X-ray reflectivity study of interdiffusion at YBa₂Cu₃O_7-x and metal interfaces

We present a study of interdiffusion at interfaces of YBa₂Cu₃O_7-x (YBCO) and metals, Au, Ag, and Pb by using X-ray reflectivity. YBCO thin films were epitaxially grown by off-axis sputter deposition and coevaporation, with the c-axis perpendicular to the SrTiO₃ substrate surfaces. The capping layers were subsequently deposited on the YBCO film in situ and ex situ near room temperature. Glancing incident X-ray reflectivity was employed to investigate the surfaces and their buried interfaces. We find that interdiffusion at the interfaces of Au/YBCO and Ag/YBCO is negligible. However, a large interdiffusion zone, ∼60 Å, is present at the Pb/YBCO interface and the lead films grown, both in situ and ex situ, were entirely oxidized. We do not observe any diffraction peaks from the Pb/YBCO films. The diffraction peaks are found up to (007) from the YBCO films of the Au/YBCO and Ag/YBCO films. This implies that the loss of crystalline structure in a ∼300 Å-thick YBCO film underneath Pb is caused by interdiffusion.