Atomic Force Microscopy Characterisation of a Micro-contact Printed, Self Assembled Thiol Monolayer

This paper describes friction experiments and pull-off force measurements using atomic force microscopy, between a non-functionalised silicon probe and a 2.5 m diameter CH3 and COOH terminated thiol self assembled monolayer pattern. The pattern is micro-contact printed onto a gold-coated silicon wafer, in air, at room temperature, with a relative humidity around 30%, and used to examine probemonolayer interactions. Atomic force microscopy imaging reveals that the patterns have been successfully reproduced on the substrate surface. We obtained force values of (8.67 ± 2.60)·10 -9 N, (2.68 ± 1.09) ·10 -8 N and (4.60 ± 0.24)·10 -8 N for CH3 terminated alkyl-thiol, COOH terminated thiol and gold substrate respectively. Normalizing these values with the tip radius we obtained (0.87 ± 0.27) N/m for CH3 terminated alkyl-thiol, (2.68 ± 1.10) N/m for COOH terminated thiol and (4.60 ± 2.50) N/m for bare gold. These interactions are discussed in terms of the chemical affinity between the probe and the substrate.