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

Abstract

A carbon±silver thin ®lm (33 at.% Ag and thickness of 2100 A Ê ) has been synthesized by co-sputtering of a C± Ag target and characterized by grazing-incidence smallangle 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 codeposition 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 ®lm 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.

Probing surface and interface morphology with Grazing Incidence Small Angle X-Ray Scattering

“…For that sake GISAXS has proved to be very helpful for analyzing the size distribution and spatial organization of buried clusters. Tuning the angle of incidence around the critical angle of total external reflection [270,271] it is possible to adjust the penetration depth of the beam and to extract a depth profile of the clusters size/shape. The quantitative analysis of the GISAXS patterns must take into account the refractions effects the X-ray beam at the interfaces.…”

“…In order to characterize encapsulated metal nanoparticles, ex situ GISAXS and TEM measurements have been performed completed in some cases with EXAFS and Mössbauer Spectroscopy. • Ag nanoparticles encapsulated in a cage of C [270,271]. Fig.…”

Treatment of grazing-incidence small-angle X-ray scattering data taken above the critical angle

“…According to the simulations reported in the previous section, the experimental intensities are now radially integrated in the range 10 9 26.5 and then corrected for refraction according to 9 av = 18 . The integration range is limited to the 9 values available for all the relevant 2 angles, taking into account that recording at 9 < 10 is hindered by the beam stop, while intensities at 9 > 26.5 are affected by the Yoneda peak (Yoneda, 1963;Babonneau et al, 1999). The correction for absorption does not produce appreciable effects, owing to the very small thickness of the implanted layer (about 1000 A Ê ).…”

“…Grazing-incidence small-angle X-ray scattering (GISAXS) (Levine et al, 1989) is a powerful tool for the structural characterization of thin (micrometre scale) super®cial layers containing nanosized particles. Samples can be obtained by ion implantation (Babonneau et al, 1999;d'Acapito et al, 1998;Cattaruzza et al, 2000), sol±gel synthesis (Kutsch et al, 1997) or vapour deposition (Naudon & Thiaudie Á re, 1997). Investigation of particles deposited on the surface is usually performed at the critical angle c ; however, when dealing with buried nanostructures, the working angle must be slightly higher than c to permit a controlled limited beam penetration in the matrix.…”

“…The use of an experimental setup consisting of a planar detector perpendicular to the incident beam assures better counting statistics, with respect to linear devices, and also allows the investigation of anisotropic implants (Babonneau et al, 1999). On the other hand, the scattered beams recorded at the same 2 but at various azimuthal 9 angles strike the sample surface with different inclination, thus requiring suitable correction for refraction.…”