Electrochemical potential arrangement of nanoclusters weakly coupled with metal surface

We investigated the electrochemical potential arrangement of Au nanoclusters, 1-3 nm in diameter, weakly coupled with bulk Au surface through tunneling junctions. The measurement of the Coulomb staircase by scanning tunneling spectroscopy and the statistical analysis for clusters reveal that [mu(0)+mu(1)]/2, where mu(n) is the electrochemical potential of the cluster when the number of excess electrons changes between n-1 and n, distributes around the Fermi level of the bulk Au electrode with the standard deviation sigma of 30-70 meV. The spacing DeltaE of the equally spaced electrochemical potentials decreases with increasing cluster size, which leads to the breakdown of the charge neutrality of the clusters below DeltaEsimilar to0.3 eV due to the competition between sigma and DeltaE. (C) 2004 American Institute of Physics.