Screw-like structures in ex situ Tl2Ba2CuO6 films

Ba2CuO6 films on single-crystal LaAlO3 was investigated using atomic force microscopy and X-ray diffraction. Most of the film surface consisted of flat areas separated by single or several unit-cell steps. This morphology suggests that the films grow predominantly by a step-flow mechanism. A Tl-2201 film grown using a precursor film deposited at 700 °C exhibited stacks of planes arranged in a screw-like manner on a flat background. Islands of 1–3 μm size and a height of 2–20 unit cells were dominant structures on the surface. Possible causes for the formation of the screw-like structures are discussed.