Combining non-specular X-ray scattering and X-ray absorption spectroscopy for the investigation of buried layers

The atomic structure and the chemical composition of buried interfaces is of high interest for many applications e.g. in multilayered samples such as oxidized metals, optic or microelectronic devices. Conventional surface analytical techniques such as X-ray photoelectron spectroscopy (XPS), Auger-electron spectroscopy (AES) or ion scattering spectroscopy (ISS) have an extremely high surface sensitivity but are not suited for the non-destructive investigation of buried layers, where a sputter-depth profiling is required. Non-specular (diffuse) X-ray scattering is another method to obtain quantitative information of buried interfaces and multilayers [1-3]. In addition to the specular X-ray reflectivity, which provides information about the structures perpendicular to the surface of the sample (namely the surface and interface roughness, layer thickness and density), the diffuse X-ray scattering gives information on the in-plane and out-of-plane structure of the involved interfaces [3]. Especially lateral correlations are accessible using this technique, making it an ideal tool for the study of multilayered samples and liquid surfaces also (see, e.g. [2, 4]). As recently shown, the combination of grazing incidence non-specular X-ray scattering with X-ray absorption spectroscopy may give additional information such as the chemical valence and the local atomic environment of atoms which are located in surface and interface regions [5, 6]. Since the angular position of the Yoneda-peak is directly correlated with the density of the X-ray scattering material (e.g. [7]), different interfaces can be selected by the choice of the scattering angles. Therefore, by measuring the X-ray absorption fine structure for well defined incidence and exit angles, it is possible to study the atomic short range order and the chemical state of a chosen element in a chosen position inside a multilayered sample. In this contribution, we will demonstrate the capabilities of the new technique for the ex-situ investigation of a metallic Cu-Au-bilayer prepared by subsequent sputtering of Au and Cu on a glass substrate.