Growth methods of c-axis oriented MgB₂ thin films by pulsed laser deposition

High-quality MgB₂ thin films have been obtained by pulsed laser deposition both on MgO and Al₂O₃ substrates using different methods. In the standard two-step procedure, an amorphous precursor layer is deposited at room temperature starting from the stoichiometric target and from the boron target. After this first step, it is annealed in a magnesium atmosphere in order to crystallize the superconducting phase. The obtained films show a strong c-axis orientation, evidenced by XRD analysis, a critical temperature up to 38 K and very high critical fields along the basal planes, up to 22 T at 15 K. Also an in situ one step technique for the realization of superconducting MgB₂ thin films has been developed. In this case, the presence of an argon buffer gas during deposition is crucial, and we observe a strong dependence of the quality of the deposited film on the background gas pressure. The influence of the Ar atmosphere has been confirmed by time- and space-resolved spectroscopy measurements on the emission spectrum of the plume. The Ar pressure strongly modifies the plasma kinetics by promoting excitation and ionization of the plume species, especially of the most volatile Mg atoms, increasing their internal energy.