The difference

for Ag and Au can be understood from the forces acting on the dopant atom. At the key relax step where the dopant atom falls to the surface, we decompose Epoxomicin price the forces acting on Ag and Au atoms into the X and Z directions at every calculation step. The results are shown in Figure 8. For the Ag dopant, the MK-2206 price component forces have negative peak values and the one in the Z direction is greater than that in the X direction, which means that the vertical attraction is greater than the lateral one when the dopant atom is falling. Finally, the Ag atom falls into the step site (see Figure 7c). For the Au dopant, however, the component force in the X direction has a greater peak value than that in the Z direction. It means that the Au dopant tends to drop onto the step terrace (see Figure 7f). Though withdrawing the tip vertically in the Z direction to position the dopant is effective for the Ag atom, it lacks general applicability. Also, the position details and

component forces reveal that it is not reliable even in small thermal disturbance (see Figures 7 and 8). Figure 7 Withdrawing the tip vertically in Z direction to position the dopant. (a – c) The positioning process of the Ag atom. (d – f) The undesirable release of the Au atom. Figure 8 The forces acting on Ag (a) and Au (b) dopant atom in every calculation step The forces acting on Ag (a) and Au (b) dopant atom in every calculation step. The red curve is the component force in the Z direction. The black curve denotes the component force in the X direction. Conclusion Based on first-principles Pritelivir molecular weight simulation, we theoretically investigate the substitutional single-atom doping on stepped Al (111) surface via atomic manipulation. An effective method is proposed in which a trimer-apex tip is adopted to extract the surface atom and then a single-apex one is used to position the single dopant atom. In the positioning process, the tip moves first in the vertical direction and then in a lateral one. Rebamipide Both Ag and Au dopants are successfully positioned to the specific site in atomic precision, which indicates that the method owns a potential of general application.

The corresponding energy curves show that both extraction and doping processes have a high reliability against thermal disturbances. Additionally, the manipulation processes are insensitive to the tip orientation, which is beneficial to the realization of such doping approach in practice. Acknowledgments This work is supported by the National Basic Research Program of China (973 Program) under Grant No. 2012CB934200 and Chinese NSF under Grant No. 11074042 and No. 51071048. References 1. Eigler DM, Schweizer EK: Positioning single atoms with a scanning tunnelling microscope. Nature 1990, 344:524.CrossRef 2. Meyer G, Bartels L, Zöphel S, Henze E, Rieder KH: Controlled atom by atom restructuring of a metal surface with the scanning tunneling microscope.