PNNL

Abstract

Gold nanoclusters dispersed in single crystal TiO2 (110) have been formed by 2 MeV Au2+ implantation to an ion fluence of 1?1017 cm-2 at 300 K and 975 K followed by annealing at 1275 K for 10 hours. The morphological features, size, crystallographic orientation of the Au nanoclusters with respect to the TiO2 matrix, and the interface structure between the Au nanoclusters and TiO2 have been investigated using conventional transmission electron microscopy (TEM), high-resolution TEM (HRTEM), electron diffractions, and high angle annular dark-filed (HAADF) imaging in an aberration corrected dedicated scanning TEM (STEM). STEM-HAADF image directly reveals that Au atoms are in the substitutional Ti atomic columns in the TiO2 lattice prior to nucleation of Au lattice. Atomic structural model of interface between Au and TiO2 was established based on HRTEM and image simulations. The precipitated Au clusters show typical (111) twins. Au clusters are facetted along Au{112}, Au{111}, and Au{220} planes. Two types of orientation relationship can be identified, Au//TiO2[001] and Au{111}//TiO2(200), and Au//TiO2[001] and Au{111}//TiO2(110). These orientation relationships as well as the {111} twining feature in Au clusters are similarly observed for Au clusters grown on stoichiometric TiO2(110) free surface, indicating that the presently established orientation corresponds to the lowest interfacial energy for Au contacted with TiO2. This is essential for understanding the catalytic properties of Au supported on TiO2.