Microstructure of precipitated Au nanoclusters in TiO_(2)

摘要

Gold nanoclusters dispersed in TiO_(2)(110) single crystal have been formed by 2 MeV Au~(2+) implantation to an ion fluence of 6.0×10~(16) cm~(-2) at 300 and 975 K followed by annealing at 1275 K for 10 h. The morphological features, size, crystallographic orientation of the Au nanoclusters with respect to the TiO_(2) matrix, and the interface structure between the Au nanoclusters and TiO_(2) have been investigated using conventional transmission electron microscopy (TEM), high-resolution TEM (HRTEM), electron diffractions, and high angle annular dark-field (HAADF) imaging in an aberration corrected scanning TEM (STEM). STEM-HAADF image directly reveals that Au atoms are in the substitutional Ti atomic columns in the TiO_(2) lattice prior to nucleation of Au cluster. An Atomic structural model of the interface between Au and TiO_(2) was established based on HRTEM and image simulations. The precipitated Au clusters show typical (111) twins. Au clusters are faceted along Au{112}, Au{111}, and Au{220} planes. Two types of orientation relationship can be identified, Au〈110〉//TiO_(2)[001] and Au{111}//TiO_(2)(200), and Au〈110〉//TiO_(2)[001] and Au{111}//TiO_(2)(110). These orientation relationships as well as the {111} twining feature in Au clusters are similarly observed for Au clusters grown on stoichiometric TiO_(2)(110) free surface, indicating that the presently established orientation corresponds to the lowest interfacial energy for Au contacted with TiO_(2). This is essential for understanding the catalytic properties of Au supported on TiO_(2).