3. Near-field optical microscopy

The early 1980s saw the emergence of new generations of scanning microscopes with atomic-scale lateral and longitudinal resolution. The first of these instruments (STM or Scanning Tunneling Microscope) uses the electron tunneling effect. If we consider the surface of a conductor, there is a cloud of electrons whose density decreases exponentially with distance from the surface. By approaching another conductive surface to within a few tenths of a nanometer, and in particular a point of theoretically monoatomic size, the electron clouds corresponding to the two conductors mix, enabling them to cross a potential barrier (tunneling). This gives rise to an electric current that decreases exponentially with distance, making it possible to scan the surface profile to within a hundredth of a nano-meter, with a lateral resolution of a few tenths of a nanometer. The use of such a device to measure...