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

The effects of TiO2 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 TiO2 surfaces. For the same number of Pt ALD cycles, the Pt surface coverage was found to depend on the thickness of the underlying TiO2. From X-ray diffraction (XRD) analysis, it was found that the amorphous microstructure of as-deposited TiO2 transforms into anatase microstructure because of an annealing effect at the elevated Pt ALD temperature, and that this effect is a function of TiO2 thickness. Transmission electron microscopy revealed that continuous growth of ALD Pt occurs on anatase TiO2 whereas island growth occurs on amorphous TiO2. These results indicate that Pt nucleation is significantly affected by the microstructure of TiO2. Effects beyond surface hydrophilicity, such as a catalytic effect, are needed to explain the different nucleation properties of ALD Pt on TiO2. These results provide insight into initial growth during metal ALD and the effects of surface structural properties on ALD nucleation.