  The strong fascination exerted by the binary compound of FeSe demands
reliable engineering protocols and more effective approaches towards inducing
superconductivity in FeSe thin films. Our study addresses the peculiarities in
pulsed laser deposition which determine FeSe thin film growth and focuses on
the film/substrate interface, the tendency for domain matching epitaxial growth
but also the disadvantage of chemical heterogeneity. We propose that
homogenization of the substrate surface improves the control of stoichiometry,
texture, and nanostrain in a way that favors superconductivity even in
ultrathin FeSe films. The controlled interface in FeSe/Fe/MgO demonstrates the
proof-of-principle.
