 mol of Li can be initially intercalated in the potential range 1.7-3.2 V (capacity of 223 mA h/g), and similar to 0.2 mol of Li per mol of MoO3 is trapped in the oxide matrix after the initial stages of intercalation. The XP Mo3d core level spectra evidenced the reduction of Mo6+ ions to Mo5+ ions after intercalation at 2.58 V and further to Mo5+ and Mo4+ ions after intercalation at 1.73 V with resulting Mo6+/Mo5+/Mo4+ ratios of 53:47:00 at % and 37:39:24 at %, respectively. Reoxidation of molybdenum is observed after deintercalation but 40 at % Mo5+ subsist at 3.2 V due to the trapping of lithium strongly bonded to the oxide matrix. The Li1s core level (at E-B = 55.80 eV) is most intense at 1.73 V and does not vanish at 3.2 V. Broadening of the Mo3d core level peaks are assigned to the distortion of the oxide matrix. Changes of the electronic structure after intercalation result from the occupation of the Mo4d states (at E-B = 1.0 eV) originally empty in the pristine oxide. The XP C1s and O1s core level spectra show the irreversible formation of a solid electrolyte interphase (SEI) layer including lithium carbonate and Li-alkoxides

Combined x‐ray reflectivity and grazing incidence x‐ray fluorescence study of Ta/Cr/Pt thin film stacks

International audienceThe Ta/Cr/Pt three‐layer system can be used as a planar x‐ray waveguide, that is to say it can guide an x‐ray beam inside its chromium layer. This property comes from the difference in density and hence in optical index between the two “heavy” or cladding tantalum and platinum layers and the “light” or guiding chromium layer. The waveguide will be efficient provided the layers are a few nanometers thick and that the interfaces are as sharp as possible. To control the quality of the stack, we combine grazing incidence x‐ray fluorescence (GIXRF) and x‐ray reflectivity (XRR) measurements on a series of Ta/Cr/Pt samples, whose only difference is the thickness of the Cr layer. The three considered samples have been deposited by magnetron sputtering and their designed structures are: Ta (8 nm)/Cr (5, 10, and 15 nm)/Pt (14 nm)/Si substrate. The combination of XRR and GIXRF tightens constraints on the parameters used to simulate the stack: thickness, roughness, composition, and density of the layers and their interlayers. For each sample we used six GIXRF curves obtained from three different characteristic x‐ray lines (Ta Lα, Cr Kα, and Pt Lβ 2,15 ) excited at three different incident photons energies (6.25, 10, and 12 keV) as well as one XRR curve obtained at 6.25 keV. The XRR‐GIXRF combined analysis demonstrates that the Ta/Cr/Pt structure is too simplistic and that it is necessary to introduce some interlayers at the top and bottom of the stacks to obtain a reliable agreement between the experimental and simulated GIXRF and XRR curves

Kossel diffraction observed with X-ray color camera during PIXE of nano-scale periodic multilayer

International audienceBy combining Kossel diffraction with particle induced X-ray emission, we have developed a new methodology to analyze nano-scale thin films. We report the Kossel diffraction generated by irradiating Pd/Y based nano-scale periodic multilayers with 2 MeV protons. The intensity of characteristic Pd Lα X-ray emission is measured as a function of the detection angle (grazing exit). An oscillation of its intensity is observed when the detection angle varies around the Bragg angle, which corresponds to the energy of the emission and the period of the multilayer. Use of the X-ray color camera enables the whole setup to be fixed so that no angular scan is required, greatly simplifying the experimental condition. From the features of the Kossel curves, we are able to deduce that nitrided Pd/Y multilayers exhibit much less layer intermixing than the non-nitrided multilayers. The experimental results show that it is possible to distinguish by the shape of Kossel curves of multilayers with B 4 C barrier layers located in different interfaces. This demonstrates that Kossel diffraction is structural sensitive

Kossel diffraction observed with X-ray color camera during PIXE of nano-scale periodic multilayer

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