Single-walled carbon nanotube AFM probes: Optimal imaging resolution of nanoclusters and biomolecules in ambient and fluid environments

Carbon nanotubes are potentially ideal atomic force microscopy (AFM) probes due to their well-defined geometry, robust mechanical properties, and in the case of single-walled nanotubes (SWNTs), diameters approaching the size of small organic molecules. Here we elucidate fundamental factors that determine AFM imaging resolution using a combination of experiments with well-characterized SWNT probes and numerical simulations. Tapping mode AFM imaging on gold nanoclusters and DNA molecules using SWNT probes shows that the tip-induced broadening reaches the geometrical limit (i.e., the diameter of the SWNT tips) in the repulsive imaging regime, and the broadening effect becomes greater than the geometrical limit in the attractive imaging regime due to long-range attractive forces. Adjusting the damping enables imaging of isolated DNA molecules with a resolution defined by the tip diameter without disrupting the sample.