We report a study of epitaxial gold nanocrystals (NCs) on rutile (TiO2 (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 parallel to [0 0 1] TiO2 and [1 - 1 0] Au parallel to [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 degrees C annealing temperatures for nanoparticles that are of similar to 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 similar to 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. (C) 2013 Elsevier B.V. All rights reserved.