Simulation of interaction force between Si tip and Si(1 1 1)3×3-Ag surface of IET structure in noncontact AFM

Simulation of the interaction force between the SiH3 tip and the Si(1 1 1)3×3-Ag surface is performed based on the first-principles electronic state calculations. First it is indicated that the inequivalent-trimer (IET) structure is a local energy minimum as a function of the rotation angle of Ag triangle. Next interaction force between the tip and the IET structured surface is calculated as a function of the tip height for the different surface sites. Lastly two-dimensional plots of the force are calculated as the first step of studying the stable structure of the Si(1 1 1)3×3-Ag surface at the room temperature. Surprisingly, the average of the force plots for the two different phases of IET structures, becomes almost the same as that for the honeycomb-chained-trimer (HCT) structure. This indicates the possibility that the observed AFM image shows an apparent HCT structure as a result of averaging the two different phases of IET structures by a thermal fluctuation.