Systematic Comparison of Eight Substrates in the Growth of FeSe${}_{0.5}$Te${}_{0.5}$ 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 $c\mathrm{/}a$. The best superconducting properties were observed in films on MgO and LaAlO${}_3$ ($T_{\mathrm{c}}^{\mathrm{z}\mathrm{e}\mathrm{r}\mathrm{o}}$ of 9.5 K). TEM 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.