ABSTRACTThe authors present the fabrication and characterization of molecular transistors comprising at most a small number of molecules, which display a distinct chemical function. The fabrication involves a self-aligned technique capable of patterning metal electrodes with interelectrode separations of ∼2nm∼2nm with very high yield. The electrodes are bridged by molecules with a metal-ion core which can be inserted by in situ designed chemical reaction. The presence or absence of the ion modulates the electrical conductance of the device.