Contrary to idealized depictions, atomic layer deposition (ALD) reactions do not always take place solely at the gas-solid interface. The iron oxide ALD system was recently shown to grow by a subsurface mechanism in which reactive oxygen is absorbed into the growing film during ozone exposure, forming an effective reservoir of oxygen. This study investigates the fundamental chemical mechanisms behind the oxygen reservoir phenomenon and extends it to other binary and multicomponent oxide ALD systems. NiO ALD is found to exhibit similar saturation behavior and crystallinity trends with ozone as Fe2O3 ALD. Oxygen uptake from ozone into the film is directly detected in situ for both processes, and in vacuo spectroscopy elucidates possible chemical states of the subsurface oxygen reservoirs in each material. In situ process characterization reveals that the reserved oxygen participates in surface combustion reactions capable of activating ALD growth. The oxygen reservoir mechanism is also shown to generalize to other oxide systems, correlating with trends in oxygen mobility, crystallinity, and metal oxidizability. Finally, the reactive oxygen reservoirs are utilized in the deposition of a multicomponent FeAlxOy material, previously unreported by ALD, revealing that the reserved oxygen can activate growth of other processes and possesses the potential to address nucleation challenges in other ALD systems.
Supporting figures and text for the main manuscript.