Microstructure-Dependent Nucleation in Atomic Layer Deposition of Pt on TiO₂

The effects of TiO 2 microstructure on Pt nucleation and on formation of continuous ultrathin Pt films by atomic layer deposition (ALD) were investigated. Pt was deposited by a metalorganic Pt precursor ((methylcyclopentadienyl)trimethylplatinum) and air as a counter reactant on in situ grown ALD TiO 2 surfaces. For the same number of Pt ALD cycles, the Pt surface coverage was found to depend on the thickness of the underlying TiO 2 . From X-ray diffraction (XRD) analysis, it was found that the amorphous microstructure of as-deposited TiO 2 transforms into anatase microstructure because of an annealing effect at the elevated Pt ALD temperature, and that this effect is a function of TiO 2 thickness. Transmission electron microscopy revealed that continuous growth of ALD Pt occurs on anatase TiO 2 whereas island growth occurs on amorphous TiO 2 . These results indicate that Pt nucleation is significantly affected by the microstructure of TiO 2 . Effects beyond surface hydrophilicity, such as a catalytic effect, are needed to explain the different nucleation properties of ALD Pt on TiO 2 . These results provide insight into initial growth during metal ALD and the effects of surface structural properties on ALD nucleation.