Growth of superconducting MgB₂ films by pulsed-laser deposition using a Nd-YAG laser

Thin films of MgB₂ on r-cut Al₂O₃ substrates have been grown by pulsed-laser deposition (PLD) using a Nd-YAG laser (fourth harmonic - 266 nm) instead of the popular KrF excimer laser. The growth window to obtain superconducting films is laser energy 350-450 mJ and vacuum pressure with Ar-buffer gas of 1-8/10 Pa (initial background vacuum 0. 5-1 × 10^-3 Pa). Films were deposited at room temperature and post-annealed in situ and ex situ at temperatures of 500-780°C and up to 1 h. Films are randomly oriented with maximum critical temperature (offset of resistive transition) of 27 K. SEM/TEM/EDS investigations show that they are mainly composed of small sphere-like particles (≤20 nm), and contain oxygen and some carbon, uniformly distributed in the flat matrix, but the amount of Mg and/or oxygen is higher in the aggregates-droplets (100-1000 nm) observed on the surface of the film's matrix. Some aspects of the processing control and dependences on film characteristics are discussed. The technique is promising for future development of coated conductors.