Theoretical modelling of tip effects in the pushing manipulation of C(60) on the Si(001) surface

We present the results of our theoretical studies on the repulsive (pushing) manipulation of a C(60) molecule on the Si(001) surface with several scanning tunnelling microscopy tips. We show that, for silicon tips, tip-C(60) bonds are formed even with tips that do not initially have dangling bonds, and this tip-C(60) interaction drives the manipulation of the molecule. The details of the atomic structure of the tip and its position relative to the molecule do not have a significant effect on the mechanism and the sequence of adsorption configurations during the pushing manipulation of C(60) along the trough, where the trough itself provides a guiding effect. The pushing manipulation is thus a very robust process that occurs largely independently of the tip structure. On the other hand, the pushing manipulation across an Si-Si dimer row into the neighbouring trough proceeds in a more complex way, with tip deformation and detachment more likely to occur. We demonstrate the role of tip deformation and tip-molecule bond rearrangement in the continuous manipulation of the molecule. Finally, we calculate and analyse the forces acting on the tip during manipulation and identify characteristic patterns.