Measurement of the friction between single polystyrene nanospheres and silicon surface using atomic force microscopy

In the present work, the individual nanoparticles have been manipulated on a silicon surface, using atomic force microscope (AFM) techniques. As a model system, near-spherical polystyrene nanoparticles with radii from 28.85 nm to 228.2 nm were deposited on a nanosmooth silicon wafer. Experiments demonstrated that when the normal force is above a threshold load, nanoparticles could steadily be pushed by the tip of the AFM along the defined pathway. The tests allow us to quantitatively study the interfacial friction between the nanoparticle and the surface. It was found that the friction could be affected by various factors such as the load, the particle size, and the surface treatment. The results showed that the friction between particles and substrate is proportional to the two-third power of the radius, which is in agreement with the Hertzian theory. It can also be seen that the ratio between the kinetic and the static friction was slightly changed from 0.3 to 0.6, depending on the size of the particles. However, the value of the ratio was little affected by other factors such as the particles' location, the tip normal force and the surface modification. The results provided new insights into the intriguing friction phenomenon on the nanoscale.