Control of the ionization state of 3 single donor atoms in silicon
  By varying the gate and substrate voltage in a short silicon-on-insulator trigate field effect transistor we control the ionization state of three arsenic donors. We obtain a good quantitative agreement between 3D electrostatic simulation and experiment for the control voltage at which the ionization takes place. It allows us observing the three doubly occupied states As- at strong electric field in the presence of nearby source-drain electrodes. 
Benoit Voisin, Manuel Cobian, Xavier Jehl, Yann-Michel Niquet,   Christophe Delerue, Silvano De Franceschi, Marc Sanquer
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