The invention of scanning tunneling microscope (STM) by Binnig and his colleagues in 1982 opened up the possibility of imaging material surfaces with spatial resolution much superior to the conventional microscopy techniques. The STM is the first instrument capable of directly obtaining three-dimensional images of solid surfaces with atomic resolution. Even though STM is capable of achieving atomic resolution, it can only be used on electrical conductors. This limitation has led to the invention of atomic force microscope (AFM) by Binnig and his co-workers in 1986. These techniques have the characteristic that their resolution is not determined by the wavelength that is used for the interaction as in.
