ENERGY DISSIPATION IN TAPPING MODE ATOMIC FORCE MICROSCOPY

There are many imaging modes in atomic force microscopy (AFM), in which the tapping mode is one of the most commonly used scanning methods. Tapping mode can provide height and phase topographies of the sample surface, in which phase topography reflects more valuable information of sample surface, such as surface energy, elasticity, hydrophilic hydrophobic properties and so on. According to the theory of vibration mechanics, the phase is related to the energy dissipation of the vibration system. The dissipation energy between the tip and sample in tapping mode of AFM is a very critical key to understanding the image mechanism. It is affected by sample properties and lab environment. The loading and unloading curves of tip and sample interaction are given based on the JKR model while the capillary force is not considered. The unstable position of jump out between the tip and sample is show, and then the energy dissipation in a complete contact and separate process is calculated. The effect of roughness of sample surfaces on energy dissipation is also discussed. It is provided that the extrusion effect is the dominant fact or in liquid bridge formation by characteristic time contrast when capillary force is considered in tapping mode AFM. The effects of relative humidity on energy dissipation are numerically calculated under isometric conditions. Finally, the relationship between phase image of AFM and sample surface energy, Young's modulus, surface roughness and relative humidity is briefly explained by one-dimensional oscillator model. The analyses show that the difference of surface roughness and ambient humidity can cause phase change, and then they are considered as the cause of artifact images.