The role of the substrate surface morphology in enhancing the MgB2 superconducting temperature

We hereby report on the role of the surface morphology of various substrates in the enhancement of the superconducting critical temperature of MgB2. MgB2 thin layers were grown by hybrid physical-chemical vapour deposition on silicon carbide SiC substrates/fibers and several other substrates, characterized by diverse surface morphologies. By investigating the structural, morphological and transport properties of MgB2 thin layers, the presented data show that the superconducting critical temperature Tc exceeds the bulk value only when the MgB2 films are grown on atomically flat (0001) SiC single crystals and on MgB2 bottom layers. These results further confirm the interpretation of the coalescence-driven tensile strain mechanism behind the enhancement of superconducting properties in MgB2 thin films.