Chemical and Structural Configuration of Pt-Doped Metal Oxide Thin Films Prepared by Atomic Layer Deposition

Pt-doped semiconducting metal oxides and Pt metal clusters embedded in an oxide matrix are of interest for applications such as catalysis and gas sensing, energy storage, and memory devices. Accurate tuning of the dopant level is crucial for adjusting the properties of these materials. Here, a novel atomic layer deposition (ALD)-based method for doping Pt into In₂O₃ specifically, and metals in metal oxides in general, is demonstrated. This approach combines alternating exposures of Pt and In₂O₃ ALD processes in a single “supercycle” followed by supercycle repetition leading to multilayered nanocomposites. The atomic-level control of ALD and its conformal nature make the method suitable for accurate dopant control even on high-surface-area supports. The oxidation state, local structural environment, and crystalline phase of the embedded Pt dopants were obtained by means of X-ray characterization methods and high-angle annular dark-field scanning transmission electron microscopy. In addition, this approach allows characterization of the nucleation stages of metal ALD processes by stacking those states multiple times in an oxide matrix. Regardless of experimental conditions, a few Pt ALD cycles lead to the formation of oxidized Pt species due to their highly dispersed nature, as proven by X-ray absorption spectroscopy. Grazing-incidence small-angle X-ray scattering and high-resolution scanning transmission electron microscopy, combined with energy-dispersive X-ray spectroscopy, show that Pt is evenly distributed in the In₂O₃ matrix without the formation of clusters. For a larger number of Pt ALD cycles, typically >10, the oxidation state gradually evolves toward fully metallic, and metallic Pt clusters are obtained within the In₂O₃ matrix. This work reveals how tuning of the ALD supercycle approach for Pt doping allows controlled engineering of the Pt compositional and structural configurations within a metal oxide matrix.