Our paper recently published in Nanotechnology presents our density-functional calculations of a model system - the C60 fullerene on the Si(001) surface. The molecule is being pushed by a model STM tip and moves laterally on the surface. The presence of the tip in the simulations allows us to investigate the features typical for the pushing manipulation, as opposed to pulling and sliding.
We find that the tip-C60 interaction plays an important role in manipulation, as the molecule inevitably interacts and forms chemical bonds with the tip. The movement of C60 therefore requires both the tip-molecule and the molecule-surface bond rearrangements. The pivoting mechanism of the molecule moving on the surface is described. We find that the tip becomes significantly deformed on the atomic scale, which allows it to adjust better to bonding with the molecule, but this deformation may also eventually lead to tip breaking and to termination of manipulation. The troughs between the dimer rows on the Si(001) surface provide a guiding effect for the movement of the molecule, while the tip drives this movement. The pushing manipulation, unlike pulling, is shown to be a very robust process whose outcome is not strongly affected by the details of the tip geometry.