First-Principles Predictions and in Situ Experimental Validation of Alumina Atomic Layer Deposition on Metal Surfaces

Abstract

The atomic layer deposition (ALD) of metal oxides on metal surfaces is of great importance in applications such as microelectronics, corrosion resistance, and catalysis. In this work, Al2O3 ALD using trimethylaluminum (TMA) and water was investigated on Pd, Pt, Ir, and Cu surfaces by combining in situ quartz crystal microbalance (QCM), quadrupole mass spectroscopy (QMS), and scanning tunneling microscopy (STM) measurements with density functional theory (DFT) calculations. These studies revealed that TMA undergoes dissociative chemisorption to form monomethyl aluminum (AlCH3*, the asterisk designates a surface species) on both Pd and Pt, which transform into Al(OH)3* during the subsequent water exposure. Furthermore, the AlCH3* can further dissociate into Al* and CH3* on stepped Pt(211). Additional DFT calculations predicted that Al2O3 ALD should proceed on Ir following a similar mechanism but not on Cu due to the endothermicity for TMA dissociation. These predictions were confirmed by in situ QCM, QMS, and STM measurements. Our combined theoretical and experimental study also found that the preferential decoration of low-coordination metal sites, especially after high temperature treatment, correlates with the differences in free energy between Al2O3 ALD on the (111) and stepped (211) surfaces. These insights into Al2O3 growth on metal surfaces can guide the future design of advanced metal/metal oxide catalysts with greater durability by protecting the metal against sintering and dissolution and enhanced selectivity by blocking low-coordination metal sites while leaving (111) facets available for catalysis.