Highly dispersed Co deposited on Al₂O₃ particles via CoCp₂ + H₂ ALD

Highly dispersed cobalt atoms were deposited on porous alumina particles using atomic layer deposition (ALD) with a CoCp₂/H₂ chemistry at approximately 7 wt%. H₂ did not completely reduce the cyclopentadienyl organic ligands bound to deposited Co atoms at ALD reaction conditions. A sharp decline in Co deposited per cycle for two or more ALD cycles indicates that much of the Al₂O₃ surface is sterically blocked from further CoCp₂ deposition after the first CoCp₂ exposure. Temperature programmed reduction confirmed that the adsorbed precursor organic ligands persist after H₂ exposures during ALD and temperatures as high as 500 °C are required to fully reduce the organic ligands to CH₄. High resolution, element sensitive imaging showed that Co atoms were dispersed on the Al₂O₃ surface and could deposit in previously unobserved multiple growth morphologies, specifically layers that were continuous over several angstroms or discrete nanoparticles. Density functional theory calculations were used to examine Co atom adsorption, show the altered haptic binding of cracked Cp ligands, and to calculate the thermodynamics of Cp ligand decomposition. The lateral steric hindrance between organic ligands bound to deposited Co atoms, Cp ligand decomposition mechanism, and local Al₂O₃ surface termination all likely determine the observed Co growth morphology during initial ALD cycles.