Microstructure determination as a function of depth in thin multilayer structures

Paul F Fewster¹, Václav Holý², Patricia Kidd¹, Katayun Barmak³ and
Norman L Andrew¹

¹PANalytical Research Centre, Sussex Innovation Centre, Science Park Square, Falmer, Brighton, BN1 9SB, U.K.

² Department of Electronic Structures, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague, Czech Republic,

and Institute of Condensed Matter Physics, Faculty of Science, Masaryk University, Kotlarska 2, 611 37 Brno, Czech Republic,

³Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, U.S.A.

This presentation describes a new approach for extracting microstructural information in polycrystalline multilayers as a function of depth. Most X-ray scattering experiments average information over large depths in multilayers, however in some cases knowledge of surface strains, relaxation and distortions is of interest. Most work on measuring structural information in thin polycrystalline layers as a function of depth has been confined to synchrotron sources, however by modification of standard laboratory equipment and the application of the unique scattering properties of periodic structures this can be performed with a laboratory sealed source.

The method has been applied to Nb-Al multilayers, and it is clear that the single element layers do not necessarily have the same state of strain nor do they necessarily have the same crystallite size. In combination with other X-ray techniques, large area reciprocal space mapping, reflectometry applied to these samples it is possible to build a fairly comprehensive view of these materials.

This method is based on in-plane scattering, whose strength is modulated in depth by a standing wave associated with the density and roughness disruption at each interface. The standing wave is modified with increasing incidence angle. This description of the process will be discussed in terms of the experimental methodology and the detailed theoretical modelling required to interpret the results.