The interaction of an atomic force microscope tip with a nano-object: a model for determining the lateral force.

A calculation of the lateral force interaction between an atomic force microscope (AFM) tip and a nano-object on a substrate is presented. In particular, the case where the AFM tip is used to manipulate the nano-object is considered; i.e., the tip is displaced across the nano-object with the feedback off. The Hamaker equations are used to calculate the force when the tip and sample are not in contact and the Johnson, Kendall and Roberts (JKR) or Derjaguin, Muller and Toporov (DMT) formalisms are used for the contact force. The effect of the material parameters, the choice of contact theory and the shape of the nano-object on the resulting lateral forces are explored. The calculation is applied to an experimental system consisting of a cadmium selenide nanorod on graphite.

Manipulation of cadmium selenide nanorods with an atomic force microscope.

We have used an atomic force microscope (AFM) to manipulate and study ligand-capped cadmium selenide nanorods deposited on highly oriented pyrolitic graphite (HOPG). The AFM tip was used to manipulate (i.e., translate and rotate) the nanorods by applying a force perpendicular to the nanorod axis. The manipulation result was shown to depend on the point of impact of the AFM tip with the nanorod and whether the nanorod had been manipulated previously. Forces applied parallel to the nanorod axis, however, did not give rise to manipulation. These results are interpreted by considering the atomic-scale interactions of the HOPG substrate with the organic ligands surrounding the nanorods. The vertical deflection of the cantilever was recorded during manipulation and was combined with a model in order to estimate the value of the horizontal force between the tip and nanorod during manipulation. This horizontal force is estimated to be on the order of a few tens of nN.

Active drift compensation applied to nanorod manipulation with an atomic force microscope.

We have developed a simple algorithm to overcome the problem of thermal drift in an atomic force microscope (AFM) operating under ambient conditions. Using our method, we demonstrate that the AFM tip remains above a 5-nm-high and 50-nm-long CdSe nanorod for more than 90 min despite the thermal drift present (6 nm/min). We have applied our drift compensation technique to the AFM manipulation of CdSe colloidal nanorods lying horizontally on a highly oriented pyrolytic graphite surface. Since we have precise control over the position of the AFM tip relative to the nanorod, we can choose to either translate or rotate the rod by changing the location of the tip-rod interaction point.