Preparation of High T sub c (Yb,Y) Ba sub 2 Cu sub 3 O sub (7-delta) Thin Films by Co-evaporation from Effusion Cells.

We have prepared superconducting thin films of (Y,Yb)Ba sub 2 Cu sub 3 O sub (7-delta) by evaporation of copper, ytterbium or yttrium, and barium fluoride from Knudsen effusion cells. A simple two chamber vacuum system produced stable evaporation rates of 5 - 10 nm/min using various Knudsen cells without real-time feedback control. Excellent stoichiometry was obtained in the films by optimizing the deposition of Cu from a dual filament cell, Yb from a single filament cell and Y and BaF sub 2 from high temperature cells. Films were deposited mainly on SrTiO sub 3 substrates at temperatures ranging from 120 to 600C and O sub 2 partial pressure up to 1.5 x 10 sup (- 5) Torr. Post deposition anneals in O sub 2 and O sub 2 + H sub 2 O produced films with room temperature resistivities as low as 227micron OMEGA-cm and T sub c (R=0) at 91K. Films were characterized using x-ray diffractometry, Rutherford backscattering spectrometry, energy dispersive x-ray analysis, scanning electron microscopy as well as electronic transport measurements.