Abstract

The phase image produced by Atomic Force Microscopy (AFM) is very important in the study of surface topography and properties. The phase difference of different domains on a surface is due to the different tip-sample interaction forces which are a consequence of different local properties. By simulating the AFM imaging procedure and the tip-sample interactions with variable viscosity and modulus, the effect of local material properties on phase lag was studied. These simulations showed that both elastic and viscous properties have an influence on the phase lag. For hard, elastic materials the dominant interaction force is the elastic force, and for soft, viscoelastic materials the viscous force is dominant. The phase lag between the probe response and the activation force is higher for soft viscoelstic domains. With the mathematical model it was demonstrated that the phase contrast between viscoelastic materials and silicon can be used to predict the local viscosity and elastic modulus. Experiments were done on a surface with a silicon domain which is hard and elastic and different viscoelastic domains. The experimental results of polybutadiene and polystyrene agree well with the simulation. The model was also applied to a block copolymer of butadiene and styrene and crystalline and amorphous polylactic acid. Finally, it is demonstrated that the AFM can detect materials properties beneath the surface.