Coplanar grazing exit X-ray diffraction on thin polycrystalline films

Zdeněk Matěj, Lea Nichtová, Radomír Kužel

Charles University, Faculty of Mathematics and Physics, Ke Karlovu 3, Prague 12116, Czech Republic

X-ray powder diffraction analysis of thin polycrystalline films in the coplanar grazing exit (GE) parallel beam geometry was tested. Dependence of the diffraction peak intensity on the beam incidence/exit angle, which cannot be interpreted by a simple formula for absorption in the film [1], was observed for very thin films (<~100 nm for TiO2). This effect is connected with the well known Yoneda peak in the transparency of the film surface interface. The refraction correction of peak positions and penetration depth [2], and also dynamical effects of multiple scattering of primary/diffracted beam in the film [3] should be considered. In comparison with the common coplanar grazing incidence geometry, by GE technique lower intensity gain for thin film can be achieved. However, if the PSD detector is used, 2D maps of scattered intensity with high resolution (because of narrow diffracted beam) can be obtained in a reasonable time. Moreover, they are not affected significantly by instrumental and sample effects. The technique is very useful for determination of the film thickness, depth profiling of phase composition, the refraction index determination and generally for study of real structure of thin films and multilayers with common laboratory diffractometers.

Simulated dependence of the integrated intensity of anatase (101) diffraction line on the exit angle Alpha_f, for powder TiO2 films of different film thickness. Measured intensity for the thinnest film (50 nm) is depicted in the right plot.

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[2] G. Lim, W. Parrish, C. Ortiz, M. Bellotto, M. Hart, J. Mater. Res. (1987) 2 (4) 471-477

[3] P. F. Fewster, N. L. Andrew, V. Holy, K. Barmak, Phys. Rev. B (2005) 72 174105