A Low-Energy Ion Scattering Approach for Studying Au Nanoclusters Grown on an H₂O Buffer Layer

A novel form of alkali low-energy ion scattering is used to probe the deposition of nanoclusters onto a solid surface via buffer layer assisted growth (BLAG) in ultrahigh vacuum. A thin amorphous solid water (ASW) buffer layer is grown on a TiO₂(110) single crystal cooled to 100 K. Au atoms deposited onto this layer arrange themselves into nanoclusters. The sample is then annealed to 320 K to desorb the ASW and enable the clusters to soft-land onto the substrate. Time-of-flight low-energy ion scattering, using Li⁺, Na⁺, and K⁺ projectiles, probes the materials during each step of the BLAG process to measure the surface composition and reveal the details of how the clusters form. The neutralization probability of Na⁺ ions singly scattered from the Au nanoclusters indicates that they increase in size after annealing and that the magnitude of the increase is a function of the buffer layer thickness. The adsorption of a thin, incomplete water layer prior to Au deposition forms nanoclusters that are possibly even smaller than those produced by direct deposition onto the clean substrate.