Protective ALD-alumina overlayer prevents agglomeration of phosphine-protected Au₉ clusters on RF-TiO₂

Full text: The research of gold metal clusters has recently been of great interest due to their potential in catalytic and photocatalytic applications including hydrogen production via water splitting. A noteworthy challenge is maintaining the cluster's size post-deposition, as they tend to agglomerate which results in the loss of their unique, size-dependent properties. Coating gold clusters with a metal oxide layer could be a suitable strategy to stabilise the clusters and prevent agglomeration. In the present work, phosphine protected Au₉ clusters deposited onto titania films were alternately exposed to H₂O and trimethylaluminum (TMA) by atomic layer deposition (ALD) to produce an ultrathin Al₂O₃ controlled overlayer. ALD layers were grown at 25°C, 120°C, 150°C and 180°C to determine the most suitable temperature for deposition to prevent agglomeration of the deposited Au₉ clusters. A range of techniques have been employed to characterize the deposited system of Al₂O₃/Au₉/TiO₂, including synchrotron x-ray photoelectron spectroscopy, x-ray photoelectron spectroscopy, angle resolved x-ray photoelectron spectroscopy, and neutral impact collision ion scattering spectroscopy. (author)