Contact mode imaging of plasma-treated poly(ethylene terephthalate) films using bare silicon nitride tips yields poor image resolution because of tip-induced disruption of the surface structure. Deposition of a hydrophobic self-assembled monolayer onto the tip enables the minimisation of the interfacial free energy of the tip-sample contact, with such good effect that images are obtained in contact mode with comparable resolution to that observed in tapping mode. Control of tip chemistry therefore presents an important strategy for the imaging of delicate polymer structures by scanning force microscopy.