Nanoscale Structure and Morphology of Atomic Layer Deposition Platinum on SrTiO3 (001)

The early stages of nucleation and growth of atomic layer deposition (ALD) platinum on SrTiO3 (001) have been studied. Scanning electron microscopy reveals the ALD Pt deposits as discrete nanoparticles that grow and coalesce with increasing number of ALD cycles, ultimately resulting in a continuous film after ∼40 cycles. Atomic force microscopy shows the films to be fine-grained and highly conformal such that the 0.4 nm atomic steps of the underlying SrTiO3 (001) surface remain visible even after 80 Pt ALD cycles. Grazing-incidence small-angle X-ray scattering (GISAXS) studies demonstrate that the early stages of Pt ALD yields nanoparticles that are well approximated as cylinders with a height to radius ratio that is nearly unity. Consistent with nanoparticle coalescence, GISAXS also reveals an interparticle spacing that increases with the number of ALD cycles. X-ray fluorescence measurements of the Pt coverage reveal growth dynamics in which the Pt deposition is initially faster than the steady-state growth rate that emerges after 40-70 ALD cycles. These experimental results are understood through the application of a model that suggests that the SrTiO3 surface is more reactive than the Pt species and that Pt diffusion is operative in nanoparticle formation. Overall, this study delineates ALD growth conditions for forming either Pt nanoparticles or continuous Pt thin films on SrTiO3 (001), thus presenting potentially useful substrates for catalysis and microelectronics, respectively.