Low energy oxygen ion beam assisted growth of BaO/EuBa2Cu3O7-δ multilayers in ultra thin vacuum

Molecular Beam Epitaxial growth of cuprate oxide superconducting thin films using a mass separated, low energy, O+ beam source, is discussed. The mono-valent O+ ion is chemically, highly reactive, and its kinetic energy at 10's of electron volts, is significant. It allows the growth of REBa2Cu3O7-δ (REBCO) thin films at low pressures and temperatures. The effective over-pressure of the O+ ions at the substrate being 2 x 10-7 Torr, and the optimum growth temperature 500 C. These conditions are below the currently accepted stability line for the growth of REBCO thin films. The authors characterize the physical and chemical properties of the O+ ion beam, and its effect on superconducting thin films. They have grown highly crystalline BaO and EuBa2Cu3O7-δ (EBCO) thin films on SrTiO3 substrates. The full width at half maximum of the rocking curves for BaO(002) = 0.07 degree and that for the EBCO (005) peak = 0.05 degree. Also, they found that BaO is a good insulating material (1.7 x 1013 Ωm at 4 K), with an excellent lattice match to EBCO (∼ 0.01%), therefore a suitable candidate as an insulating layer in multilayer structures. The results of the first growth studies of BaO/EBCO multilayers are discussed