A. Naudon

Structural and magnetic properties of Fex–C1−x nanocomposite thin films

Iron–carbon nanocomposite thin films with iron concentrations ranging from 12 to 74 at. % were grown by ion-beam sputtering codeposition at different substrate temperatures. The microstructure of the films was characterized by transmission electron microscopy, atomic force microscopy, extended x-ray absorption fine structure, and grazing incidence small-angle x-ray scattering. A granular morphology consisting of body-centered-cubic iron-rich nanoparticles (2–5 nm in diameter and 3–8 nm in height with a relatively sharp size distribution) regularly distributed within a more or less graphitic matrix was obtained. Structural properties as well as magnetic ones were found to depend strongly on composition, substrate temperature, and postdeposition treatments (annealing or Ar+ irradiation). The temperature dependence of the susceptibility exhibited a superparamagnetic response with blocking temperature in the range of 13–180 K. The maximum low-temperature (5 K) coercivity value obtained in this study was 850 O...

Evidence for a self-organized growth in granular Co/Al2O3 multilayers

By sequential deposition of thin layers of cobalt and alumina by sputtering, we have fabricated granular multilayers consisting of successive planes of nanosized cobalt clusters separated by alumina along the growth direction. Combining grazing-incidence small-angle x-ray scattering and transmission electron microscopy experiments, we show that, in a given range of thickness, the vertical arrangement of clusters from plane to plane is not random but shows a topology-induced self-organization.

Grazing-incidence small-angle X-ray scattering applied to the characterization of aggregates in surface regions

Abstract Ion-beam sputtering deposition has been used to elaborate discontinuous gold and granular carbon–platinum thin films. The morphology of the deposited gold islands and buried platinum clusters so obtained has been studied by grazing incidence small-angle X-ray scattering (GISAXS). The full potentiality of this non-destructive technique at grazing incidence is obtained when it is coupled with a synchrotron radiation beam and two-dimensional detectors. The influence of argon ion-implantation performed during Au or C–Pt growth has been studied. A relevant information to understand and control the structural properties of such materials is then achieved.

Morphology of encapsulated iron nanoparticles obtained by co-sputtering and implantation: a GISAXS study

A grazing incidence small-angle X-ray scattering (GISAXS) study is presented on the morphology of iron nanoparticles buried in carbon matrices, obtained either by ion-beam sputtering co-deposition or by ion-implantation. It is shown that, depending on the experimental synthesis conditions, the shape of the iron nanoparticles is either spherical or elongated perpendicularly to the substrate. The possible growth mechanisms are examined in terms of volume and surface diffusion, defect density, interfacial energy and residual stress.

X‐ray small‐angle scattering analysis of porous silicon layers

A small‐angle x‐ray scattering study of porous layers prepared on lightly doped and heavily doped silicon wafers reveals strong differences according to the dopant type. The p‐type silicon layers show a roughness between matter and voids below a space‐correlation length of about 10 nm and a fractal dimension of aggregates for a length scale higher than 25 nm. The lightly doped n‐type is different: the scattering curve obeys the Porod law according to the rod‐like structure of the pores. However, the structure of the heavily doped p+ sample is more complicated and not yet well understood.A small‐angle x‐ray scattering study of porous layers prepared on lightly doped and heavily doped silicon wafers reveals strong differences according to the dopant type. The p‐type silicon layers show a roughness between matter and voids below a space‐correlation length of about 10 nm and a fractal dimension of aggregates for a length scale higher than 25 nm. The lightly doped n‐type is different: the scattering curve obeys the Porod law according to the rod‐like structure of the pores. However, the structure of the heavily doped p+ sample is more complicated and not yet well understood.

Low-temperature mixing in Cu/W superlattices irradiated with light and heavy ions

Ion irradiation effects, induced at low temperature in Cu/W superlattices prepared by ion sputtering, were studied and compared using in situ resistivity measurements and x‐ray diffraction. The influence of the particle mass was particularly investigated in order to measure the role of spike effects in this immiscible system. It is shown that a more important mixing can be obtained with light‐ion irradiation. Nevertheless, the contribution of ‘‘thermally’’ activated jumps opposing ballistic effects is significant even when small and weakly energetic cascades are formed. A dependence of the microstructural state and of the compositional substructure on the irradiating particle is also evidenced. Light‐ion irradiation favors grain growth, restores grain texture, and preserves the composition modulation.

Co-sputtering C-Cu thin film synthesis : microstructural study of copper precipitates encapsulated into a carbon matrix

Abstract Co-sputtered C-Cu thin film depositions have been performed in the temperature range 80-873 K, the atomic carbon concentration varying from 16% to 96%. To characterize the microstructure of the C-Cu thin films, transmission electron microscopy, extended X-ray absorption fine structure and grazing incidence small angle X-ray scattering experiments have been used. During the deposition process, a demixing occurs of the carbon and copper species due to their very low solubilities that leads to the formation of nanometric copper precipitates homogeneously distributed in a more or less graphitic matrix. These precipitates have an elongated shape in the direction of the thin film growth. When the deposition was performed at 273 K for copper atomic concentrations CCu > 55%, as well as for all thin films synthesized at 573 K whatever the CCu value, the formation of graphene layers parallel to the surface of the copper precipitates was observed so that an encapsulation of the Cu aggregates in carbon cages...

Scattering of X-rays

Small-Angle Scattering (SAS) or scattering at low angles can give information on size, shape, quantity and arrangement of “scattering objets” or “particles” whose “characteristic length” is large by comparison to the interatomic spacing.

Relation between the optical properties of composite Si3N4 thin films with embedded Cu clusters and the clusters morphology: Irradiation effects

Ion beam sputtering codeposition has been used to elaborate ceramic–metal (cermet) composite thin films consisting of copper nanoclusters embedded in an amorphous Si3N4 matrix. As prepared, the clusters have a size smaller than 3 nm and postirradiation by high energetic Ar+ ions leads to an homogenization of the clusters’ morphology and an increase of the clusters’ size to an average diameter of 4.5 nm. This work deals with the relation between the morphology of the clusters, characterized by extended x-ray absorption fine spectroscopy and grazing incidence small angle x-ray scattering, and the optical properties (obtained by spectroscopic ellipsometry) of the cermets, which are classically modeled with the help of the effective medium theory. In the case of the as-prepared sample, the Bruggeman effective medium theory has been successfully used. This comes from the fact that the clusters are sufficiently close to each other to create mutual interactions. On the other hand, the morphology of the postirrad...

Determination of the morphology of deposited islands by grazing-incidence small-angle scattering

It is shown that grazing-incidence small-angle X-ray scattering (GISAXS) is a suitable technique to study the morphology of gold islands deposited on a silicon wafer covered by a carbon sublayer. New possibilities of this technique are realized when using a synchrotron source (flux and collimation) and when patterns are recorded with image plates (IPs). It is possible to study the anisotropic shape of the scattering pattern and to deduce the dimensions of the deposited clusters which are formed by the Volmer-Weber mechanism of film growth. Quantitative measurements can be made with a reference sample, leading to an absolute value of the scattered intensity.