Crystalline structure and orientation of gold clusters grown in preformed nanometer-sized pits

Gold clusters were produced by condensing evaporated gold in nanometer-sized preformed pits on the surface of highly oriented pyrolytic graphite (HOPG). The height of the clusters was 6.7 f 0.7 nm as measured with scanning tunneling microscopy in ultrahigh vacuum, the lateral width was 10.1 f 1.9 nm as determined with transmission electron microscopy (TEM). Using TEM for electron diffraction, we obtained information on the crystalline structure of the clusters. The intensity of the observed diffraction rings shows the preferential orientation of the clusters with the (111) plane of the gold lattice parallel to the (0001) surface of HOPG. This was compared to the diffraction pattern of gold clusters produced in the gas phase by inert-gas evaporation and deposited on a flat HOPG surface at room temperature as complete units which showed no preferential orientation. The directional alignment in the surface plane as it is described in the literature for larger gold crystallites grown on a flat HOPG surface is not observed for the nanometer-sized clusters grown in pits.