Coulomb blockade on imaged mesoscopic lead grains

Low-temperature scanning-tunneling-microscope (STM) studies of charging effects have been carried out on granular lead films. Well-defined Coulomb-staircase and Coulomb-blockade I-V characteristics were frequently observed. For the first time, the latter were observed in the tunneling characteristics of grains imaged with scanning tunneling microscopy. Capacitances (<${10}^{\mathrm{-}18}$ F) calculated from the I-V characteristics are compared to the values estimated from the STM images of these grains. In addition to the charging effects, an anomalous nonlinearity in the tunneling current was observed.