Manipulation of van der Waals forces to improve image resolution in atomic-force microscopy

Although the atomic force microscope (AFM) resembles superficially the scanning tunneling microscope (STM), its imaging resolution is in general much coarser. For the AFM, long-range interactions—most notably the van der Waals force—imply that image resolution is set by the macroscopic tip radius rather than by a single atom, as with the STM. Experimentally, we show that van der Waals forces can be measured using an AFM. By immersing tip and sample in an appropriate fluid, we can effectively eliminate the van der Waals force, leading to a marked improvement in AFM image quality.