Contact resonance imaging - A simple approach to improve the resolution of AFM for biological and polymeric materials

It is frequently observed that high resolution is difficult to achieve when using atomic force microscopy (AFM) to image "soft-and-sticky" surfaces, such as polymers and biomaterials. A new and simple method, contact resonance imaging (CRI), is introduced to address these issues. In CRI, the sample is modulated at a resonance frequency of the tip-sample contact, while the average position of the tip still remains in contact with the surface, i.e. in the repulsive region of the force-distance curve. The improvement in image resolution is demonstrated using various biological and polymeric specimens under ambient laboratory conditions and in liquid media. The possible mechanism of the resolution improvement is discussed in comparison to other techniques, such as tapping-mode imaging.