Buffer Layer Assisted Chemistry over Amorphous Solid Water: Oxide Thin Film or Metallic Nanoparticles Formation

Novel procedures to grow pure thin metal oxide films are always welcome in view of their wide range of applications including photocatalysis, solar cells, sensors, and more. In this paper we present a unique way to grow pure nanofilms of metal oxides in vacuo at the temperature range 110-170 K. The reactive layer assisted deposition (RLAD) procedure for thin oxide films growth is based on the evaporation of a reactive metal element on top of a condensed layer of amorphous solid water (D₂O-ASW). When applied to metals that do not react with the water layer, the process yields metal nanoclusters on the substrate. We observed that metal oxide films are formed if the redox potential is of -1.0 V or less, leading to deuterium molecules ejection to the gas phase (e.g., Ti and Al) while metals such as Zn, Fe, and Ag, with redox potentials more than -1.0 V, transform into nanoclusters, as revealed by SEM studies. We conclude that the redox potential ia a parameter that enables one to predict the nature and outcome of the ASW buffer layer assisted chemistry.