Abstract
This thesis presented an investigation of the temperature effect on adhesion phenomenon and its physical behavior between contact bodies in the nano-scale by using molecular dynamics simulation and experiments. In the molecular dynamics simulation, the Morse potential function was employed to simulate the intermolecular forces between atoms. The system model is arranged in order according to face-centered cubic (FCC) structure and constructed as the AFM tip and substrate system, which consists of about 10800 Au atoms. The tip with the pyramidal shape was formed from 3632 Au atoms, while the substrate with the cuboid shape was from 7168 Au atoms. The simulation results reveal that the system temperature affects the atomistic jump-to-contact behavior. The higher the system temperature is, the earlier the contact occurs. In addition, owing to the atom migrations caused by adhesion, an extended neck is gradually formed upon the retraction of the tip from contact and the neck height is positively correlated to the system temperature. After the neck breaks, an island shape structure is formed on the substrate and the size of the structure also has a positive correlation with the system temperature. Adhesion force is calculated during the tip ascending period, the results also show the adhesion force is decreasing with the increase of system temperature. In the experimental study, the Au-coated Si tip and substrate are utilized to plot the force curve at different ambient temperature. The adhesion force is measured from the force curve. The trends of adhesion force agree with the results of simulation, it demonstrated that the adhesion force for the Au tip and substrate is decreasing with increasing temperature. By comparing with the adhesion forces estimated from the classical adhesion theories, the experimental results exhibit a huge variance. This variance on the adhesion force may attribute to the applicability of the continuum theory for the mesoscopic bodies. So, using the classical adhesion theories to estimate the physical behavior of the contact bodies in the nano-scale may not be appropriate.