An Al thin film, produced by evaporation on an amorphous carbon film, has been investigated with selected area electron diffraction (SAED). The powder SAED patterns were collected with a CCD camera using the largest diaphragm in order to have complete diffraction discs with reliable statistics. The patterns were integrated using the software Fit2D, after refining the camera length, the beam center, and the tilt of the CCD detector. The resulting intensity vs 2Q spectrum, collected with the sample normal to the beam, was analyzed with the Rietveld method GSAS, after inserting the electron scattering factor for Al to check if a Rietveld refinement is possible. The fit is acceptable only if a strong preferential orientation of a [111] direction normal to the film is considered. In order to directly investigate the texture of the film, we tilted the sample along the two orthogonal axes of the sample holder, and collected electron diffraction patterns at 5° intervals. Texture analysis was carried out adapting a consolidated texture analysis procedure for synchrotron hard X-ray diffraction data [1] using the MAUD software. After importing the electron structure factors F_hkl for cubic Al, we proceeded with texture analysis using the EWIMV algorithm, refining experimental geometry parameters, peak profile function coefficients, backgrounds, scale factor and texture. Pole figures obtained for the aluminum film are plotted in the figure, and clearly show a strong (111) fiber texture. As a check, the analysis was carried out both without sample symmetry and with axial symmetry imposed and the resulting texture data are practically identical. Even without imposing symmetry the analysis was surprisingly stable. We present here for the first time, a texture analysis based on the Rietveld method applied to electron diffraction data. This new procedure seems very suitable to study textures in nanocrystalline materials and seems mature enough to be applied to more complex systems.

References:
[1] G. Ischia, H.-R. Wenk, L. Lutterotti, F. Berberich.  J. Appl. Cryst., 38, 377-380, 2005.

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