Attaching a carbon nanotube (CNT) to a conventional atomic force microscope tip can offer a performance upgrade thanks to a reduction in tip-sample contact area and by taking advantage of the nanomaterial's excellent mechanical properties. In a recent study, researchers in China and Australia have performed atomistic simulations and discuss the mechanical stability of these slender probes for applications such as surface topology imaging or nanomanipulation.

A slender rod, when subjected to a compressive load, buckles with transverse displacements. When mounted in an AFM or used as nanomanipulators to move nano-objects, this effect of axial buckling causes deleterious errors in mapping. According to simulation results for both flat and corrugated surfaces, and follow-up analysis, it is shown that these unpleasant effects can be well understood by considering both the tip-surface interaction (for example, van der Waals forces) and surface roughness at the atomic scale.

Effective stiffness

Under the premise that these issues can be surmounted, a cantilever model developed under known requirements for the structural characteristics of CNT probes is shown to be able to assess imaging fidelity. Based on this model, an effective stiffness, k = D4L–3, is defined where D and L are the diameter and length of the CNT tip, respectively.

The team finds that the deviation of measured surface topology from the actual one can be reduced dramatically with increased values of k. By choosing carbon nanotubes with higher bending rigidities and thus better resistance to axial buckling, the original surface information can be extracted accurately. This work offers an effective guide to the selection and design of CNT probes for AFM.

More details on the technique can be found in the journal Nanotechnology.