Ultrathin MgB2 films fabricated by molecular beam epitaxy and rapid annealing

Abstract

Ultrathin MgB2 films with thicknesses between 5 and 50 nm were fabricated using molecular-beam epitaxy and rapid annealing. The rapid annealing increases Tc and Jc without degrading the surface flatness. A 10 nm-thick film shows Tc(0) = 24 K, Jc(0) = 8 × 106 A cm−2 with a root mean square roughness of 0.35 nm. Cross-sectional transmission electron microscopy and energy dispersion spectroscopy elemental analyses also revealed that the surfaces of the MgB2 films are oxidized to a thickness of 5 nm.