MBE growth of FeSe and Sr1−xKxFe2As2

We report molecular beam epitaxy growth of FeSe and Sr1−xKxFe2As2. In FeSe growth, the compositional window to obtain the superconducting phase (β-FeSe) is very limited. The use of Al2O3–R substrates instead lattice-matched LaAlO3 substrates slightly expands the compositional window, and we observed a substantial drop of resistivity but with no zero resistivity attained. In Sr1−xKxFe2As2 growth, the largest problem is the volatility of K. Films grown at substrate temperatures higher than 300 °C contain no K. Superconducting films of Sr1−xKxFe2As2 can be obtained at the growth temperature of 250 °C with very low As flux. The best film has T c on = 30.3 K and T c end = 22.9 K .