From Single Atoms to Nanoparticles: Autocatalysis and Metal Aggregation in Atomic Layer Deposition of Pt on TiO2 Nanopowder

Fabio Grillo; Hao Van Bui; Damiano La Zara; Antonius A I Aarnink; Alexey Y Kovalgin; Patricia Kooyman; Michiel T Kreutzer; Jan Rudolf van Ommen

doi:10.1002/smll.201800765

From Single Atoms to Nanoparticles: Autocatalysis and Metal Aggregation in Atomic Layer Deposition of Pt on TiO₂ Nanopowder

Small. 2018 Jun;14(23):e1800765. doi: 10.1002/smll.201800765. Epub 2018 May 10.

Authors

Fabio Grillo¹, Hao Van Bui¹, Damiano La Zara¹, Antonius A I Aarnink², Alexey Y Kovalgin², Patricia Kooyman³, Michiel T Kreutzer¹, Jan Rudolf van Ommen¹

Affiliations

¹ Department of Chemical Engineering, Delft University of Technology, 2629 HZ, Delft, The Netherlands.
² MESA+ Institute for Nanotechnology, University of Twente, 7500 AE, Enschede, The Netherlands.
³ Department of Chemical Engineering, University of Cape Town, 7701, Cape Town, South Africa.

PMID: 29745008
DOI: 10.1002/smll.201800765

Abstract

A fundamental understanding of the interplay between ligand-removal kinetics and metal aggregation during the formation of platinum nanoparticles (NPs) in atomic layer deposition of Pt on TiO₂ nanopowder using trimethyl(methylcyclo-pentadienyl)platinum(IV) as the precursor and O₂ as the coreactant is presented. The growth follows a pathway from single atoms to NPs as a function of the oxygen exposure (P_O2 × time). The growth kinetics is modeled by accounting for the autocatalytic combustion of the precursor ligands via a variant of the Finke-Watzky two-step model. Even at relatively high oxygen exposures (<120 mbar s) little to no Pt is deposited after the first cycle and most of the Pt is atomically dispersed. Increasing the oxygen exposure above 120 mbar s results in a rapid increase in the Pt loading, which saturates at exposures >> 120 mbar s. The deposition of more Pt leads to the formation of NPs that can be as large as 6 nm. Crucially, high P_O2 (≥5 mbar) hinders metal aggregation, thus leading to narrow particle size distributions. The results show that ALD of Pt NPs is reproducible across small and large surface areas if the precursor ligands are removed at high P_O2 .

Keywords: aggregation; atomic layer deposition; kinetics; nanoparticles; size distribution.