Crossover from three-dimensional to two-dimensional geometries of Au nanostructures on thin MgO(001) films: a confirmation of theoretical predictions.

In this Letter, we report a low-temperature scanning tunneling microscopy study aiming to explore the adsorption properties of Au with respect to the thickness of supported MgO films. For different MgO film thicknesses (3 ML and 8 ML), we find significant differences in the distribution of Au adsorption sites and in the Au cluster geometry, in line with recent calculations and electron paramagnetic resonance experiments. On the surface of thick MgO films or unsupported MgO, Au adsorbs on O sites [Phys. Rev. Lett. 96, 146804 (2006)], and the equilibrium cluster geometry is three-dimensional. In contrast, on thin MgO films, the calculations predicted (i) a change of the preferred Au nucleation site [Phys. Rev. Lett. 94, 226104 (2005)] and (ii) a stabilization of two-dimensional Au cluster geometries [Phys. Rev. Lett. 97, 036106 (2006)].