PREPARATION OF NDBA2CU3O7-DELTA FILMS IN ULTRAHIGH-VACUUM WITH A NO2 SUPERSONIC MOLECULAR-BEAM

Superconducting NdBa2Cu307-beta thin films have been prepared in ultrahigh vacuum by the molecular beam epitaxy (MBE) method using a supersonic molecular beam of nitrogen dioxide as an oxidizing agent. A new type of supersonic molecular beam source has been developed, which has a liquid nitrogen trap for cryogenic pumping and is small enough in size to be installed in a conventional MBE system. Films with a transition temperature of about 30 K have been obtained in situ without post-deposition annealing. Throughout deposition epitaxial growth of the films was observed in situ by reflection high-energy electron diffraction.