A new atomic force microscopy (AFM) technique, which would allow users to precisely detect and map the charge distribution within molecules, has been developed by researchers in Europe. The team has used its method to demonstrate the difference in bond polarity between two structurally identical but chemically distinct molecules. It hopes the technique could someday be used to map charge movement within photovoltaic materials – something that could potentially help to improve solar cells.
In 1991 a variation of AFM – dubbed Kelvin probe force spectroscopy (KPFS) – was invented, and is used to measure the charge distribution on a surface. As a nanoscale tip oscillates at a tiny distance from the surface, a bias voltage is applied between the two. The electrostatic interaction with the surface pushes and pulls on the tip, changing its oscillation frequency. By measuring the frequency at various points, one can calculate the potential difference between tip and surface, and thereby infer the surface distribution of electronic charge.