X-ray standing waves in a heterostructure: application to a Zn(1−x)Co(x)O epilayer on ZnO(00.-1)–O substrate

• Published in: Acta crystallographica. Section A, Foundations of crystallography Foundations of crystallography, 2004-07, Vol.60 (4), p.339-350
• Main Authors: Zheng, Yun-Lin, Boulliard, Jean-Claude, Soyer, Alain, Petroff, J.F.
• Format: Article
• Language: English
• Subjects: Condensed Matter; Materials Science; Physics
• ISSN: 0108-7673; 1600-5724
• DOI: 10.1107/S0108767304014473

X-ray standing waves (XSW) in a thin epitaxic film are treated in the framework of the dynamical theory. It is demonstrated that the fluorescence yield around the main peak of the rocking curve has essentially the same characteristics asthat of the usual XSW on a bulk crystal surface. Thus, XSW provide a directmethod to probe the atom position in a thin ®lm. The method was applied to anepilayer of the diluted magnetic semiconductor Zn0.94Co0.06O, in order todetermine the Co-atom position. The XSW established that Co atoms occupythe substitutional Zn site in the ZnO matrix, although their coherent fraction,which measures the degree of order, is rather low. Moreover, the measurementof the Zn fluorescence in the film gives approximately the same value for thecoherent fraction of the Zn atoms. Besides, by using the substrate rocking curve,it is shown that the XSW signal of the Zn atoms in the substrate can be detectedthrough the film. This interesting approach allows the coherent fraction of anelement of a substrate below an interface to be probed in situ. For the Zn fluorescence, the coherent fraction is lower near the interface than in the bulk.These results should relate to strains and defects on both sides of the interface.