Ultrathin MgB₂films fabricated by the co-evaporation method at high Mg evaporation rates

Ultrathin MgB2 films were fabricated by using a co-evaporation method. We increased the Mg evaporation rate up to 32 nm s−1 by adjusting the chamber configuration and succeeded in fabricating MgB2 thin films with high quality at a high substrate temperature of 350 °C. The thickness dependence of the thin film characteristics showed that an ultrathin film with a thickness of 4.2 nm had superconducting properties with a critical temperature of 8 K and a resistivity of 1200 µΩ cm at 40 K. The mean roughness of a 15 nm thick MgB2 thin film was 0.18 nm, which indicated that our MgB2 thin films have the potential to fabricate sub-micron size patterns.