Influence of annealing atmosphere on structural and superconducting properties of MgB2 thin films

- Superconducting MgB2 thin film were deposited by co-deposition using the thermal and e-beam evaporation.
- Ex situ annealing process was done using various atmospheres.
- Influence of annealing atmosphere and temperature on superconducting and structural properties were studied.
- Possible mechanisms of the formation and crystallization of MgB2 thin film are discussed.

Influence of an ex situ annealing temperature and atmosphere on chemical composition and structural and superconducting properties of MgB2 thin films deposited by vacuum evaporation has been investigated. The annealing has been done in Ar, N2 and Ar + 5%H2 atmospheres at pressure of 700 Pa and temperature varying from 700 to 800 °C. It has been shown that annealing in Ar and N2 atmosphere at 700-800 °C produces relatively thick MgO layer on the surface of the films, while creation of such layer is highly reduced if the annealing is done in reducing Ar + 5%H2 atmosphere. The XPS and XRD results suggest that the MgO layer prevents out-diffusion of Mg from the film during the annealing, what assures better stoichiometry of the films as well as creation of larger MgB2 grains. The films with the highest amount of MgO on the surface, annealed in nitrogen atmosphere, thus paradoxically exhibited the highest critical temperature of Tc0 = 34.8 K with very sharp transition width of 0.1 K.