Trajectory fluctuations accompanying the manipulation of spherical nanoparticles

We relate the frictional forces acting on spherical nanoparticles pushed by a scanning probe tip on a flat surface to the trajectories of the particles. Based on a simple collisional model, we predict that the average direction of motion of the nanoparticles is almost independent of the friction force, whereas the fluctuations of the particle directions are inversely proportional to friction. The model is applied to interpret the trajectory fluctuations and the apparent discontinuities observed when spherical gold particles are manipulated on a silicon-oxide surface by atomic force microscopy.