Systematic Comparison of Eight Substrates in the Growth of FeSe0.5Te0.5 Superconducting Thin Films

We have investigated the crystal structures and superconducting properties of thin films of FeSe 0.5 Te 0.5 grown on eight different substrates. Superconductivity is not correlated with the lattice mismatch; rather it is correlated with the degree of in-plane orientation and with the lattice parameter ratio $c/a$. The best superconducting properties were observed in films on MgO and LaAlO 3 ($T_{\text{c}}^{\text{zero}}$ of 9.4 K). Transmission electron microscopy observation showed that the presence or absence of an amorphous-like layer at the substrate surface plays a key role in determining the structural and superconducting properties of the grown films.