Flash Evaporation as an Attempt for Preparation of YBCO Superconductor Thin Films

A home-made flash evaporation attachment was used to prepare YBCO
superconductor in the form of thin film on Si wafer substrate. Structural study
was achieved by XRD analysis and electric resistance was measured by linear
four-probe method down to 77 K. The whole-pattern fitting of Rietveld method
was applied to verify the presence of the orthorhombic YBCO phase in the
prepared bulk sample used as a source for thin film deposition. Thin films
deposited onto Si(111) wafer showed crystalline phase in case of substrate
temperature ≥ 450 oC and post annealing at temperature ≥ 850 oC. The best
and unexpected characteristics (Tc = 125 K, ΔT = 0.5 K) were obtained at
critical thickness of 85 nm for films deposited at substrate temperature of 500
oC and subjected to post annealing in oxygen at 950 oC. This was attributed to
the preferred orientation (c-axis normal to the substrate) and to the optimum Si
concentration by interdiffusion under the proposed preparation condition.
Increasing the film thickness than 100 nm deteriorates the superconducting
behaviour. On the other hand, films of thickness less than 80 nm did not show
superconducting behaviour.