Dynamics of tunneling to and from small metal particles.

Abstract

The charge-transfer process between a small metal particle and a nearby electrode is investigated with electron tunneling experiments. The small particles are produced as an island film embedded in a capacitor, separated from one plate by a thin tunnel barrier and from the other by a thick insulator. The device properties reflect an ensemble average of independent particle-electrode tunneling systems. A significant property of the small-particle capacitor is that the potential change e/c associated with the transfer of a single electron is a non-negligible quantity. The experiments investigate the dynamics of the charge transfer process between particle and electrode by measuring the device capacitance C and dissipation constant D as a function of frequency \ensuremath{\omega}, temperature T, and ac voltage amplitude V. Experiments are carried out in the regime kT/e, V<e/c so that at most one electron transfer to or from a particle is induced during a cycle of the applied voltage. A model for the suppression of the tunneling rate by the Coulomb charging energy is presented which predicts C and D should scale as \ensuremath{\omega}/T in the zero-voltage limit and \ensuremath{\omega}/V in the zero-temperature limit. Experimental results verify these scaling laws. It is shown that at low temperature and voltages, a quantum size effect may cause the results to deviate from these scaling laws. Experimental results are presented which qualitatively support this prediction. Additional experiments investigate the transport between a small particle and a superconductor.