Epitaxial growth of superconducting niobium thin films by ultrahigh vacuum evaporation

A series of thin films of niobium have been grown on various orientations of single crystal sapphire by e-beam evaporation in an ultrahigh vacuum molecular beam epitaxy system. The films were grown at temperatures between 600 and 950 °C and at growth rates from 0.1 to 10 Å/s. The films were single-crystal as determined by both in situ reflection high energy electron diffraction patterns and by Read photographs. The best films had rocking curve widths of the order of 1/10 of a degree. The superconducting transition temperature was measured as a function of film thickness and crystal orientation and ranged up to 9.35 K for a thick sample grown on [11̄02] sapphire.