Scanning force microscopy three-dimensional modes applied to the study of the dielectric response of adsorbed DNA molecules

We have developed a set of working modes for scanning probe microscopy (SPM), which generalizes the usual method of acquiring data. We call these modes three-dimensional (3D) modes. Using these modes it is possible to measure typical SPM magnitudes, such as, for example, the tunnel current, the normal force and the amplitude or frequency of the cantilever oscillation, as a function of any other two magnitudes of the system: f(x(1), x(2)). In this paper we present different examples of 3D modes. In particular, we have applied 3D modes to the study of the electrostatic interaction of co-adsorbed single walled carbon nanotubes and individual DNA molecules with a metallic scanning force microscopy tip. The data indicate that adsorbed DNA has a dielectric constant similar to that of the glass substrate.