Mechanism of the formation of ultrafine gold particles on MgO(100) as investigated by molecular dynamics and computer graphics

The applicability of a new molecular-dynamics (MD) code developed by us and the computer graphics technique to investigating the mechanism of the formation of ultrafine Au particles on the MgO(100) plane was demonstrated. MD calculations were performed to understand the effect of temperature of the MgO substrate on the mechanism. Lower temperatures led to more Au atoms being fixed on the MgO(100) plane. The effect of defects, such as point defects and steps, in the MgO(100) plane was also investigated. Au clusters were formed and fixed just over the defect sites at low temperature, namely 300 K, in agreement with the experimental results. This behavior was in marked contrast to that at high temperature, namely 1000 K. In the latter case, there is no single favorable location of Au clusters and the Au clusters were considerably mobile on the surface, similar to the behavior on a smooth MgO(100) plane. Hence the location of Au clusters was not affected by the presence of defects at 1000 K. Furthermore, an Au atom trapped in the defects is shown to play the role of a nucleation center in the formation processes of Au clusters on the MgO(100) plane at low temperatures, such as 300 K. These results suggested that a low temperature of the MgO substrate and the presence of defects on MgO(100) are required for the formation of atomically controlled ultrafine Au particles on the MgO(100) plane.