Detection of single PSS polymers on rough surface by pulsed-force-mode scanning force microscopy

Samples of nanosize single polymers to be imaged by scanning force microscopy (SFM) are preferentially deposited on a molecularly flat substrate. However, many substrates are modified and acquire rough surfaces resulting in poor definition of single-polymer molecules. This work dealt with the imaging of single poly(sodium 4-styrenesulfonate) (PSS) polymers on a rough surface with a novel measuring mode, pulsed-force-mode (PFM). Adhesive forces can be mapped simultaneously with topographic imaging with this mode. Force-distance curves show the differences of adhesive forces of the tip/sample and the tip/surface couples, so that sample materials can be distinguished in terms of surface adhesive properties. PFM increases the roughness limit of substrates from 0.8 to 6.1 nm, allowing the observation of single molecules down to 1.0 nm height, and greatly expanding potential substrates for imaging of single polymers.