Fine structure in the energy spectra of ultrasmall Au nanoparticles

We have studied tunneling into individual Au nanoparticles of estimated dia meters 2-5 nm, at dilution refrigerator temperatures. The I-V curves indica te resonant tunneling via discrete energy levels of the particle. Unlike pr eviously studied normal metal particles of Au and Al, in these samples we f ind that the lowest energy tunneling resonances are split into clusters of 2-10 subresonances. Such effects appear to be increasingly important in sma ller grains, as might be expected from the larger characteristic energies.