Sintered AlN ceramics were implanted by Ti, Fe and Cu ions up to 1.9 x 10 17 atoms/cm 2 at mean energies of 70-110 keV in order to investigate the role of the chemical properties of the implanted species. on the phase formed during the impłantation process. X-ray absorption studies were performed at room and at liquid nitrogen temperature to give information on the resulting systems and local environments of the Ti, Fe and Cu atks. We observe the formation of .TiN even for as-implanted samples, while the Cu ions aggregate to clusters. The Fe implanted samples show an intermediate behavior with both nitride formation and Fe clustering. In conclusion, the heat of formation is found to be a key parameter for the final system.

Influence of an extra electron yield induced by the fluorescence process has been experimentally shown and analytically described. Analyse of the conversion electron yield (CEY) signal induced by pure bulk Ag (Ag K edge) and pure bulk Ni or Cu recovered by a thin Fe layer (Ni and Cu K edges) has been performed. This fluorescence electron yield leads to enhancement of the edge height, modification of the shape of the X-ray absorption near-edge structure and decrease of the extended X-ray absorption fine-structure (EXAFS) amplitude. Extrapolation of the model concerning unrecovered bulk samples was carried out in order to explain the EXAFS amplitude reduction often observed in CEY measurements with respect to that obtained in the transmission mode. The reduction Delta chi/chi increases with increasing atomic number Z of the studied element. Delta chi/chi can be considered as negligible for low-Z elements (Ni and Cu). It becomes important for high-Z elements. The k dependence of the amplitude reduction is rather limited and this reduction can be simply explained by a proportional factor. In order to correct this unwanted effect, a theoretical calculation process can be performed or the sample structure can be specially designed to minimize it. Thin films deposited on a substrate consisting of a low-Z element do not generate significantly this extra electron yield.

Heterogeneous Co x Ag 1− x and Ni x Ag 1− x alloys have giant magnetoresistance properties. Such alloys, with atomic concentrations x = 0.20 and 0.37, were studied by transmission X-ray Absorption Spectroscopy at the Co or Ni K -edge after in situ thermal annealing. For alloys as-deposited and annealed at 200 °C, Extended X-ray Absorption Fine Structure analysis displays both Co-Co (Ni-Ni) bonds related to Co (Ni) atoms agglomerated in magnetic particles and Co-Ag (Ni-Ag) bonds related to Co (Ni) atoms in substitutional sites in the Ag matrix. At the same alloy concentration, the miscibility in the Ag matrix is found larger for Ni than for Co. After annealing around 250 °C, the marked decrease of the Ag neighbour peak corresponds to a diffusion of magnetic atoms outside the Ag matrix. The Co-Co coordination number increases regularly with annealing temperatures up to 450 °C reflecting a progressive expansion of Co particles. On the contrary, for Ni alloys, no further particle expansion has been observed in the same annealing range. This different behaviour may be linked both to the difference between the as-deposited structural states and to the Co/Ag and Ni/Ag interfaces energies. Using a simple model, evolution of the mean particle size has been estimated as a function of annealing.

Ni0.35Ag0.65 thin films were studied by means of both x-ray absorption spectroscopy and x-ray diffraction, in the as-deposited and annealed states. Short-range-order investigation has established that nickel atoms are either clustered in small pure Ni aggregates or dispersed in an Ag-rich solid solution. For the as-deposited and 250 °C annealed samples, an accurate interpretation of the diffraction spectra requires one to take into account a degree of structural coherence between these two phases, which are preferentially oriented with the dense planes parallel to the surface. Local order and long-range-order characterizations then give coherent results. The mean size of the pure Ni aggregates increases from approximately 1 nm in the as-deposited state to 3-5 nm after a 400 °C anneal. The maximum Ni solubility in the Ag matrix was estimated to be around 7 at.% for these samples. All of the reported results - the natures of the various phases, and mean sizes, shapes and orientations of the aggregates - are discussed with regard to the other structural (extended x-ray absorption fine-structure, anomalous small-angle x-ray scattering) and magnetic information.

