Morphological characterization of ion-sputtered C–Ag, C/C–Ag and Ag/C films by GISAXS

A carbon–silver thin film (33 at.% Ag and thickness of 2100 Å) has been synthesized by co-sputtering of a C–Ag target and characterized by grazing-incidence small-angle X-ray scattering (GISAXS), a technique that gives a considerably enhanced surface sensitivity. Experiments have been carried out at or near the critical angle of the layer. It is shown that, because C and Ag show no mutual solubility, a demixing occurs during the co-deposition process and silver clusters form within an amorphous carbon matrix. Using different incident angles of the X-ray beam, it is demonstrated that two populations of clusters are present in the layer: some large and nearly spherical on the surface, others smaller and elongated along the direction of the growth of the thin film in the bulk. In the case of a C/C–Ag bilayer, the surface diffusion is avoided just after the co-deposition process and it is shown that only the small and elongated clusters in the bulk are formed. In the case of a very thin Ag/C layer, there is only surface diffusion and it is shown that large silver islands are formed on the carbon surface. Such experiments demonstrate that the growth mechanism that takes place during the co-deposition process involves mainly a surface diffusion of silver and carbon atoms, as opposed to a volume diffusion.

Grazing-Incidence Small-Angle Scattering. Morphology of Deposited Clusters and Nanostructure of Thin Films

It is shown that grazing-incidence small-angle X-ray scattering (GISAXS) is a new experimental technique that combines both grazing incidence and scattering at low angles. The experiments are carried out at or near the critical angle: the result is a considerably enhanced surface sensitivity. It allows morphological characterization of aggregates deposited or gathered on a flat substrate, such as silicon wafer or Coming glass. The full potential of this technique is realized when using a synchrotron source (flux, collimation and choice of wavelength in order to avoid fluorescence or to perform anomalous measurements) and when patterns are recorded with two-dimensional detectors: gas detectors or imaging plates (IPs). It is then possible to study the anisotropic shape of the scattering pattern and to determine the sizes of the aggregates. Results are presented for gold clusters deposited on a silicon wafer covered by a carbon sublayer in order to make a comparison with transmission electron microscopy and with scanning probe microscopy. Other examples are presented in order to highlight the advantages of such a technique applied to small inclusions in thin surface layers.