Analysis of the number of hydrogen bond groups of a multiwalled carbon nanotube probe tip for chemical force microscopy

In this paper, we describe a statistical method of quantification of the number of functional groups at the contact area of a probe tip for atomic force microscopy from the result of repetitive pull-off force measurements. We have investigated laboratory-made carbon nanotube (CNT) probe tips to apply them for chemical force microscopy because limited number of functional groups at the tip-end is expected. Using a CNT tip, we conducted repetitive pull-off force measurements against a self-assembled monolayer terminated with carboxyl group and analyzed them in terms of the number of hydrogen bond groups at the CNT tip. The elementary hydrogen bond rupture force quantum in n-decane medium was estimated to be 84.2 ± 0.5 pN in the present system. Thus it was revealed that only a couple of hydrogen bond groups of the CNT tip were participating in hydrogen bonding with the sample on an average in this experimental system.