Mapping charge transfers between quantum levels using noncontact atomic force microscopy

We demonstrate the possibility to map nanoscale charge transfers between quantum electronic levels at room temperature, using noncontact atomic force microscopy and Kelvin force microscopy in a regime of weak electromechanical coupling. A two-level system is studied, consisting of degenerately doped silicon nanocrystals on silicon substrates, with size in the 2-50 nm range, in which the energy spacing is tuned by the nanocrystal quantum confinement over a ≈1eV range. The nanocrystal ionization is found to follow an energy compensation mechanism driven by quantum confinement, in quantitative agreement with parametrized tight-binding calculations of its band structure.