NiAg heterogeneous alloys were studied by x-ray diffraction and x-ray absorption spectroscopy at the Ni K-edge using a total electron yield detection. In the as-deposited alloys of 0.10 and 0.15 Ni atomic fraction, most of the Ni atoms are in substitutional sites in the Ag matrix. At higher Ni concentration, the Ni atoms outside the Ag-rich phase become numerous enough to group together in small clusters. An important disorder in the neighbourhood of Ni atoms is demonstrated. At low annealing temperature (up to C), in and , some Ni atoms are still present in substitutional sites in the Ag matrix and the small Ni particles are under strain. A very short-range order exists in this state. After a C annealing, the Ni particles grow, and the Ag-rich phase remains in a steady structural state. After a higher annealing (C), the local Ni atomic environment becomes well ordered and typical of the pure Ni FCC phase. The Ag-rich crystallites are impoverished in Ni atoms and grow with elimination of defects. Ni grains are generally smaller than 1 nm for as-deposited alloys and reach several nanometres after a C annealing for 10 min.

Heterogeneous alloys Ni0.20Ag0.80, presenting giant magnetoresistance properties, have been studied by Total Electron Yield X-ray absorption spectroscopy at liquid nitrogen temperature at the Ni K edge from as-deposited to annealed stages. Up to 150 degrees C annealing, the Ni atoms are mainly in small poorly ordered agglomerates and the local Ni atomic environment is very stable and disordered. Up to 250 degrees C annealing, some Ni atoms occupy substitutional sites in the Ag matrix and 40 to 50 % of the Ni nearest neighbors are Ag atoms. After annealing at 400 degrees C during 10 mn, the nanostructures evolve towards larger, more compact and well ordered granules. The Ni-Ni distance varies from 0.246 to 0.248 nm as the annealing temperature increases indicating that the small agglomerates are under strain in the Ag matrix.

Electron detection in EXAFS is commonly used at room temperature for thick samples (where transmission measurements are not possible) or nanostructures with high element concentrations (where fluorescence detection is not appropriate). Recently, a Total Electron Yield detector with He gas flow at atmospheric pressure working at liquid nitrogen temperature has been developed and successfully tested on the French CRG/IF beamline at ESRF. At 80 K, the substantial decrease of the dynamic part of the Debye-Waller (DW) factor enables to record EXAFS signals on a larger k range and hence to obtain better signal-to-noise ratio of the corresponding Fourier Transform. A variation of the temperature of the sample from 80 to 300 K can be performed to evaluate the vibrational and the structural part of the DW factors. Moreover, in order to get rid of Bragg peaks in the EXAFS signal in case of monocrystalline samples, a special 360° rotating sample holder has been designed. Finally, polarization studies for anisotropic systems may be realized by simply rotating the sample holder by 90° from the in-plane to the out-of-plane polarization sample geometry.

X-ray diffraction and absorption spectroscopy measurements have been performed in metastable solid materials obtained by mechanical attrition or codeposition process of immiscible systems in view to investigate the short and long range order obtained inside these solutions. Firstly, experiments show that Cu 80 Fe 10 Co 10 milled powders are in quasi perfect solid solution: this result arouses interest because giant magnetoresistance is more readily controlled by decomposition of a supersatured solid solution. Secondly, codeposition of Cu 50 Mo 50 presents a long range order typical of a well-defined cristalline structure whereas the short range order appears very disordered.

Total electron yield (TEY) Co K edge extended X-ray absorption fine structure (EXAFS) experiments have been performed at low temperature on as deposited and annealed CoxAg1−x granular alloys with Co volume concentrations x = 0.2 and 0.35. A new design for a total electron yield detector operating close to liquid nitrogen temperature has been tested with success at ESRF and used for the experiments reported here. A very interesting feature of this study concerns the evolution of the neighbourhood of the Co atoms in these alloys as a function of x and of the annealing temperature. For x = 0.2, at the as deposited stage, one observes clearly the presence of an important fraction of Co in the substitutional sites of the Ag f.c.c. matrix, in addition to Co agglomerates. For x = 0.35 the Co precipitation process seems more advanced compared to x = 0.2. From the evolution of the intensity of the different peaks of the radial distribution, one can follow the agglomeration process of Co in the Ag matrix.

les multicouches Au/Pt de faible periode ont ete etudiees par diffraction des rayons X et par spectrometrie d'absorption X. Les spectres de diffraction mesures pour tous les echantillons presentent un seul systeme de raies caracteristiques d'une structure cubique face centree dont le parametre de maille serait compris entre ceux de l'or et du platine massifs. L'influence de la periodicite est clairement mise en evidence sur les spectres de diffraction X aux petits et grands angles. Les resultats de diffraction des rayons X sont en desaccord avec les resultats de spectrometrie d'absorption X. Cette contradiction entre les resultats apportes par ces deux techniques souligne l'interet de les conjuguer pour etudier des systemes multicouches de tres faibles periodes.

