Comparison of silicon and OH-modified AFM tips for adhesion force analysis on functionalised surfaces and natural polymers

- Flat model surfaces containing polar and non-polar areas where studied with AFM using adhesion force mapping.
- Native Silicon tips and functionalised tips were used.
- Polarity contrast could be resolved better with native Silicon tips.
- A rougher wood/wax sample was studied in the same way.
- Polarity contrast was also found to be higher in the case of native silicon tips.

In this paper, the position resolved adhesion behaviour of AFM cantilevers with standard silicon tips, rounded silicon tips and OH-modified tips was compared. Surfaces of a flat functionalised microscopy glass slide (hydrophilic background with hydrophobic spots) and of a comparably rough wood/wax sample were scanned in gaseous atmosphere. These two samples were chosen because both of them contain polar and non-polar regions within an area small enough to be scanned at once by the AFM without relevant quality loss due high scan speeds. Moreover, OH and CH3 modified cantilever chips providing very flat functionalised surfaces were scanned. Except for the wood/wax sample, measurements were performed at different humidity levels - with only very little influence on the measured adhesion. Both silicon and OH modified tips showed a higher adhesion on the polar regions of each sample than on the non-polar ones. The difference between the adhesion values on the polar and non-polar surfaces was however systematically higher when standard silicon tips were used. This was also true on the wood/wax sample. As silicon tips are relatively cheap, robust and have a much smaller radius than typical functionalised tips, they allow simple high resolution differentiation of polar and non-polar domains even when the sample surface is relatively rough, as it is the case for natural wood-based polymers.

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