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(?5-cyclopentadienyl)Co(II) [Co(?5-C 5H5)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.