SEM observations of YBCO on as-received and heat-treated MgO substrates

Pulsed-laser deposition (PLD) of YBa2Cu3O7−δ (YBCO) thin films onto (100) MgO substrates is performed employing a frequency quadrupled Nd-YAG laser (λ = 266 nm). Three different MgO substrates are employed with varying surface finishes: ‘As-received’ (manufacturerʹs polish), ‘intermediate anneal’ (acid wash and shorter anneal) and ‘fully annealed’ (longer anneal). The surface morphologies of the substrates, which differ greatly, are characterised in all cases by SEM observation prior to deposition. After deposition, thin-film microstructures again are inspected in the SEM. Significant improvement is seen in the surface morphology, via the minimisation of ‘outgrowths’, of films grown on annealed substrates as compared with those grown on as-received, polished substrates, with the degree of improvement being sensitive to the pre-deposition surface treatment.