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RBS/Channeling characterization of Ru(0001) and thin epitaxial Ru/Al$_2$O$_3$(0001) films

Thin epitaxial films of metals on insulating substrates are essential for many applications, as conducting layers, in magnetic devices or as templates for further growth. In this work, we report on the growth of epitaxial Ru films on single-crystalline Al$_2$O$_3$(0001) substrates by magnetron sputtering and their subsequent systematic characterization using Rutherford backscattering spectrometry of He ions both in random and in channeling conditions. We include results of a Ru(0001) single crystal for comparison. Analysis of channeling shows that films thicker than 35 nm grow with (0001) orientation, a well-defined epitaxial relation with the substrate and a high degree of crystal quality, comparable to the Ru(0001) single crystal. Thinner films of down to 7 nm in thickness, for which relaxation of epitaxial strain is not complete, produce a similar degree of dechanneling. The surface of the films can be prepared in a clean and ordered state in order to allow further epitaxial growth on top.