MOCVD deposition of CoAl2O4 films

Cobalt aluminate (CoAl2O4) thin films were grown in a low-pressure hot wall metal organic chemical vapour deposition (MOCVD) reactor on Si(1 0 0) and quartz substrates with a total pressure of 2 Torr using bis(η5-cyclopentadienyl)Co(II) [Co(η5-C5H5)2] and aluminium dimethylisopropoxide [AlMe2(OiPr)] as precursors at 500 and 900 °C. Films showed a dark-brown and dark-green colouration, respectively, and after an overnight heat treatment in air at 1200 °C, they turned blue. Film microstructure, composition and morphology were investigated in detail by X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), scanning electron microscopy (SEM) and secondary ion mass spectrometry (SIMS) analyses. Films were polycrystalline and the UV–vis spectra showed three electronic transitions allowed by the spin (540–630 nm range) characteristic of Co(II) ions with 3d7 configuration in tetrahedral coordination. SEM micrographs of the heat-treated CoAl2O4 samples revealed the presence of agglomerated crystallites with a highly porous structure.