In situ RHEED study of epitaxial gold nanocrystals on TiO ₂ (1 1 0) surfaces

We report a study of epitaxial gold nanocrystals (NCs) on rutile (TiO ₂ (1 1 0)) surfaces using reflection high energy electron diffraction (RHEED) and ex situ electron imaging. The NCs are determined by RHEED have almost pure (1 1 1) out-of-plane epitaxy with the twin in-plane orientation relationships of [-1 1 0] Au - [0 0 1] TiO₂ and [1 -1 0] Au - [0 0 1] TiO₂. The epitaxial Au NCs are formed by thermal annealing after depositing 0.1-0.4 nm nominal thick Au on TiO₂. In situ RHEED monitoring shows that significant Au NC crystallization occurs at >500°C annealing temperatures for nanoparticles that are of ∼2 nm in diameter. The NCs are faceted as evidenced by the shape of RHEED diffraction spots and electron imaging. The sharpness of the epitaxial Au RHEED diffraction spots with ∼0.55 nm^-1 FWHM allows a measurement of thermal properties of Au/TiO₂, such as thermal expansion and Debye temperature of Au NCs on TiO₂.