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-(delta ) (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 degrees C. These conditions are below the currently accepted stability line for the growth of REBCO thin films. We characterize the physical and chemical properties of the O+ ion beam, and its effect on superconducting thin films. We have grown highly crystalline BaO and EuBa2Cu3O7-(delta ) (EBCO) thin films on SrTiO3 substrates. The full width at half maximum of the rocking curves for BaO(002) equals 0.07 degrees and that for the EBCO (005) peak equals 0.05 degrees. Also, we found that BaO is a good insulating material (1.7 X 1013 (Omega) m at 4K), with an excellent lattice match to EBCO, therefore a suitable candidate as an insulating layer in multilayer structures. The results of the first growth studies of BaO/EBCO multilayers are discussed.