Evaluation of the van der Waals force for atomic force microscopy

The attractive van der Waals force between a conical silicon atomic force microscope tip and a carbon single-walled nanotube SWNT is calculated using parameters derived from the bulk dielectric response of silicon and of graphite. This configuration was used in a recent experiment [Phys. Rev. Lett. 93, 136101 (2004)] in which the force between the tip and the nanotube was measured in the noncontact mode. The calculations depend on the shape of the tip and whether there is an oxide layer or a layer of amorphous silicon. There is a fair level of agreement between the calculations and measurements for tip-SWNT separations in the range 0.50.3em0exto0.3em0ex1.00.3em0exnm.