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Morphology of Superconducting FeSe thin films deposited by co-sputtering and MBE

The presumably unconventional superconductor Beta-FeSe was deposited by radio frequency sputtering and molecular beam epitaxy (MBE) from two elementary sources. Superconducting thin films were grown in (001)-orientation on MgO(100) and YAlO3(010) substrates. The morphology of the samples was studied and directly related to the superconducting properties of the Beta-FeSe thin films. The MBE grown thin films show microcracks down to the substrate and a roughness of about 100~nm. In contrast, sputter deposited superconducting thin films show a smooth surface with almost no precipitates. In both cases resistive superconducting transitions with critical temperature up to 8.5 K were observed. However, the smoothness of the sputter deposited films is crucial for future surface dependent investigations.