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

TL;DR

This paper explores different pulsed laser deposition methods for growing high-quality c-axis oriented MgB2 thin films, highlighting the effects of substrate choice, annealing procedures, and argon atmosphere on film quality and superconducting properties.

Contribution

It introduces an in situ one-step deposition technique and analyzes the influence of argon atmosphere on film quality and plasma kinetics.

Findings

Films show c-axis orientation and critical temperature up to 38 K.

Argon atmosphere significantly affects plasma excitation and film quality.

High critical fields up to 22T at 15K achieved in films.

Abstract

High quality MgB2 thin films have been obtained by pulsed laser deposition both on MgO and on Al2O3 substrates using different methods. In the standard two-step procedure, an amorphous precursor layer is deposited at room temperature starting both from stoichiometric target and from boron target: after this first step, it is annealed in magnesium atmosphere in order to crystallize the superconducting phase. The so 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 22T at 15K. 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 modifies strongly the plasma kinetics by promoting excitation and ionization of the plume species, especially of the most volatile Mg atoms, increasing their internal energy.