Nonlinear single-electron tunneling through individually coated colloid particles at room temperature

Single-electron tunneling (SET) has been observed with nanometer coated colloid gold particles at room temperature. We have made the smallest (3-nm) thiol- and silicon dioxide $\left({\mathrm{SiO}}_2\right)$-coated gold particles, from which we obtained SET signals using a scanning tunneling microscope (STM). STM images reveal individual particles supported by an atomically flat metal surface. The STM tip is used to obtain SET signals from the individual particles, whose shapes have been characterized. The current-voltage curves of the particles exhibit well-defined Coulomb staircases that resemble those obtained at 4.2 K, indicating a strong Coulomb repulsive interaction at room temperature. The clear Coulomb staircases are due to a nonlinearity in the current steps. We suggest a possible 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 spectroscopy. We describe the advantages of using the coated nanometer particles for making devices for room-temperature operations.