RF magnetron sputtered aluminium oxide coatings on iridium

The effects of process parameters on the microstructural morphology of aluminium oxide (Al₂O₃) coatings on Ir have been studied. Al₂O₃ coatings were deposited on Ir-coated isotropic graphite (IG) substrates at substrate temperatures of room temperature (RT)-1073 K, RF power of 200-600 W in an Ar, or Ar + 1-10% O₂, sputtering gas atmosphere by RF magnetron sputtering. Al₂O₃ coatings which were deposited at high substrate temperatures and high RF powers in an Ar, or an Ar + O₂, sputtering gas atmosphere were found to contain a dense, fine columnar structure with a γ-Al₂O₃ phase, low Ar content and a relatively high hardness value of ca. 1050 H_v. Furthermore, high resolution transmission electron microscopy (HRTEM) results revealed the epitaxial growth of Al₂O₃ coatings on Ir-coated IG substrate. It was found that the interface between Al₂O₃ and Ir coatings was sharp and Al₂O₃ coatings remained intact with the Ir-coated IG substrate.