Physical Review Letters

Direct Determination of the Energy Required to Operate a Single Molecule Switch

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Using a noncontact atomic-force and scanning-tunneling microscope in ultrahigh vacuum, we have measured the switching energy of a single molecule switch based on the rotation of a di-butyl-phenyl leg in a Cu-tetra-3,5 di-tertiary-butyl-phenyl porphyrin. The mechanics and intramolecular conformation of the switched leg is controlled by the tip apex of the noncontact atomic-force microscope. The comparison between experimental and calculated force curves shows that the rotation of the leg requires an energy less than [Formula presented], which is 4 orders of magnitude lower than state-of-the-art transistors. © 2003 The American Physical Society.