Preparation of high Tc (Yb, Y)Ba2Cu3O7-δ thin films by co-evaporation from effusion cells
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We have prepared superconducting thin films of (Yb,Y)Ba2Cu3O7-δ 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 realtime 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 BaF2 from high temperature cells. Films were deposited mainly on SrTiO3 substrates at temperatures ranging from 120 to 600° C and O2 partial pressure up to 1.5 ⋻ 10−5 Torr. Post deposition anneals in O2 and O2 + H2O produced films with room temperature resistivities as low as 227μΩ-cm andT c (R = 0) at 91 K. Films were characterized using x-ray diffractometry, Rutherford backscattering spectrometry, energy dispersive x-ray analysis, scanning electron microscopy as well as electronic transport measurements.
Key wordsEffusion cell deposition oxide superconductor thin films
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