Extended X-ray absorption fine-structure (EXAFS) and X-ray absorption near-edge spectroscopy (XANES) have been used to study the local order in FexAl1-x alloys (x = 0.5, 0.53, 0.60 and 0.62). Using the same technique, we also analyze the chemical disorder variations induced in Fe60Al40 samples irradiated with N+ ions at damage rates of the order of 0.1, 0.2 and 0.9 dpa. The EXAFS results related to FexAl1-x, samples reveal that all alloys are chemically ordered. In what concerns the implanted Fe60Al40 samples, an EXAFS analysis of the experimental data confirms unambiguously that irradiation creates an ion beam induced chemical disorder in the material. For the damage rate of 0.1 dpa, it corresponds to a chemical disorder of about 34%. All these results are correlated with the evolution of the XANES fine structures that were analyzed theoretically with more details for the equiatomic composition.

The NiTi coatings studied here are deposited using ion sputtering technique. The target consists of Ni0.49Ti0.51 and the sputtering ions are reactive nitrogen N+ or inert argon Ar+, or a mixture of both argon and nitrogen ions. In this paper, we relate the tribological properties of these thin films to their microstructure, for different experimental preparation conditions. The structure of the sputtered coatings are characterised by X-Ray Diffraction (XRD) and mainly by Extended X-Ray Absorption Fine Structure (EXAFS). The results reveal that chemical affinity between titanium and nitrogen largely dominates the other phenomena and that coatings are composed of TiN crystalline particles, embedded in an amorphous matrix. It is shown that the wear improvement depends on the size of the precipitates and also on the composition of amorphous matrix. Best tribological results are obtained with an amorphous NixN1−x matrix type with x close to 0.75.

Metastable CuMo thin films have been deposited on quartz substrates by ion beam Sputtering. The structural and mechanical state characterisation in these as-deposited films have been performed using X-ray diffraction. The size of the coherently diffracting domains is small (1.5 – 2.0 nm) and the micro-strains are very large (0.3 – 1.9%). The value of these parameters depends on the Mo concentration. The sin2 Ψ method was applied to extract stresses and the stress-free lattice parameter a0 in the Cu30 Mo70 films. In-plane stress is compressive and its amplitude is very high (4.5 GPa). The presence of such high intrinsic compressive stresses is related to lattice distortions induced by an ‘atomic peening’' effect and Ar interstitials during the deposition process. After thermal annealing, one observes the demixing of the solid solution (a0 evolution) and an inversion of stress sign (compressive to tensile).

Mn films were grown on (001) and (111) fcc Ir lattices by molecular beam epitaxy, extended x-ray absorption fine structure (EXAFS) experiments were performed on these films in order to determine the Mn structures. As Mn can adopt different crystalline structures, it is first shown that the usual Fourier treatment of EXAFS oscillations is not an appropriate technique for this purpose. On the contrary, the application of multiple scattering theory of x-ray-absorption fine structure allows us to identify the structures. For relaxed (polycrystalline) thick Mn deposits, Mn crystallizes in the Mn\ensuremath{\alpha} structure. For unrelaxed (single-crystalline) thick Mn films, the Mn EXAFS oscillations are well simulated assuming a mixing of fcc and Mn\ensuremath{\alpha} structure. For thin Mn films in Mn/Ir (111) and (001) superlattices, this multiple scattering approach allows us to show that Mn is in a trigonal structure when it is grown on Ir(111) and a tetragonal structure when it is grown on Ir(001). Finally, the (\ensuremath{\surd}3\ifmmode\times\else\texttimes\fi{}\ensuremath{\surd}3)R30\ifmmode^\circ\else\textdegree\fi{} superstructure of Mn films grown on (111) Ir is shown to come from the epitaxy of a mixed fcc and Mn\ensuremath{\alpha} structures and not from the occurence of Mn Laves phases like ${\mathrm{Cu}}_{2}$Mg or ${\mathrm{Zn}}_{2}$Mg as assumed by several workers. \textcopyright{} 1996 The American Physical Society.

Supermirrors, which are NixC1-x/Ti aperiodic multilayers, have become more and more important for use in neutron guides. The effects of neutron radiation on the structural and optical properties of such stacks have been studied to estimate the lifetime of the neutron guides. The results presented here have been obtained by neutron reflectivity, X-ray diffraction, Conversion-Electron Extended X-ray Absorption Fine Structure and High Resolution Transmission Electron Microscopy. It has been observed that the reflecting performances of the supermirrors were not altered by irradiation, but that a structural change did occur in the Ti layers.