Growth of superconducting MgB2 thin films via postannealing techniques

We report the effect of annealing on the superconductivity of MgB2 thin films as a function of the postannealing temperature in the range from 700 to 950 degreesC and of the postannealing time in the range from 30 to 120 min. On annealing at 900 degreesC for 30 min, we obtained the best-quality MgB2 films with a transition temperature of 39 K and a critical current density of similar to10(7) A/cm(2). Using scanning electron microscopy, we also investigated the film growth mechanism. The samples annealed at higher temperatures showed larger grain sizes, well-aligned crystal structures with preferential orientation along the c-axis, and smooth surface morphologies. However, a longer annealing time prevented the alignment of grains and reduced superconductivity, indicating a strong interfacial reaction between the substrate and the MgB2 film. (C) 2002 Elsevier Science B.V. All rights reserved.