COULOMB-BLOCKADE OSCILLATION IN A SINGLE ATOMIC JUNCTION

The first observation of the Coulomb blockade effect in the smallest p ossible system with a single atom as the central island of a double-ba rrier tunnel junction is reported. Our system consists of a single tun gsten atom as the central island and a tungsten STM tip and a silicon (100)2 x 1 reconstructed surface as the two electrodes. The use of a s ingle atom as the central island makes the change in the electrostatic potential due to a variation of number of electrons in the island of the order of 1 eV and thus the Coulomb blockade effect is made more co ntrollable and stable even at room temperature. A specific shape of th e tip apex forms a tunnel junction between an apex atom and the rest o f the tip with the energy-level broadening of the apex atom smaller th an the change in the charging energy due to the change in the number o f electrons in the single tungsten atom. This theoretical prediction w as confirmed by the experimental results of I-V measurements with an S IM tip made from a W(111) single-crystal wire where the change in the charging energy is 1.1 eV.