Pulsed-Force-Mode AFM Studies of Polyphenylene Dendrimers on Self-Assembled Monolayers

Pulsed-force-mode atomic force microscopy (PFM-AFM) with a chemically modified tip was employed to measure the topography and adhesion force images of homoaggregates of fourth generation polyphenylene and carboxylic-acid- functionalized second generation polyphenylene dendrimers on hydrophilic self-assembled monolayers (SAMs). Although from the AFM topographic image the dendrimers could not be discriminated, from the adhesion image, the respective homoaggregates were easily discriminated. The determination is based on the different adhesive interactions between the dendrimers and the chemically modified tip, which are related to the chemical nature of the outer-surface functional groups, and the adsorbed water layer on hydrophilic surfaces under ambient conditions. It shows that PFM-AFM with chemically modified tips has nanoscale chemical spatial resolution.