In situ RHEED study of epitaxial gold nanocrystals on TiO2 (1Â 1Â 0) surfaces

► Transformation from randomly oriented Au nanoparticles to epitaxial Au nanocrystals upon annealing is revealed by in situ RHEED. ► Significant Au nanocrystal 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. ► High quality RHEED patterns allow the measurement of thermal expansion coefficients and Debye-Temperature of Au nanocrystals.