Publication Type
Journal
Journal Name
Physical Review Letters
Publication Date
Volume
106
Issue
18
Abstract
The ability to explore the interior of materials for presence of inhomogeneities was recently demon-
strated by mode synthesizing atomic force microscopy [Tetard et al. Nature Nanotechnology (2010)].
However, the underlying mechanism of signal and image formation remain unexplored and not fully
understood. Proposing a semi-empirical nonlinear force, we show that di erence frequency gener-
ation, regarded as the simplest synthesized subsurface probe, occurs optimally when the force is
tuned to Van der Waals form. From a parametric study in the probe-sample excitation plane, we
show that the predicted behavior of the generated di erence-frequency oscillation amplitude agrees
well with experimental measurements. We then introduce the concept of virtual resonance to show
that probe oscillations at the generated di erence frequency can e ciently be enhanced.
