NONLINEAR SINGLE-ELECTRON TUNNELING THROUGH INDIVIDUALLY COATED COLLOID PARTICLES AT ROOM-TEMPERATURE

Single-electron tunneling (SET) has been observed with nanometer coate d colloid gold particles at room temperature. We have made the smalles t (3-nm) thiol- and silicon dioxide (SiO2)-coated gold particles, from which we obtained SET signals using a scanning tunneling microscope ( STM). STM images reveal individual particles supported by an atomicall y flat metal surface. The STM tip is used to obtain SET signals from t he individual particles, whose shapes have been characterized. The cur rent-voltage curves of the particles exhibit well-defined Coulomb stai rcases that resemble those obtained at 4.2 K, indicating a strong Coul omb repulsive interaction at room temperature. The clear Coulomb stair cases are due to a nonlinearity in the current steps. We suggest a pos sible mechanism for the nonlinearity in terms of many-body excitations in the particle. We have also identified the region of the particles, where the SET signal originates, using current-imaging-tunneling spec troscopy. We describe the advantages of using the coated nanometer par ticles for making devices for room-temperature operations.