Imaging of single polymer chains based on their elasticity

In this work we apply a force modulation technique to a standard atomic force microscope (AFM) in order to study the elasticity of individual polystyrene molecules. The sample mounted on a piezoelectric tube was forced to vibrate along the z direction. The corresponding modulation of the cantilever, which reflects the spring constant of the sample, was phase sensitively detected and measured as a function of the surface topography. The image contrast in these images is based on local variations of the surface elasticity. Compared to the conventional AFM topography image, the elasticity image shows an enhanced contrast with pronounced molecular structure