Compositional dependence of thin films of BiPbSrCaCuO on target to substrate distance
Using magnetron sputtering techniques, several thin films of superconducting BiPbSrCaCuO were fabricated by varying the distance between the substrate (single crystal of MgO with polished (100) plane) and the targets. During the deposition the gas pressure was kept constant at 0.3 mbar (1 mbar = 0.1 kPa) and the substrate temperature was kept at 700 °C. An energy-dispersive X-ray fluorescence was designed using a radioisotope source with a secondary target and a Si(Li) X-ray spectrometer and it was used to measure the atomic composition of the film quantitatively. It was found that the Ca concentration relative to Sr increases linearly as the distance between the substrate and the targets increases. However, both Cu and Bi show a more complex variation of concentration with distance. The X-ray diffraction results also indicated that the films are grown epitaxially along the C axis, which showed a semiconducting behaviour with TC,zero below 60 K.