CHARACTERIZATION OF A RADIO-FREQUENCY PLASMA SOURCE FOR MOLECULAR-BEAM EPITAXIAL-GROWTH OF HIGH-TC SUPERCONDUCTOR FILMS

The growth of superconducting oxides in vacuum conditions compatible with molecular beam epitaxy (MBE) requires a form of activated oxygen. The activated oxygen species can be either atomic oxygen (O) or ozone (O3). Here we characterize a rf plasma source by measuring the oxidation rate of a silver film on a quartz crystal deposition monitor as a function of the oxygen flow. The initial oxidation rate provides a lower limit for the actual atomic oxygen flux. If the frequency change of the quartz signal is entirely due to the oxidation of silver by atomic oxygen and we assume a detection efficiency of one, then the total cracking efficiency of the source is estimated to be around 30%. The source was used in a MBE machine to deposit thin (200 angstrom) high-T(c) films of DyBa2Co3O7 on SrTiO3 with a T(c)onset of 88K and a T(c)zero of 86 K.